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POSTOPERATIVE WOUND DEHISCENCE AFTER : A USEFUL HEALTH CARE QUALITY INDICATOR? A COHORT STUDY BASED ON NORWEGIAN HOSPITAL ADMINISTRATIVE DATA

ForJournal: peerBMJ Open review only

Manuscript ID bmjopen-2018-026422

Article Type: Research

Date Submitted by the Author: 31-Aug-2018

Complete List of Authors: Helgeland , Jon ; Norwegian Institute of Public Health, Division of Health Services Tomic, Oliver; Norwegian University of Life Sciences, Department of Mathematic Sciences and Technology Hansen, Tonya; Norwegian Institute of Public Health, Division of Health Services Kristoffersen, Doris; Norwegian Institute of Public Health, Division of Health Services Hassani, Sahar; Oslo University Hospital, Department of Medical Genetics;

University of Oslo, KG Jebsen Centre for Psychosis Research, Institute of http://bmjopen.bmj.com/ Clinical Medicine Lindahl, Anne; Akershus University Hospital Trust, Division of

Quality in health care < HEALTH SERVICES ADMINISTRATION & Keywords: MANAGEMENT, SURGERY, Patient safety

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1 2 3 4 1 POSTOPERATIVE WOUND DEHISCENCE AFTER LAPAROTOMY: A 5 6 7 2 USEFUL HEALTH CARE QUALITY INDICATOR? A COHORT STUDY 8 9 10 3 BASED ON NORWEGIAN HOSPITAL ADMINISTRATIVE DATA 11 12 4 Jon Helgeland1,6, Oliver Tomic2, Tonya Moen Hansen1, Doris Tove Kristoffersen1, Sahar Hassani3,4, 13 14 5 Anne Karin Lindahl5 15 16 6 1 Division of HealthFor Services, Norwegianpeer Institute review of Public Health, only Oslo, Norway 17

18 2 19 7 Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Ås, 20 21 8 Norway 22 3 23 9 Department of Medical Genetics, Oslo University Hospital, Oslo, Norway 24 25 10 4 NORMENT, KG Jebsen Centre for Psychosis Research, Institute of Clinical Medicine, University of 26 27 11 Oslo, Oslo, Norway 28 29 12 5 Division of Surgery, Akershus University Hospital Trust 30 http://bmjopen.bmj.com/ 31 13 6Corresponding author: Jon Helgeland, [email protected] 32 33 14 34 35 15 Word count: 2643 36 37 38 16 39 on October 1, 2021 by guest. Protected copyright. 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 2 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 17 ABSTRACT 4 5 6 18 Objectives 7 8 19 Postoperative wound dehiscence (PWD) is a serious complication to laparotomy, leading to higher 9 10 20 mortality, readmissions and cost. The aims of the present study are to investigate whether risk 11 12 21 adjusted PWD rates could reliably differentiate between Norwegian hospitals, and whether PWD 13 14 22 rates were associated with hospital characteristics such as hospital type and laparotomy volume. 15 16 For peer review only 17 18 23 Design 19 20 24 Observational study using patient administrative data from all Norwegian hospitals, obtained from 21 22 25 the Norwegian Patient Registry, for the period 2011-2015, and linked using the unique person 23 24 26 identification number. 25 26 27 28 27 Participants 29 30

28 All patients undergoing laparotomy, at least 15 years old, with length of stay at least two days, and http://bmjopen.bmj.com/ 31 32 29 no diagnosis code for immunocompromised state or relating to pregnancy, childbirth and 33 34 30 puerperium. The final data set comprised 69 424 patients with 80 279 laparotomy episodes from 47 35 36 37 31 hospitals. 38 39 on October 1, 2021 by guest. Protected copyright. 40 32 Outcomes 41 42 33 The outcome was wound dehiscence, identified by the presence of a wound reclosure code, risk 43 44 45 34 adjusted for patient characteristics and operation type. 46 47 48 35 Results 49 50 36 The final data set comprised 1 487 wound dehiscences. Crude PWD rates varied from 0% to 5.1% 51 52 53 37 among hospitals, with an overall rate of 1.85%. Three hospitals with statistically significantly higher 54 55 56 57 58 59 2 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 3 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 38 PWD than average were identified. Hospital volume was not associated with PWD rate, except that 4 5 39 hospitals with very few had lower PWD rates. 6 7 8 40 Conclusions 9 10 11 41 Among Norwegian hospitals, there is considerable variation in PWD rate that cannot be explained by 12 13 42 operation type, age or comorbidity. This warrants further investigation into possible causes, such as 14 15 43 surgical technique, perioperative procedures or handling of complications, e.g. wound infections. The 16 For peer review only 17 44 risk adjusted PWD rate after laparotomy is a candidate quality indicator for Norwegian hospitals. 18 19 20 21 45 STRENGTHS AND LIMITATIONS OF THIS STUDY 22 23 46 • Includes all laparotomies performed in the nation over a five-year period, with patients 24 25 47 followed across hospitals 26 27 28 48 • Extends previous studies to a new health system and a new coding system 29 30 49 • The statistical analysis uses methods for low event rates, avoiding asymptotic approximation 31 http://bmjopen.bmj.com/ 32 50 • Results may be subject to coding inaccuracy and incompleteness, as well as selection effects 33 34 51 • There were no data for surgical technique, as well as some relevant comorbidities. 35 36 37 38 52 INTRODUCTION 39 on October 1, 2021 by guest. Protected copyright. 40 53 The past decades have seen a major growth in initiatives for measuring, monitoring, and improving 41 42 43 54 the quality of health care services. Quality indicators are regularly published in many health care 44 45 55 systems. Performance of health care systems is also compared across nations, for instance in the 46 1 2 47 56 OECD Health Care Quality and Outcomes (HCQO) initiative, which Norway is a part of. Norway has 48 49 57 a national quality indicator system for monitoring and comparing hospital performance, however, 50 51 58 not all areas of hospital performance are covered by existing national quality indicators. While there 52 53 59 are quality indicators for outcomes such as mortality and process measures such as waiting times, 54 55 56 57 58 59 3 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 4 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 60 complications following hospital care is less explored, which is especially relevant following surgical 4 5 61 procedures. 6 7 8 62 Postoperative wound dehiscence (PWD) rates after open abdominal surgery (laparotomies) was 9 10 63 introduced as a patient safety indicator in the United States and later as a quality indicator by 11 12 64 OECD.3-6 Norway reported the second highest numbers for 2014-2015, with a PWD rate of 1.02%. The 13

14 5 15 65 overall range was 0.055% to 1.05% . Neighbouring Sweden, with comparable population health and 16 For peer review only 17 66 health care, reported 0.30%. Moreover, a recent study comparing adverse events in Norway and 18 19 67 Sweden found significantly higher adverse event rates of surgical complications in Norwegian 20 21 68 hospitals, compared to Swedish hospitals.7 22 23 24 69 PWD is a serious complication that leads to higher mortality rates, higher implicit, explicit and social 25

26 8 9 27 70 costs as well as increased readmission rates. The PWD rate has been studied elsewhere as a quality

28 10 11 29 71 indicator for hospitals, and found to have a high positive predictive value. There are typically few 30 31 72 wound dehiscence events per hospital, making it more difficult to identify outlier hospitals for quality http://bmjopen.bmj.com/ 32 33 73 improvement. 34 35 36 74 Previous research has identified a number of risk factors for PWD. Examples of such factors are: (I) 37 38 12 13 9 14

75 patient related variables: smoking and obesity ; (II) procedure related factors: operation type , on October 1, 2021 by guest. Protected copyright. 39

40 15-17 18 41 76 type of incision and closure and length of operation time ; (III) postoperative parameters: clean 42 18 9 13 43 77 wound classification and coughing ; (IV) operative scenario: surgical team and nursing staff , etc. 44 45 46 78 The objectives of this study are to investigate the incidence of PWD after laparotomy at Norwegian 47 48 79 hospitals, and the potential usefulness of a PWD indicator for the Norwegian health care system, 49 50 80 computed from patient administrative data. More specifically we aimed at 1) investigate the 51 52 81 possibility to identify hospitals with higher or lower laparotomy PWD rate than average, 2) to study 53 54 55 56 57 58 59 4 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 5 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 82 the variability of the PWD rate among hospitals and its relation to hospital type and laparotomy 4 5 83 volume. 6 7 8 9 84 MATERIAL AND METHODS 10 11 85 Patient administrative data from all Norwegian hospitals were provided by the Norwegian Patient 12 13 86 Registry (NPR) for the period 2011-2015.19 This comprised individual patient data from all 14 15 87 department stays: type of admission (acute or elective), primary and secondary diagnosis codes 16 For peer review only 17 88 according to the Norwegian version20 of ICD-10, surgical and medical procedures, age, gender, date 18 19 20 89 and time of ward admission and discharge. Surgical procedures and operations are coded according 21 21 22 90 to the Norwegian version of the NOMESCO Classification of Surgical Procedures (NCSP-N). 23 24 91 Procedure time and date were not available. It was therefore not possible to exclude reclosures of 25 26 92 wounds occurring before or on the same day as laparotomies within the same episode, as requested 27 28 93 in the OECD indicator specification. The NPR data files were checked for missing values and 29 30 94 inconsistencies between variables, such as date and time of discharge before admission, valid ICD-10 31 http://bmjopen.bmj.com/ 32 95 code etc. 33 34 35 36 96 All permanent residents in Norway have a Personal Identification Number (PIN). NPR prepared an 37 38 97 encrypted PIN for all patients with a valid PIN, allowing tracking of patients over time and between 39 on October 1, 2021 by guest. Protected copyright. 40 98 hospitals. The data were linked with the National Registry to provide data of death (when 41 42 99 applicable), using the PIN. 43 44 45 46 100 Ward admissions for each patient, at more than one hospital in case of transfers, were linked into 47 48 101 episodes of care when less than eight hours elapsed from time of discharge to the next ward 49 22 50 102 admission. Wound dehiscence was defined as the occurrence of a code for a reclosure operation. 51 52 103 Laparotomies and wound reclosure operations were identified according to procedure codes. Each 53 54 104 reclosure episode was linked to the laparotomy episode immediately preceding or coinciding with it. 55 56 105 Reclosure episodes with no preceding laparotomy episode within 30 days, as well as laparotomy or 57 58 59 5 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 6 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 106 reclosure episodes following a reclosure episode within 30 days, were excluded. Note that the linking 4 5 107 of laparotomies and reclosures was not part of the original OECD specification, but is required in 6 7 108 order to attribute PWD to hospitals and to enable risk adjustment. Laparotomy episodes (and any 8 9 109 linked reclosure episode) were excluded if a diagnosis code for immunosuppression or relating to 10 11 110 pregnancy, childbirth and puerperium was present, if the length of stay was less than two days, or if 12 13 111 the patient’s age was less than 15 years. Hospitals with less than 10 laparotomies over the five-year 14 15 112 period were excluded. The hospitals belonged to one of three types: regional, large with acute 16 For peer review only 17 113 function and small with acute function. For details of codes used, see the online supplement. 18 19 20 21 114 The Charlson comorbidities were determined from previous admissions three years prior to, but not 22 23 115 including the current episode of care.22-24 Diagnoses were grouped according to the Clinical Condition 24 25 116 Summary system (CCS), adapted to the Norwegian version of ICD-10.25 26 27 28 29 117 Statistical methods 30 31 118 Risk adjusted probabilities for a laparotomy episode resulting in a reclosure operation were http://bmjopen.bmj.com/ 32 33 119 estimated by bias corrected logistic regression.26 The following case-mix variables were included: age 34 35 120 (modelled by natural splines), gender, indicators for the individual Charlson comorbidities, number of 36 37 121 previous hospital admissions two years prior to current admission, and whether the episode was 38 39 on October 1, 2021 by guest. Protected copyright. 122 acute or elective. A linear trend in admission year was also included. Based on previous studies of risk 40 41 123 factors 9 14, procedures were categorized into 13 types, according to the body system or organ 42 43 44 124 involved. The effects of operation types were normalized to have zero sum. The final model was fit 45 46 125 by stepwise regression with the BIC criterion, including two-way interactions. 47 48 49 126 To identify outlier hospitals, i.e. those with high or low risk adjusted PWD probabilities, estimated 50 51 127 hospital effects were compared to a reference value, defined as the 25% trimmed mean of the 52 53 128 hospital effects on the logistic scale.27 As some hospitals reported zero reclosures, ordinary maximum 54

55 28 56 129 likelihood estimates of the model parameters do not exist, due to separation , and the estimated 57 58 59 6 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 7 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 130 variances of the fitted parameters, based on their asymptotic distribution, become unreliable. The 4 5 131 comparison used an exact test based on the Poisson binomial distribution for the number of PWDs 6 7 132 per hospital, using the estimated probabilities for each case, together with parametric bootstrapping 8 9 133 to account for the estimation uncertainty in the model parameters. Tests for significance were 10 11 134 corrected for multiple comparisons using the Guo-Romano method 29, and outlier status assigned 12 13 135 according to the false discovery rate (FDR). An FDR not exceeding 5% was regarded as significant. For 14 15 136 sensitivity analysis, two alternative risk adjustment models were tested, with either a four-category 16 For peer review only 17 137 grouping of procedures or with diagnosis categories instead of the 13-category procedure grouping. 18 19 138 In addition, a model with the four Norwegian hospital regions was also estimated. Hospital volume, 20 21 22 139 modelled by splines, was tested for inclusion in the model. 23 24 25 140 Finally, the hospital specific effects were modelled as a mixture of two normal distributions. The 26 27 141 expectation-maximization (EM) algorithm was used, taking into account the estimation variances. 28 29 142 The mixture model yielded estimates of the quartiles of the hospital odds ratios and the scaled 30 31 http://bmjopen.bmj.com/ 143 interquartile range (normalized by dividing by 1.349, to give the standard deviation in the case of a 32 33 34 144 normal distribution) was computed as a measure of spread among hospitals. Bootstrapping of the 35 36 145 mixture model was used to find a 95% confidence interval for the scaled interquartile range. 37 38 on October 1, 2021 by guest. Protected copyright. 39 146 Patient and Public Involvement 40 41 147 Patients were not involved in this study. The policy of the Norwegian Institute of Public health to 42 43 44 148 publish hospital quality indicators, when they have been successfully validated. 45 46 47 149 48 RESULTS 49 50 150 The initial data set comprised 98 782 episodes with laparotomy and 1 909 with a reclosure operation. 51 52 151 After restricting data to reclosures paired with a laparotomy within 30 days, 1 487 reclosures 53 54 152 remained. After exclusions for pregnancy, childbirth and puerperium or immunocompromised state, 55 56 153 age and LOS, 80 469 laparotomies remained (no reclosures were excluded). Lastly, hospitals with less 57 58 59 7 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 8 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 154 than 10 laparotomies were excluded, yielding a final data set with 69 424 patients, 80 279 4 5 155 laparotomies from 47 hospitals. Descriptive statistics for the dataset are shown in Table 1. 6 7 8 156 Table 1. Descriptive statistics 9 10 PWD No PWD 11 12 Age, median (quartiles) 69 ( 61 - 78 ) 65 ( 51 - 74 ) 13 Females, % 35 55 14 15 Acute primary episode, % 44 33 16 PWD as primary Fordiagnosis, peer reclosure episode, review % 3 only — 17 18 Hospital type 19 Regional 546 28 274 20 21 Large, with acute function 819 42 271 22 Small, with acute function 122 8 247 23 24 Diabetes with chronic complications 1.3 1.1 25 Hemiplegia or paraplegia 1.1 0.5 26 27 Chronic pulmonary disease 13.2 6.5 28 Renal disease 4.4 3.5 29 30 30 day mortality (primary episode) 4.5 3.3 31 LOS days primary episode, median (quartiles) 18.8 ( 11.2 - 29.1 ) 7.2 ( 4.3 - 12.3 ) http://bmjopen.bmj.com/ 32 33 Percentage of reoperations in same episode 82 — 34 157 35 36 37 158 From 2011 to 2015, the annual volume of laparotomies decreased somewhat, from 17 468 to 14 728, 38 on October 1, 2021 by guest. Protected copyright. 39 159 while the proportion of acute laparotomies remained stable at around 33%. 40 41 42 43 160 The overall rate of PWD for the five-year period was 1.8%. Crude PWD rates varied from 0% to 5.1% 44 45 161 among hospitals. After risk adjustment, the range was 0.1% - 5.2% . Table 2 shows the odds ratios of 46 47 162 the final logistic regression model. The model showed good fit according to the modified Hosmer- 48 49 163 Lemeshow test30 (p=0.8) and good predictive ability, with an area under the operating characteristic 50 51 164 (AUC) of 0.73. 52 53 54 55 165 Table 2. Final model for risk adjustment 56 57 58 59 8 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 9 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 Variable Odds ratio (95% confidence interval) 4 5 6 Year of admission 0.93 (0.90,0.97) 7 8 Spline function 1 4.07 (2.42,6.85) 9 Spline function 2 3.63 (2.45,5.36) 10 Spline function 3 6.17 (1.85,20.55) 11 12 Spline function 4 2.61 (1.26,5.43) 13 Female 1 14 15 Male 2.36 (2.10,2.64) 16 Elective For peer review only 1 17 18 Acute 1.36 (1.22,1.52) 19 Chronic Pulmonary disease 1.72 (1.48,2.01) 20 21 Operation type 22 Several organs 2.15 (1.69,2.75) 23 24 2.80 (2.16,3.64) 25 Thoracoabdominal aorta 1.58 (0.58,4.31) 26 27 Abdominal wall 0.66 (0.21,2.10) 28 2.22 (1.84,2.67) 29 30 1.27 (0.81,2.00) 31 Biliary tract 0.24 (0.12,0.48) http://bmjopen.bmj.com/ 32 33 0.76 (0.40,1.46) 34 Spleen 0.99 (0.37,2.67) 35 Other digestive system 1.95 (1.50,2.53) 36 37 Kidney 0.22 (0.11,0.45) 38

Other urinary and male genital organs 0.42 (0.31,0.58) on October 1, 2021 by guest. Protected copyright. 39 40 Female genital organs 1.39 (1.02,1.89) 41 Peripheral vessels 1.23 (0.94,1.60) 42 43 Hospital 44 Scaled interquartile range 0.30 (0.23,0.34) 45 46 166 47 167 In Figure 1, risk-adjusted PWD rates are shown for each hospital, plotted versus laparotomy volume 48 49 50 168 and hospital type. 51 52 53 54 55 56 57 58 59 9 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 10 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 169 After significance testing, we identified three hospitals with higher PWD and none with lower PWD 4 5 170 than average, when correcting for multiple testing. Without multiple test correction, one additional 6 7 171 hospital with high PWD was found. 8 9 10 172 In the alternative model including volume, the PWD increased with yearly laparotomy volume from a 11 12 173 very low level up to 120 laparotomies per year, after which it remained fairly constant, see Figure 1. 13 14 15 174 The effect of volume was significant (p<0.001). Hospital type coincided almost completely with a 16 For peer review only 17 175 grouping of hospitals by volume, and was therefore not tested separately. There was significant 18 19 176 variation among regions, with the Northern region having the highest and the South-Eastern region 20 21 177 the lowest rates (data not shown). Using diagnosis categories or aggregated operation type as risk 22 23 178 adjustment variables resulted in very small changes in risk adjusted PWD rates. 24 25 26 27 179 DISCUSSION 28 29 180 We have studied a quality indicator for wound dehiscence after laparotomy, based on the OECD 30 31 http://bmjopen.bmj.com/ 32 181 specification, that discriminated between Norwegian hospitals. The indicator was risk adjusted for 33 34 182 differences in age, gender, comorbidity and type of surgery, and showed little sensitivity to changes 35 36 183 in the set of risk adjustment variables. The overall PWD rate was 1.8%. After risk adjustment, the 37 38 184 hospitals’ PWD rate varied between 0.1% and 5.2%. Laparotomy volume and type of hospital had 39 on October 1, 2021 by guest. Protected copyright. 40 185 little effect on the PWD rate, except for hospitals with very low volume. Age, male gender, chronic 41 42 186 pulmonary disease, and emergency laparotomy were all significant risk factors for PWD. There were 43 44 187 significant PWD differences according to the organ system targeted. The overall rate of PWD showed 45 46 188 a small but statistically significant decline over the observation period 2011-2015. The relatively large 47 48 189 variation of PWD rates between hospitals after correction for patient characteristics and operation 49 50 190 type, indicates possible variation in the quality of healthcare in different hospitals. This may be due 51 52 53 191 to variation in surgical technique and perioperative care, as well as the handling of postoperative 54 14 55 192 complications, such as wound infection, which is known to be a risk factor for PWD. We found PWD 56 57 58 59 10 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 11 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 9 13 14 18 31-33 3 193 rates well within the range reported in international studies. Also, the risk factors 4 5 194 identified are in accordance with previous studies, albeit limited to administrative data. Laparotomy 6 7 195 volume has negligible effect apart from the few hospitals with very low volume. The effect is likely a 8 9 196 result of differences in types of operations performed at these hospitals, compared to the other 10 11 197 hospitals. 12 13 14 15 198 Our study is based on complete data from all Norwegian hospitals performing laparotomies. To the 16 For peer review only 17 199 best of our knowledge, no similar study has been performed. NPR, the data source, has been 18 34-37 19 200 validated for several disease categories and has a very high degree of completeness. It was 20 21 201 possible to track patients during transfers and reoperations at different hospitals. 22 23 24 202 There is regional variation in the prevalence of smoking and obesity in Norway which could cause 25

26 38 27 203 some PWD variation among hospitals. Obesity is more prevalent in Northern Norway, where PWD 28 29 204 rates are somewhat higher. However, in other regions where obesity is less prevalent, the rates are 30 31 205 similar. There is no consistent correspondence between the known variation in smoking among http://bmjopen.bmj.com/ 32 33 206 counties and PWD rates. Some surgical procedures are performed only at regional hospitals, and it is 34 35 207 therefore possible that selection effects are present. In that case, one would expect larger changes in 36 37 208 PWD rates after risk adjustment for operation type, which was not found. One potential source of 38 on October 1, 2021 by guest. Protected copyright. 39 209 error in our study is the completeness and correctness of coding in the NPR, particularly the coding 40 41 210 of reclosure operations. The risk adjustment depends on data from previous hospitalization and may 42 43 211 not capture all comorbidities. Moreover, selection effects cannot not be ruled out. Differing policies 44 45 212 for operations on patients with known risk factors, e.g. obesity or smoking, would likely cause 46 47 48 213 variation in PWD rates. No attempt was made to identify main operation or operation intent, as this 49 50 214 would require a classification effort outside the scope of the present study. There could be a residual 51 52 215 imbalance in case mix, affecting PWD through e.g. operation duration, which is a known risk factor. 53 54 216 The observed effect of laparotomy volume is likely a result of differences in types of operations 55 56 217 performed at the hospitals with very low volume, compared to the other hospitals. 57 58 59 11 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 12 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 218 Previous studies have shown that the quality indicator has high positive predictive value, but only 4 10 5 219 moderate sensitivity. Since we have used specific wound reclosure codes, similar to those used in 6 7 220 previous studies, we expect a high positive predictive value in Norway as well. Conceivably, the 8 9 221 sensitivity depends on the coding system, in particular the various alternative codes related to 10 11 222 complications. Sensitivity in Norway may thus differ from that of other healthcare systems. 12 13 14 15 223 Conclusions 16 For peer review only 17 224 Among Norwegian hospitals, there is a significant variation in PWD rate that cannot be explained by 18 19 225 operation type, age or comorbidity. This warrants further investigation into possible causes, such as 20 21 226 surgical technique, perioperative procedures or handling of complications, e.g. wound infections. The 22 23 227 risk adjusted PWD rate after laparotomy is a candidate for use as a quality indicator for Norwegian 24 25 228 hospitals, and will make it possible to identify hospitals with apparent quality problems. To achieve 26 27 229 sufficient discrimination, however, five-year data are desirable, making it more difficult to monitor 28 29 230 changes in hospital performance resulting from quality improvement efforts. It lies outside the scope 30 31 http://bmjopen.bmj.com/ 231 of the present study to perform a comprehensive validation of the PWD rate as a quality indicator 32 33 34 232 suitable for public reporting. There are uncertainties and potential biases in the indicator, implying 35 36 233 that it must be regarded as a signal for follow-up within hospitals, rather than giving a final verdict of 37 38 234 inferior or superior quality. For reporting on surgical quality, several indicators should be used to give 39 on October 1, 2021 by guest. Protected copyright. 40 235 a balanced view of the different aspects of quality and patient safety. 41 42 43 44 236 FOOTNOTES 45 46 47 237 Funding 48 49 238 This research received no specific grant from any funding agency in the public, commercial or not- 50 51 239 for-profit sectors. 52 53 54 55 56 57 58 59 12 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 13 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 240 Competing interests 4 5 241 The authors have no competing interests. 6 7 8 9 242 Authors’ contributions 10 11 243 AKL and OT conceived the study. DTK, TMH, OT, and SH participated in data preparation. OT, SH and 12 13 244 AKL contributed to the analysis. OT helped draft the manuscript. JH was responsible for the statistical 14 15 245 analysis and final manuscript. All authors revised and approved the final manuscript. 16 For peer review only 17 18 19 246 Ethics approval 20 21 247 The study was approved by the Norwegian Directorate of Health and the Norwegian Data Protection 22 23 248 Authority. 24 25 26 27 249 Data sharing 28 29 250 The data set contains indirectly identifiable personal data, and cannot be shared without express 30 31 251 permission from the Norwegian Patient Registry. For further information, contact the corresponding http://bmjopen.bmj.com/ 32 33 252 author. 34 35 36 37 253 Figure 1. Risk adjusted PWD rates versus yearly laparotomy volume, by hospital type. Trend 38 254 curve is obtained by smoothing the scatterplot 39 on October 1, 2021 by guest. Protected copyright. 40 255 REFERENCES 41 42 43 256 1. Carinci F, Van Gool K, Mainz J, et al. Towards actionable international comparisons of health 44 257 system performance: expert revision of the OECD framework and quality indicators. Int J 45 258 Qual Health Care 2015;27(2):137-46. doi: 10.1093/intqhc/mzv004 [published Online First: 46 259 2015/03/12] 47 260 2. OECD. Health Care Quality and Outcomes: OECD; 2018 [Available from: 48 261 http://www.oecd.org/health/health-systems/health-care-quality-and-outcomes.htm 49 262 accessed 2018-06-06 2018. 50 263 3. Hannan EL. Using mortality data for profiling hospital quality of care and targeting substandard 51 264 care. J Soc Health Syst 1989;1(1):31-48. 52 265 4. Miller MR, Elixhauser A, Zhan C, et al. Patient Safety Indicators: using administrative data to 53 266 identify potential patient safety concerns. Health Serv Res 2001;36(6 Pt 2):110-32. 54 267 5. OECD. Health Care Quality Indicators - Patient Safety 2018 [Available from: 55 268 http://www.oecd.org/health/health-systems/hcqi-patient-safety.htm accessed 2018-06-06 56 269 2018. 57 58 59 13 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 14 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

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304 19. Health NDo. Norsk pasientregister - innhold og kvalitet: Norwegian Directorate of Health; 2018 on October 1, 2021 by guest. Protected copyright. 39 305 [Available from: https://helsedirektoratet.no/norsk-pasientregister-npr/innhold-og-kvalitet 40 41 306 accessed 2018-06-06 2018. 42 307 20. eHealth NDo. Helsefaglige kodeverk: Norwegian Directorate of eHealth 2018 [Available from: 43 308 https://ehelse.no/standarder-kodeverk-og-referansekatalog/helsefaglige-kodeverk accessed 44 309 2018-06-06 2018. 45 310 21. Norwegian Directorate of eHealth. NCMP, NCSP og NCRP: Klassifikasjon av medisinske, kirurgiske 46 311 og radiologiske prosedyrer Norwegian Directorate of eHealth; 2018 [Available from: 47 312 https://finnkode.ehelse.no/#ncmpncsp/0/0/0/-1 accessed 15th May 2018. 48 313 22. Hassani S, Lindman AS, Kristoffersen DT, et al. 30-Day Survival Probabilities as a Quality Indicator 49 314 for Norwegian Hospitals: Data Management and Analysis. PLoS One 2015;10(9):e0136547. 50 315 doi: 10.1371/journal.pone.0136547 51 316 23. Quan HD, Sundararajan V, Halfon P, et al. Coding algorithms for defining comorbidities in ICD-9- 52 317 CM and ICD-10 administrative data. Med Care 2005;43(11):1130-39. doi: DOI 53 318 10.1097/01.mlr.0000182534.19832.83 54 319 24. Quan H, Li B, Couris CM, et al. Updating and validating the Charlson comorbidity index and score 55 320 for risk adjustment in hospital discharge abstracts using data from 6 countries. Am J 56 321 Epidemiol 2011;173(6):676-82. doi: 10.1093/aje/kwq433 57 58 59 14 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 15 of 41 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 322 25. (HCUP) HCaUP. Beta Clinical Classifications Software (CCS) for ICD-10-CM/PCS: Agency for 4 323 Healthcare Research and Quality; 2018 [Available from: https://www.hcup- 5 324 us.ahrq.gov/toolssoftware/ccs10/ccs10.jsp accessed 2018-06-06 2018. 6 325 26. Firth D. Bias Reduction of Maximum-Likelihood-Estimates. Biometrika 1993;80(1):27-38. doi: DOI 7 326 10.1093/biomet/80.1.27 8 327 27. Kristoffersen DT, Helgeland J, Clench-Aas J, et al. Observed to expected or logistic regression to 9 328 identify hospitals with high or low 30-day mortality? PLoS One 2018;13(4) doi: ARTN 10 329 e0195248 10.1371/journal.pone.0195248 11 330 28. Albert A, Anderson JA. On the Existence of Maximum Likelihood Estimates in Logistic Regression 12 331 Models. Biometrika 1984;71(1):1-10. doi: 10.2307/2336390 13 332 29. Guo W, Romano JP. On stepwise control of directional errors under independence and some 14 333 dependence. Journal of Statistical Planning and Inference 2015;163:21-33. doi: 15 334 https://doi.org/10.1016/j.jspi.2015.02.009 16 335 30. Paul P, PennellFor ML, Lemeshow peer S. Standardizing review the power of theonly Hosmer-Lemeshow goodness of 17 336 fit test in large data sets. Stat Med 2013;32(1):67-80. doi: 10.1002/sim.5525 18 337 31. Sandy-Hodgetts K, Carville K, Leslie GD. Determining risk factors for surgical wound dehiscence: a 19 338 literature review. Int Wound J 2015;12(3):265-75. doi: 10.1111/iwj.12088 20 21 339 32. Kenig J, Richter P, Lasek A, et al. The efficacy of risk scores for predicting abdominal wound 22 340 dehiscence: a case-controlled validation study. BMC Surg 2014;14:65. doi: 10.1186/1471- 23 341 2482-14-65 24 342 33. Walming S, Angenete E, Block M, et al. Retrospective review of risk factors for surgical wound 25 343 dehiscence and incisional hernia. BMC Surg 2017;17(1):19. doi: 10.1186/s12893-017-0207-0 26 344 34. Bakken IJ, Gystad SO, Christensen OO, et al. Comparison of data from the Norwegian Patient 27 345 Register and the Cancer Registry of Norway. Tidsskr Nor Laegeforen 2012;132(11):1336-40. 28 346 doi: 10.4045/tidsskr.11.1099 [published Online First: 2012/06/22] 29 347 35. Hoiberg MP, Gram J, Hermann P, et al. The incidence of hip fractures in Norway -accuracy of the 30 348 national Norwegian patient registry. BMC Musculoskelet Disord 2014;15:372. doi: 31 349 10.1186/1471-2474-15-372 [published Online First: 2014/11/15] http://bmjopen.bmj.com/ 32 350 36. Oie LR, Madsbu MA, Giannadakis C, et al. Validation of intracranial hemorrhage in the Norwegian 33 351 Patient Registry. Brain and behavior 2018;8(2):e00900. doi: 10.1002/brb3.900 [published 34 352 Online First: 2018/02/28] 35 353 37. Varmdal T, Bakken IJ, Janszky I, et al. Comparison of the validity of stroke diagnoses in a medical 36 354 quality register and an administrative health register. Scandinavian journal of public health 37 355 2016;44(2):143-9. doi: 10.1177/1403494815621641 [published Online First: 2015/12/15] 38

356 38. Health NIoP. Public Health report: Norwegian Institute of Public Health; 2018 [Available from: on October 1, 2021 by guest. Protected copyright. 39 357 https://www.fhi.no/en/op/hin/ accessed 2018-06-06 2018. 40 41 42 358 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 15 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 16 of 41 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 For peer review only 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 http://bmjopen.bmj.com/ 32 33 34 35 36 37 38 39 Figure 1. Risk adjusted PWD rates versus yearly laparotomy volume, by hospital type. Trend curve is on October 1, 2021 by guest. Protected copyright. obtained by smoothing the scatterplot 40 41 149x149mm (300 x 300 DPI) 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 17 of 41 BMJ Open

1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Online supplement 6 7 8 Table 1. ICD-10 diagnosis codes contained in MDC 14 (Pregnancy, childbirth, and puerperium) 9 10 Code Title 11 A34 Obstetrical tetanus 12 F53.0 Mild mental and behavioural disorders associated with the puerperium, not elsewhere classified 13 F53.1 Severe mental and behavioural disorders associated with the puerperium, not elsewhere classified 14 F53.8 Other mental and behavioural disorders associated with the puerperium, not elsewhere classified 15 F53.9 Puerperal mental disorder, unspecified 16 Oxx.x Pregnancy, childbirth and puerperium 17 18 Z32.0 Pregnancy, notFor (yet) confirmed peer review only 19 Z32.1 Pregnancy confirmed 20 Z33 Pregnant state, incidental 21 Z34.0 Supervision of normal first pregnancy 22 Z34.8 Supervision of other normal pregnancy 23 Z34.9 Supervision of normal pregnancy, unspecified 24 Z35.0 Supervision of pregnancy with history of infertility 25 Z35.1 Supervision of pregnancy with history of abortive outcome 26 Z35.2 Supervision of pregnancy with other poor reproductive or obstetric history 27 28 Z35.3 Supervision of pregnancy with history of insufficient antenatal care 29 Z35.4 Supervision of pregnancy with grand multiparity 30 Z35.5 Supervision of elderly primigravida 31 Z35.6 Supervision of very young primigravida 32 Z35.8 Supervision of other high-risk pregnancies 33 Z35.9 Supervision of high-risk pregnancy, unspecified 34 Z36.0 Antenatal screening for chromosomal anomalies http://bmjopen.bmj.com/ 35 Z36.1 Antenatal screening for raised alphafetoprotein level 36 Z36.2 Other antenatal screening based on amniocentesis 37 Z36.3 Antenatal screening for malformations using ultrasound and other physical methods 38 39 Z36.4 Antenatal screening for fetal growth retardation using ultrasound and other physical methods 40 Z36.5 Antenatal screening for isoimmunization 41 Z36.8 Other antenatal screening 42 Z36.9 Antenatal screening, unspecified 43 Z37.0 Single live birth on October 1, 2021 by guest. Protected copyright. 44 Z37.1 Single stillbirth 45 Z37.2 Twins, both liveborn 46 Z37.3 Twins, one liveborn and one stillborn 47 Z37.4 Twins, both stillborn 48 Z37.5 Other multiple births, all liveborn 49 50 Z37.6 Other multiple births, some liveborn 51 Z37.7 Other multiple births, all stillborn 52 Z37.9 Outcome of delivery, unspecified 53 Z39.0 Care and examination immediately after delivery 54 Z39.1 Care and examination of lactating mother 55 Z39.2 Routine postpartum follow-up 56 Z64.0 Problems related to unwanted pregnancy 57 58

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1 2 3 Table 2. ICD-10 diagnosis codes for immunocompromised state BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Code Title 6 B20.0 HIV disease resulting in mycobacterial infection 7 B20.1 HIV disease resulting in other bacterial infections 8 B20.2 HIV disease resulting in cytomegaloviral disease 9 B20.3 HIV disease resulting in other viral infections 10 11 B20.4 HIV disease resulting in candidiasis 12 B20.5 HIV disease resulting in other mycoses 13 B20.6 HIV disease resulting in Pneumocystis carinii pneumonia 14 B20.7 HIV disease resulting in multiple infections 15 B20.8 HIV disease resulting in other infectious and parasitic diseases 16 B20.9 HIV disease resulting in unspecified infectious or parasitic disease 17 B21.0 HIV disease resulting in Kaposi's sarcoma 18 B21.1 HIV disease resultingFor in Burkitt'speer lymphoma review only 19 B21.2 HIV disease resulting in other types of non-Hodgkin's lymphoma 20 B21.3 HIV disease resulting in other malignant neoplasms of lymphoid, haematopoietic and related tissue 21 B21.7 HIV disease resulting in multiple malignant neoplasms 22 B21.8 HIV disease resulting in other malignant neoplasms 23 B21.9 HIV disease resulting in unspecified malignant neoplasm 24 B22.0 HIV disease resulting in encephalopathy 25 26 B22.1 HIV disease resulting in lymphoid interstitial pneumonitis 27 B22.2 HIV disease resulting in wasting syndrome 28 B22.7 HIV disease resulting in multiple diseases classified elsewhere 29 B23.1 HIV disease resulting in (persistent) generalized lymphadenopathy 30 B23.2 HIV disease resulting in haematological and immunological abnormalities, not elsewhere classified 31 B23.8 HIV disease resulting in other specified conditions 32 B24 Unspecified human immunodeficiency virus [HIV] disease 33 B59 Pneumocystosis 34 D47.1 Chronic myeloproliferative disease http://bmjopen.bmj.com/ 35 D70 Agranulocytosis 36 D71 Functional disorders of polymorphonuclear neutrophils 37 D72.0 Genetic anomalies of leukocytes 38 D80.0 Hereditary hypogammaglobulinaemia 39 40 D80.1 Nonfamilial hypogammaglobulinaemia 41 D80.2 Selective deficiency of immunoglobulin A [IgA] 42 D80.3 Selective deficiency of immunoglobulin G [IgG] subclasses 43 D80.4 Selective deficiency of immunoglobulin M [IgM] on October 1, 2021 by guest. Protected copyright. 44 D80.5 Immunodeficiency with increased immunoglobulin M [IgM] 45 D80.6 Antibody deficiency with near-normal immunoglobulins or with hyperimmunoglobulinaemia 46 D80.7 Transient hypogammaglobulinaemia of infancy 47 D80.8 Other immunodeficiencies with predominantly antibody defects 48 D80.9 Immunodeficiency with predominantly antibody defects, unspecified 49 D81.0 Severe combined immunodeficiency [SCID] with reticular dysgenesis 50 D81.1 Severe combined immunodeficiency [SCID] with low T- and B-cell numbers 51 D81.2 Severe combined immunodeficiency [SCID] with low or normal B-cell numbers 52 D81.3 Adenosine deaminase [ADA] deficiency 53 D81.4 Nezelof's syndrome 54 55 D81.5 Purine nucleoside phosphorylase [PNP] deficiency 56 D81.6 Major histocompatibility complex class I deficiency 57 D81.7 Major histocompatibility complex class II deficiency 58 D81.8 Other combined immunodeficiencies 59 D81.9 Combined immunodeficiency, unspecified 60 D82.0 Wiskott-Aldrich syndrome

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1 2 3 D82.1 Di George's syndrome BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 D82.2 Immunodeficiency with short-limbed stature 5 D82.3 Immunodeficiency following hereditary defective response to Epstein-Barr virus 6 D82.4 Hyperimmunoglobulin E [IgE] syndrome 7 D82.8 Immunodeficiency associated with other specified major defects 8 D82.9 Immunodeficiency associated with major defect, unspecified 9 D83.0 Common variable immunodeficiency with predominant abnormalities of B-cell numbers and function 10 11 D83.1 Common variable immunodeficiency with predominant immunoregulatory T-cell disorders 12 D83.2 Common variable immunodeficiency with autoantibodies to B- or T-cells 13 D83.8 Other common variable immunodeficiencies 14 D83.9 Common variable immunodeficiency, unspecified 15 D84.0 Lymphocyte function antigen-1 [LFA-1] defect 16 D84.1 Defects in the complement system 17 D84.8 Other specified immunodeficiencies 18 D84.9 Immunodeficiency,For unspecified peer review only 19 D89.8 Other specified disorders involving the immune mechanism, not elsewhere classified 20 D89.9 Disorder involving the immune mechanism, unspecified 21 E40 Kwashiorkor 22 E41 Nutritional marasmus 23 E42 Marasmic kwashiorkor 24 E43 Unspecified severe protein-energy malnutrition 25 26 I12.0 Hypertensive renal disease with renal failure 27 I13.1 Hypertensive heart and renal disease with renal failure 28 I13.2 Hypertensive heart and renal disease with both (congestive) heart failure and renal failure 29 K91.2 Postsurgical , not elsewhere classified 30 N18.0 End-stage renal disease 31 N18.5 Chronic kidney disease, stage 5 32 N18.8 Other chronic renal failure 33 T86.0 Bone-marrow transplant rejection 34 T86.1 Kidney transplant failure and rejection 35 T86.2 Heart transplant failure and rejection http://bmjopen.bmj.com/ 36 T86.3 Heart-lung transplant failure and rejection 37 T86.4 Liver transplant failure and rejection 38 T86.8 Failure and rejection of other transplanted organs and tissues 39 T86.9 Failure and rejection of unspecified transplanted organ and tissue 40 41 Y83.0 Surgical Operation with transplant of whole organ or tissue 42 Z49.0 Preparatory care for dialysis 43 Z49.1 Extracorporeal dialysis on October 1, 2021 by guest. Protected copyright. 44 Z49.2 Other dialysis 45 Z94.0 Kidney transplant status 46 Z94.1 Heart transplant status 47 Z94.2 Lung transplant status 48 Z94.3 Heart and lungs transplant status 49 Z94.4 Liver transplant status 50 Z94.8 Other transplanted organ and tissue status 51 Z94.9 Transplanted organ and tissue status, unspecified 52

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 Procedure codes for laparotomy and operation types. Laparotomy codes are the total of 5 6 codes in tables 3-16. Note that a last code digit of 0,3 or 6 signifies an open or other non- 7 endoscopic operation or procedure. 8 9 Table 3. NCSP-N codes for reclosure procedures 10 11 Code Title 12 JWA00 Repair of wound dehiscence in gastroenterological surgery 13 KWA00 Repair of wound dehiscence in urological surgery 14 15 LWA00 Repair of wound dehiscence in gynaecological surgery 16 PWA00 Repair of wound dehiscence in surgery of peripheral vessels and lymphatic system 17 18 For peer review only 19 Table 4. NCSP-N codes for repair of thoracoabdominal aorta 20 21 Code Title 22 23 FCD00 Suture of thoracoabdominal aorta 24 FCD10 Reinforcement of thoracoabdominal aorta using suture 25 FCD30 Repair of thoracoabdominal aorta using patch 26 FCD40 Partial resection and suture of thoracoabdominal aorta 27 28 FCD50 Resection and reconstruction of thoracoabdominal aorta using tube graft 29 FCD60 Resection of thoracoabdominal aorta and reimplantation of branches 30 FCD70 Bypass of thoracoabdominal aorta using tube graft 31 32 FCD80 Removal of foreign body from thoracoabdominal aorta 33 FCD96 Other repair of thoracoabdominal aorta 34 35 http://bmjopen.bmj.com/ 36 Table 5. NCSP-N code for procedures on the abdominal wall 37 38 Code Title 39 JAA00 Incision of abdominal wall 40 41 42 43 Table 6. NCSP-N codes for on October 1, 2021 by guest. Protected copyright. 44 45 Code Title 46 JBB00 Repair of paraoesophageal hernia 47 JBB10 Repair of congenital diaphragmatic hernia 48 JBB96 Repair of other diaphragmatic hernia 49 50 JBC00 Gastro-oesophageal antireflux operation 51 52 53 Table 7. NCSP-N codes for procedures on the digestive tract: oesophagus, and 54 intestines 55 56 Code Title 57 58 JCA00 Oesophagotomy 59 JCA20 Ligature of oesophageal varices 60

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1 2 3 JCA60 Transcervical excision of diverticulum of oesophagus BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JCA96 Other local operation on oesophagus 5 6 JCB00 Oesophagostomy 7 JCC00 Transhiatal partial oesophagectomy without interposition 8 JCC10 Transthoracic partial oesophagectomy without interposition 9 JCC20 Transhiatal partial oesophagectomy with interposition of intestine 10 11 JCC30 Transthoracic partial oesophagectomy with interposition of intestine 12 JCC96 Other partial oesophagectomy 13 JCD00 Subcutaneous anastomosis of oesophagus without interposition 14 JCD03 Subcutaneous anastomosis of oesophagus with interposition of intestine 15 16 JCD10 Intrathoracic anastomosis of oesophagus without interposition 17 JCD13 Intrathoracic oesophageal anastomosis with interposition of intestine 18 JCD20 TranssectionFor of oesophagus peer review only 19 20 JCD96 Other anastomosis of oesophagus without resection 21 JCE00 Suture of oesophagus 22 JCE10 Plastic repair of stenosis of cardia 23 JCE20 Cardiomyotomy 24 25 JCE30 Repair of oesophageal atresia or congenital tracheo-oesophageal fistula 26 JCE33 Closure of acquired tracheo-oesophageal or broncho-oesophageal fistula 27 JCE40 Reconstruction of oesophagus using flap 28 JCE50 Reconstruction of oesophagus using free microvascular graft of intestine 29 30 JCE96 Other reconstruction of oesophagus 31 JCF00 Insertion of oesophageal stent 32 JCW96 Other operation on oesophagus 33 JDA00 Gastrotomy 34 35 JDA60 Closure of perforated ulcer of stomach http://bmjopen.bmj.com/ 36 JDA63 Local excision of lesion of stomach 37 JDC00 Partial and gastroduodenostomy 38 39 JDC10 Partial gastrectomy and gastrojejunostomy 40 JDC20 Partial gastrectomy and Roux-en-Y reconstruction 41 JDC30 Partial gastrectomy with interposition of jejunum 42 JDC40 Partial gastrectomy and oesophagogastrostomy 43 on October 1, 2021 by guest. Protected copyright. 44 JDC96 Partial gastrectomy with other reconstruction 45 JDD00 Total gastrectomy and Roux-en-Y oesophagojejunostomy 46 JDD96 Total gastrectomy with other reconstruction 47 JDE00 Gastrojejunostomy 48 49 JDE10 Conversion of gastrojejunostomy to Roux-en-Y anastomosis 50 JDE20 Conversion of gastrojejunostomy to gastroduodenostomy with interposition of jejunum 51 JDE96 Other anastomosis of stomach without concurrent gastrectomy 52 53 JDF00 Gastroplasty 54 JDF10 Gastric bypass 55 JDF20 Gastric banding 56 JDF96 Other bariatric operation on stomach 57 58 JDG00 Truncal 59 JDG10 Proximal gastric vagotomy 60 JDG96 Other vagotomy

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1 2 3 JDH00 Duodenotomy BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JDH40 Duodenostomy on duodenal bulb 5 6 JDH50 Local excision of lesion of duodenal bulb 7 JDH60 8 JDH63 Pyloroplasty 9 JDH70 Closure of perforated ulcer of duodenum 10 11 JDW96 Other operation on stomach or duodenum 12 JEA00 13 JEA10 Appendectomy with drainage 14 JEW96 Other operation on appendix 15 16 JFA00 Enterotomy 17 JFA10 Colotomy 18 JFA16 Biopsy of wallFor of colon peerwithout colotomy review only 19 20 JFA60 Stricturoplasty in 21 JFA63 Stricturoplasty in colon 22 JFA70 Suture of small intestine 23 JFA73 Excision of lesion of small intestine 24 25 JFA76 Closure of fistula of small intestine 26 JFA80 Suture of colon 27 JFA83 Excision of lesion of colon 28 JFA86 Closure of fistula of colon 29 30 JFA96 Other local operation on intestine 31 JFB00 Partial resection of small intestine 32 JFB10 Reversal of segment of small intestine 33 JFB13 Plastic repair of small intestine with lengthening 34 35 JFB20 Ileocaecal resection http://bmjopen.bmj.com/ 36 JFB30 Right hemicolectomy 37 JFB33 Other resection comprising small intestine and colon 38 39 JFB40 Resection of transverse colon 40 JFB43 Left hemicolectomy 41 JFB46 Resection of sigmoid colon 42 JFB50 Other resection of colon 43 on October 1, 2021 by guest. Protected copyright. 44 JFB53 Resection of sigmoid colon with partial proctectomy 45 JFB60 Resection of sigmoid colon with end 46 JFB63 Other resection of colon with proximal colostomy and closure of distal stump 47 JFB96 Other partial excision of intestine 48 49 JFC00 Entero-enterostomy 50 JFC10 Ileotransversostomy 51 JFC20 Other enterocolostomy 52 53 JFC30 Colo-colostomy 54 JFC40 Ileorectostomy 55 JFC50 Colorectostomy 56 JFD00 57 58 JFD03 Duodenoileal bypass with biliopancreatic diversion 59 JFD10 Revision of jejunoileal bypass 60 JFD13 Revision of duodenoileal bypass

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1 2 3 JFD20 Restoration of continuity after jejunoileal bypass BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JFD23 Restoration of continuity after duodenoileal bypass 5 6 JFD96 Other intestinal bypass operation 7 JFE00 Transplantation of small intestine 8 JFE96 Other operation relating to transplantation of small intestine 9 JFF00 Catheter enterostomy 10 11 JFF10 Loop enterostomy 12 JFF13 Terminal enterostomy 13 JFF20 Caecostomy 14 JFF23 Transversostomy 15 16 JFF26 Sigmoidostomy 17 JFF30 Other colostomy 18 JFF40 AppendicostomyFor peer review only 19 20 JFF50 Exteriorisation of loop of colon without opening 21 JFF60 Opening of exteriorised loop of colon 22 JFF96 Other exteriorisation of intestine or creation of intestinal stoma 23 JFG00 Closure of loop enterostomy without resection 24 25 JFG10 Closure of loop colostomy without resection 26 JFG20 Closure of enterostomy with resection of exteriorised loop 27 JFG23 Closure of terminal enterostomy with anastomosis to small intestine 28 JFG26 Closure of terminal enterostomy with anastomosis to colon 29 30 JFG30 Closure of colostomy with resection of exteriorised loop 31 JFG33 Closure of terminal colostomy with anastomosis to colon 32 JFG36 Closure of terminal colostomy with anastomosis to 33 JFG40 Revision of enterostomy or colostomy without laparotomy 34 35 JFG50 Laparotomy with revision of enterostomy or colostomy http://bmjopen.bmj.com/ 36 JFG53 Revision of ileal pelvic pouch 37 JFG56 Revision of colonic pelvic pouch 38 39 JFG60 Conversion of conventional to continent ileostomy 40 JFG70 Conversion of continent ileostomy to conventional ileostomy 41 JFG73 Excision of ileal pelvic pouch 42 JFG76 Excision of colonic pelvic pouch with colorectal or coloanal anastomosis 43 on October 1, 2021 by guest. Protected copyright. 44 JFG80 Excision of ileal pouch with construction of new continent ileostomy 45 JFG83 Excision of colonic pelvic pouch and construction of new pouch 46 JFG86 Excision of ileal pelvic pouch and construction of new pouch 47 JFG96 Other operation on intestinal stoma or pouch 48 49 JFH00 Total and ileorectal anastomosis 50 JFH10 Total colectomy and ileostomy 51 JFH20 Proctocolectomy and ileostomy 52 53 JFH30 Total colectomy, mucosal proctectomy and ileoanal anastomosis without ileostomy 54 JFH33 Total colectomy, mucosal proctectomy, ileoanal anastomosis and ileostomy 55 JFH40 Proctocolectomy and continent ileostomy 56 JFH96 Other total colectomy 57 58 JFJ00 Coecopexy 59 JFJ96 Other enteropexy or colopexy 60 JFK00 Division of adhesive band in intestinal obstruction

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1 2 3 JFK10 Freeing of adhesions in intestinal obstruction BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JFK20 Freeing of adhesions and plication of small intestine 5 6 JFK96 Other operation on adhesions in intestinal obstruction 7 JFL00 Open reduction of intussusception of intestine 8 JFL10 Laparotomy and manipulation of obstructed intestine 9 JFL20 Laparotomy and manipulation of impacted material 10 11 JFL96 Other operation for intestinal obstruction without resection or freeing of adhesions 12 JFM00 Intraoperative irrigation of colon 13 JFW96 Other operation on intestine 14 JGA00 Proctotomy 15 16 JGA60 Suture of rectum 17 JGA70 Proctotomy and excision of lesion of rectum 18 JGA73 Transanal excisionFor of lesionpeer of rectum review only 19 20 JGA76 Stapled transanal rectal resection 21 JGA96 Other proctotomy or local operation on rectum 22 JGB00 Partial proctectomy and colorectal or coloanal anastomosis 23 JGB03 Partial proctectomy with partial excision of mesorectum 24 25 JGB06 Partial proctectomy with total excision of mesorectum 26 JGB10 Partial proctectomy and end colostomy 27 JGB20 Partial rectosigmoidectomy and abdominoperineal pull-through anastomosis 28 JGB30 Abdominoperineal excision of rectum 29 30 JGB33 Abdominoperineal excision of rectum with intersphincteric dissection 31 JGB36 Wide excision of rectum 32 JGB40 Excision of rectum and end ileostomy 33 JGB50 Mucosal proctectomy and ileoanal anastomosis 34 35 JGB60 Excision of rectum and ileoanal anastomosis http://bmjopen.bmj.com/ 36 JGB96 Other proctectomy or excision of rectum 37 JGC00 Rectopexy 38 39 JGC10 Perineal rectopexy 40 JGC20 Transanal suture 41 JGC30 Excision and suture of rectal mucosa with imbrication of muscular layer 42 JGC40 Anorectal repair of anal atresia 43 on October 1, 2021 by guest. Protected copyright. 44 JGC96 Other reconstructive operation on rectum 45 JGD00 Excision of perineal local recurrence of tumour 46 JGW96 Other operation on rectum 47

48

49 50 Table 8. NCSP-N codes for procedures on the liver 51 52 Code Title 53 JJA00 Exploration of liver 54 JJA10 Hepatotomy 55 56 JJA20 Open biopsy of liver 57 JJA23 Open needle biopsy of liver 58 JJA30 Fenestration of cyst of liver 59 JJA40 Excision of lesion of liver 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 JJA43 Destruction of lesion of liver 4 5 JJA50 Suture of liver 6 JJA96 Other local operation on liver 7 JJB00 Wedge resection of liver 8 JJB10 Atypical resection of liver 9 10 JJB20 Excision of single segment of liver 11 JJB30 Excision of two segments of liver 12 JJB40 Excision of segments II, III and IV of liver 13 14 JJB50 Excision of segments V, VI, VII and VIII of liver 15 JJB53 Excision of segments IV,V, VI, VII and VIII of liver 16 JJB60 Other excision of three or more segments of liver 17 18 JJB96 Other resectionFor of liver peer review only 19 JJC00 Allogenic transplantation of liver 20 JJC10 Allogenic partial transplantation of liver 21 22 JJC20 Allogenic partial transplantation of liver from living donor 23 JJC30 Xenogenic transplantation of liver 24 JJC40 Xenogenic partial transplantation of liver 25 26 JJC50 Resection of transplanted liver 27 JJC60 Total excision of transplanted liver 28 JJC96 Other transplantation of liver or related operation 29 JJW96 Other operation on liver 30 31 32 33 Table 9. NCSP-N codes for procedures on biliary tract 34 35 Code Title http://bmjopen.bmj.com/ 36 JKA00 Cholecystotomy 37 38 JKA10 39 JKA13 Percutaneous cholecystostomy 40 JKA20 41 42 JKA96 Other operation on 43 JKB00 Incision of duct on October 1, 2021 by guest. Protected copyright. 44 JKB20 Intraoperative cholangioscopy 45 JKB40 Suture of 46 47 JKB96 Other incision or related operation on bile duct 48 JKC00 Incision of bile duct and local excision of lesion 49 JKC10 Partial excision and anastomosis of bile duct 50 51 JKC20 Partial excision of bile duct and anastomosis to duodenum 52 JKC30 Partial excision of bile duct and anastomosis to jejunum 53 JKC40 Partial excision of right or left hepatic duct and anastomosis to jejunum 54 55 JKC50 Excision of papilla of Vater and anastomosis of bile duct to duodenum or jejunum 56 JKC96 Other excision of bile duct 57 JKD00 Anastomosis of gallbladder to jejunum 58 59 JKD10 Anastomosis of bile duct to duodenum 60 JKD20 Anastomosis of bile duct to jejunum

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 JKD30 Extrahepatic anastomosis of right or left hepatic duct to jejunum 4 5 JKD40 Anastomosis of intrahepatic bile duct to jejunum 6 JKD50 Hepatoportoenterostomy 7 JKD96 Other biliodigestive anastomosis without excision 8 JKE00 Transduodenal papillotomy 9 10 JKE06 Transduodenal sphincteroplasty 11 JKE96 Other transduodenal open operation on bile duct or ampulla of Vater 12 JKF00 Excision of cystic duct 13 14 JKF10 Percutaneous extraction of biliary calculus 15 JKF96 Other secondary operation on biliary tract 16 JKW96 Other operation on biliary tract 17

18 For peer review only

19 20 Table 10. NCSP-N codes for procedures on the pancreas 21 22 Code Title 23 JLA00 Exploration of pancreas 24 JLA10 Biopsy of pancreas 25 26 JLA20 Needle biopsy of pancreas 27 JLB00 Incision of pancreas 28 JLB10 Pancreaticolithotomy 29 30 JLB96 Other incision, drainage or dilatation of pancreas 31 JLC00 Excision of lesion of pancreas 32 JLC10 Distal 33 34 JLC20 Total pancreatectomy 35 JLC30 Pancreatoduodenectomy http://bmjopen.bmj.com/ 36 JLC40 Total pancreatoduodenectomy 37 JLC50 Atypical pancreatectomy 38 39 JLC96 Other pancreatectomy 40 JLD00 Pancreaticojejunostomy 41 JLD10 Anastomosis of pancreatic pseudocyst to stomach 42 43 JLD20 Anastomosis of pancreatic pseudocyst to jejunum on October 1, 2021 by guest. Protected copyright. 44 JLE00 Allogenic total transplantation of pancreas with pancraticocystostomy 45 JLE03 Allogenic total transplantation of pancreas with pancreaticoenterostomy 46 47 JLE10 Allogenic segmental transplantation of pancreas 48 JLE16 Allogenic segmental transplantation of pancreas from living donor 49 JLE20 Allogenic islet cell transplantation 50 51 JLE30 Xenogenic islet cell transplantation 52 JLE40 Total excision of transplanted pancreas 53 JLE50 Occlusion of duct of transplanted pancreas 54 55 JLE56 Conversion of pancreaticocystostomy to pancreaticoenterostomy 56 JLE96 Other transplantation of pancreas or related operation 57 JLW96 Other operation on pancreas 58 59 60

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1 2 3 Table 11. NCSP-N codes for procedures on the spleen BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Code Title 6 JMA00 Partial splenectomy 7 8 JMA10 Transabdominal total splenectomy 9 JMA20 Transthoracic total splenectomy 10 JMB00 Biopsy of spleen 11 JMB10 Repair of spleen 12 13 JMW96 Other operation on spleen 14 15 16 Table 12. NCSP-N codes for other digestive system procedures 17 18 Code Title For peer review only 19 JAH00 Laparotomy 20 21 JAH20 Staging laparotomy 22 JAH30 Laparostomy 23 JAH33 Revision of laparostomy 24 25 JAH40 Thoracolaparotomy 26 JAJ00 Rectal incision and drainage of pelvic abscess 27 JAK00 Laparotomy and drainage of peritoneal cavity 28 29 JAK03 Laparotomy and peritoneal irrigation 30 JAK10 Laparotomy and insertion of catheter 31 JAL00 Biopsy of 32 33 JAL10 Laparotomy and removal of foreign body 34 JAL20 Excision or destruction of lesion of peritoneum 35 JAL23 Excision of local lesion of pelvic wall http://bmjopen.bmj.com/ 36 JAL30 Omentectomy 37 38 JAL50 Intraabdominal revision of shunt of ventricle of brain 39 JAL96 Other local operation on peritoneum or peritoneal cavity 40 JAM00 Transposition of omentum 41 42 JAM10 Operation for malrotation of intestine 43 JAN00 Creation of peritoneovenous shunt on October 1, 2021 by guest. Protected copyright. 44 JAN10 Revision of peritoneovenous shunt 45 46 JAN20 Removal of peritoneovenous shunt 47 JAP00 Freeing of adhesions in the peritoneal cavity 48 JAQ00 Extensive excision of peritoneum 49 50 JAQ10 Intraoperative hypertermic chemotherapeutic perfusion of abdominal cavity 51 JAW96 Other operation on abdominal wall, peritoneum, mesentery or omentum 52 JBA00 Transabdominal repair of diaphragm for rupture 53 54 JBA10 Transabdominal biopsy or excision of lesion of diaphragm 55 JBA20 Transabdominal partial excision of diaphragm 56 Other transabdominal operation on diaphragm or operation for gastro-oesophageal 57 JBW96 reflux 58 59 JKT00 Extracorporeal shock wave of gallbladder 60 JKT10 Extracorporeal shock wave lithotripsy of biliary duct

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Table 13. NCSP-N codes for procedures on kidney and pelvis of kidney 6 7 Code Title 8 KAA00 Exploration of kidney 9 10 KAA20 Exploratory nephrotomy 11 KAA30 Exploratory pyelotomy 12 KAA96 Other exploration of kidney or pelvis of kidney 13 KAB00 Biopsy of kidney or pelvis of kidney 14 15 KAC00 Nephrectomy 16 KAC20 Nephroureterectomy 17 KAD00 Partial nephrectomy 18 For peer review only 19 KAD10 Heminephrectomy 20 KAD40 Partial excision of pelvis of kidney 21 KAD50 Destruction of tumour of pelvis of kidney 22 KAD56 Destruction of lesion of renal parenchyma 23 24 KAD60 Percutaneous destruction of lesion of renal parenchyma 25 KAD96 Other partial excision of kidney or pelvis of kidney 26 KAE00 Nephrolithotomy 27 KAE10 Pyelolithotomy 28 29 KAE96 Other removal of calculus from kidney or pelvis of kidney 30 KAF00 Removal of foreign body from kidney 31 KAF10 Removal of foreign body from pelvis of kidney 32 KAH00 Suture of kidney 33 34 KAH10 Suture of pelvis of kidney 35 KAH30 Pyeloureteroplasty without division of ureteropelvic junction http://bmjopen.bmj.com/ 36 KAH40 Pyeloureteroplasty with division of ureteropelvic junction 37 38 KAH50 Ureterocalyceal anastomosis 39 KAH70 Freeing of adhesions of ureteropelvic junction 40 KAH80 Nephropexy 41 KAH96 Other reconstruction of kidney or pelvis of kidney 42 43 KAS00 Autotransplantation of kidney on October 1, 2021 by guest. Protected copyright. 44 KAS10 Allogenic transplantation of kidney from cadaver donor 45 KAS20 Allogenic transplantation of kidney from living donor 46 KAS40 Excision of transplanted kidney 47 48 KAS50 Nephrocystostomy in transplanted kidney 49 KAS60 Operation for lymphocele of transplanted kidney 50 KAS96 Other transplantation of kidney or related procedure 51 KAW96 Other operation on kidney or pelvis of kidney 52 53 54 55 56 57 58 59 60

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1 2 3 Table 14. NCSP-N codes for procedures on other urinary and male genital organs: ureter, bladder, BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 urethra, prostate and seminal vesicles 5 6 Code Title 7 8 KBA00 Exploration of ureter 9 KBA10 Exploratory ureterotomy 10 KBA96 Other exploration of ureter 11 12 KBB00 Biopsy of ureter 13 KBC00 Ureterectomy 14 KBD00 Partial excision of ureter 15 KBD20 Destruction of tumour of ureter 16 17 KBD30 Excision of stump of ureter 18 KBD96 Other partialFor excision peer of ureter or reviewdestruction of tumour only of ureter 19 KBE00 Ureterolithotomy 20 21 KBE96 Other operation for calculus of ureter 22 KBF00 Removal of foreign body from ureter 23 KBH00 Suture of ureter 24 25 KBH06 Ureteroureterostomy 26 KBH10 Connection of ureter to contralateral ureter 27 KBH20 Replantation of ureter 28 29 KBH30 Ileal replacement of ureter 30 KBH40 Plastic repair of ureter 31 KBH50 Ureterolysis 32 33 KBH96 Other repair or connection of ureter 34 KBJ00 Cutaneous ureterostomy 35 KBJ10 Cutaneous ureteroenterostomy http://bmjopen.bmj.com/ 36 KBJ20 Cutaneous ureteroenterostomy with reservoir 37 38 KBJ40 Ureteroenterostomy 39 KBJ60 Anastomosis of ureter to urethra with interposition of ileum 40 KBJ70 Removal of calculus from ileal conduit or reservoir 41 42 KBJ80 Operation for malfunction of urinary diversion 43 KBJ96 Other urinary diversion from ureter or related operation on October 1, 2021 by guest. Protected copyright. 44 KBT00 Extracorporeal shock wave lithotripsy of ureter 45 46 KBV00 Insertion of stent into ureter 47 KBV10 Removal of stent from ureter 48 KBV40 Incision or excision of ureterocele 49 50 KBW96 Other operation on ureter 51 KCA00 Exploratory cystotomy 52 KCB00 Biopsy of bladder 53 54 KCC00 Cystectomy 55 KCC10 Cystoprostatectomy 56 KCC20 Cystoprostatourethrectomy 57 KCC30 Cystectomy with excision of female internal genital organs 58 59 KCC96 Other cystectomy 60 KCD10 Partial cystectomy

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1 2 3 KCD20 Excision of diverticulum of bladder BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 KCD30 Destruction of tumour of bladder 6 KCD40 Excision of urachus 7 KCD96 Other partial excision or destruction of tumour of bladder 8 KCE00 Cystolithotomy 9 10 KCF00 Cystotomy and removal of foreign body from bladder 11 KCH00 Suture of bladder 12 KCH10 Enterocystoplasty 13 14 KCH20 Reduction cystoplasty 15 KCH30 Closure of vesicointestinal fistula 16 KCH40 Incision or resection of bladder neck 17 18 KCH96 Other reconstructiveFor peer operation on review bladder only 19 KCJ00 Cystostomy 20 KCJ10 Cutaneous cystoenterostomy 21 22 KCJ20 Continent cutaneous cystoenterostomy 23 KCJ96 Other cystostomy 24 KCT00 Extracorporeal shock wave lithotripsy of bladder 25 26 KCV10 Denervation of bladder 27 KCV20 Freeing of bladder 28 KCW96 Other operations on bladder 29 KDC00 Urethrectomy 30 31 KDD00 Partial excision of urethra 32 KDD10 Excision of diverticulum of urethra 33 KDD30 Destruction of tumour of urethra 34 35 KDD40 Resection of external sphincter of urethra http://bmjopen.bmj.com/ 36 KDD50 Excision of urethral valve 37 KDD80 Partial excision of urethra and repair using graft or flap 38 39 KDD96 Other partial excision of urethra 40 KDG00 Retropubic suspension of urethra 41 KDG10 Abdominovaginal suspension of bladder neck 42 43 KDG20 Abdominal colposuspension on October 1, 2021 by guest. Protected copyright. 44 KDG30 Suprapubic sling urethrocystopexy 45 KDG40 Suprapubic urethrocystopexy 46 47 KDG43 Transobturatorial sling urethrocystopexy 48 KDG50 Transabdominal plastic repair of pelvic floor for urinary incontinence 49 KDG60 Implantation of adjustable expander around bladder neck 50 KDG96 Other operation on urethra or bladder neck for incontinence 51 52 KDH00 Suture of urethra 53 KDH10 Meatoplasty of urethra 54 KDH30 Closure of urethrocutaneous fistula 55 56 KDH50 Closure of urethrointestinal fistula 57 KDH70 Plastic repair of stricture of urethra 58 KDH96 Other reconstructive operation on urethra 59 60 KDJ00 Urethrostomy

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1 2 3 KDK00 Implantation of artificial urinary sphincter around bladder neck BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 KDK10 Implantation of artificial urinary sphincter around bulbar urethra 6 KDK30 Revision of artificial urethral sphincter 7 KDK40 Removal of artificial urethral sphincter 8 KDV00 Insertion of stent into urethra 9 10 KDV10 Internal urethrotomy 11 KDV20 Submucous urethral injection 12 KDW96 Other operation on urethra 13 14 KEA00 Exploration of prostate 15 KEA10 Prostatotomy 16 KEA20 Incision of seminal vesicle 17 18 KEC00 RetropubicFor radical prostatectomy peer review only 19 KEC10 Perineal radical prostatectomy 20 KEC20 Transsacral radical prostatectomy 21 22 KED00 Transvesical prostatectomy 23 KED80 Percutaneous cryotherapy of prostate 24 KED96 Other partial excision of prostate 25 26 KEE00 Prostatolithotomy 27 KEE10 Removal of foreign body from prostate 28 KEW96 Other operation on prostate or seminal vesicle 29 30 31 32 33 Table 15- NCSP-N codes for procedures on female genital organs: ovary, fallopian tube, uterus and 34 uterine ligaments 35 http://bmjopen.bmj.com/ 36 Code Title 37 LAA00 Puncture of ovarian cyst 38 LAB00 Ovariotomy 39 40 LAB10 Biopsy of ovary 41 LAB96 Other incision or biopsy of ovary 42 LAC00 Excision of ovarian cyst 43 on October 1, 2021 by guest. Protected copyright. 44 LAC10 Fenestration of ovarian cyst 45 LAC20 Destruction of lesion of ovary 46 LAC30 Excision of paraovarian cyst 47 48 LAC96 Other excision or destruction of lesion of ovary 49 LAD00 Partial excision of ovary 50 LAE10 Unilateral oophorectomy 51 LAE20 Bilateral oophorectomy 52 53 LAF00 Unilateral salpingo-oophorectomy 54 LAF10 Bilateral salpingo-oophorectomy 55 LAF20 Unilateral transvaginal salpingo-oophorectomy 56 57 LAF30 Bilateral transvaginal salpingo-oophorectomy 58 LAG00 Freeing of adhesions of ovary 59 LAG10 Oophoropexy 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 LAG20 Detorsion of ovary 4 5 LAG96 Other reconstructive operation on ovary 6 LAW96 Other operation on ovary 7 LBB00 Biopsy of Fallopian tube 8 LBB96 Other biopsy of Fallopian tube 9 10 LBC10 Removal of products of conception from Fallopian tube 11 LBC20 Salpingotomy and removal of products of conception 12 LBC96 Other tube conserving operation for tubal pregnancy 13 14 LBD00 Partial excision of Fallopian tube 15 LBE00 Salpingectomy 16 LBF00 Perfusion of Fallopian tube 17 18 LBF03 Perfusion ofFor Fallopian tubepeer after reconstruction review only 19 LBF20 Transcervical catheter salpingoplasty 20 LBF30 Salpingolysis 21 22 LBF40 Fimbrioplasty 23 LBF50 Salpingostomy 24 LBF60 Partial excision and anastomosis of Fallopian tube 25 26 LBF70 Partial excision and reimplantation of Fallopian tube 27 LBF96 Other operation on Fallopian tube for infertility 28 LBW96 Other operation on Fallopian tube 29 LCA00 Biopsy of uterus or uterine ligaments 30 31 LCB00 Hysterotomy 32 LCB10 Myomectomy 33 LCB20 Transvaginal myomectomy 34 35 LCB96 Other excision of lesion of uterus http://bmjopen.bmj.com/ 36 LCC00 Partial excision of uterus 37 LCC10 Supravaginal hysterectomy 38 39 LCC20 Vaginal supravaginal hysterectomy 40 LCC96 Other partial excision of uterus 41 LCD00 Hysterectomy 42 43 LCD10 Vaginal hysterectomy on October 1, 2021 by guest. Protected copyright. 44 LCD30 Radical hysterectomy 45 LCD40 Radical vaginal hysterectomy 46 47 LCD96 Other hysterectomy 48 LCE00 Anterior exenteration of female pelvis 49 LCE10 Posterior exenteration of female pelvis 50 51 LCE20 Total exenteration of female pelvis 52 LCE96 Other exenteration of female pelvis 53 LCF00 Excision of lesion of parametrium 54 LCF10 Excision of female varicocele 55 56 LCF96 Other excision of lesion of parametrium 57 LCG10 Suture of uterus 58 LCG20 Hysteropexy 59 60 LCG30 Resection or transcision of sacrouterine ligaments

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 LCG40 Reconstruction of uterus 4 5 LCG96 Other reconstructive operation on uterus 6 LCW96 Other operation on uterus and uterine ligaments 7 8 9 10 11 Table 16. NCSP-N codes for procedures on the peripheral vessels of the abdomen 12 13 Code Title 14 15 PCB20 Ligature of coeliac trunk and branches 16 PCB30 Ligature of superior mesenteric artery 17 PCB40 Ligature of renal artery 18 For peer review only 19 PCB99 Ligature of other visceral artery 20 PCC10 Suture of suprarenal or juxtarenal abdominal aorta 21 PCC20 Suture of coeliac trunk and branches 22 PCC30 Suture of superior mesenteric artery 23 24 PCC40 Suture of renal artery 25 PCC99 Suture of other visceral artery 26 PCE30 Thrombectomy or embolectomy of superior mesenteric artery 27 28 PCE40 Thrombectomy or embolectomy of renal artery 29 PCE99 Thrombectomy or embolectomy of other visceral artery 30 PCF20 Thrombendarterectomy of coeliac trunk and branches 31 32 PCF30 Thrombendarterectomy of superior mesenteric artery 33 PCF40 Thrombendarterectomy of renal artery 34 PCF99 Thrombendarterectomy of other visceral artery 35 http://bmjopen.bmj.com/ 36 PCG10 Operation for aneurysm of supracoeliac or juxtarenal abdominal aorta 37 PCG20 Operation for aneurysm of coeliac trunk and branches 38 PCG30 Operation for aneurysm of superior mesenteric artery 39 40 PCG40 Operation for aneurysm of renal artery 41 PCG99 Operation for aneurysm of other visceral artery 42 PCH10 Bypass from supracoeliac or juxtarenal abdominal aorta 43 on October 1, 2021 by guest. Protected copyright. PCH20 Bypass from coeliac trunk and branches 44 45 PCH30 Bypass from superior mesenteric artery 46 PCH40 Bypass from renal artery 47 PCH99 Bypass from other visceral artery 48 49 PCJ30 Transposition of superior mesenteric artery 50 PCJ40 Transposition of renal artery 51 PCJ99 Transposition of other visceral artery 52 53 PCK20 Reimplantation of coeliac trunk and branches 54 PCK30 Reimplantation of superior mesenteric artery 55 PCK40 Reimplantation of renal artery 56 57 PCK50 Reimplantation of inferior mesenteric artery 58 PCK99 Reimplantation of other visceral artery 59 PCN20 Plastic repair of coeliac trunk and branches 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 PCN30 Plastic repair of superior mesenteric artery 4 5 PCN40 Plastic repair of renal artery 6 PCN99 Plastic repair of other visceral artery 7 PCU70 Exploration of previous reconstruction of suprarenal abdominal aorta or visceral arteries 8 Thrombectomy or embolectomy in bypass from suprarenal abdominal aorta and visceral 9 PCU74 arteries 10 11 Closure of persisting arteriovenous fistula of bypass from suprarenal abdominal aorta and 12 PCU81 visceral arteries 13 PCU82 Plastic repair in bypass from suprarenal abdominal aorta and visceral arteries 14 PCU99 Other repair after previous reconstruction of suprarenal abdominal aorta and visceral arteries 15 16 PCW99 Other operation on suprarenal abdominal aorta and visceral arteries 17 PDA10 Exploration of infrarenal abdominal aorta 18 PDA30 Exploration Forof iliac artery peer review only 19 20 PDC10 Suture of infrarenal abdominal aorta 21 PDC30 Suture of iliac artery 22 PDE10 Thrombectomy or embolectomy of infrarenal abdominal aorta 23 24 PDE30 Thrombectomy or embolectomy of iliac artery 25 PDF10 Thrombendarterectomy of infrarenal abdominal aorta 26 PDF30 Thrombendarterectomy of iliac artery 27 PDG10 Operation on infrarenal abdominal aorta for aneurysm 28 29 PDG20 Bypass from aorta to iliac artery for aneurysm 30 PDG21 Bypass from aorta to bilateral iliac arteries for aneurysm 31 PDG22 Bypass from aorta to iliac and contralateral femoral artery for aneurysm 32 33 PDG23 Bypass from aorta to femoral artery for aneurysm 34 PDG24 Bypass from aorta to bilateral femoral arteries for aneurysm http://bmjopen.bmj.com/ 35 PDG30 Operation on iliac artery for aneurysm 36 37 PDG35 Bypass from iliac to femoral artery for aneurysm 38 PDG99 Other operation for aneurysm of infrarenal abdominal aorta and iliac arteries 39 PDH10 Bypass from infrarenal abdominal aorta 40 41 PDH20 Bypass from aorta to iliac artery 42 PDH21 Bypass from aorta to bilateral iliac arteries 43 PDH22 Bypass from aorta to iliac and contralateral femoral artery on October 1, 2021 by guest. Protected copyright. 44 45 PDH23 Bypass from aorta to femoral artery 46 PDH24 Bypass from aorta to bilateral femoral arteries 47 PDH30 Bypass from iliac artery 48 PDH35 Bypass from iliac to femoral artery 49 50 PDH99 Other bypass from abdominal aorta or iliac artery 51 PDN10 Plastic repair of infrarenal abdominal aorta 52 PDN30 Plastic repair of iliac artery 53 54 Exploration of previous reconstruction of infrarenal abdominal aorta or iliac arteries and distal 55 PDU70 connections 56 PDU74 Thrombectomy or embolectomy in bypass from infrarenal abdominal aorta or iliac artery 57 Closure of persisting arteriovenous fistula of bypass from infrarenal abdominal aorta or iliac 58 PDU81 artery 59 60 PDU82 Plastic repair of bypass from infrarenal abdominal aorta or iliac artery

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1 2 3 Other repair after previous reconstruction of infrarenal abdominal aorta and iliac arteries and BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 PDU99 distal 5 6 PDW99 Other operation on infrarenal abdominal aorta and iliac arteries and distal connections 7 PHB23 Ligature of iliac vein 8 PHB30 Ligature of inferior vena cava 9 PHB31 Ligature of renal vein 10 11 PHB32 Ligature of portal vein 12 PHB33 Ligature of superior mesenteric vein 13 PHB34 Ligature of inferior mesenteric vein 14 15 PHB36 Ligature of spermatic vein 16 PHC23 Suture of iliac vein 17 PHC30 Suture of inferior vena cava 18 For peer review only 19 PHC31 Suture of renal vein 20 PHC32 Suture of portal vein 21 PHC33 Suture of superior mesenteric vein 22 23 PHC34 Suture of inferior mesenteric vein 24 PHD30 Resection of inferior vena cava 25 PHD32 Resection of portal vein 26 27 PHD33 Resection of superior mesenteric vein 28 PHD34 Resection of inferior mesenteric vein 29 PHD36 Resection of spermatic vein 30 PHE23 Thrombectomy of iliac vein 31 32 PHE30 Thrombectomy of inferior vena cava 33 PHE31 Thrombectomy of renal vein 34 PHH25 Bypass from iliac vein 35 http://bmjopen.bmj.com/ 36 PHH30 Bypass from inferior vena cava 37 PHN30 Plastic repair of inferior vena cava 38 PHN32 Plastic repair of portal vein 39 40 PHN33 Plastic repair of superior mesenteric vein 41 PHN34 Plastic repair of inferior mesenteric vein 42 PHW35 Portosystemic shunt or bypass 43 on October 1, 2021 by guest. Protected copyright.

44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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in press. press. in Commons ( Attribution Creative under isprotected *Checklist Working RECORD SM, the von HT, Elm E, Sørensen Langan I, Petersen D, Moher K, Harron A, SmeethGuttmann L, EI, Benchimol *Reference: Statement. health (RECORD) Data Routinely-collected Observational using Conducted studies of REporting The Committee. Accessibility of of Accessibility and data, code Funding Funding 22 and funding of source the Give Other Information Other Generalisability Generalisability 21 generalisability the Discuss protocol, raw raw protocol, programming 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 41 of BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

POSTOPERATIVE WOUND DEHISCENCE AFTER LAPAROTOMY: A USEFUL HEALTH CARE QUALITY INDICATOR? A COHORT STUDY BASED ON NORWEGIAN HOSPITAL ADMINISTRATIVE DATA

ForJournal: peerBMJ Open review only Manuscript ID bmjopen-2018-026422.R1

Article Type: Research

Date Submitted by the 16-Dec-2018 Author:

Complete List of Authors: Helgeland , Jon ; Norwegian Institute of Public Health, Division of Health Services Tomic, Oliver; Norwegian University of Life Sciences, Department of Mathematic Sciences and Technology Hansen, Tonya; Norwegian Institute of Public Health, Division of Health Services Kristoffersen, Doris; Norwegian Institute of Public Health, Division of Health Services

Hassani, Sahar; University of Oslo, KG Jebsen Centre for Psychosis http://bmjopen.bmj.com/ Research, Institute of Clinical Medicine; Oslo University Hospital, Department of Medical Genetics Lindahl, Anne; Akershus University Hospital Trust, Division of Surgery; University of Oslo, Department of Health Administration and Health Economics

Primary Subject Surgery Heading:

Secondary Subject Heading: Health services research on October 1, 2021 by guest. Protected copyright.

Quality in health care < HEALTH SERVICES ADMINISTRATION & Keywords: MANAGEMENT, Patient safety, WOUND MANAGEMENT

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 1 POSTOPERATIVE WOUND DEHISCENCE AFTER LAPAROTOMY: A 6 7 8 9 10 2 USEFUL HEALTH CARE QUALITY INDICATOR? A COHORT STUDY 11 12 13 14 3 BASED ON NORWEGIAN HOSPITAL ADMINISTRATIVE DATA 15 16 17 18 4 Jon Helgeland1,7, OliverFor Tomic 2,peer Tonya Moen reviewHansen1, Doris Tove only Kristoffersen1, Sahar Hassani3,4, 19 20 5 Anne Karin Lindahl5,6 21 22 1 23 6 Division of Health Services, Norwegian Institute of Public Health, Oslo, Norway 24 25 7 2 Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Ås, 26 27 8 Norway 28 29 9 3 NORMENT, KG Jebsen Centre for Psychosis Research, Division of Mental Health and Addiction, Oslo 30 31 32 10 University Hospital and Institute of Clinical Medicine, University of Oslo, Oslo, Norway 33 34 11 4 Department of Medical Genetics, Oslo University Hospital, Oslo, Norway 35 http://bmjopen.bmj.com/ 36 12 5 Division of Surgery, Akershus University Hospital Trust, Lørenskog, Norway 37 38 13 6Department of Health administration and health economics, Institute of Health and Society, 39 40 14 University of Oslo, Oslo, Norway 41 42 7 43 15 Corresponding author: Jon Helgeland, [email protected] on October 1, 2021 by guest. Protected copyright. 44 45 16 Norwegian Institute of Public Health, PO Box 222 Skøyen, N-0213 Oslo 46 47 17 Word count: 3106 48 49 18 Keywords: Postoperative wound dehiscence, Surgical Quality, Quality Indicators, Patient Safety 50 51 52 53 19 54 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 20 ABSTRACT 5 6 7 8 9 21 Objectives 10 11 12 22 Postoperative wound dehiscence (PWD) is a serious complication to laparotomy, leading to higher 13 14 23 mortality, readmissions and cost. The aims of the present study are to investigate whether risk 15 16 24 adjusted PWD rates could reliably differentiate between Norwegian hospitals, and whether PWD 17 18 25 rates were associatedFor with hospital peer characteristics review such as hospital only type and laparotomy volume. 19 20 21 22 23 26 Design 24 25 26 27 Observational study using patient administrative data from all Norwegian hospitals, obtained from 27 28 28 the Norwegian Patient Registry, for the period 2011-2015, and linked using the unique person 29 30 29 identification number. 31 32 33 34 35 30 Participants http://bmjopen.bmj.com/ 36 37 38 31 All patients undergoing laparotomy, at least 15 years old, with length of stay at least two days, and 39 40 32 no diagnosis code for immunocompromised state or relating to pregnancy, childbirth and 41 42

33 puerperium. The final data set comprised 66 925 patients with 78 086 laparotomy episodes from 47 on October 1, 2021 by guest. Protected copyright. 43 44 45 34 hospitals. 46 47 48 49 35 Outcomes 50 51 52 36 The outcome was wound dehiscence, identified by the presence of a wound reclosure code, risk 53 54 37 adjusted for patient characteristics and operation type. 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 38 Results 5 6 7 39 The final data set comprised 1 477 wound dehiscences. Crude PWD rates varied from 0% to 5.1% 8 9 40 among hospitals, with an overall rate of 1.89%. Three hospitals with statistically significantly higher 10 11 41 PWD than average were identified, after case mix adjustment and correction for multiple 12 13 14 42 comparisons. Hospital volume was not associated with PWD rate, except that hospitals with very few 15 16 43 laparotomies had lower PWD rates. 17 18 For peer review only 19 20 44 Conclusions 21 22 23 45 Among Norwegian hospitals, there is considerable variation in PWD rate that cannot be explained by 24 25 26 46 operation type, age or comorbidity. This warrants further investigation into possible causes, such as 27 28 47 surgical technique, perioperative procedures or handling of complications. The risk adjusted PWD 29 30 48 rate after laparotomy is a candidate quality indicator for Norwegian hospitals. 31 32 33 34 35 49 STRENGTHS AND LIMITATIONS OF THIS STUDY http://bmjopen.bmj.com/ 36 37 38 39 50  Includes all laparotomies performed in the nation over a five-year period, with patients 40 41 51 followed across hospitals 42 43 52  Extends previous studies to a new health system and a new coding system on October 1, 2021 by guest. Protected copyright. 44 45 53  The statistical analysis uses methods for low event rates, avoiding asymptotic approximation 46 47 48 54  Results may be subject to coding inaccuracy and incompleteness, as well as selection effects 49 50 55  There were no data for surgical technique, nor for some clinical factors known to be relevant. 51 52 53 54 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 56 INTRODUCTION 5 6 7 8 57 The past decades have seen a major growth in initiatives for measuring, monitoring, and improving 9 10 58 the quality of health care services. Quality indicators are regularly published in many health care 11 12 59 systems. Performance of health care systems is also compared across nations, for instance in the 13

14 1 2 15 60 OECD Health Care Quality and Outcomes (HCQO) initiative, which Norway is a part of. Norway has 16 17 61 a national quality indicator system for monitoring and comparing hospital performance, however, 18 For peer review only 19 62 not all areas of hospital performance are covered by existing national quality indicators. While there 20 21 63 are quality indicators for outcomes such as mortality and process measures such as waiting times, 22 23 64 complications following hospital care is less explored, which is especially relevant following surgical 24 25 26 65 procedures. 27 28 29 66 Postoperative wound dehiscence (PWD) rates after open abdominal surgery (laparotomies) was 30 31 32 67 introduced as a patient safety indicator in the United States and later as a quality indicator by 33 34 68 OECD.3-6 Norway reported the second highest numbers for 2014-2015, with a PWD rate of 1.02%. The 35 http://bmjopen.bmj.com/ 36 69 overall range was 0.055% to 1.05%.5 Neighbouring Sweden, with comparable population health and 37 38 70 health care, reported 0.30%. Moreover, a recent study comparing adverse events in Norway and 39 40 41 71 Sweden found significantly higher adverse event rates of surgical complications in Norwegian 42 43 72 hospitals, compared to Swedish hospitals.7 on October 1, 2021 by guest. Protected copyright. 44 45 46 47 73 PWD is a serious complication that leads to higher mortality rates, higher implicit, explicit and social 48 49 74 costs as well as increased readmission rates.8 9 The PWD rate has been studied elsewhere as a quality 50 51 75 indicator for hospitals, and found to have a high positive predictive value.10 11 It is useful as a quality 52 53 76 indicator, since several of the risk factors are modifiable and within control of the hospital and 54 55 56 77 surgical team. There are few events per hospital, making it challenging to identify outlier hospitals for 57 58 78 quality improvement because of the high statistical uncertainty. 59 60

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1 2 3 79 Previous research has identified a number of risk factors for PWD. Examples of such factors are: (I) BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 80 patient related variables and comorbidities: smoking12, obesity13, chronic pulmonary disease, renal 6 7 14 15 16 8 81 insufficiency or diabetes and use of immunosuppressive agents ; (II) procedure related factors: 9 10 82 operation type9 17, type of incision and closure18-20 and length of operation time21; (III) postoperative 11 12 83 parameters: clean wound classification21, coughing9 and wound infection9 14; (IV) operative scenario: 13 14 84 e.g. qualifications of the surgeon21-23 and of the perioperative team, and whether the surgery is 15 16 9 13 17 85 emergent. 18 For peer review only 19 20 86 The objectives of this study are to study the occurrence and variation of PWD after laparotomy at 21 22 23 87 Norwegian hospitals, and the potential usefulness of a PWD indicator for the Norwegian health care 24 25 88 system, computed from patient administrative data. More specifically we aimed to 1) investigate the 26 27 89 possibility to identify hospitals with higher or lower laparotomy PWD rate than average, after 28 29 90 appropriate risk adjustment, 2) study the variability of the PWD rate among hospitals, and its relation 30 31 32 91 to hospital type and laparotomy volume. 33 34 35 http://bmjopen.bmj.com/ 36 92 MATERIAL AND METHODS 37 38 39 40 93 Patient administrative data from all Norwegian hospitals were provided by the Norwegian Patient 41 42 94 Registry (NPR) for the period 2011-2015.24 This comprised individual patient data from all 43 on October 1, 2021 by guest. Protected copyright. 44 95 department stays: type of admission (acute or elective), primary and secondary diagnosis codes 45 46 25 47 96 according to the Norwegian version of ICD-10, surgical and medical procedures, age, gender, date 48 49 97 and time of ward admission and discharge. Surgical procedures and operations were coded according 50 51 98 to the Norwegian version of the NOMESCO Classification of Surgical Procedures (NCSP-N).26 52 53 99 Procedure time and date were not available. It was therefore not possible to exclude reclosures of 54 55 56 100 wounds occurring before or on the same day as laparotomies within the same episode, as requested 57 58 101 in the OECD indicator specification. The NPR data files were checked for missing values and 59 60

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1 2 3 102 inconsistencies between variables, such as date and time of discharge before admission or invalid BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 103 ICD-10 code. 6 7 8 9 104 Wound dehiscence was defined as the occurrence of a code for a reclosure operation, i.e. a 10 11 105 reoperation for wound dehiscence. This excludes superficial dehiscences, as these are usually not 12 13 14 106 resutured, and the code for reclosure operation is restricted to deep wound dehiscences. 15 16 107 Laparotomies and wound reclosure operations were identified according to procedure codes. An 17 18 108 operation coded withFor a laparotomy peer code, signifies review an incision into only the abdominal wall, through the 19 20 109 fascia and with an opening of the abdominal cavity. Laparoscopic and endoscopic procedures were 21 22 23 110 not included. Details of the codes used can be found in the online supplement. 24 25 26 111 All permanent residents in Norway have a Personal Identification Number (PIN), registered in the 27 28 29 112 NPR. NPR prepared an encrypted PIN for all patients with a valid PIN, allowing tracking of patients 30 31 113 over time and between hospitals. The data were linked with the National Registry to provide data of 32 33 114 death (when applicable), using the PIN. 34 35 http://bmjopen.bmj.com/ 36 37 115 Ward admissions for each patient, at more than one hospital in case of transfers, were linked into 38 39 116 episodes of care when less than eight hours elapsed from time of discharge to the next ward 40 41 117 admission.27 An episode was regarded as acute if the first admission in the episode was coded as 42 43 on October 1, 2021 by guest. Protected copyright. 118 non-elective, as a laparotomy episode if it included any procedure code for laparotomy (reclosures 44 45 46 119 not included), and a reclosure episode if a reclosure code was found. The initial data set consisted of 47 48 120 all laparotomy and reclosure episodes. Each reclosure episode was linked to the laparotomy episode 49 50 121 immediately preceding or coinciding with it. Reclosure episodes with no preceding laparotomy 51 52 122 episode within 30 days, as well as laparotomy or reclosure episodes following a reclosure episode 53 54 55 123 within 30 days, were excluded. Note that the linking of laparotomies and reclosures was not part of 56 57 124 the original OECD specification, but is required in order to attribute PWD to hospitals and to enable 58 59 125 risk adjustment. Following the OECD specification, laparotomy episodes (and consequently any 60

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1 2 3 126 linked reclosure episodes) were excluded if a diagnosis code for immunocompromised state or BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 127 relating to pregnancy, childbirth and puerperium was present, if the length of stay was less than two 6 7 8 128 days, or if the patient’s age was less than 15 years. Hospitals with less than 10 laparotomies over the 9 10 129 five-year period were excluded. The hospitals belonged to one of three types: regional, large with 11 12 130 acute function and small with acute function. For details of the diagnosis and operation codes used, 13 14 131 see the online supplement. For risk adjustment, Charlson comorbidities were determined from 15 16 27-29 17 132 previous admissions three years prior to, but not including the current episode of care. Diagnoses 18 For peer review only 19 133 were grouped according to the Clinical Condition Summary system (CCS), adapted to the Norwegian 20 21 134 version of ICD-10.30 22 23 24 25 135 Statistical methods 26 27 28 29 136 Risk adjusted probabilities for a laparotomy episode resulting in a reclosure operation were 30 31 137 estimated by bias corrected logistic regression.31 The final model was fit by stepwise regression with 32 33 138 the BIC criterion, allowing for potential two-way interactions. 34 35 http://bmjopen.bmj.com/ 36 37 139 To identify outlier hospitals, i.e. those with high or low risk adjusted PWD probabilities, estimated 38 39 140 hospital effects were compared to a reference value, defined as the 25% trimmed mean of the 40 41 141 hospital effects on the logistic scale.32 As some hospitals reported zero reclosures, ordinary maximum 42 on October 1, 2021 by guest. Protected copyright. 43 33 44 142 likelihood estimates of the model parameters do not exist, due to separation , and the estimated 45 46 143 variances of the fitted parameters, based on their asymptotic distribution, become unreliable. The 47 48 144 comparison used an exact test based on the Poisson binomial distribution for the number of PWDs 49 50 145 per hospital, using the estimated probabilities for each case, together with parametric bootstrapping 51 52 146 to account for the estimation uncertainty in the model parameters. Tests for significance were 53 54 34 55 147 corrected for multiple comparisons using the Guo-Romano method , and outlier status assigned 56 57 148 according to the false discovery rate (FDR). An FDR not exceeding 5% was regarded as significant. For 58 59 149 sensitivity analysis, two alternative risk adjustment models were tested, with either a four-category 60

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1 2 3 150 grouping of procedures, or with diagnosis categories, instead of the 13-category procedure grouping. BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 151 In addition, a model with the four Norwegian hospital regions was also estimated. 6 7 8 9 152 Hospital volume, modelled by splines35, was tested for inclusion in the model. We also performed 10 11 153 this test after exclusion of hospitals with zero reclosures. 12 13 14 15 154 Finally, the hospital specific effects were modelled as a mixture of two normal distributions. The 16 17 155 expectation-maximization (EM) algorithm was used, taking into account the estimation variances. 18 For peer review only 19 20 156 The mixture model yielded estimates of the quartiles of the hospital odds ratios and the scaled 21 22 157 interquartile range (normalized by dividing by 1.349, to give the standard deviation in the case of a 23 24 158 normal distribution) was computed as a measure of spread among hospitals. Bootstrapping of the 25 26 159 mixture model was used to find a 95% confidence interval for the scaled interquartile range. 27 28 29 30 31 160 Risk adjustment 32 33 34 161 The following case-mix variables were included as candidates in the stepwise regression: age, gender, 35 http://bmjopen.bmj.com/ 36 162 indicators for the individual Charlson comorbidities, number of previous hospital admissions two 37 38 163 years prior to current admission, and whether the episode was acute or elective. A linear trend in 39 40 41 164 admission year was also included. Age was modelled by natural splines with knots at the median and 42 43 165 quartiles.35 Based on previous studies of risk factors9 17, procedures were categorized into 13 types, on October 1, 2021 by guest. Protected copyright. 44 45 166 according to the body system or organ involved. The effects of operation types were normalized to 46 47 167 have zero sum on the logistic scale. 48 49 50 51 168 For a quality indicator, only characteristics of the patient when entering the hospital, are meaningful 52 53 169 risk adjustment variables. No data were available for smoking, obesity or other patient or case 54 55 170 characteristics such as nutritional status. There was no information about operation urgency beyond 56 57 58 171 the status of the hospital admission or episode as elective or acute. 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 172 Patient and Public Involvement 5 6 7 173 Patients were not involved in the planning, conduct or analysis of this study. The policy of the 8 9 174 Norwegian Institute of Public health is to publish hospital quality indicators, when they have been 10 11 175 successfully validated. 12 13 14 15 16 176 RESULTS 17 18 For peer review only 19 20 177 The initial data set comprised 96 102 episodes with laparotomy and 1 909 with a reclosure operation. 21 22 178 After restricting data to reclosures paired with a laparotomy within 30 days, 1 580 reclosures 23 24 179 remained. After exclusions for pregnancy, childbirth and puerperium or immunocompromised state, 25 26 27 180 age and LOS, 78 299 laparotomies remained. Lastly, hospitals with less than 10 laparotomies were 28 29 181 excluded, yielding a final data set with 66 925 unique patients, 78 086 laparotomies and 1 477 30 31 182 reclosures from 47 hospitals. Descriptive statistics for the dataset are shown in Table 1. The 32 33 183 operation types are tabulated in the online Supplement. 34 35 http://bmjopen.bmj.com/ 36 37 184 Table 1. Descriptive statistics for final data set 38 39 PWD No PWD 40 41 Age, years, median (quartiles) 69 (61-78) 65 (51-75) 42 Gender, females, n (%) 517 (35) 43 094 (56) 43 on October 1, 2021 by guest. Protected copyright. 44 Acute laparotomy episode, n (%) 657 (44) 26 381 (34) 45 Main diagnosis for reclosure episode coded as PWD, n (%) 45 (3.1) — 46 Main diagnosis for reclosure episode coded as deep wound infection, 47 274 (19) — 48 n (%) 49 Hospital type for laparotomy episodes 50 51 Regional, n (%) 545 (37) 28 104 (37) 52 Large with acute function, n (%) 810 (55) 40 291 (53) 53 Small with acute function, n (%) 122 (8.3) 8 214 (11) 54 55 Comorbidities 56 Diabetes with complications, n (%) 18 (1.2) 893 (1.2) 57 58 Chronic pulmonary disease, n (%) 196 (13) 5 147 (6.7) 59 Renal disease, n (%) 66 (4.5) 2 716 (3.5) 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 30 day mortality (laparotomy episode), % 67 (4.5) 2 668 (3.5) 4 5 Length of stay (LOS) laparotomy episode, days, median (quartiles) 19 (11-29) 7.4 (4.4-13) 6 Reclosure and matched laparotomy in same episode, n (%) 1 211 (82) — 7 8 Converted from or to laparotomy, n (%) 12 (0.81) 578 (0.75) 9 Robot assistance in laparotomy, n (%) 3 (0.2) 404 (0.53) 10 11 185 12 186 From 2011 to 2015, the annual volume of laparotomies decreased somewhat, from 16 730 to 14 419, 13 14 187 while the proportion of acute laparotomies remained stable at around 35%. 15 16 17 18 188 The overall rate of PWDFor for the peer five-year period review was 1.89%. Crude only PWD rates varied from 0% to 5.1% 19 20 189 among hospitals. After risk adjustment, the range was 0.1% - 5.4%. Table 2 shows the odds ratios of 21 22 190 the final logistic regression model. No interactions were included. The model showed good fit 23 24 36 25 191 according to the modified Hosmer-Lemeshow test (p=0.53) and good predictive ability, with an area 26 27 192 under the operating characteristic (c-statistic) of 0.73. 28 29 30 31 193 Table 2. Final multivariate logistic model for risk adjustment 32 33 Variable Adjusted odds ratio (95% confidence interval) 34

Year of admission 0.93 (0.90-0.96) http://bmjopen.bmj.com/ 35 36 Age, spline function 37 40 (reference) 1.00 38 39 50 1.37 (1.25-1.49) 40 60 1.97 (1.65-2.36) 41 42 70 2.39 (1.97-2.90) 43 Gender on October 1, 2021 by guest. Protected copyright. 44 45 Female (reference) 1 46 Male 2.42 (2.16-2.72) 47 48 Elective laparotomy episode (reference) 1 49 Acute laparotomy episode 1.36 (1.21-1.52) 50 Chronic pulmonary disease 1.72 (1.47-2.01) 51 52 Operation typea 53 2.40 (1.78-3.24) 54 55 Hernia (diaphragmal) 2.57 (1.37-4.81) 56 Thoracoabdominal aorta 2.08 (0.85-5.09) 57 58 Gastrointestinal tract 2.04 (1.69-2.46) 59 Liver 1.14 (0.69-1.87) 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 Biliary tract 0.12 (0.05-0.28) 4 5 Pancreas 0.79 (0.40-1.58) 6 Spleen 1.20 (0.45-3.24) 7 8 Other digestive system 1.46 (1.03-2.07) 9 Kidney 0.09 (0.03-0.28) 10 11 Other urinary and male genital organs 0.52 (0.37-0.71) 12 Female genital organs 1.43 (1.06-1.92) 13 14 Peripheral vascular surgery 1.21 (0.93-1.57) 15 More than one type of surgeryb 2.58 (2.12-3.15) 16 17 Hospital 18 Scaled interquartileFor range peer 0.30review only(0.23-0.34) 19 194 a Odds ratios for operation type is scaled to have geometric mean 20 21 195 b Not counting exploratory laparotomy 22 23 196 24 25 26 27 197 In Figure 1, risk-adjusted PWD rates are shown for each hospital, plotted versus laparotomy volume 28 29 198 and hospital type. 30 31 32 33 199 After significance testing, we identified three hospitals with higher PWD and none with lower PWD 34 35 200 than average, when correcting for multiple testing. Without multiple test correction, one additional http://bmjopen.bmj.com/ 36 37 201 hospital with high PWD was found to be marginally significant (p=0.053). 38 39 40 41 202 In the alternative model including volume, the PWD increased with yearly laparotomy volume from a 42 43 203 very low level up to 120 laparotomies per year, after which it remained fairly constant, see Figure 1. on October 1, 2021 by guest. Protected copyright. 44 45 204 The effect of volume was significant (p<0.001), also after exclusion of the four smallest volume 46 47 48 205 hospitals with zero reclosures (p=0.008). Hospital type coincided almost completely with a grouping 49 50 206 of hospitals by volume, and was therefore not tested separately. There was significant variation 51 52 207 among regions (p<0.001), with the Northern region having the highest and the South-Eastern region 53 54 208 the lowest rates. Details can be found in the online supplement. Using diagnosis categories or 55 56 57 209 aggregated operation type as risk adjustment variables resulted in very small changes in risk adjusted 58 59 210 PWD rates. 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 211 DISCUSSION 5 6 7 8 212 We have studied wound dehiscence after laparotomy, as a quality indicator based on the OECD 9 10 213 specification, and found that it discriminated between Norwegian hospitals. The indicator was risk 11 12 214 adjusted for differences in age, gender, comorbidity and type of surgery, and showed little sensitivity 13 14 15 215 to changes in the set of risk adjustment variables. The overall PWD rate was 1.89%. After risk 16 17 216 adjustment, the hospitals’ PWD rate varied between 0.1% and 5.4%. Laparotomy volume and type of 18 For peer review only 19 217 hospital had little effect on the PWD rate, except for hospitals with very low volume. Advanced age, 20 21 218 male gender, chronic pulmonary disease, and emergency laparotomy were all significant risk factors 22 23 219 for PWD. There were significant PWD differences according to the organ system targeted. The overall 24 25 26 220 rate of PWD showed a small but statistically significant decline over the observation period 2011- 27 28 221 2015. The relatively large variation of PWD rates between hospitals, after correction for patient 29 30 222 characteristics and operation type, indicates possible variation in the quality of healthcare among 31 32 223 hospitals. This may be due to variation in surgical technique and perioperative care, as well as the 33 34 35 224 handling of postoperative complications, such as wound infection, which is known to be a risk factor http://bmjopen.bmj.com/ 36 37 225 for PWD.17 We found PWD rates well within the range reported in international studies.9 13 14 17 21 37 38 38 39 226 Also, the risk factors identified are in accordance with previous studies, albeit limited to 40 41 227 administrative data. Laparotomy volume has negligible effect apart from the few hospitals with very 42 43 on October 1, 2021 by guest. Protected copyright. 44 228 low volume. A Japanese study reported a similar conclusion, while volume was found to have effect 45 46 229 in US hospitals.39 40 The effect is likely a result of the types of operations performed at the low- 47 48 230 volume hospitals, compared with the other hospitals. 49 50 51 52 231 Our study is based on complete data from all Norwegian hospitals performing laparotomies. It was 53 54 232 possible to track patients during transfers and reoperations at different hospitals. To the best of our 55 56 233 knowledge, no similar study has been performed. NPR, the data source, has been validated for 57 58 59 234 several disease categories with respect to identification of cases based on diagnoses and/or 60

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1 2 3 235 procedures, and found to have a very high degree of completeness, compared to Norwegian national BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 236 medical quality registries.41-44 At the time of writing, the completeness of NPR, after 24 registries 6 7 24 8 237 have been studied, ranges from 83.5% to 99.8%. 9 10 11 238 We cannot exclude a residual imbalance in case mix, affecting PWD through e.g. smoking or obesity, 12 13 14 239 which are known risk factors. There is regional variation in the prevalence of smoking and obesity in 15 16 240 Norway.45 Obesity is more prevalent in Northern Norway, where PWD rates are somewhat higher. 17 18 241 However, in some otherFor areas wherepeer obesity review is less prevalent, theonly rates are similar. There is no 19 20 242 consistent correspondence between the known variation in smoking among counties and PWD rates. 21 22 23 243 Some surgical procedures are performed only at regional hospitals, and it is therefore possible that 24 25 244 selection effects are present. In that case, one would expect larger changes in PWD rates after risk 26 27 245 adjustment for operation type, which was not found. One potential source of error in our study is the 28 29 246 completeness and correctness of coding in the NPR, particularly the coding of reclosure operations. 30 31 32 247 The risk adjustment depends on data from previous hospitalization and may not capture all 33 34 248 comorbidities. Moreover, selection effects cannot not be ruled out. Differing policies for operations 35 http://bmjopen.bmj.com/ 36 249 on patients with known risk factors, e.g. obesity or smoking, would likely cause variation in PWD 37 38 250 rates. Patients who die before reoperation or are managed by other means will not be registered. 39 40 251 We believe that this applies to very few patients and would not influence our results. No attempt 41 42 43 252 was made to identify main operation or operation intent, as this would require a classification effort on October 1, 2021 by guest. Protected copyright. 44 45 253 outside the scope of the present study. 46 47 48 49 254 Previous studies have shown that the quality indicator has high positive predictive value, but only 50 51 255 moderate sensitivity.10 46 47Since we have used specific wound reclosure codes, similar to those used 52 53 256 in previous studies, we expect a high positive predictive value in Norway as well. Conceivably, the 54 55 257 sensitivity depends on the coding system, in particular the various alternative codes related to 56 57 58 258 complications. Sensitivity in Norway may thus differ from that of other healthcare systems. A recent 59 60 259 retrospective medical record study from neighbouring Sweden reports that 86.9% of wound

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1 2 3 260 dehiscences were reoperated.38 Norway has an activity-based system for financing hospitals, which is BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 261 an incentive to report all reclosure operations. 6 7 8 9 262 Conclusions 10 11 263 Among Norwegian hospitals, there is a significant variation in PWD rate after laparotomies that 12 13 14 264 cannot be explained by operation type, age, comorbidity or whether the admission was elective or 15 16 265 acute. This warrants further investigation into possible causes, such as patient related factors, 17 18 266 surgical technique, perioperativeFor peer procedures review or handling of complications, only e.g. wound infections. 19 20 267 Some of these factors are known to be amenable.20 48 The relatively large between-hospital variation 21 22 23 268 found in the present study is an indication of potential for improvement. The risk adjusted PWD rate 24 25 269 after laparotomy is a candidate for use as a quality indicator for Norwegian hospitals, and will make it 26 27 270 possible to identify hospitals with apparent quality problems. To achieve sufficient discrimination, 28 29 271 however, five-year data are desirable, making it more difficult to monitor changes in hospital 30 31 32 272 performance resulting from quality improvement efforts. It lies outside the scope of the present 33 34 273 study to perform a comprehensive validation of the PWD rate as a quality indicator suitable for 35 http://bmjopen.bmj.com/ 36 274 public reporting. There are uncertainties and potential biases in the indicator, implying that it must 37 38 275 be regarded as a signal for follow-up within hospitals, rather than giving a final verdict of inferior or 39 40 41 276 superior quality. For reporting on surgical quality, several indicators should be used to give a 42 43 277 balanced view of the different aspects of quality and patient safety. on October 1, 2021 by guest. Protected copyright. 44 45 46 47 278 FOOTNOTES 48 49 50 51 52 279 Funding 53 54 55 280 This research did not receive any grants from any funding agency in the public, commercial or not- 56 57 281 for-profit sectors. 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 282 Competing interests 5 6 7 283 The authors have no competing interests. 8 9 10 11 284 Authors’ contributions 12 13 14 285 AKL and OT conceived the study. DTK, TMH, OT, and SH participated in data preparation. OT, SH and 15 16 17 286 AKL contributed to the analysis. OT helped draft the manuscript. JH was responsible for the statistical 18 For peer review only 19 287 analysis and final manuscript. All authors revised and approved the final manuscript. 20 21 22 23 288 Ethics approval 24 25 26 289 The study was approved by the Norwegian Directorate of Health and the Norwegian Data Protection 27 28 29 290 Authority. 30 31 32 33 291 Data sharing 34 35 http://bmjopen.bmj.com/ 36 292 The data set contains indirectly identifiable personal data, and cannot be shared without express 37 38 293 permission from the Norwegian Patient Registry. For further information, contact the corresponding 39 40 41 294 author. 42 43 on October 1, 2021 by guest. Protected copyright. 44 295 45 Figure 1. Risk adjusted PWD rates versus yearly laparotomy volume, by hospital type. Trend 46 296 curve is obtained by smoothing the scatterplot. Significance testing is adjusted for multiple 47 297 comparisons 48 49 50 298 REFERENCES 51 52 53 54 299 55 56 300 57 58 301 1. Carinci F, Van Gool K, Mainz J, et al. Towards actionable international comparisons of health 59 302 system performance: expert revision of the OECD framework and quality indicators. Int J 60

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1 2 3 303 Qual Health Care 2015;27(2):137-46. doi: 10.1093/intqhc/mzv004 [published Online First: BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 304 2015/03/12] 5 305 2. OECD. Health Care Quality and Outcomes: OECD; 2018 [Available from: 6 7 306 http://www.oecd.org/health/health-systems/health-care-quality-and-outcomes.htm 8 307 accessed 2018-06-06 2018. 9 308 3. Hannan EL. Using mortality data for profiling hospital quality of care and targeting substandard 10 309 care. J Soc Health Syst 1989;1(1):31-48. 11 310 4. Miller MR, Elixhauser A, Zhan C, et al. Patient Safety Indicators: using administrative data to 12 311 identify potential patient safety concerns. Health Serv Res 2001;36(6 Pt 2):110-32. [published 13 312 Online First: 2005/09/09] 14 313 5. OECD. Health Care Quality Indicators - Patient Safety 2018 [Available from: 15 314 http://www.oecd.org/health/health-systems/hcqi-patient-safety.htm accessed 2018-06-06 16 17 315 2018. 18 316 6. OECD. Definitions forFor Health peerCare Quality Indicatorsreview 2016-2017 only HCQI Data Collection: OECD, 19 317 2016:113. 20 318 7. Deilkas ET, Risberg MB, Haugen M, et al. Exploring similarities and differences in hospital adverse 21 319 event rates between Norway and Sweden using Global Trigger Tool. BMJ open 22 320 2017;7(3):e012492. doi: 10.1136/bmjopen-2016-012492 23 321 8. Hannan EL, Bernard HR, O'Donnell JF, et al. A methodology for targeting hospital cases for quality 24 322 of care record reviews. Am J Public Health 1989;79(4):430-6. 25 26 323 9. van Ramshorst GH, Nieuwenhuizen J, Hop WC, et al. Abdominal wound dehiscence in adults: 27 324 development and validation of a risk model. World J Surg 2010;34(1):20-7. doi: 28 325 https://dx.doi.org/10.1007/s00268-009-0277-y 29 326 10. Romano PS, Mull HJ, Rivard PE, et al. Validity of selected AHRQ patient safety indicators based on 30 327 VA National Surgical Quality Improvement Program data. Health Serv Res 2009;44(1):182- 31 328 204. doi: https://dx.doi.org/10.1111/j.1475-6773.2008.00905.x 32 329 11. Rosen AK, Itani KM, Cevasco M, et al. Validating the patient safety indicators in the Veterans 33 330 Health Administration: do they accurately identify true safety events? Med Care 34 35 331 2012;50(1):74-85. doi: https://dx.doi.org/10.1097/MLR.0b013e3182293edf http://bmjopen.bmj.com/ 36 332 12. Kean J. The effects of smoking on the wound healing process. J Wound Care 2010;19(1):5-8. doi: 37 333 10.12968/jowc.2010.19.1.46092 38 334 13. Shanmugam VK, Fernandez SJ, Evans KK, et al. Postoperative wound dehiscence: Predictors and 39 335 associations. Wound Repair Regen 2015;23(2):184-90. doi: 40 336 https://dx.doi.org/10.1111/wrr.12268 41 337 14. Sandy-Hodgetts K, Carville K, Leslie GD. Determining risk factors for surgical wound dehiscence: a 42 338 literature review. Int Wound J 2015;12(3):265-75. doi: 10.1111/iwj.12088 43 on October 1, 2021 by guest. Protected copyright. 339 15. Roine E, Bjork IT, Oyen O. Targeting risk factors for impaired wound healing and wound 44 45 340 complications after kidney transplantation. Transplant Proc 2010;42(7):2542-6. doi: 46 341 https://dx.doi.org/10.1016/j.transproceed.2010.05.162 47 342 16. Stephan RN, Munschauer CE, Kumar MS. Surgical wound infection in renal transplantation: 48 343 outcome data in 102 consecutive patients without perioperative systemic antibiotic 49 344 coverage. Arch Surg 1997;132(12):1315-8; discussion 18-9. 50 345 17. Sorensen LT, Hemmingsen U, Kallehave F, et al. Risk factors for tissue and wound complications in 51 346 gastrointestinal surgery. Ann Surg 2005;241(4):654-8. 52 347 18. Mahey RG, Smruti; Rajpurohit, Jitesh; Desai, Desai; Suryawanshi, Sachin;. A prospective study of 53 54 348 risk factors for abdominal wound dehiscence. International Surgery Journal 2017;4(1):24-28. 55 349 doi: http://dx.doi.org/10.18203/2349-2902.isj20163983 56 350 19. Deerenberg EB, Harlaar JJ, Steyerberg EW, et al. Small bites versus large bites for closure of 57 351 abdominal midline incisions (STITCH): a double-blind, multicentre, randomised controlled 58 352 trial. Lancet 2015;386(10000):1254-60. doi: 10.1016/s0140-6736(15)60459-7 [published 59 353 Online First: 2015/07/21] 60

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1 2 3 354 20. Israelsson LA, Millbourn D. Prevention of Incisional Hernias: How to Close a Midline Incision. Surg BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 355 Clin North Am 2013;93(5):1027-40. doi: https://doi.org/10.1016/j.suc.2013.06.009 5 356 21. Webster C, Neumayer L, Smout R, et al. Prognostic models of abdominal wound dehiscence after 6 7 357 laparotomy. J Surg Res 2003;109(2):130-7. 8 358 22. Bucknall TE, Cox PJ, Ellis H. Burst abdomen and incisional hernia: a prospective study of 1129 9 359 major laparotomies. Br Med J (Clin Res Ed) 1982;284(6320):931-3. [published Online First: 10 360 1982/03/27] 11 361 23. Gislason H, Soreide O, Viste A. Wound complications after major gastrointestinal operations. The 12 362 surgeon as a risk factor. Dig Surg 1999;16(6):512-4. doi: 10.1159/000018778 13 363 24. Health NDo. Norsk pasientregister - innhold og kvalitet: Norwegian Directorate of Health; 2018 14 364 [Available from: https://helsedirektoratet.no/norsk-pasientregister-npr/innhold-og-kvalitet 15 365 accessed 2018-12-06 2018. 16 17 366 25. eHealth NDo. Helsefaglige kodeverk: Norwegian Directorate of eHealth 2018 [Available from: 18 367 https://ehelse.no/standarder-kodeverk-og-referansekatalog/helsefaglige-kodeverkFor peer review only accessed 19 368 2018-06-06 2018. 20 369 26. Norwegian Directorate of eHealth. NCMP, NCSP og NCRP: Klassifikasjon av medisinske, kirurgiske 21 370 og radiologiske prosedyrer Norwegian Directorate of eHealth; 2018 [Available from: 22 371 https://finnkode.ehelse.no/#ncmpncsp/0/0/0/-1 accessed 15th May 2018. 23 372 27. Hassani S, Lindman AS, Kristoffersen DT, et al. 30-Day Survival Probabilities as a Quality Indicator 24 373 for Norwegian Hospitals: Data Management and Analysis. PLoS One 2015;10(9):e0136547. 25 26 374 doi: 10.1371/journal.pone.0136547 27 375 28. Quan HD, Sundararajan V, Halfon P, et al. Coding algorithms for defining comorbidities in ICD-9- 28 376 CM and ICD-10 administrative data. Med Care 2005;43(11):1130-39. doi: DOI 29 377 10.1097/01.mlr.0000182534.19832.83 30 378 29. Quan H, Li B, Couris CM, et al. Updating and validating the Charlson comorbidity index and score 31 379 for risk adjustment in hospital discharge abstracts using data from 6 countries. Am J 32 380 Epidemiol 2011;173(6):676-82. doi: 10.1093/aje/kwq433 33 381 30. (HCUP) HCaUP. Beta Clinical Classifications Software (CCS) for ICD-10-CM/PCS: Agency for 34 35 382 Healthcare Research and Quality; 2018 [Available from: https://www.hcup- http://bmjopen.bmj.com/ 36 383 us.ahrq.gov/toolssoftware/ccs10/ccs10.jsp accessed 2018-06-06 2018. 37 384 31. Firth D. Bias Reduction of Maximum-Likelihood-Estimates. Biometrika 1993;80(1):27-38. doi: DOI 38 385 10.1093/biomet/80.1.27 39 386 32. Kristoffersen DT, Helgeland J, Clench-Aas J, et al. Observed to expected or logistic regression to 40 387 identify hospitals with high or low 30-day mortality? PLoS One 2018;13(4) doi: ARTN 41 388 e0195248 10.1371/journal.pone.0195248 42 389 33. Albert A, Anderson JA. On the Existence of Maximum Likelihood Estimates in Logistic Regression 43 on October 1, 2021 by guest. Protected copyright. 390 Models. Biometrika 1984;71(1):1-10. doi: 10.2307/2336390 44 45 391 34. Guo W, Romano JP. On stepwise control of directional errors under independence and some 46 392 dependence. Journal of Statistical Planning and Inference 2015;163:21-33. doi: 47 393 https://doi.org/10.1016/j.jspi.2015.02.009 48 394 35. Chambers JM, Hastie TJ, Eds. Statistical models in S. Pacific Grove: Wadsworth & Brooks/Cole 49 395 1992. 50 396 36. Paul P, Pennell ML, Lemeshow S. Standardizing the power of the Hosmer-Lemeshow goodness of 51 397 fit test in large data sets. Stat Med 2013;32(1):67-80. doi: 10.1002/sim.5525 52 398 37. Kenig J, Richter P, Lasek A, et al. The efficacy of risk scores for predicting abdominal wound 53 54 399 dehiscence: a case-controlled validation study. BMC Surg 2014;14:65. doi: 10.1186/1471- 55 400 2482-14-65 56 401 38. Walming S, Angenete E, Block M, et al. Retrospective review of risk factors for surgical wound 57 402 dehiscence and incisional hernia. BMC Surg 2017;17(1):19. doi: 10.1186/s12893-017-0207-0 58 403 39. Kitazawa T, Matsumoto K, Fujita S, et al. Perioperative patient safety indicators and hospital 59 404 surgical volumes. BMC Res Notes 2014;7:117. doi: 10.1186/1756-0500-7-117 [published 60 405 Online First: 2014/03/04]

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1 2 3 406 40. Hernandez-Boussard T, Downey JR, McDonald K, et al. Relationship between Patient Safety and BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 407 Hospital Surgical Volume. Health Serv Res 2012;47(2):756-69. doi: doi:10.1111/j.1475- 5 408 6773.2011.01310.x 6 7 409 41. Bakken IJ, Gystad SO, Christensen OO, et al. Comparison of data from the Norwegian Patient 8 410 Register and the Cancer Registry of Norway. Tidsskr Nor Laegeforen 2012;132(11):1336-40. 9 411 doi: 10.4045/tidsskr.11.1099 [published Online First: 2012/06/22] 10 412 42. Hoiberg MP, Gram J, Hermann P, et al. The incidence of hip fractures in Norway -accuracy of the 11 413 national Norwegian patient registry. BMC Musculoskelet Disord 2014;15:372. doi: 12 414 10.1186/1471-2474-15-372 [published Online First: 2014/11/15] 13 415 43. Oie LR, Madsbu MA, Giannadakis C, et al. Validation of intracranial hemorrhage in the Norwegian 14 416 Patient Registry. Brain and behavior 2018;8(2):e00900. doi: 10.1002/brb3.900 [published 15 417 Online First: 2018/02/28] 16 17 418 44. Varmdal T, Bakken IJ, Janszky I, et al. Comparison of the validity of stroke diagnoses in a medical 18 419 quality registerFor and an peeradministrative review health register. Scandinavian only journal of public health 19 420 2016;44(2):143-9. doi: 10.1177/1403494815621641 [published Online First: 2015/12/15] 20 421 45. Health NIoP. Public Health report: Norwegian Institute of Public Health; 2018 [Available from: 21 422 https://www.fhi.no/en/op/hin/ accessed 2018-06-06 2018. 22 423 46. Cevasco M, Borzecki AM, McClusky DA, 3rd, et al. Positive predictive value of the AHRQ Patient 23 424 Safety Indicator "postoperative wound dehiscence". J Am Coll Surg 2011;212(6):962-7. doi: 24 425 https://dx.doi.org/10.1016/j.jamcollsurg.2011.01.053 25 26 426 47. Borzecki AM, Cevasco M, Mull H, et al. Improving the identification of postoperative wound 27 427 dehiscence missed by the Patient Safety Indicator algorithm. Am J Surg 2013;205(6):674-80. 28 428 doi: https://dx.doi.org/10.1016/j.amjsurg.2012.07.040 29 429 48. Berríos-Torres SI, Umscheid CA, Bratzler DW, et al. Centers for disease control and prevention 30 430 guideline for the prevention of surgical site infection, 2017. JAMA Surg 2017;152(8):784-91. 31 431 doi: 10.1001/jamasurg.2017.0904 32 33 34 432 35 http://bmjopen.bmj.com/ 36 37 38 39 40 41 42 43 on October 1, 2021 by guest. Protected copyright. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 For peer review only 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 http://bmjopen.bmj.com/ 32 33 34 35 36 37 38 39 Figure 1. Risk adjusted PWD rates versus yearly laparotomy volume, by hospital type. Trend curve is on October 1, 2021 by guest. Protected copyright. obtained by smoothing the scatterplot. Significance testing is adjusted for multiple comparisons 40 41 149x149mm (300 x 300 DPI) 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 20 of 45

1 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Online supplement 6 7 8 Table 1. Hospital types 9 10 Hospital type Number 11 12 Small hospitals with acute function 21 13 Large hospitals with acute function 22 14 15 Regional hospitals 4 16 17 18 Table 2. LaparotomyFor cases after peer operation review type (primary episode)only 19 20 Operation type Frequency, n (%) 21 22 Gastrointestinal tract 30 404 (38.9) 23 More than one type of surgerya 14 051 (18.0) 24 Female genital organs 10 720 (13.7) 25 26 Other urinary and male genital organs 6 536 (8.4) 27 Peripheral vascular surgery 4 628 (5.9) 28 29 Biliary tract 2 739 (3.5) 30 Other digestive system 2 226 (2.9) 31 32 Kidney 2 152 (2.8) 33 Exploratory laparotomy 2 061 (2.6) 34 35 Liver 1 122 (1.4) http://bmjopen.bmj.com/ 36 Pancreas 775 (1.0) 37 38 Hernia (diaphragmal) 274 (0.4) 39 Spleen 248 (0.3) 40 41 Thoracoabdominal aorta 150 (0.2) 42 aNot counting exploratory laparotomy 43 on October 1, 2021 by guest. Protected copyright. 44 45 Table 3. Effect of hospital region, after risk adjustment. Odds ratio standardized to have 46 47 geometric mean one. 48 49 Hospital region Adjusted odds ratio (95% confidence interval) 50 South-Eastern Norway Region 0.85 (0.78 - 0.92) 51 52 Central Norway Region 0.99 (0.89 - 1.10) 53 Western Norway Region 1.06 (0.96 - 1.17) 54 55 Northern Norway Region 1.13 (1.001 - 1.27) 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 21 of 45 BMJ Open

2 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Diagnoses 6 7 Table 4. ICD-10 diagnosis codes contained in MDC 14 (Pregnancy, childbirth, and puerperium) 8 Code Title 9 10 A34 Obstetrical tetanus 11 F53.0 Mild mental and behavioural disorders associated with the puerperium, not elsewhere classified 12 F53.1 Severe mental and behavioural disorders associated with the puerperium, not elsewhere classified 13 F53.8 Other mental and behavioural disorders associated with the puerperium, not elsewhere classified 14 F53.9 Puerperal mental disorder, unspecified 15 Oxx.x Pregnancy, childbirth and puerperium 16 Z32.0 Pregnancy, not (yet) confirmed 17 Z32.1 Pregnancy confirmed 18 Z33 Pregnant state,For incidental peer review only 19 20 Z34.0 Supervision of normal first pregnancy 21 Z34.8 Supervision of other normal pregnancy 22 Z34.9 Supervision of normal pregnancy, unspecified 23 Z35.0 Supervision of pregnancy with history of infertility 24 Z35.1 Supervision of pregnancy with history of abortive outcome 25 Z35.2 Supervision of pregnancy with other poor reproductive or obstetric history 26 Z35.3 Supervision of pregnancy with history of insufficient antenatal care 27 Z35.4 Supervision of pregnancy with grand multiparity 28 Z35.5 Supervision of elderly primigravida 29 Z35.6 Supervision of very young primigravida 30 31 Z35.8 Supervision of other high-risk pregnancies 32 Z35.9 Supervision of high-risk pregnancy, unspecified 33 Z36.0 Antenatal screening for chromosomal anomalies 34 Z36.1 Antenatal screening for raised alphafetoprotein level 35 Z36.2 Other antenatal screening based on amniocentesis http://bmjopen.bmj.com/ 36 Z36.3 Antenatal screening for malformations using ultrasound and other physical methods 37 Z36.4 Antenatal screening for fetal growth retardation using ultrasound and other physical methods 38 Z36.5 Antenatal screening for isoimmunization 39 Z36.8 Other antenatal screening 40 41 Z36.9 Antenatal screening, unspecified 42 Z37.0 Single live birth 43 Z37.1 Single stillbirth on October 1, 2021 by guest. Protected copyright. 44 Z37.2 Twins, both liveborn 45 Z37.3 Twins, one liveborn and one stillborn 46 Z37.4 Twins, both stillborn 47 Z37.5 Other multiple births, all liveborn 48 Z37.6 Other multiple births, some liveborn 49 Z37.7 Other multiple births, all stillborn 50 Z37.9 Outcome of delivery, unspecified 51 52 Z39.0 Care and examination immediately after delivery 53 Z39.1 Care and examination of lactating mother 54 Z39.2 Routine postpartum follow-up 55 Z64.0 Problems related to unwanted pregnancy 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 22 of 45

3 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Table 5. ICD-10 diagnosis codes for immunocompromised state 6 7 Code Title 8 B20.0 HIV disease resulting in mycobacterial infection 9 B20.1 HIV disease resulting in other bacterial infections 10 B20.2 HIV disease resulting in cytomegaloviral disease 11 B20.3 HIV disease resulting in other viral infections 12 B20.4 HIV disease resulting in candidiasis 13 B20.5 HIV disease resulting in other mycoses 14 B20.6 HIV disease resulting in Pneumocystis carinii pneumonia 15 B20.7 HIV disease resulting in multiple infections 16 B20.8 HIV disease resulting in other infectious and parasitic diseases 17 B20.9 HIV disease resulting in unspecified infectious or parasitic disease 18 B21.0 HIV disease Forresulting in Kaposi'speer sarcoma review only 19 B21.1 HIV disease resulting in Burkitt's lymphoma 20 B21.2 HIV disease resulting in other types of non-Hodgkin's lymphoma 21 B21.3 HIV disease resulting in other malignant neoplasms of lymphoid, haematopoietic and related tissue 22 B21.7 HIV disease resulting in multiple malignant neoplasms 23 B21.8 HIV disease resulting in other malignant neoplasms 24 B21.9 HIV disease resulting in unspecified malignant neoplasm 25 B22.0 HIV disease resulting in encephalopathy 26 B22.1 HIV disease resulting in lymphoid interstitial pneumonitis 27 B22.2 HIV disease resulting in wasting syndrome 28 B22.7 HIV disease resulting in multiple diseases classified elsewhere 29 B23.1 HIV disease resulting in (persistent) generalized lymphadenopathy 30 B23.2 HIV disease resulting in haematological and immunological abnormalities, not elsewhere classified 31 B23.8 HIV disease resulting in other specified conditions 32 B24 Unspecified human immunodeficiency virus [HIV] disease 33 B59 Pneumocystosis 34 D47.1 Chronic myeloproliferative disease 35 D70 Agranulocytosis http://bmjopen.bmj.com/ 36 D71 Functional disorders of polymorphonuclear neutrophils 37 D72.0 Genetic anomalies of leukocytes 38 D80.0 Hereditary hypogammaglobulinaemia 39 D80.1 Nonfamilial hypogammaglobulinaemia 40 D80.2 Selective deficiency of immunoglobulin A [IgA] 41 D80.3 Selective deficiency of immunoglobulin G [IgG] subclasses 42 D80.4 Selective deficiency of immunoglobulin M [IgM] 43 D80.5 Immunodeficiency with increased immunoglobulin M [IgM] on October 1, 2021 by guest. Protected copyright. 44 D80.6 Antibody deficiency with near-normal immunoglobulins or with hyperimmunoglobulinaemia 45 D80.7 Transient hypogammaglobulinaemia of infancy 46 D80.8 Other immunodeficiencies with predominantly antibody defects 47 D80.9 Immunodeficiency with predominantly antibody defects, unspecified 48 D81.0 Severe combined immunodeficiency [SCID] with reticular dysgenesis 49 D81.1 Severe combined immunodeficiency [SCID] with low T- and B-cell numbers 50 D81.2 Severe combined immunodeficiency [SCID] with low or normal B-cell numbers 51 D81.3 Adenosine deaminase [ADA] deficiency 52 D81.4 Nezelof's syndrome 53 D81.5 Purine nucleoside phosphorylase [PNP] deficiency 54 D81.6 Major histocompatibility complex class I deficiency 55 D81.7 Major histocompatibility complex class II deficiency 56 D81.8 Other combined immunodeficiencies 57 D81.9 Combined immunodeficiency, unspecified 58 D82.0 Wiskott-Aldrich syndrome 59 D82.1 Di George's syndrome 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 23 of 45 BMJ Open

4 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 D82.2 Immunodeficiency with short-limbed stature 5 D82.3 Immunodeficiency following hereditary defective response to Epstein-Barr virus 6 D82.4 Hyperimmunoglobulin E [IgE] syndrome 7 D82.8 Immunodeficiency associated with other specified major defects 8 D82.9 Immunodeficiency associated with major defect, unspecified 9 D83.0 Common variable immunodeficiency with predominant abnormalities of B-cell numbers and function 10 D83.1 Common variable immunodeficiency with predominant immunoregulatory T-cell disorders 11 D83.2 Common variable immunodeficiency with autoantibodies to B- or T-cells 12 D83.8 Other common variable immunodeficiencies 13 D83.9 Common variable immunodeficiency, unspecified 14 D84.0 Lymphocyte function antigen-1 [LFA-1] defect 15 D84.1 Defects in the complement system 16 D84.8 Other specified immunodeficiencies 17 D84.9 Immunodeficiency, unspecified 18 D89.8 Other specifiedFor disorders peer involving the immune review mechanism, not elsewhereonly classified 19 D89.9 Disorder involving the immune mechanism, unspecified 20 E40 Kwashiorkor 21 E41 Nutritional marasmus 22 E42 Marasmic kwashiorkor 23 E43 Unspecified severe protein-energy malnutrition 24 I12.0 Hypertensive renal disease with renal failure 25 I13.1 Hypertensive heart and renal disease with renal failure 26 I13.2 Hypertensive heart and renal disease with both (congestive) heart failure and renal failure 27 K91.2 Postsurgical malabsorption, not elsewhere classified 28 N18.0 End-stage renal disease 29 N18.5 Chronic kidney disease, stage 5 30 N18.8 Other chronic renal failure 31 T86.0 Bone-marrow transplant rejection 32 T86.1 Kidney transplant failure and rejection 33 T86.2 Heart transplant failure and rejection 34 T86.3 Heart-lung transplant failure and rejection 35 T86.4 Liver transplant failure and rejection http://bmjopen.bmj.com/ 36 T86.8 Failure and rejection of other transplanted organs and tissues 37 T86.9 Failure and rejection of unspecified transplanted organ and tissue 38 Y83.0 Surgical Operation with transplant of whole organ or tissue 39 Z49.0 Preparatory care for dialysis 40 Z49.1 Extracorporeal dialysis 41 Z49.2 Other dialysis 42 Z94.0 Kidney transplant status 43 Z94.1 Heart transplant status on October 1, 2021 by guest. Protected copyright. 44 Z94.2 Lung transplant status 45 Z94.3 Heart and lungs transplant status 46 Z94.4 Liver transplant status 47 Z94.8 Other transplanted organ and tissue status 48 Z94.9 Transplanted organ and tissue status, unspecified 49 50 51 52 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 24 of 45

5 1 2 3 Operations BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Procedure codes for laparotomy and operation types. Laparotomy codes are the total of 6 codes in tables 6-19. Note that a last code digit of 0, 3 or 6 signifies an open or other non- 7 endoscopic operation or procedure, except for peripheral vascular surgery. 8 9 Table 6. NCSP-N codes for reclosure procedures 10 11 Code Title 12 JWA00 Repair of wound dehiscence in gastroenterological surgery 13 14 KWA00 Repair of wound dehiscence in urological surgery 15 LWA00 Repair of wound dehiscence in gynaecological surgery 16 PWA00 Repair of wound dehiscence in surgery of peripheral vessels and lymphatic system 17

18 For peer review only 19 20 Table 7. NCSP-N code for exploratory laparotomy and opening of abdominal cavity 21 22 Code Title 23 JAA00 Incision of abdominal wall 24 JAH00 Laparotomy 25 JAH20 Staging laparotomy 26 27 JAH30 Laparostomy 28 JAH33 Opening of laparostomy 29 JAH40 Thoracolaparotomy 30 31 32 33 Table 8. NCSP-N codes for diaphragmal hernia repair 34

Code Title http://bmjopen.bmj.com/ 35 36 JBB00 Repair of paraoesophageal hernia 37 JBB10 Repair of congenital diaphragmatic hernia 38 JBB96 Repair of other diaphragmatic hernia 39 JBC00 Gastro-oesophageal antireflux operation 40 41 42 43 Table 9. NCSP-N codes for repair of thoracoabdominal aorta on October 1, 2021 by guest. Protected copyright. 44 45 Code Title 46 FCD00 Suture of thoracoabdominal aorta 47 FCD10 Reinforcement of thoracoabdominal aorta using suture 48 49 FCD30 Repair of thoracoabdominal aorta using patch 50 FCD40 Partial resection and suture of thoracoabdominal aorta 51 FCD50 Resection and reconstruction of thoracoabdominal aorta using tube graft 52 FCD60 Resection of thoracoabdominal aorta and reimplantation of branches 53 54 FCD70 Bypass of thoracoabdominal aorta using tube graft 55 FCD80 Removal of foreign body from thoracoabdominal aorta 56 FCD96 Other repair of thoracoabdominal aorta 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 25 of 45 BMJ Open

6 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Table 10. NCSP-N codes for procedures on the gastrointestinal tract: oesophagus, stomach 6 7 and intestines 8 Code Title 9 10 JCB00 Oesophagostomy 11 JCC00 Transhiatal partial oesophagectomy without interposition 12 JCC10 Transthoracic partial oesophagectomy without interposition 13 JCC20 Transhiatal partial oesophagectomy with interposition of intestine 14 15 JCC30 Transthoracic partial oesophagectomy with interposition of intestine 16 JCC96 Other partial oesophagectomy 17 JCD00 Subcutaneous anastomosis of oesophagus without interposition 18 JCD03 SubcutaneousFor anastomosis peer of oesophagus review with interposition of intestineonly 19 20 JCD10 Intrathoracic anastomosis of oesophagus without interposition 21 JCD13 Intrathoracic oesophageal anastomosis with interposition of intestine 22 JCD20 Transsection of oesophagus 23 JCD96 Other anastomosis of oesophagus without resection 24 25 JCE00 Suture of oesophagus 26 JCE10 Plastic repair of stenosis of cardia 27 JCE20 Cardiomyotomy 28 JCE30 Repair of oesophageal atresia or congenital tracheo-oesophageal fistula 29 30 JCE33 Closure of acquired tracheo-oesophageal or broncho-oesophageal fistula 31 JCE40 Reconstruction of oesophagus using flap 32 JCE50 Reconstruction of oesophagus using free microvascular graft of intestine 33 JCE96 Other reconstruction of oesophagus 34 35 JCF00 Insertion of oesophageal stent http://bmjopen.bmj.com/ 36 JCW96 Other operation on oesophagus 37 JDA00 Gastrotomy 38 JDA60 Closure of perforated ulcer of stomach 39 40 JDA63 Local excision of lesion of stomach 41 JDB00 42 JDB10 Percutaneous gastrostomy 43 on October 1, 2021 by guest. Protected copyright. JDC00 Partial gastrectomy and gastroduodenostomy 44 45 JDC10 Partial gastrectomy and gastrojejunostomy 46 JDC20 Partial gastrectomy and Roux-en-Y reconstruction 47 JDC30 Partial gastrectomy with interposition of jejunum 48 JDC40 Partial gastrectomy and oesophagogastrostomy 49 50 JDC96 Partial gastrectomy with other reconstruction 51 JDD00 Total gastrectomy and Roux-en-Y oesophagojejunostomy 52 JDD96 Total gastrectomy with other reconstruction 53 JDE00 Gastrojejunostomy 54 55 JDE10 Conversion of gastrojejunostomy to Roux-en-Y anastomosis 56 JDE20 Conversion of gastrojejunostomy to gastroduodenostomy with interposition of jejunum 57 JDE96 Other anastomosis of stomach without concurrent gastrectomy 58 JDF00 Gastroplasty 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 26 of 45

7 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JDF10 Gastric bypass 5 6 JDF20 Gastric banding 7 JDF96 Other bariatric operation on stomach 8 JDG00 Truncal vagotomy 9 JDG10 Proximal gastric vagotomy 10 11 JDG96 Other vagotomy 12 JDH00 Duodenotomy 13 JDH40 Duodenostomy on duodenal bulb 14 JDH50 Local excision of lesion of duodenal bulb 15 16 JDH60 Pyloromyotomy 17 JDH63 Pyloroplasty 18 JDH70 Closure of perforatedFor ulcer peer of duodenum review only 19 JDW96 Other operation on stomach or duodenum 20 21 JEA00 Appendectomy 22 JEA10 Appendectomy with drainage 23 JEW96 Other operation on appendix 24 JFA00 Enterotomy 25 26 JFA10 Colotomy 27 JFA16 Biopsy of wall of colon without colotomy 28 JFA60 Stricturoplasty in small intestine 29 JFA63 Stricturoplasty in colon 30 31 JFA70 Suture of small intestine 32 JFA73 Excision of lesion of small intestine 33 JFA76 Closure of fistula of small intestine 34 JFA80 Suture of colon 35 http://bmjopen.bmj.com/ 36 JFA83 Excision of lesion of colon 37 JFA86 Closure of fistula of colon 38 JFA96 Other local operation on intestine 39 JFB00 Partial resection of small intestine 40 41 JFB10 Reversal of segment of small intestine 42 JFB13 Plastic repair of small intestine with lengthening 43 JFB20 Ileocaecal resection on October 1, 2021 by guest. Protected copyright. 44 JFB30 Right hemicolectomy 45 46 JFB33 Other resection comprising small intestine and colon 47 JFB40 Resection of transverse colon 48 JFB43 Left hemicolectomy 49 JFB46 Resection of sigmoid colon 50 51 JFB50 Other resection of colon 52 JFB53 Resection of sigmoid colon sigmoideum with partial resection of rectum 53 JFB60 Resection of sigmoid colon with end colostomy 54 JFB63 Other resection of colon with proximal colostomy and closure of distal stump 55 56 JFB96 Other partial excision of intestine 57 JFC00 Entero-enterostomy 58 JFC10 Ileotransversostomy 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 27 of 45 BMJ Open

8 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JFC20 Other enterocolostomy 5 6 JFC30 Colo-colostomy 7 JFC40 Ileorectostomy 8 JFC50 Colorectostomy 9 JFD00 Jejunoileal bypass 10 11 JFD03 Duodenoileal bypass with biliopancreatic diversion 12 JFD10 Revision of jejunoileal bypass 13 JFD13 Revision of duodenoileal bypass 14 JFD20 Restoration of continuity after jejunoileal bypass 15 16 JFD23 Restoration of continuity after duodenoileal bypass 17 JFD96 Other intestinal bypass operation 18 JFE00 TransplantationFor of small intestinepeer review only 19 JFE96 Other operation relating to transplantation of small intestine 20 21 JFF00 Catheter enterostomy 22 JFF10 Loop enterostomy 23 JFF13 Terminal enterostomy 24 JFF16 Conversion of ileoanal anastomosis to ileostomy 25 26 JFF20 Caecostomy 27 JFF23 Transversostomy 28 JFF26 Sigmoidostomy 29 JFF30 Other colostomy 30 31 JFF40 Appendicostomy 32 JFF50 Exteriorisation of loop of colon without opening 33 JFF60 Opening of exteriorised loop of colon 34 JFF96 Other exteriorisation of intestine or creation of intestinal stoma 35 http://bmjopen.bmj.com/ 36 JFG00 Closure of loop enterostomy without resection 37 JFG10 Closure of loop colostomy without resection 38 JFG20 Closure of enterostomy with resection of exteriorised loop 39 JFG23 Closure of terminal enterostomy with anastomosis to small intestine 40 41 JFG26 Closure of terminal enterostomy with anastomosis to colon 42 JFG30 Closure of colostomy with resection of exteriorised loop 43 JFG33 Closure of terminal colostomy with anastomosis to colon on October 1, 2021 by guest. Protected copyright. 44 JFG36 Closure of terminal colostomy with anastomosis to rectum 45 46 JFG40 Revision of enterostomy or colostomy without laparotomy 47 JFG50 Laparotomy with revision of enterostomy or colostomy 48 JFG53 Revision of ileal pelvic pouch 49 JFG56 Revision of colonic pelvic pouch 50 51 JFG60 Conversion of conventional ileostomy to continent ileostomy 52 JFG70 Conversion of continent ileostomy to conventional ileostomy 53 JFG73 Excision of ileal pelvic pouch 54 JFG76 Excision of colonic pelvic pouch with colorectal or coloanal anastomosis 55 56 JFG80 Excision of ileal pouch with construction of new continent ileostomy 57 JFG83 Excision of colonic pelvic pouch and construction of new pouch 58 JFG86 Excision of ileal pelvic pouch and construction of new pouch 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 28 of 45

9 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JFG96 Other operation on intestinal stoma or pouch 5 6 JFH00 Total colectomy and ileorectal anastomosis 7 JFH10 Total colectomy and ileostomy 8 JFH20 Proctocolectomy and ileostomy 9 JFH30 Total colectomy, mucosal proctectomy and ileoanal anastomosis without ileostomy 10 11 JFH33 Total colectomy, mucosal proctectomy, ileoanal anastomosis and ileostomy 12 JFH40 Proctocolectomy and continent ileostomy 13 JFH96 Other total colectomy 14 JFJ00 Coecopexy 15 16 JFJ96 Other enteropexy or colopexy 17 JFK00 Division of adhesive band in intestinal obstruction 18 JFK10 Freeing of adhesionsFor in intestinalpeer obstruction review only 19 JFK20 Freeing of adhesions and plication of small intestine 20 21 JFK96 Other operation on adhesions in intestinal obstruction 22 JFL00 Open reduction of intussusception of intestine 23 JFL10 Laparotomy and manipulation of obstructed intestine 24 JFL20 Laparotomy and manipulation of impacted material 25 26 JFL96 Other operation for intestinal obstruction without resection or freeing of adhesions 27 JFW96 Other operation on intestine 28 JGA00 Proctotomy 29 JGA60 Suture of rectum 30 31 JGA70 Proctotomy and excision of lesion of rectum 32 JGA96 Other proctotomy or local operation on rectum 33 JGB00 Partial proctectomy and colorectal or coloanal anastomosis 34 JGB03 Partial proctectomy with partial excision of mesorectum 35 http://bmjopen.bmj.com/ 36 JGB06 Total mesorectal excision 37 JGB10 Partial proctectomy and end colostomy 38 JGB20 Partial rectosigmoidectomy and abdominoperineal pull-through anastomosis 39 JGB30 Abdominoperineal excision of rectum 40 41 JGB33 Abdominoperineal excision of rectum and intersphincter resection 42 JGB36 Wide excision of rectum 43 JGB40 Excision of rectum and end ileostomy on October 1, 2021 by guest. Protected copyright. 44 JGB50 Mucosal proctectomy and ileoanal anastomosis 45 46 JGB60 Excision of rectum and ileoanal anastomosis 47 JGB96 Other proctectomy or excision of rectum 48 JGC00 Rectopexy 49 JGC30 Excision and suture of rectal mucosa with imbrication of muscular layer 50 51 JGC96 Other reconstructive operation on rectum 52 JGW96 Other operation on rectum 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 29 of 45 BMJ Open

10 1 2 3 Table 11. NCSP-N codes for procedures on the liver BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Code Title 6 JJA00 Exploration of liver 7 JJA10 Hepatotomy 8 9 JJA20 Open biopsy of liver 10 JJA23 Open needle biopsy of liver 11 JJA30 Fenestration of cyst of liver 12 JJA40 Excision of lesion of liver 13 14 JJA43 Destruction of lesion of liver 15 JJA50 Suture of liver 16 JJA96 Other local operation on liver 17 JJB00 Wedge resection of liver 18 For peer review only 19 JJB10 Atypical resection of liver 20 JJB20 Excision of single segment of liver 21 JJB30 Excision of two segments of liver 22 JJB40 Excision of segments II, III and IV of liver 23 24 JJB50 Excision of segments V, VI, VII and VIII of liver 25 JJB53 Excision of segments IV,V, VI, VII and VIII of liver 26 JJB60 Other excision of three or more segments of liver 27 JJB96 Other resection of liver 28 29 JJC00 Allogenic transplantation of liver 30 JJC10 Allogenic partial transplantation of liver 31 JJC20 Allogenic partial transplantation of liver from living donor 32 JJC30 Xenogenic transplantation of liver 33 34 JJC40 Xenogenic partial transplantation of liver 35 JJC50 Resection of transplanted liver http://bmjopen.bmj.com/ 36 JJC60 Total excision of transplanted liver 37 JJC96 Other transplantation of liver or related operation 38 39 JJW96 Other operation on liver 40 41 42 Table 12. NCSP-N codes for procedures on biliary tract 43 on October 1, 2021 by guest. Protected copyright. 44 Code Title 45 JKA00 Cholecystotomy 46 47 JKA10 Cholecystostomy 48 JKA20 Cholecystectomy 49 JKA96 Other operation on gallbladder 50 JKB00 Incision of bile duct 51 52 JKB20 Intraoperative cholangioscopy 53 JKB30 Percutaneous transhepatic biliary drainage 54 JKB40 Suture of bile duct 55 JKB96 Other incision or related operation on bile duct 56 57 JKC00 Incision of bile duct and local excision of lesion 58 JKC10 Partial excision and anastomosis of bile duct 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 30 of 45

11 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JKC20 Partial excision of bile duct and anastomosis to duodenum 5 6 JKC30 Partial excision of bile duct and anastomosis to jejunum 7 JKC40 Partial excision of right or left hepatic duct and anastomosis to jejunum 8 JKC50 Excision of papilla of Vater and anastomosis of bile duct to duodenum or jejunum 9 JKC96 Other excision of bile duct 10 11 JKD00 Anastomosis of gallbladder to jejunum 12 JKD10 Anastomosis of bile duct to duodenum 13 JKD20 Anastomosis of bile duct to jejunum 14 JKD30 Extrahepatic anastomosis of right or left hepatic duct to jejunum 15 16 JKD40 Anastomosis of intrahepatic bile duct to jejunum 17 JKD50 Hepatoportoenterostomy 18 JKD96 Other biliodigestiveFor anastomosis peer without excisionreview only 19 JKE00 Transduodenal papillotomy 20 21 JKE06 Transduodenal sphincteroplasty 22 JKE96 Other transduodenal open operation on bile duct or ampulla of Vater 23 JKF00 Excision of cystic duct 24 JKF96 Other secondary operation on biliary tract 25 26 JKW96 Other operation on biliary tract 27 28 29 30 Table 13. NCSP-N codes for procedures on the pancreas 31 32 Code Title 33 JLA00 Exploration of pancreas 34 JLA10 Biopsy of pancreas 35 http://bmjopen.bmj.com/ 36 JLB00 Incision of pancreas 37 JLB10 Pancreaticolithotomy 38 JLB96 Other incision, drainage or dilatation of pancreas 39 JLC00 Excision of lesion of pancreas 40 41 JLC10 Distal pancreatectomy 42 JLC20 Total pancreatectomy 43 JLC30 Pancreatoduodenectomy on October 1, 2021 by guest. Protected copyright. 44 JLC40 Total pancreatoduodenectomy 45 46 JLC50 Atypical pancreatectomy 47 JLC96 Other pancreatectomy 48 JLD00 Pancreaticojejunostomy 49 JLD10 Anastomosis of pancreatic pseudocyst to stomach 50 51 JLD20 Anastomosis of pancreatic pseudocyst to jejunum 52 JLE00 Allogenic total transplantation of pancreas with pancraticocystostomy 53 JLE03 Allogenic total transplantation of pancreas with pancreaticoenterostomy 54 JLE10 Allogenic segmental transplantation of pancreas 55 56 JLE16 Allogenic segmental transplantation of pancreas from living donor 57 JLE20 Allogenic islet cell transplantation 58 JLE30 Xenogenic islet cell transplantation 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 31 of 45 BMJ Open

12 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JLE40 Total excision of transplanted pancreas 5 6 JLE50 Occlusion of duct of transplanted pancreas 7 JLE56 Conversion of pancreaticocystostomy to pancreaticoenterostomy 8 JLE96 Other transplantation of pancreas or related operation 9 JLW96 Other operation on pancreas 10 11 12 13 14 Table 14. NCSP-N codes for procedures on the spleen 15 16 Code Title 17 JMA00 Partial splenectomy 18 JMA10 TransabdominalFor total splenectomy peer review only 19 JMA20 Transthoracic total splenectomy 20 21 JMB00 Biopsy of spleen 22 JMB10 Repair of spleen 23 JMW96 Other operation on spleen 24

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27 28 Table 15. NCSP-N codes for other digestive system procedures 29 30 Code Title 31 JAA10 Excision of lesion of abdominal wall 32 JAA13 Wide excision of extensive necrotising conditions of abdominal wall 33 JAA96 Other local operation on abdominal wall 34

JAK00 Laparotomy and drainage of peritoneal cavity http://bmjopen.bmj.com/ 35 36 JAK03 Laparotomy and peritoneal irrigation 37 JAK10 Laparotomy and insertion of peritoneal dialysis catheter 38 JAL00 Biopsy of peritoneum 39 JAL10 Laparotomy and removal of foreign body 40 41 JAL20 Excision or destruction of lesion of peritoneum 42 JAL23 Excision of local lesion of pelvic wall 43 JAL30 Omentectomy on October 1, 2021 by guest. Protected copyright. 44 JAL50 Intraabdominal revision of shunt of ventricle of brain 45 46 JAL96 Other excision of lesion of peritoneum 47 JAM00 Transposition of omentum 48 JAM10 Operation for malrotation of intestine 49 JAN00 Creation of peritoneovenous shunt 50 51 JAN10 Revision of peritoneovenous shunt 52 JAN20 Removal of peritoneovenous shunt 53 JAP00 Freeing of adhesions in the peritoneal cavity 54 JAQ00 Extensive excision of peritoneum 55 56 JAQ10 Intraoperative hypertermic chemotherapeutic perfusion of abdominal cavity 57 JAW96 Other operation on abdominal wall, peritoneum, mesentery or omentum 58 JBA00 Transabdominal repair of diaphragm for rupture 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 32 of 45

13 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JBA10 Transabdominal biopsy or excision of lesion of diaphragm 5 6 JBA20 Transabdominal partial excision of diaphragm 7 JBW96 Other transabdominal operation on diaphragm or operation for gastro-oesophageal reflux 8 9 Table 16. NCSP-N codes for procedures on kidney and pelvis of kidney 10 11 Code Title 12 KAA00 Exploration of kidney 13 14 KAA20 Exploratory nephrotomy 15 KAA30 Exploratory pyelotomy 16 KAA96 Other exploration of kidney or pelvis of kidney 17 KAB00 Biopsy of kidney or pelvis of kidney 18 For peer review only 19 KAC00 Nephrectomy 20 KAC20 Nephroureterectomy 21 KAD00 Partial nephrectomy 22 KAD10 Heminephrectomy 23 24 KAD40 Partial excision of pelvis of kidney 25 KAD50 Destruction of tumour of pelvis of kidney 26 KAD56 Destruction of lesion of renal parenchyma 27 KAD60 Percutaneous destruction of lesion of renal parenchyma 28 29 KAD96 Other partial excision of kidney or pelvis of kidney 30 KAE00 Nephrolithotomy 31 KAE10 Pyelolithotomy 32 KAE96 Other removal of calculus from kidney or pelvis of kidney 33 34 KAF00 Removal of foreign body from kidney 35 KAF10 Removal of foreign body from pelvis of kidney http://bmjopen.bmj.com/ 36 KAH00 Suture of kidney 37 KAH10 Suture of pelvis of kidney 38 39 KAH30 Pyeloureteroplasty without division of ureteropelvic junction 40 KAH40 Pyeloureteroplasty with division of ureteropelvic junction 41 KAH50 Ureterocalyceal anastomosis 42 KAH70 Freeing of adhesions of ureteropelvic junction 43 on October 1, 2021 by guest. Protected copyright. 44 KAH80 Nephropexy 45 KAH96 Other reconstruction of kidney or pelvis of kidney 46 KAS00 Autotransplantation of kidney 47 KAS10 Allogenic transplantation of kidney from cadaver donor 48 49 KAS13 Allogenic transplantation of kidney from cadaver donor 50 KAS20 Allogenic transplantation of kidney from living donor with minimally invasive technique 51 KAS23 Allogenic transplantation of kidney from living donor with minimally invasive technique 52 KAS40 Excision of transplanted kidney 53 54 KAS50 Nephrocystostomy in transplanted kidney 55 KAS60 Operation for lymphocele of transplanted kidney 56 KAS96 Other transplantation of kidney or related procedure 57 KAW96 Other operation on kidney or pelvis of kidney 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 33 of 45 BMJ Open

14 1 2 3 Table 17. NCSP-N codes for procedures on other urinary and male genital organs: ureter, bladder, BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 urethra, prostate and seminal vesicles 5 6 Code Title 7 KBA00 Exploration of ureter 8 9 KBA10 Exploratory ureterotomy 10 KBA96 Other exploration of ureter 11 KBB00 Biopsy of ureter 12 KBC00 Ureterectomy 13 14 KBD00 Partial excision of ureter 15 KBD20 Destruction of tumour of ureter 16 KBD30 Excision of stump of ureter 17 KBD96 Other partial excision of ureter or destruction of tumour of ureter 18 For peer review only 19 KBE00 Ureterolithotomy 20 KBE96 Other operation for calculus of ureter 21 KBF00 Removal of foreign body from ureter 22 KBH00 Suture of ureter 23 24 KBH06 Ureteroureterostomy 25 KBH10 Connection of ureter to contralateral ureter 26 KBH20 Replantation of ureter 27 KBH30 Ileal replacement of ureter 28 29 KBH40 Plastic repair of ureter 30 KBH50 Ureterolysis 31 KBH96 Other repair or connection of ureter 32 KBJ00 Cutaneous ureterostomy 33 34 KBJ10 Cutaneous ureteroenterostomy 35 KBJ20 Cutaneous ureteroenterostomy with reservoir http://bmjopen.bmj.com/ 36 KBJ40 Ureteroenterostomy 37 KBJ60 Anastomosis of ureter to urethra with interposition of ileum 38 39 KBJ70 Removal of calculus from ileal conduit or reservoir 40 KBJ80 Operation for malfunction of urinary diversion 41 KBJ96 Other urinary diversion from ureter or related operation 42 KBV00 Insertion of stent into ureter 43 on October 1, 2021 by guest. Protected copyright. 44 KBV10 Removal of stent from ureter 45 KBV40 Incision or excision of ureterocele 46 KBW96 Other operation on ureter 47 KCA00 Exploratory cystotomy 48 49 KCB00 Biopsy of bladder 50 KCC00 Cystectomy 51 KCC10 Cystoprostatectomy 52 KCC20 Cystoprostatourethrectomy 53 54 KCC30 Cystectomy with excision of female internal genital organs 55 KCC96 Other cystectomy 56 KCD10 Partial cystectomy 57 KCD20 Excision of diverticulum of bladder 58 59 KCD30 Destruction of tumour of bladder 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 34 of 45

15 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 KCD40 Excision of urachus or other vesicocutaneous fistula 5 6 KCD96 Other partial excision or destruction of tumour of bladder 7 KCE00 Cystolithotomy 8 KCF00 Cystotomy and removal of foreign body from bladder 9 KCH00 Suture of bladder 10 11 KCH10 Enterocystoplasty 12 KCH20 Reduction cystoplasty 13 KCH30 Closure of vesicointestinal fistula 14 KCH40 Incision or resection of bladder neck 15 16 KCH96 Other reconstructive operation on bladder 17 KCJ00 Cystostomy 18 KCJ10 Cutaneous cystoenterostomyFor peer review only 19 KCJ20 Continent cutaneous cystoenterostomy 20 21 KCJ96 Other cystostomy 22 KCV10 Denervation of bladder 23 KCV20 Freeing of bladder 24 KCW96 Other operations on bladder 25 26 KDC00 Urethrectomy 27 KDD00 Partial excision of urethra 28 KDD10 Excision of diverticulum of urethra 29 KDD30 Destruction of tumour of urethra 30 31 KDD40 Resection of external sphincter of urethra 32 KDD50 Excision of urethral valve 33 KDD80 Partial excision of urethra and repair using graft or flap 34 KDD96 Other partial excision of urethra 35 http://bmjopen.bmj.com/ 36 KDG00 Retropubic suspension of urethra 37 KDG20 Abdominal colposuspension 38 KDG30 Suprapubic sling urethrocystopexy 39 KDG40 Suprapubic urethrocystopexy 40 41 KDG43 Transobturatorial sling urethrocystopexy 42 KDG50 Transabdominal plastic repair of pelvic floor for urinary incontinence 43 KDG60 Implantation of adjustable expander around bladder neck on October 1, 2021 by guest. Protected copyright. 44 KDG70 Exploration of urethra 45 46 KDG96 Other operation on urethra or bladder neck for incontinence 47 KDH00 Suture of urethra 48 KDH10 Meatoplasty of urethra 49 KDH30 Closure of urethrocutaneous fistula 50 51 KDH50 Closure of urethrointestinal fistula 52 KDH70 Plastic repair of stricture of urethra 53 KDH96 Other reconstructive operation on urethra 54 KDJ00 Urethrostomy 55 56 KDK00 Implantation of artificial urinary sphincter around bladder neck 57 KDK10 Implantation of artificial urinary sphincter around bulbar urethra 58 KDK30 Revision of artificial urethral sphincter 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 35 of 45 BMJ Open

16 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 KDK40 Removal of artificial urethral sphincter 5 6 KDW96 Other operation on urethra 7 KEA00 Exploration of prostate 8 KEA10 Prostatotomy 9 KEA20 Incision of seminal vesicle 10 11 KEB00 Biopsy of prostate 12 KED96 Other partial excision of prostate 13 KEE00 Prostatalithotomy 14 KEE10 Removal of foreign body from prostate 15 16 KEW96 Other operation on prostate or seminal vesicle 17 18 For peer review only 19 Table 18- NCSP-N codes for procedures on female genital organs: ovary, fallopian tube, uterus and 20 uterine ligaments 21 22 Code Title 23 LAA00 Puncture of ovarian cyst 24 LAB00 Ovariotomy 25 26 LAB10 Biopsy of ovary 27 LAB96 Other incision or biopsy of ovary 28 LAC00 Excision of ovarian cyst 29 LAC10 Fenestration of ovarian cyst 30 31 LAC20 Destruction of lesion of ovary 32 LAC30 Excision of paraovarian cyst 33 LAC96 Other excision or destruction of lesion of ovary 34 LAD00 Partial excision of ovary 35 http://bmjopen.bmj.com/ 36 LAE10 Unilateral oophorectomy 37 LAE20 Bilateral oophorectomy 38 LAF00 Unilateral salpingo-oophorectomy 39 LAF10 Bilateral salpingo-oophorectomy 40 41 LAF20 Unilateral transvaginal salpingo-oophorectomy 42 LAF30 Bilateral transvaginal salpingo-oophorectomy 43 LAG00 Freeing of adhesions of ovary on October 1, 2021 by guest. Protected copyright. 44 LAG10 Oophoropexy 45 46 LAG20 Detorsion of ovary 47 LAG96 Other reconstructive operation on ovary 48 LAW96 Other operation on ovary 49 LBB00 Biopsy of Fallopian tube 50 51 LBB96 Other biopsy of Fallopian tube 52 LBC10 Removal of products of conception from Fallopian tube 53 LBC20 Salpingotomy and removal of products of conception 54 LBC96 Other tube conserving operation for tubal pregnancy 55 56 LBD00 Partial excision of Fallopian tube 57 LBE00 Salpingectomy 58 LBF00 Perfusion of Fallopian tube 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 36 of 45

17 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 LBF03 Perfusion of Fallopian tube after reconstruction 5 6 LBF20 Transcervical catheter salpingoplasty 7 LBF30 Salpingolysis 8 LBF40 Fimbrioplasty 9 LBF50 Salpingostomy 10 11 LBF60 Partial excision and anastomosis of Fallopian tube 12 LBF70 Partial excision and reimplantation of Fallopian tube 13 LBF96 Other operation on Fallopian tube for infertility 14 LBW96 Other operation on Fallopian tube 15 16 LCA00 Biopsy of uterus or uterine ligaments 17 LCB00 Hysterotomy 18 LCB10 MyomectomyFor peer review only 19 LCB96 Other excision of lesion of uterus 20 21 LCC00 Partial excision of uterus 22 LCC10 Supravaginal hysterectomy 23 LCC20 Vaginal supravaginal hysterectomy 24 LCC96 Other partial excision of uterus 25 26 LCD00 Hysterectomy 27 LCD10 Vaginal hysterectomy 28 LCD30 Radical hysterectomy 29 LCD40 Radical vaginal hysterectomy 30 31 LCD96 Other hysterectomy 32 LCE00 Anterior exenteration of female pelvis 33 LCE10 Posterior exenteration of female pelvis 34 LCE20 Total exenteration of female pelvis 35 http://bmjopen.bmj.com/ 36 LCE96 Other exenteration of female pelvis 37 LCF00 Excision of lesion of parametrium 38 LCF10 Excision of female varicocele 39 LCF96 Other excision of lesion of parametrium 40 41 LCG10 Suture of uterus 42 LCG20 Hysteropexy 43 LCG30 Resection or transcision of sacrouterine ligaments on October 1, 2021 by guest. Protected copyright. 44 LCG40 Reconstruction of uterus 45 46 LCG96 Other reconstructive operation on uterus 47 LCW96 Other operation on uterus and uterine ligaments 48 49 50 51 52 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 37 of 45 BMJ Open

18 1 2 3 Table 19. NCSP-N codes for procedures on the peripheral vessels of the abdomen BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Code Title 6 PCB20 Ligature of coeliac trunk and branches 7 PCB30 Ligature of superior mesenteric artery 8 9 PCB40 Ligature of renal artery 10 PCB99 Ligature of other visceral artery 11 PCC10 Suture of suprarenal or juxtarenal abdominal aorta 12 PCC20 Suture of coeliac trunk and branches 13 14 PCC30 Suture of superior mesenteric artery 15 PCC40 Suture of renal artery 16 PCC99 Suture of other visceral artery 17 PCE30 Thrombectomy or embolectomy of superior mesenteric artery 18 For peer review only 19 PCE40 Thrombectomy or embolectomy of renal artery 20 PCE99 Thrombectomy or embolectomy of other visceral artery 21 PCF20 Thrombendarterectomy of coeliac trunk and branches 22 PCF30 Thrombendarterectomy of superior mesenteric artery 23 24 PCF40 Thrombendarterectomy of renal artery 25 PCF99 Thrombendarterectomy of other visceral artery 26 PCG10 Operation for aneurysm of supracoeliac or juxtarenal abdominal aorta 27 PCG20 Operation for aneurysm of coeliac trunk and branches 28 29 PCG30 Operation for aneurysm of superior mesenteric artery 30 PCG40 Operation for aneurysm of renal artery 31 PCG99 Operation for aneurysm of other visceral artery 32 PCH10 Bypass from supracoeliac or juxtarenal abdominal aorta 33 34 PCH20 Bypass to/from coeliac trunk and branches 35 PCH30 Bypass from superior mesenteric artery http://bmjopen.bmj.com/ 36 PCH40 Bypass from renal artery 37 PCH99 Bypass from other visceral artery 38 39 PCJ30 Transposition of superior mesenteric artery 40 PCJ40 Transposition of renal artery 41 PCJ99 Transposition of other visceral artery 42

PCK20 Reimplantation of coeliac trunk and branches on October 1, 2021 by guest. Protected copyright. 43 44 PCK30 Reimplantation of superior mesenteric artery 45 PCK40 Reimplantation of renal artery 46 PCK50 Reimplantation of inferior mesenteric artery 47 PCK99 Reimplantation of other visceral artery 48 49 PCN20 Plastic repair of coeliac trunk and branches 50 PCN30 Plastic repair of superior mesenteric artery 51 PCN40 Plastic repair of renal artery 52 PCN99 Plastic repair of other visceral artery 53 54 PCU70 Exploration of previous reconstruction of suprarenal abdominal aorta or visceral arteries 55 PCU74 Thrombectomy or embolectomy in bypass from suprarenal abdominal aorta and visceral arteries 56 PCU81 Closure of persisting arteriovenous fistula of bypass from suprarenal abdominal aorta and visceral arteries 57 PCU82 Plastic repair in bypass from suprarenal abdominal aorta and visceral arteries 58 59 PCU99 Other repair after previous reconstruction of suprarenal abdominal aorta and visceral arteries 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 38 of 45

19 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 PCW99 Other operation on suprarenal abdominal aorta and visceral arteries 5 6 PDA10 Exploration of infrarenal abdominal aorta 7 PDA30 Exploration of iliac artery 8 PDC10 Suture of infrarenal abdominal aorta 9 PDC30 Suture of iliac artery 10 11 PDE10 Thrombectomy or embolectomy of infrarenal abdominal aorta 12 PDE30 Thrombectomy or embolectomy of iliac artery 13 PDF10 Thrombendarterectomy of infrarenal abdominal aorta 14 PDF30 Thrombendarterectomy of iliac artery 15 16 PDG10 Operation on infrarenal abdominal aorta for aneurysm 17 PDG20 Bypass from aorta to iliac artery for aneurysm 18 PDG21 Bypass from Foraorta to bilateral peer iliac arteries review for aneurysm only 19 PDG22 Bypass from aorta to iliac and contralateral femoral artery for aneurysm 20 21 PDG23 Bypass from aorta to femoral artery for aneurysm 22 PDG24 Bypass from aorta to bilateral femoral arteries for aneurysm 23 PDG30 Operation on iliac artery for aneurysm 24 PDG35 Bypass from iliac to femoral artery for aneurysm 25 26 PDG99 Other operation for aneurysm of infrarenal abdominal aorta and iliac arteries 27 PDH10 Bypass from infrarenal abdominal aorta 28 PDH20 Bypass from aorta to iliac artery 29 PDH21 Bypass from aorta to bilateral iliac arteries 30 31 PDH22 Bypass from aorta to iliac and contralateral femoral artery 32 PDH23 Bypass from aorta to femoral artery 33 PDH24 Bypass from aorta to bilateral femoral arteries 34 PDH30 Bypass from iliac artery 35 http://bmjopen.bmj.com/ 36 PDH35 Bypass from iliac to femoral artery 37 PDH99 Other bypass from abdominal aorta or iliac artery 38 PDN10 Plastic repair of infrarenal abdominal aorta 39 PDN30 Plastic repair of iliac artery 40 41 PDU70 Exploration of previous reconstruction of infrarenal abdominal aorta or iliac arteries and distal connections 42 PDU74 Thrombectomy or embolectomy in bypass from infrarenal abdominal aorta or iliac artery 43 PDU81 Closure of persisting arteriovenous fistula of bypass from infrarenal abdominal aorta or iliac artery on October 1, 2021 by guest. Protected copyright. 44 PDU82 Plastic repair of bypass from infrarenal abdominal aorta or iliac artery 45 46 PDU99 Other repair after previous reconstruction of infrarenal abdominal aorta and iliac arteries and distal 47 PDW99 Other operation on infrarenal abdominal aorta and iliac arteries and distal connections 48 PHB23 Ligature of iliac vein 49 PHB30 Ligature of inferior vena cava 50 51 PHB31 Ligature of renal vein 52 PHB32 Ligature of portal vein 53 PHB33 Ligature of v. mesenterica superior 54 PHB34 Ligature of v. mesenterica inferior 55 56 PHB36 Ligature of v. spermatica 57 PHC23 Suture of iliac vein 58 PHC30 Suture of inferior vena cava 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 39 of 45 BMJ Open

20 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 PHC31 Suture of renal vein 5 6 PHC32 Suture of portal vein 7 PHC33 Suture of v. mesenterica superior 8 PHC34 Suture of v. mesenterica inferior 9 PHD30 Resection of inferior vena cava 10 11 PHD32 Resection of portal vein 12 PHD33 Resection of v. mesenterica superior 13 PHD34 Resection of v. mesenterica inferior 14 PHD36 Resection of v. spermatica 15 16 PHE23 Thrombectomy of iliac vein 17 PHE30 Thrombectomy of inferior vena cava 18 PHE31 ThrombectomyFor of renal veinpeer review only 19 PHH25 Bypass from iliac vein 20 21 PHH30 Bypass from inferior vena cava 22 PHN30 Plastic repair of inferior vena cava 23 PHN32 Plastic repair of portal vein 24 PHN33 Plastic repair of v. mesenterica superior 25 26 PHN34 Plastic repair of v. mesenterica inferior 27 PHW35 Portosystemic shunt or bypass 28 29 30 31 32 33 34 35 http://bmjopen.bmj.com/ 36 37 38 39 40 41 42 43 on October 1, 2021 by guest. Protected copyright. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from Page 40 of 45

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in press. press. in Commons ( Attribution Creative under isprotected *Checklist Working RECORD SM, the von HT, Elm E, Sørensen Langan I, Petersen D, Moher K, Harron A, SmeethGuttmann L, EI, Benchimol *Reference: Statement. health (RECORD) Data Routinely-collected Observational using Conducted studies of REporting The Committee. Accessibility of of Accessibility and data, code Funding Funding 22 and funding of source the Give Other Information Other Generalisability Generalisability 21 generalisability the Discuss protocol, raw raw protocol, programming 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 45 of BMJ Open BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from

POSTOPERATIVE WOUND DEHISCENCE AFTER LAPAROTOMY: A USEFUL HEALTH CARE QUALITY INDICATOR? A COHORT STUDY BASED ON NORWEGIAN HOSPITAL ADMINISTRATIVE DATA

ForJournal: peerBMJ Open review only Manuscript ID bmjopen-2018-026422.R2

Article Type: Research

Date Submitted by the 01-Feb-2019 Author:

Complete List of Authors: Helgeland , Jon ; Norwegian Institute of Public Health, Division of Health Services Tomic, Oliver; Norwegian University of Life Sciences, Department of Mathematic Sciences and Technology Hansen, Tonya; Norwegian Institute of Public Health, Division of Health Services Kristoffersen, Doris; Norwegian Institute of Public Health, Division of Health Services

Hassani, Sahar; University of Oslo, KG Jebsen Centre for Psychosis http://bmjopen.bmj.com/ Research, Institute of Clinical Medicine; Oslo University Hospital, Department of Medical Genetics Lindahl, Anne; Akershus University Hospital Trust, Division of Surgery; University of Oslo, Department of Health Administration and Health Economics

Primary Subject Surgery Heading:

Secondary Subject Heading: Health services research on October 1, 2021 by guest. Protected copyright.

Quality in health care < HEALTH SERVICES ADMINISTRATION & Keywords: MANAGEMENT, Patient safety, WOUND MANAGEMENT

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 1 POSTOPERATIVE WOUND DEHISCENCE AFTER LAPAROTOMY: A 6 7 8 9 10 2 USEFUL HEALTH CARE QUALITY INDICATOR? A COHORT STUDY 11 12 13 14 3 BASED ON NORWEGIAN HOSPITAL ADMINISTRATIVE DATA 15 16 17 18 4 Jon Helgeland1,7, OliverFor Tomic 2,peer Tonya Moen reviewHansen1, Doris Tove only Kristoffersen1, Sahar Hassani3,4, 19 20 5 Anne Karin Lindahl5,6 21 22 1 23 6 Division of Health Services, Norwegian Institute of Public Health, Oslo, Norway 24 25 7 2 Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Ås, 26 27 8 Norway 28 29 9 3 NORMENT, KG Jebsen Centre for Psychosis Research, Division of Mental Health and Addiction, Oslo 30 31 32 10 University Hospital and Institute of Clinical Medicine, University of Oslo, Oslo, Norway 33 34 11 4 Department of Medical Genetics, Oslo University Hospital, Oslo, Norway 35 http://bmjopen.bmj.com/ 36 12 5 Division of Surgery, Akershus University Hospital Trust, Lørenskog, Norway 37 38 13 6Department of Health administration and health economics, Institute of Health and Society, 39 40 14 University of Oslo, Oslo, Norway 41 42 7 43 15 Corresponding author: Jon Helgeland, [email protected] on October 1, 2021 by guest. Protected copyright. 44 45 16 Norwegian Institute of Public Health, PO Box 222 Skøyen, N-0213 Oslo 46 47 17 Word count: 3106 48 49 18 Keywords: Postoperative wound dehiscence, Surgical Quality, Quality Indicators, Patient Safety 50 51 52 53 19 54 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 20 ABSTRACT 5 6 7 8 9 21 Objectives 10 11 12 22 Postoperative wound dehiscence (PWD) is a serious complication to laparotomy, leading to higher 13 14 23 mortality, readmissions and cost. The aims of the present study are to investigate whether risk 15 16 24 adjusted PWD rates could reliably differentiate between Norwegian hospitals, and whether PWD 17 18 25 rates were associatedFor with hospital peer characteristics review such as hospital only type and laparotomy volume. 19 20 21 22 23 26 Design 24 25 26 27 Observational study using patient administrative data from all Norwegian hospitals, obtained from 27 28 28 the Norwegian Patient Registry, for the period 2011-2015, and linked using the unique person 29 30 29 identification number. 31 32 33 34 35 30 Participants http://bmjopen.bmj.com/ 36 37 38 31 All patients undergoing laparotomy, at least 15 years old, with length of stay at least two days, and 39 40 32 no diagnosis code for immunocompromised state or relating to pregnancy, childbirth and 41 42

33 puerperium. The final data set comprised 66 925 patients with 78 086 laparotomy episodes from 47 on October 1, 2021 by guest. Protected copyright. 43 44 45 34 hospitals. 46 47 48 49 35 Outcomes 50 51 52 36 The outcome was wound dehiscence, identified by the presence of a wound reclosure code, risk 53 54 37 adjusted for patient characteristics and operation type. 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 38 Results 5 6 7 39 The final data set comprised 1 477 wound dehiscences. Crude PWD rates varied from 0% to 5.1% 8 9 40 among hospitals, with an overall rate of 1.89%. Three hospitals with statistically significantly higher 10 11 41 PWD than average were identified, after case mix adjustment and correction for multiple 12 13 14 42 comparisons. Hospital volume was not associated with PWD rate, except that hospitals with very few 15 16 43 laparotomies had lower PWD rates. 17 18 For peer review only 19 20 44 Conclusions 21 22 23 45 Among Norwegian hospitals, there is considerable variation in PWD rate that cannot be explained by 24 25 26 46 operation type, age or comorbidity. This warrants further investigation into possible causes, such as 27 28 47 surgical technique, perioperative procedures or handling of complications. The risk adjusted PWD 29 30 48 rate after laparotomy is a candidate quality indicator for Norwegian hospitals. 31 32 33 34 35 49 STRENGTHS AND LIMITATIONS OF THIS STUDY http://bmjopen.bmj.com/ 36 37 38 39 50  Includes all laparotomies performed in the nation over a five-year period, with patients 40 41 51 followed across hospitals 42 43 52  Extends previous studies to a new health system and a new coding system on October 1, 2021 by guest. Protected copyright. 44 45 53  The statistical analysis uses methods for low event rates, avoiding asymptotic approximation 46 47 48 54  Results may be subject to coding inaccuracy and incompleteness, as well as selection effects 49 50 55  There were no data for surgical technique, nor for some clinical factors known to be relevant. 51 52 53 54 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 56 INTRODUCTION 5 6 7 8 57 The past decades have seen a major growth in initiatives for measuring, monitoring, and improving 9 10 58 the quality of health care services. Quality indicators are regularly published in many health care 11 12 59 systems. Performance of health care systems is also compared across nations, for instance in the 13

14 1 2 15 60 OECD Health Care Quality and Outcomes (HCQO) initiative, which Norway is a part of. Norway has 16 17 61 a national quality indicator system for monitoring and comparing hospital performance, however, 18 For peer review only 19 62 not all areas of hospital performance are covered by existing national quality indicators. While there 20 21 63 are quality indicators for outcomes such as mortality and process measures such as waiting times, 22 23 64 complications following hospital care is less explored, which is especially relevant following surgical 24 25 26 65 procedures. 27 28 29 66 Postoperative wound dehiscence (PWD) rates after open abdominal surgery (laparotomies) was 30 31 32 67 introduced as a patient safety indicator in the United States and later as a quality indicator by 33 34 68 OECD.3-6 Norway reported the second highest numbers for 2014-2015, with a PWD rate of 1.02%. The 35 http://bmjopen.bmj.com/ 36 69 overall range was 0.055% to 1.05%.5 Neighbouring Sweden, with comparable population health and 37 38 70 health care, reported 0.30%. Moreover, a recent study comparing adverse events in Norway and 39 40 41 71 Sweden found significantly higher adverse event rates of surgical complications in Norwegian 42 43 72 hospitals, compared to Swedish hospitals.7 on October 1, 2021 by guest. Protected copyright. 44 45 46 47 73 PWD is a serious complication that leads to higher mortality rates, higher implicit, explicit and social 48 49 74 costs as well as increased readmission rates.8 9 The PWD rate has been studied elsewhere as a quality 50 51 75 indicator for hospitals, and found to have a high positive predictive value.10 11 It is useful as a quality 52 53 76 indicator, since several of the risk factors are modifiable and within control of the hospital and 54 55 56 77 surgical team. There are few events per hospital, making it challenging to identify outlier hospitals for 57 58 78 quality improvement because of the high statistical uncertainty. 59 60

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1 2 3 79 Previous research has identified a number of risk factors for PWD. Examples of such factors are: (I) BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 80 patient related variables and comorbidities: smoking12, obesity13, chronic pulmonary disease, renal 6 7 14 15 16 8 81 insufficiency or diabetes and use of immunosuppressive agents ; (II) procedure related factors: 9 10 82 operation type9 17, type of incision and closure18-20 and length of operation time21; (III) postoperative 11 12 83 parameters: clean wound classification21, coughing9 and wound infection9 14; (IV) operative scenario: 13 14 84 e.g. qualifications of the surgeon21-23 and of the perioperative team, and whether the surgery is 15 16 9 13 17 85 emergent. 18 For peer review only 19 20 86 The objectives of this study are to study the occurrence and variation of PWD after laparotomy at 21 22 23 87 Norwegian hospitals, and the potential usefulness of a PWD indicator for the Norwegian health care 24 25 88 system, computed from patient administrative data. More specifically we aimed to 1) investigate the 26 27 89 possibility to identify hospitals with higher or lower laparotomy PWD rate than average, after 28 29 90 appropriate risk adjustment, 2) study the variability of the PWD rate among hospitals, and its relation 30 31 32 91 to hospital type and laparotomy volume. 33 34 35 http://bmjopen.bmj.com/ 36 92 MATERIAL AND METHODS 37 38 39 40 93 Patient administrative data from all Norwegian hospitals were provided by the Norwegian Patient 41 42 94 Registry (NPR) for the period 2011-2015.24 This comprised individual patient data from all 43 on October 1, 2021 by guest. Protected copyright. 44 95 department stays: type of admission (acute or elective), primary and secondary diagnosis codes 45 46 25 47 96 according to the Norwegian version of ICD-10, surgical and medical procedures, age, gender, date 48 49 97 and time of ward admission and discharge. Surgical procedures and operations were coded according 50 51 98 to the Norwegian version of the NOMESCO Classification of Surgical Procedures (NCSP-N).26 52 53 99 Procedure time and date were not available. It was therefore not possible to exclude reclosures of 54 55 56 100 wounds occurring before or on the same day as laparotomies within the same episode, as requested 57 58 101 in the OECD indicator specification. The NPR data files were checked for missing values and 59 60 102 inconsistencies between variables, such as date and time of discharge before admission or invalid

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1 2 3 103 ICD-10 code. We had no access to clinical data, such as e.g. type of suture, which would have enabled BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 104 us to study the causes of the reported dehiscences. 6 7 8 9 105 Wound dehiscence was defined as the occurrence of a code for a reclosure operation, i.e. a 10 11 106 reoperation for wound dehiscence. This excludes superficial dehiscences, as these are usually not 12 13 14 107 resutured, and the code for reclosure operation is restricted to deep wound dehiscences. 15 16 108 Laparotomies and wound reclosure operations were identified according to procedure codes. An 17 18 109 operation coded withFor a laparotomy peer code, signifies review an incision into only the abdominal wall, through the 19 20 110 fascia and with an opening of the abdominal cavity. Laparoscopic and endoscopic procedures were 21 22 23 111 not included. Details of the codes used can be found in the online supplement. 24 25 26 112 All permanent residents in Norway have a Personal Identification Number (PIN), registered in the 27 28 29 113 NPR. NPR prepared an encrypted PIN for all patients with a valid PIN, allowing tracking of patients 30 31 114 over time and between hospitals. The data were linked with the National Registry to provide data of 32 33 115 death (when applicable), using the PIN. 34 35 http://bmjopen.bmj.com/ 36 37 116 Ward admissions for each patient, at more than one hospital in case of transfers, were linked into 38 39 117 episodes of care when less than eight hours elapsed from time of discharge to the next ward 40 41 118 admission.27 An episode was regarded as acute if the first admission in the episode was coded as 42 43 on October 1, 2021 by guest. Protected copyright. 119 non-elective, as a laparotomy episode if it included any procedure code for laparotomy (reclosures 44 45 46 120 not included), and a reclosure episode if a reclosure code was found. The initial data set consisted of 47 48 121 all laparotomy and reclosure episodes. Each reclosure episode was linked to the laparotomy episode 49 50 122 immediately preceding or coinciding with it. Reclosure episodes with no preceding laparotomy 51 52 123 episode within 30 days, as well as laparotomy or reclosure episodes following a reclosure episode 53 54 55 124 within 30 days, were excluded. Note that the linking of laparotomies and reclosures was not part of 56 57 125 the original OECD specification, but is required in order to attribute PWD to hospitals and to enable 58 59 126 risk adjustment. Following the OECD specification, laparotomy episodes (and consequently any 60

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1 2 3 127 linked reclosure episodes) were excluded if a diagnosis code for immunocompromised state or BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 128 relating to pregnancy, childbirth and puerperium was present, if the length of stay was less than two 6 7 8 129 days, or if the patient’s age was less than 15 years. Hospitals with less than 10 laparotomies over the 9 10 130 five-year period were excluded. The hospitals belonged to one of three types: regional, large with 11 12 131 acute function and small with acute function. For details of the diagnosis and operation codes used, 13 14 132 see the online supplement. For risk adjustment, Charlson comorbidities were determined from 15 16 27-29 17 133 previous admissions three years prior to, but not including the current episode of care. Diagnoses 18 For peer review only 19 134 were grouped according to the Clinical Condition Summary system (CCS), adapted to the Norwegian 20 21 135 version of ICD-10.30 22 23 24 25 136 Statistical methods 26 27 28 29 137 Risk adjusted probabilities for a laparotomy episode resulting in a reclosure operation were 30 31 138 estimated by bias corrected logistic regression.31 The final model was fit by stepwise regression with 32 33 139 the BIC criterion, allowing for potential two-way interactions. 34 35 http://bmjopen.bmj.com/ 36 37 140 To identify outlier hospitals, i.e. those with high or low risk adjusted PWD probabilities, estimated 38 39 141 hospital effects were compared to a reference value, defined as the 25% trimmed mean of the 40 41 142 hospital effects on the logistic scale.32 As some hospitals reported zero reclosures, ordinary maximum 42 on October 1, 2021 by guest. Protected copyright. 43 33 44 143 likelihood estimates of the model parameters do not exist, due to separation , and the estimated 45 46 144 variances of the fitted parameters, based on their asymptotic distribution, become unreliable. The 47 48 145 comparison used an exact test based on the Poisson binomial distribution for the number of PWDs 49 50 146 per hospital, using the estimated probabilities for each case, together with parametric bootstrapping 51 52 147 to account for the estimation uncertainty in the model parameters. Tests for significance were 53 54 34 55 148 corrected for multiple comparisons using the Guo-Romano method , and outlier status assigned 56 57 149 according to the false discovery rate (FDR). An FDR not exceeding 5% was regarded as significant. For 58 59 150 sensitivity analysis, two alternative risk adjustment models were tested, with either a four-category 60

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1 2 3 151 grouping of procedures, or with diagnosis categories, instead of the 13-category procedure grouping. BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 152 In addition, a model with the four Norwegian hospital regions was also estimated. 6 7 8 9 153 Hospital volume, modelled by splines35, was tested for inclusion in the model. We also performed 10 11 154 this test after exclusion of hospitals with zero reclosures. 12 13 14 15 155 Finally, the hospital specific effects were modelled as a mixture of two normal distributions. The 16 17 156 expectation-maximization (EM) algorithm was used, taking into account the estimation variances. 18 For peer review only 19 20 157 The mixture model yielded estimates of the quartiles of the hospital odds ratios and the scaled 21 22 158 interquartile range (normalized by dividing by 1.349, to give the standard deviation in the case of a 23 24 159 normal distribution) was computed as a measure of spread among hospitals. Bootstrapping of the 25 26 160 mixture model was used to find a 95% confidence interval for the scaled interquartile range. 27 28 29 30 31 161 Risk adjustment 32 33 34 162 The following case-mix variables were included as candidates in the stepwise regression: age, gender, 35 http://bmjopen.bmj.com/ 36 163 indicators for the individual Charlson comorbidities, number of previous hospital admissions two 37 38 164 years prior to current admission, and whether the episode was acute or elective. A linear trend in 39 40 41 165 admission year was also included. Age was modelled by natural splines with knots at the median and 42 43 166 quartiles.35 Based on previous studies of risk factors9 17, procedures were categorized into 13 types, on October 1, 2021 by guest. Protected copyright. 44 45 167 according to the body system or organ involved. The effects of operation types were normalized to 46 47 168 have zero sum on the logistic scale. 48 49 50 51 169 For a quality indicator, only characteristics of the patient when entering the hospital, are meaningful 52 53 170 risk adjustment variables. No data were available for smoking, obesity or other patient or case 54 55 171 characteristics such as nutritional status. There was no information about operation urgency beyond 56 57 58 172 the status of the hospital admission or episode as elective or acute. 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 173 Patient and Public Involvement 5 6 7 174 Patients were not involved in the planning, conduct or analysis of this study. The policy of the 8 9 175 Norwegian Institute of Public health is to publish hospital quality indicators, when they have been 10 11 176 successfully validated. 12 13 14 15 16 177 RESULTS 17 18 For peer review only 19 20 178 The initial data set comprised 96 102 episodes with laparotomy and 1 909 with a reclosure operation. 21 22 179 After restricting data to reclosures paired with a laparotomy within 30 days, 1 580 reclosures 23 24 180 remained. After exclusions for pregnancy, childbirth and puerperium or immunocompromised state, 25 26 27 181 age and LOS, 78 299 laparotomies remained. Lastly, hospitals with less than 10 laparotomies were 28 29 182 excluded, yielding a final data set with 66 925 unique patients, 78 086 laparotomies and 1 477 30 31 183 reclosures from 47 hospitals. Descriptive statistics for the dataset are shown in Table 1. The 32 33 184 operation types are tabulated in the online Supplement. 34 35 http://bmjopen.bmj.com/ 36 37 185 Table 1. Descriptive statistics for final data set 38 39 PWD No PWD 40 41 Age, years, median (quartiles) 69 (61-78) 65 (51-75) 42 Gender, females, n (%) 517 (35) 43 094 (56) 43 on October 1, 2021 by guest. Protected copyright. 44 Acute laparotomy episode, n (%) 657 (44) 26 381 (34) 45 Main diagnosis for reclosure episode coded as PWD, n (%) 45 (3.1) — 46 Main diagnosis for reclosure episode coded as deep wound infection, 47 274 (19) — 48 n (%) 49 Hospital type for laparotomy episodes 50 51 Regional, n (%) 545 (37) 28 104 (37) 52 Large with acute function, n (%) 810 (55) 40 291 (53) 53 Small with acute function, n (%) 122 (8.3) 8 214 (11) 54 55 Comorbidities 56 Diabetes with complications, n (%) 18 (1.2) 893 (1.2) 57 58 Chronic pulmonary disease, n (%) 196 (13) 5 147 (6.7) 59 Renal disease, n (%) 66 (4.5) 2 716 (3.5) 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 30 day mortality (laparotomy episode), % 67 (4.5) 2 668 (3.5) 4 5 Length of stay (LOS) laparotomy episode, days, median (quartiles) 19 (11-29) 7.4 (4.4-13) 6 Reclosure and matched laparotomy in same episode, n (%) 1 211 (82) — 7 8 Converted from laparoscopy or endoscopy to laparotomy, n (%) 12 (0.81) 578 (0.75) 9 Robot assistance in laparotomy, n (%) 3 (0.2) 404 (0.53) 10 11 186 12 187 From 2011 to 2015, the annual volume of laparotomies decreased somewhat, from 16 730 to 14 419, 13 14 188 while the proportion of acute laparotomies remained stable at around 35%. 15 16 17 18 189 The overall rate of PWDFor for the peer five-year period review was 1.89%. Crude only PWD rates varied from 0% to 5.1% 19 20 190 among hospitals. After risk adjustment, the range was 0.1% - 5.4%. Table 2 shows the odds ratios of 21 22 191 the final logistic regression model. No interactions were included. The model showed good fit 23 24 36 25 192 according to the modified Hosmer-Lemeshow test (p=0.53) and good predictive ability, with an area 26 27 193 under the operating characteristic (c-statistic) of 0.73. 28 29 30 31 194 Table 2. Final multivariate logistic model for risk adjustment 32 33 Variable Adjusted odds ratio (95% confidence interval) 34

Year of admission 0.93 (0.90-0.96) http://bmjopen.bmj.com/ 35 36 Age, spline function 37 40 (reference) 1.00 38 39 50 1.37 (1.25-1.49) 40 60 1.97 (1.65-2.36) 41 42 70 2.39 (1.97-2.90) 43 Gender on October 1, 2021 by guest. Protected copyright. 44 45 Female (reference) 1 46 Male 2.42 (2.16-2.72) 47 48 Elective laparotomy episode (reference) 1 49 Acute laparotomy episode 1.36 (1.21-1.52) 50 Chronic pulmonary disease 1.72 (1.47-2.01) 51 52 Operation typea 53 Exploratory laparotomy 2.40 (1.78-3.24) 54 55 Hernia (diaphragmal) 2.57 (1.37-4.81) 56 Thoracoabdominal aorta 2.08 (0.85-5.09) 57 58 Gastrointestinal tract 2.04 (1.69-2.46) 59 Liver 1.14 (0.69-1.87) 60

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1 2 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 3 Biliary tract 0.12 (0.05-0.28) 4 5 Pancreas 0.79 (0.40-1.58) 6 Spleen 1.20 (0.45-3.24) 7 8 Other digestive system 1.46 (1.03-2.07) 9 Kidney 0.09 (0.03-0.28) 10 11 Other urinary and male genital organs 0.52 (0.37-0.71) 12 Female genital organs 1.43 (1.06-1.92) 13 14 Peripheral vascular surgery 1.21 (0.93-1.57) 15 More than one type of surgeryb 2.58 (2.12-3.15) 16 17 Hospital 18 Scaled interquartileFor range peer 0.30review only(0.23-0.34) 19 195 a Odds ratios for operation type is scaled to have geometric mean 20 21 196 b Not counting exploratory laparotomy 22 23 197 24 25 26 27 198 In Figure 1, risk-adjusted PWD rates are shown for each hospital, plotted versus laparotomy volume 28 29 199 and hospital type. 30 31 32 33 200 After significance testing, we identified three hospitals with higher PWD and none with lower PWD 34 35 201 than average, when correcting for multiple testing. Without multiple test correction, one additional http://bmjopen.bmj.com/ 36 37 202 hospital with high PWD was found to be marginally significant (p=0.053). 38 39 40 41 203 In the alternative model including volume, the PWD increased with yearly laparotomy volume from a 42 43 204 very low level up to 120 laparotomies per year, after which it remained fairly constant, see Figure 1. on October 1, 2021 by guest. Protected copyright. 44 45 205 The effect of volume was significant (p<0.001), also after exclusion of the four smallest volume 46 47 48 206 hospitals with zero reclosures (p=0.008). Hospital type coincided almost completely with a grouping 49 50 207 of hospitals by volume, and was therefore not tested separately. There was significant variation 51 52 208 among regions (p<0.001), with the Northern region having the highest and the South-Eastern region 53 54 209 the lowest rates. Details can be found in the online supplement. Using diagnosis categories or 55 56 57 210 aggregated operation type as risk adjustment variables resulted in very small changes in risk adjusted 58 59 211 PWD rates. 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 212 DISCUSSION 5 6 7 8 213 We have studied wound dehiscence after laparotomy, as a quality indicator based on the OECD 9 10 214 specification, and found that it discriminated between Norwegian hospitals. The indicator was risk 11 12 215 adjusted for differences in age, gender, comorbidity and type of surgery, and showed little sensitivity 13 14 15 216 to changes in the set of risk adjustment variables. The overall PWD rate was 1.89%. After risk 16 17 217 adjustment, the hospitals’ PWD rate varied between 0.1% and 5.4%. Laparotomy volume and type of 18 For peer review only 19 218 hospital had little effect on the PWD rate, except for hospitals with very low volume. Advanced age, 20 21 219 male gender, chronic pulmonary disease, and emergency laparotomy were all significant risk factors 22 23 220 for PWD. There were significant PWD differences according to the organ system targeted. The overall 24 25 26 221 rate of PWD showed a small but statistically significant decline over the observation period 2011- 27 28 222 2015. The relatively large variation of PWD rates between hospitals, after correction for patient 29 30 223 characteristics and operation type, indicates possible variation in the quality of healthcare among 31 32 224 hospitals. This may be due to variation in surgical technique and perioperative care, as well as the 33 34 35 225 handling of postoperative complications, such as wound infection, which is known to be a risk factor http://bmjopen.bmj.com/ 36 37 226 for PWD.17 We found PWD rates well within the range reported in international studies.9 13 14 17 21 37 38 38 39 227 Also, the risk factors identified are in accordance with previous studies, albeit limited to 40 41 228 administrative data. Laparotomy volume has negligible effect apart from the few hospitals with very 42 43 on October 1, 2021 by guest. Protected copyright. 44 229 low volume. A Japanese study reported a similar conclusion, while volume was found to have effect 45 46 230 in US hospitals.39 40 The effect is likely a result of the types of operations performed at the low- 47 48 231 volume hospitals, compared with the other hospitals. 49 50 51 52 232 Our study is based on complete data from all Norwegian hospitals performing laparotomies. It was 53 54 233 possible to track patients during transfers and reoperations at different hospitals. To the best of our 55 56 234 knowledge, no similar study has been performed. NPR, the data source, has been validated for 57 58 59 235 several disease categories with respect to identification of cases based on diagnoses and/or 60

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1 2 3 236 procedures, and found to have a very high degree of completeness, compared to Norwegian national BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 237 medical quality registries.41-44 At the time of writing, the completeness of NPR, after 24 registries 6 7 24 8 238 have been studied, ranges from 83.5% to 99.8%. 9 10 11 239 We cannot exclude a residual imbalance in case mix, affecting PWD through e.g. smoking or obesity, 12 13 14 240 which are known risk factors. There is regional variation in the prevalence of smoking and obesity in 15 16 241 Norway.45 Obesity is more prevalent in Northern Norway, where PWD rates are somewhat higher. 17 18 242 However, in some otherFor areas wherepeer obesity review is less prevalent, theonly rates are similar. There is no 19 20 243 consistent correspondence between the known variation in smoking among counties and PWD rates. 21 22 23 244 Some surgical procedures are performed only at regional hospitals, and it is therefore possible that 24 25 245 selection effects are present. In that case, one would expect larger changes in PWD rates after risk 26 27 246 adjustment for operation type, which was not found. One potential source of error in our study is the 28 29 247 completeness and correctness of coding in the NPR, particularly the coding of reclosure operations. 30 31 32 248 The risk adjustment depends on data from previous hospitalization and may not capture all 33 34 249 comorbidities. Moreover, selection effects cannot not be ruled out. Differing policies for operations 35 http://bmjopen.bmj.com/ 36 250 on patients with known risk factors, e.g. obesity or smoking, would likely cause variation in PWD 37 38 251 rates. Patients who die before reoperation or are managed by other means will not be registered. 39 40 252 We believe that this applies to very few patients and would not influence our results. No attempt 41 42 43 253 was made to identify main operation or operation intent, as this would require a classification effort on October 1, 2021 by guest. Protected copyright. 44 45 254 outside the scope of the present study. No clinical details about surgical technique and patient 46 47 255 condition were available. Therefore, the causes of the observed PWD rate variation could not be 48 49 256 investigated. 50 51 52 53 257 Previous studies have shown that the quality indicator has high positive predictive value, but only 54 55 258 moderate sensitivity.10 46 47Since we have used specific wound reclosure codes, similar to those used 56 57 58 259 in previous studies, we expect a high positive predictive value in Norway as well. Conceivably, the 59 60 260 sensitivity depends on the coding system, in particular the various alternative codes related to

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1 2 3 261 complications. Sensitivity in Norway may thus differ from that of other healthcare systems. A recent BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 262 retrospective medical record study from neighbouring Sweden reports that 86.9% of wound 6 7 38 8 263 dehiscences were reoperated. Norway has an activity-based system for financing hospitals, which is 9 10 264 an incentive to report all reclosure operations. 11 12 13 14 265 Conclusions 15 16 266 Among Norwegian hospitals, there is a significant variation in PWD rate after laparotomies that 17 18 267 cannot be explained byFor operation peer type, age, reviewcomorbidity or whether only the admission was elective or 19 20 268 acute. This warrants further investigation into possible causes, such as patient related factors, 21 22 23 269 surgical technique, perioperative procedures or handling of complications, e.g. wound infections. 24 25 270 Some of these factors are known to be amenable.20 48 The relatively large between-hospital variation 26 27 271 found in the present study is an indication of potential for improvement. The risk adjusted PWD rate 28 29 272 after laparotomy is a candidate for use as a quality indicator for Norwegian hospitals, and will make it 30 31 32 273 possible to identify hospitals with apparent quality problems. To achieve sufficient discrimination, 33 34 274 however, five-year data are desirable, making it more difficult to monitor changes in hospital 35 http://bmjopen.bmj.com/ 36 275 performance resulting from quality improvement efforts. It lies outside the scope of the present 37 38 276 study to perform a comprehensive validation of the PWD rate as a quality indicator suitable for 39 40 41 277 public reporting. There are uncertainties and potential biases in the indicator, implying that it must 42 43 278 be regarded as a signal for follow-up within hospitals, rather than giving a final verdict of inferior or on October 1, 2021 by guest. Protected copyright. 44 45 279 superior quality. For reporting on surgical quality, several indicators should be used to give a 46 47 280 balanced view of the different aspects of quality and patient safety. 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 281 FOOTNOTES 5 6 7 8 9 282 Funding 10 11 12 283 This research did not receive any grants from any funding agency in the public, commercial or not- 13 14 284 for-profit sectors. 15 16 17 18 285 Competing interestsFor peer review only 19 20 21 22 286 The authors have no competing interests. 23 24 25 26 287 Authors’ contributions 27 28 29 288 AKL and OT conceived the study. DTK, TMH, OT, and SH participated in data preparation. OT, SH and 30 31 289 AKL contributed to the analysis. OT helped draft the manuscript. JH was responsible for the statistical 32 33 290 analysis and final manuscript. All authors revised and approved the final manuscript. 34 35 http://bmjopen.bmj.com/ 36 37 38 291 Ethics approval 39 40 41 292 The study was approved by the Norwegian Directorate of Health and the Norwegian Data Protection 42 43 293 Authority. on October 1, 2021 by guest. Protected copyright. 44 45 46 47 48 294 Data sharing 49 50 51 295 The data set contains indirectly identifiable personal data, and cannot be shared without express 52 53 296 permission from the Norwegian Patient Registry. For further information, contact the corresponding 54 55 297 author. 56 57 58 59 60

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1 2 3 298 Figure 1. Risk adjusted PWD rates versus yearly laparotomy volume, by hospital type. Trend BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 299 curve is obtained by smoothing the scatterplot. Significance testing is adjusted for multiple 5 6 300 comparisons 7 8 9 301 REFERENCES 10 11 12 13 302 14 15 303 16 17 304 1. Carinci F, Van Gool K, Mainz J, et al. Towards actionable international comparisons of health 18 305 system performance:For expertpeer revision review of the OECD framework only and quality indicators. Int J 19 306 Qual Health Care 2015;27(2):137-46. doi: 10.1093/intqhc/mzv004 [published Online First: 20 307 2015/03/12] 21 308 2. OECD. Health Care Quality and Outcomes: OECD; 2018 [Available from: 22 309 http://www.oecd.org/health/health-systems/health-care-quality-and-outcomes.htm 23 310 accessed 2018-06-06 2018. 24 311 3. Hannan EL. Using mortality data for profiling hospital quality of care and targeting substandard 25 26 312 care. J Soc Health Syst 1989;1(1):31-48. 27 313 4. Miller MR, Elixhauser A, Zhan C, et al. Patient Safety Indicators: using administrative data to 28 314 identify potential patient safety concerns. Health Serv Res 2001;36(6 Pt 2):110-32. [published 29 315 Online First: 2005/09/09] 30 316 5. OECD. Health Care Quality Indicators - Patient Safety 2018 [Available from: 31 317 http://www.oecd.org/health/health-systems/hcqi-patient-safety.htm accessed 2018-06-06 32 318 2018. 33 319 6. OECD. Definitions for Health Care Quality Indicators 2016-2017 HCQI Data Collection: OECD, 34

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1 2 3 342 15. Roine E, Bjork IT, Oyen O. Targeting risk factors for impaired wound healing and wound BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 343 complications after kidney transplantation. Transplant Proc 2010;42(7):2542-6. doi: 5 344 https://dx.doi.org/10.1016/j.transproceed.2010.05.162 6 7 345 16. Stephan RN, Munschauer CE, Kumar MS. Surgical wound infection in renal transplantation: 8 346 outcome data in 102 consecutive patients without perioperative systemic antibiotic 9 347 coverage. Arch Surg 1997;132(12):1315-8; discussion 18-9. 10 348 17. Sorensen LT, Hemmingsen U, Kallehave F, et al. Risk factors for tissue and wound complications in 11 349 gastrointestinal surgery. Ann Surg 2005;241(4):654-8. 12 350 18. Mahey RG, Smruti; Rajpurohit, Jitesh; Desai, Desai; Suryawanshi, Sachin;. A prospective study of 13 351 risk factors for abdominal wound dehiscence. International Surgery Journal 2017;4(1):24-28. 14 352 doi: http://dx.doi.org/10.18203/2349-2902.isj20163983 15 353 19. Deerenberg EB, Harlaar JJ, Steyerberg EW, et al. Small bites versus large bites for closure of 16 17 354 abdominal midline incisions (STITCH): a double-blind, multicentre, randomised controlled 18 355 trial. Lancet 2015;386(10000):1254-60.For peer review doi: 10.1016/s0140-6736(15)60459-7 only [published 19 356 Online First: 2015/07/21] 20 357 20. Israelsson LA, Millbourn D. Prevention of Incisional Hernias: How to Close a Midline Incision. Surg 21 358 Clin North Am 2013;93(5):1027-40. doi: https://doi.org/10.1016/j.suc.2013.06.009 22 359 21. Webster C, Neumayer L, Smout R, et al. Prognostic models of abdominal wound dehiscence after 23 360 laparotomy. J Surg Res 2003;109(2):130-7. 24 361 22. Bucknall TE, Cox PJ, Ellis H. Burst abdomen and incisional hernia: a prospective study of 1129 25 26 362 major laparotomies. Br Med J (Clin Res Ed) 1982;284(6320):931-3. [published Online First: 27 363 1982/03/27] 28 364 23. Gislason H, Soreide O, Viste A. Wound complications after major gastrointestinal operations. The 29 365 surgeon as a risk factor. Dig Surg 1999;16(6):512-4. doi: 10.1159/000018778 30 366 24. Health NDo. Norsk pasientregister - innhold og kvalitet: Norwegian Directorate of Health; 2018 31 367 [Available from: https://helsedirektoratet.no/norsk-pasientregister-npr/innhold-og-kvalitet 32 368 accessed 2018-12-06 2018. 33 369 25. eHealth NDo. Helsefaglige kodeverk: Norwegian Directorate of eHealth 2018 [Available from: 34 35 370 https://ehelse.no/standarder-kodeverk-og-referansekatalog/helsefaglige-kodeverk accessed http://bmjopen.bmj.com/ 36 371 2018-06-06 2018. 37 372 26. Norwegian Directorate of eHealth. NCMP, NCSP og NCRP: Klassifikasjon av medisinske, kirurgiske 38 373 og radiologiske prosedyrer Norwegian Directorate of eHealth; 2018 [Available from: 39 374 https://finnkode.ehelse.no/#ncmpncsp/0/0/0/-1 accessed 15th May 2018. 40 375 27. Hassani S, Lindman AS, Kristoffersen DT, et al. 30-Day Survival Probabilities as a Quality Indicator 41 376 for Norwegian Hospitals: Data Management and Analysis. PLoS One 2015;10(9):e0136547. 42 377 doi: 10.1371/journal.pone.0136547 43 on October 1, 2021 by guest. Protected copyright. 378 28. Quan HD, Sundararajan V, Halfon P, et al. Coding algorithms for defining comorbidities in ICD-9- 44 45 379 CM and ICD-10 administrative data. Med Care 2005;43(11):1130-39. doi: DOI 46 380 10.1097/01.mlr.0000182534.19832.83 47 381 29. Quan H, Li B, Couris CM, et al. Updating and validating the Charlson comorbidity index and score 48 382 for risk adjustment in hospital discharge abstracts using data from 6 countries. Am J 49 383 Epidemiol 2011;173(6):676-82. doi: 10.1093/aje/kwq433 50 384 30. (HCUP) HCaUP. Beta Clinical Classifications Software (CCS) for ICD-10-CM/PCS: Agency for 51 385 Healthcare Research and Quality; 2018 [Available from: https://www.hcup- 52 386 us.ahrq.gov/toolssoftware/ccs10/ccs10.jsp accessed 2018-06-06 2018. 53 54 387 31. Firth D. Bias Reduction of Maximum-Likelihood-Estimates. Biometrika 1993;80(1):27-38. doi: DOI 55 388 10.1093/biomet/80.1.27 56 389 32. Kristoffersen DT, Helgeland J, Clench-Aas J, et al. Observed to expected or logistic regression to 57 390 identify hospitals with high or low 30-day mortality? PLoS One 2018;13(4) doi: ARTN 58 391 e0195248 10.1371/journal.pone.0195248 59 392 33. Albert A, Anderson JA. On the Existence of Maximum Likelihood Estimates in Logistic Regression 60 393 Models. Biometrika 1984;71(1):1-10. doi: 10.2307/2336390

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1 2 3 394 34. Guo W, Romano JP. On stepwise control of directional errors under independence and some BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 395 dependence. Journal of Statistical Planning and Inference 2015;163:21-33. doi: 5 396 https://doi.org/10.1016/j.jspi.2015.02.009 6 7 397 35. Chambers JM, Hastie TJ, Eds. Statistical models in S. Pacific Grove: Wadsworth & Brooks/Cole 8 398 1992. 9 399 36. Paul P, Pennell ML, Lemeshow S. Standardizing the power of the Hosmer-Lemeshow goodness of 10 400 fit test in large data sets. Stat Med 2013;32(1):67-80. doi: 10.1002/sim.5525 11 401 37. Kenig J, Richter P, Lasek A, et al. The efficacy of risk scores for predicting abdominal wound 12 402 dehiscence: a case-controlled validation study. BMC Surg 2014;14:65. doi: 10.1186/1471- 13 403 2482-14-65 14 404 38. Walming S, Angenete E, Block M, et al. Retrospective review of risk factors for surgical wound 15 405 dehiscence and incisional hernia. BMC Surg 2017;17(1):19. doi: 10.1186/s12893-017-0207-0 16 17 406 39. Kitazawa T, Matsumoto K, Fujita S, et al. Perioperative patient safety indicators and hospital 18 407 surgical volumes.For BMC peerRes Notes 2014;7:117. review doi: 10.1186/1756-0500-7-117 only [published 19 408 Online First: 2014/03/04] 20 409 40. Hernandez-Boussard T, Downey JR, McDonald K, et al. Relationship between Patient Safety and 21 410 Hospital Surgical Volume. Health Serv Res 2012;47(2):756-69. doi: doi:10.1111/j.1475- 22 411 6773.2011.01310.x 23 412 41. Bakken IJ, Gystad SO, Christensen OO, et al. Comparison of data from the Norwegian Patient 24 413 Register and the Cancer Registry of Norway. Tidsskr Nor Laegeforen 2012;132(11):1336-40. 25 26 414 doi: 10.4045/tidsskr.11.1099 [published Online First: 2012/06/22] 27 415 42. Hoiberg MP, Gram J, Hermann P, et al. The incidence of hip fractures in Norway -accuracy of the 28 416 national Norwegian patient registry. BMC Musculoskelet Disord 2014;15:372. doi: 29 417 10.1186/1471-2474-15-372 [published Online First: 2014/11/15] 30 418 43. Oie LR, Madsbu MA, Giannadakis C, et al. Validation of intracranial hemorrhage in the Norwegian 31 419 Patient Registry. Brain and behavior 2018;8(2):e00900. doi: 10.1002/brb3.900 [published 32 420 Online First: 2018/02/28] 33 421 44. Varmdal T, Bakken IJ, Janszky I, et al. Comparison of the validity of stroke diagnoses in a medical 34 35 422 quality register and an administrative health register. Scandinavian journal of public health http://bmjopen.bmj.com/ 36 423 2016;44(2):143-9. doi: 10.1177/1403494815621641 [published Online First: 2015/12/15] 37 424 45. Health NIoP. Public Health report: Norwegian Institute of Public Health; 2018 [Available from: 38 425 https://www.fhi.no/en/op/hin/ accessed 2018-06-06 2018. 39 426 46. Cevasco M, Borzecki AM, McClusky DA, 3rd, et al. Positive predictive value of the AHRQ Patient 40 427 Safety Indicator "postoperative wound dehiscence". J Am Coll Surg 2011;212(6):962-7. doi: 41 428 https://dx.doi.org/10.1016/j.jamcollsurg.2011.01.053 42 429 47. Borzecki AM, Cevasco M, Mull H, et al. Improving the identification of postoperative wound 43 on October 1, 2021 by guest. Protected copyright. 430 dehiscence missed by the Patient Safety Indicator algorithm. Am J Surg 2013;205(6):674-80. 44 45 431 doi: https://dx.doi.org/10.1016/j.amjsurg.2012.07.040 46 432 48. Berríos-Torres SI, Umscheid CA, Bratzler DW, et al. Centers for disease control and prevention 47 433 guideline for the prevention of surgical site infection, 2017. JAMA Surg 2017;152(8):784-91. 48 434 doi: 10.1001/jamasurg.2017.0904 49 50 51 435 52 53 54 55 56 57 58 59 60

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 For peer review only 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 http://bmjopen.bmj.com/ 32 33 34 35 36 37 38 39 Figure 1. Risk adjusted PWD rates versus yearly laparotomy volume, by hospital type. Trend curve is on October 1, 2021 by guest. Protected copyright. obtained by smoothing the scatterplot. Significance testing is adjusted for multiple comparisons 40 41 149x149mm (300 x 300 DPI) 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 20 of 45

1 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Online supplement 6 7 8 Table 1. Hospital types 9 10 Hospital type Number 11 12 Small hospitals with acute function 21 13 Large hospitals with acute function 22 14 15 Regional hospitals 4 16 17 18 Table 2. LaparotomyFor cases after peer operation review type (primary episode)only 19 20 Operation type Frequency, n (%) 21 22 Gastrointestinal tract 30 404 (38.9) 23 More than one type of surgerya 14 051 (18.0) 24 Female genital organs 10 720 (13.7) 25 26 Other urinary and male genital organs 6 536 (8.4) 27 Peripheral vascular surgery 4 628 (5.9) 28 29 Biliary tract 2 739 (3.5) 30 Other digestive system 2 226 (2.9) 31 32 Kidney 2 152 (2.8) 33 Exploratory laparotomy 2 061 (2.6) 34 35 Liver 1 122 (1.4) http://bmjopen.bmj.com/ 36 Pancreas 775 (1.0) 37 38 Hernia (diaphragmal) 274 (0.4) 39 Spleen 248 (0.3) 40 41 Thoracoabdominal aorta 150 (0.2) 42 aNot counting exploratory laparotomy 43 on October 1, 2021 by guest. Protected copyright. 44 45 Table 3. Effect of hospital region, after risk adjustment. Odds ratio standardized to have 46 47 geometric mean one. 48 49 Hospital region Adjusted odds ratio (95% confidence interval) 50 South-Eastern Norway Region 0.85 (0.78 - 0.92) 51 52 Central Norway Region 0.99 (0.89 - 1.10) 53 Western Norway Region 1.06 (0.96 - 1.17) 54 55 Northern Norway Region 1.13 (1.001 - 1.27) 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 21 of 45 BMJ Open

2 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Diagnoses 6 7 Table 4. ICD-10 diagnosis codes contained in MDC 14 (Pregnancy, childbirth, and puerperium) 8 Code Title 9 10 A34 Obstetrical tetanus 11 F53.0 Mild mental and behavioural disorders associated with the puerperium, not elsewhere classified 12 F53.1 Severe mental and behavioural disorders associated with the puerperium, not elsewhere classified 13 F53.8 Other mental and behavioural disorders associated with the puerperium, not elsewhere classified 14 F53.9 Puerperal mental disorder, unspecified 15 Oxx.x Pregnancy, childbirth and puerperium 16 Z32.0 Pregnancy, not (yet) confirmed 17 Z32.1 Pregnancy confirmed 18 Z33 Pregnant state,For incidental peer review only 19 20 Z34.0 Supervision of normal first pregnancy 21 Z34.8 Supervision of other normal pregnancy 22 Z34.9 Supervision of normal pregnancy, unspecified 23 Z35.0 Supervision of pregnancy with history of infertility 24 Z35.1 Supervision of pregnancy with history of abortive outcome 25 Z35.2 Supervision of pregnancy with other poor reproductive or obstetric history 26 Z35.3 Supervision of pregnancy with history of insufficient antenatal care 27 Z35.4 Supervision of pregnancy with grand multiparity 28 Z35.5 Supervision of elderly primigravida 29 Z35.6 Supervision of very young primigravida 30 31 Z35.8 Supervision of other high-risk pregnancies 32 Z35.9 Supervision of high-risk pregnancy, unspecified 33 Z36.0 Antenatal screening for chromosomal anomalies 34 Z36.1 Antenatal screening for raised alphafetoprotein level 35 Z36.2 Other antenatal screening based on amniocentesis http://bmjopen.bmj.com/ 36 Z36.3 Antenatal screening for malformations using ultrasound and other physical methods 37 Z36.4 Antenatal screening for fetal growth retardation using ultrasound and other physical methods 38 Z36.5 Antenatal screening for isoimmunization 39 Z36.8 Other antenatal screening 40 41 Z36.9 Antenatal screening, unspecified 42 Z37.0 Single live birth 43 Z37.1 Single stillbirth on October 1, 2021 by guest. Protected copyright. 44 Z37.2 Twins, both liveborn 45 Z37.3 Twins, one liveborn and one stillborn 46 Z37.4 Twins, both stillborn 47 Z37.5 Other multiple births, all liveborn 48 Z37.6 Other multiple births, some liveborn 49 Z37.7 Other multiple births, all stillborn 50 Z37.9 Outcome of delivery, unspecified 51 52 Z39.0 Care and examination immediately after delivery 53 Z39.1 Care and examination of lactating mother 54 Z39.2 Routine postpartum follow-up 55 Z64.0 Problems related to unwanted pregnancy 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 22 of 45

3 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Table 5. ICD-10 diagnosis codes for immunocompromised state 6 7 Code Title 8 B20.0 HIV disease resulting in mycobacterial infection 9 B20.1 HIV disease resulting in other bacterial infections 10 B20.2 HIV disease resulting in cytomegaloviral disease 11 B20.3 HIV disease resulting in other viral infections 12 B20.4 HIV disease resulting in candidiasis 13 B20.5 HIV disease resulting in other mycoses 14 B20.6 HIV disease resulting in Pneumocystis carinii pneumonia 15 B20.7 HIV disease resulting in multiple infections 16 B20.8 HIV disease resulting in other infectious and parasitic diseases 17 B20.9 HIV disease resulting in unspecified infectious or parasitic disease 18 B21.0 HIV disease Forresulting in Kaposi'speer sarcoma review only 19 B21.1 HIV disease resulting in Burkitt's lymphoma 20 B21.2 HIV disease resulting in other types of non-Hodgkin's lymphoma 21 B21.3 HIV disease resulting in other malignant neoplasms of lymphoid, haematopoietic and related tissue 22 B21.7 HIV disease resulting in multiple malignant neoplasms 23 B21.8 HIV disease resulting in other malignant neoplasms 24 B21.9 HIV disease resulting in unspecified malignant neoplasm 25 B22.0 HIV disease resulting in encephalopathy 26 B22.1 HIV disease resulting in lymphoid interstitial pneumonitis 27 B22.2 HIV disease resulting in wasting syndrome 28 B22.7 HIV disease resulting in multiple diseases classified elsewhere 29 B23.1 HIV disease resulting in (persistent) generalized lymphadenopathy 30 B23.2 HIV disease resulting in haematological and immunological abnormalities, not elsewhere classified 31 B23.8 HIV disease resulting in other specified conditions 32 B24 Unspecified human immunodeficiency virus [HIV] disease 33 B59 Pneumocystosis 34 D47.1 Chronic myeloproliferative disease 35 D70 Agranulocytosis http://bmjopen.bmj.com/ 36 D71 Functional disorders of polymorphonuclear neutrophils 37 D72.0 Genetic anomalies of leukocytes 38 D80.0 Hereditary hypogammaglobulinaemia 39 D80.1 Nonfamilial hypogammaglobulinaemia 40 D80.2 Selective deficiency of immunoglobulin A [IgA] 41 D80.3 Selective deficiency of immunoglobulin G [IgG] subclasses 42 D80.4 Selective deficiency of immunoglobulin M [IgM] 43 D80.5 Immunodeficiency with increased immunoglobulin M [IgM] on October 1, 2021 by guest. Protected copyright. 44 D80.6 Antibody deficiency with near-normal immunoglobulins or with hyperimmunoglobulinaemia 45 D80.7 Transient hypogammaglobulinaemia of infancy 46 D80.8 Other immunodeficiencies with predominantly antibody defects 47 D80.9 Immunodeficiency with predominantly antibody defects, unspecified 48 D81.0 Severe combined immunodeficiency [SCID] with reticular dysgenesis 49 D81.1 Severe combined immunodeficiency [SCID] with low T- and B-cell numbers 50 D81.2 Severe combined immunodeficiency [SCID] with low or normal B-cell numbers 51 D81.3 Adenosine deaminase [ADA] deficiency 52 D81.4 Nezelof's syndrome 53 D81.5 Purine nucleoside phosphorylase [PNP] deficiency 54 D81.6 Major histocompatibility complex class I deficiency 55 D81.7 Major histocompatibility complex class II deficiency 56 D81.8 Other combined immunodeficiencies 57 D81.9 Combined immunodeficiency, unspecified 58 D82.0 Wiskott-Aldrich syndrome 59 D82.1 Di George's syndrome 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 23 of 45 BMJ Open

4 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 D82.2 Immunodeficiency with short-limbed stature 5 D82.3 Immunodeficiency following hereditary defective response to Epstein-Barr virus 6 D82.4 Hyperimmunoglobulin E [IgE] syndrome 7 D82.8 Immunodeficiency associated with other specified major defects 8 D82.9 Immunodeficiency associated with major defect, unspecified 9 D83.0 Common variable immunodeficiency with predominant abnormalities of B-cell numbers and function 10 D83.1 Common variable immunodeficiency with predominant immunoregulatory T-cell disorders 11 D83.2 Common variable immunodeficiency with autoantibodies to B- or T-cells 12 D83.8 Other common variable immunodeficiencies 13 D83.9 Common variable immunodeficiency, unspecified 14 D84.0 Lymphocyte function antigen-1 [LFA-1] defect 15 D84.1 Defects in the complement system 16 D84.8 Other specified immunodeficiencies 17 D84.9 Immunodeficiency, unspecified 18 D89.8 Other specifiedFor disorders peer involving the immune review mechanism, not elsewhereonly classified 19 D89.9 Disorder involving the immune mechanism, unspecified 20 E40 Kwashiorkor 21 E41 Nutritional marasmus 22 E42 Marasmic kwashiorkor 23 E43 Unspecified severe protein-energy malnutrition 24 I12.0 Hypertensive renal disease with renal failure 25 I13.1 Hypertensive heart and renal disease with renal failure 26 I13.2 Hypertensive heart and renal disease with both (congestive) heart failure and renal failure 27 K91.2 Postsurgical malabsorption, not elsewhere classified 28 N18.0 End-stage renal disease 29 N18.5 Chronic kidney disease, stage 5 30 N18.8 Other chronic renal failure 31 T86.0 Bone-marrow transplant rejection 32 T86.1 Kidney transplant failure and rejection 33 T86.2 Heart transplant failure and rejection 34 T86.3 Heart-lung transplant failure and rejection 35 T86.4 Liver transplant failure and rejection http://bmjopen.bmj.com/ 36 T86.8 Failure and rejection of other transplanted organs and tissues 37 T86.9 Failure and rejection of unspecified transplanted organ and tissue 38 Y83.0 Surgical Operation with transplant of whole organ or tissue 39 Z49.0 Preparatory care for dialysis 40 Z49.1 Extracorporeal dialysis 41 Z49.2 Other dialysis 42 Z94.0 Kidney transplant status 43 Z94.1 Heart transplant status on October 1, 2021 by guest. Protected copyright. 44 Z94.2 Lung transplant status 45 Z94.3 Heart and lungs transplant status 46 Z94.4 Liver transplant status 47 Z94.8 Other transplanted organ and tissue status 48 Z94.9 Transplanted organ and tissue status, unspecified 49 50 51 52 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 24 of 45

5 1 2 3 Operations BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Procedure codes for laparotomy and operation types. Laparotomy codes are the total of 6 codes in tables 6-19. Note that a last code digit of 0, 3 or 6 signifies an open or other non- 7 endoscopic operation or procedure, except for peripheral vascular surgery. 8 9 Table 6. NCSP-N codes for reclosure procedures 10 11 Code Title 12 JWA00 Repair of wound dehiscence in gastroenterological surgery 13 14 KWA00 Repair of wound dehiscence in urological surgery 15 LWA00 Repair of wound dehiscence in gynaecological surgery 16 PWA00 Repair of wound dehiscence in surgery of peripheral vessels and lymphatic system 17

18 For peer review only 19 20 Table 7. NCSP-N code for exploratory laparotomy and opening of abdominal cavity 21 22 Code Title 23 JAA00 Incision of abdominal wall 24 JAH00 Laparotomy 25 JAH20 Staging laparotomy 26 27 JAH30 Laparostomy 28 JAH33 Opening of laparostomy 29 JAH40 Thoracolaparotomy 30 31 32 33 Table 8. NCSP-N codes for diaphragmal hernia repair 34

Code Title http://bmjopen.bmj.com/ 35 36 JBB00 Repair of paraoesophageal hernia 37 JBB10 Repair of congenital diaphragmatic hernia 38 JBB96 Repair of other diaphragmatic hernia 39 JBC00 Gastro-oesophageal antireflux operation 40 41 42 43 Table 9. NCSP-N codes for repair of thoracoabdominal aorta on October 1, 2021 by guest. Protected copyright. 44 45 Code Title 46 FCD00 Suture of thoracoabdominal aorta 47 FCD10 Reinforcement of thoracoabdominal aorta using suture 48 49 FCD30 Repair of thoracoabdominal aorta using patch 50 FCD40 Partial resection and suture of thoracoabdominal aorta 51 FCD50 Resection and reconstruction of thoracoabdominal aorta using tube graft 52 FCD60 Resection of thoracoabdominal aorta and reimplantation of branches 53 54 FCD70 Bypass of thoracoabdominal aorta using tube graft 55 FCD80 Removal of foreign body from thoracoabdominal aorta 56 FCD96 Other repair of thoracoabdominal aorta 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 25 of 45 BMJ Open

6 1 2 3 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Table 10. NCSP-N codes for procedures on the gastrointestinal tract: oesophagus, stomach 6 7 and intestines 8 Code Title 9 10 JCB00 Oesophagostomy 11 JCC00 Transhiatal partial oesophagectomy without interposition 12 JCC10 Transthoracic partial oesophagectomy without interposition 13 JCC20 Transhiatal partial oesophagectomy with interposition of intestine 14 15 JCC30 Transthoracic partial oesophagectomy with interposition of intestine 16 JCC96 Other partial oesophagectomy 17 JCD00 Subcutaneous anastomosis of oesophagus without interposition 18 JCD03 SubcutaneousFor anastomosis peer of oesophagus review with interposition of intestineonly 19 20 JCD10 Intrathoracic anastomosis of oesophagus without interposition 21 JCD13 Intrathoracic oesophageal anastomosis with interposition of intestine 22 JCD20 Transsection of oesophagus 23 JCD96 Other anastomosis of oesophagus without resection 24 25 JCE00 Suture of oesophagus 26 JCE10 Plastic repair of stenosis of cardia 27 JCE20 Cardiomyotomy 28 JCE30 Repair of oesophageal atresia or congenital tracheo-oesophageal fistula 29 30 JCE33 Closure of acquired tracheo-oesophageal or broncho-oesophageal fistula 31 JCE40 Reconstruction of oesophagus using flap 32 JCE50 Reconstruction of oesophagus using free microvascular graft of intestine 33 JCE96 Other reconstruction of oesophagus 34 35 JCF00 Insertion of oesophageal stent http://bmjopen.bmj.com/ 36 JCW96 Other operation on oesophagus 37 JDA00 Gastrotomy 38 JDA60 Closure of perforated ulcer of stomach 39 40 JDA63 Local excision of lesion of stomach 41 JDB00 Gastrostomy 42 JDB10 Percutaneous gastrostomy 43 on October 1, 2021 by guest. Protected copyright. JDC00 Partial gastrectomy and gastroduodenostomy 44 45 JDC10 Partial gastrectomy and gastrojejunostomy 46 JDC20 Partial gastrectomy and Roux-en-Y reconstruction 47 JDC30 Partial gastrectomy with interposition of jejunum 48 JDC40 Partial gastrectomy and oesophagogastrostomy 49 50 JDC96 Partial gastrectomy with other reconstruction 51 JDD00 Total gastrectomy and Roux-en-Y oesophagojejunostomy 52 JDD96 Total gastrectomy with other reconstruction 53 JDE00 Gastrojejunostomy 54 55 JDE10 Conversion of gastrojejunostomy to Roux-en-Y anastomosis 56 JDE20 Conversion of gastrojejunostomy to gastroduodenostomy with interposition of jejunum 57 JDE96 Other anastomosis of stomach without concurrent gastrectomy 58 JDF00 Gastroplasty 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 26 of 45

7 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JDF10 Gastric bypass 5 6 JDF20 Gastric banding 7 JDF96 Other bariatric operation on stomach 8 JDG00 Truncal vagotomy 9 JDG10 Proximal gastric vagotomy 10 11 JDG96 Other vagotomy 12 JDH00 Duodenotomy 13 JDH40 Duodenostomy on duodenal bulb 14 JDH50 Local excision of lesion of duodenal bulb 15 16 JDH60 Pyloromyotomy 17 JDH63 Pyloroplasty 18 JDH70 Closure of perforatedFor ulcer peer of duodenum review only 19 JDW96 Other operation on stomach or duodenum 20 21 JEA00 Appendectomy 22 JEA10 Appendectomy with drainage 23 JEW96 Other operation on appendix 24 JFA00 Enterotomy 25 26 JFA10 Colotomy 27 JFA16 Biopsy of wall of colon without colotomy 28 JFA60 Stricturoplasty in small intestine 29 JFA63 Stricturoplasty in colon 30 31 JFA70 Suture of small intestine 32 JFA73 Excision of lesion of small intestine 33 JFA76 Closure of fistula of small intestine 34 JFA80 Suture of colon 35 http://bmjopen.bmj.com/ 36 JFA83 Excision of lesion of colon 37 JFA86 Closure of fistula of colon 38 JFA96 Other local operation on intestine 39 JFB00 Partial resection of small intestine 40 41 JFB10 Reversal of segment of small intestine 42 JFB13 Plastic repair of small intestine with lengthening 43 JFB20 Ileocaecal resection on October 1, 2021 by guest. Protected copyright. 44 JFB30 Right hemicolectomy 45 46 JFB33 Other resection comprising small intestine and colon 47 JFB40 Resection of transverse colon 48 JFB43 Left hemicolectomy 49 JFB46 Resection of sigmoid colon 50 51 JFB50 Other resection of colon 52 JFB53 Resection of sigmoid colon sigmoideum with partial resection of rectum 53 JFB60 Resection of sigmoid colon with end colostomy 54 JFB63 Other resection of colon with proximal colostomy and closure of distal stump 55 56 JFB96 Other partial excision of intestine 57 JFC00 Entero-enterostomy 58 JFC10 Ileotransversostomy 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 27 of 45 BMJ Open

8 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JFC20 Other enterocolostomy 5 6 JFC30 Colo-colostomy 7 JFC40 Ileorectostomy 8 JFC50 Colorectostomy 9 JFD00 Jejunoileal bypass 10 11 JFD03 Duodenoileal bypass with biliopancreatic diversion 12 JFD10 Revision of jejunoileal bypass 13 JFD13 Revision of duodenoileal bypass 14 JFD20 Restoration of continuity after jejunoileal bypass 15 16 JFD23 Restoration of continuity after duodenoileal bypass 17 JFD96 Other intestinal bypass operation 18 JFE00 TransplantationFor of small intestinepeer review only 19 JFE96 Other operation relating to transplantation of small intestine 20 21 JFF00 Catheter enterostomy 22 JFF10 Loop enterostomy 23 JFF13 Terminal enterostomy 24 JFF16 Conversion of ileoanal anastomosis to ileostomy 25 26 JFF20 Caecostomy 27 JFF23 Transversostomy 28 JFF26 Sigmoidostomy 29 JFF30 Other colostomy 30 31 JFF40 Appendicostomy 32 JFF50 Exteriorisation of loop of colon without opening 33 JFF60 Opening of exteriorised loop of colon 34 JFF96 Other exteriorisation of intestine or creation of intestinal stoma 35 http://bmjopen.bmj.com/ 36 JFG00 Closure of loop enterostomy without resection 37 JFG10 Closure of loop colostomy without resection 38 JFG20 Closure of enterostomy with resection of exteriorised loop 39 JFG23 Closure of terminal enterostomy with anastomosis to small intestine 40 41 JFG26 Closure of terminal enterostomy with anastomosis to colon 42 JFG30 Closure of colostomy with resection of exteriorised loop 43 JFG33 Closure of terminal colostomy with anastomosis to colon on October 1, 2021 by guest. Protected copyright. 44 JFG36 Closure of terminal colostomy with anastomosis to rectum 45 46 JFG40 Revision of enterostomy or colostomy without laparotomy 47 JFG50 Laparotomy with revision of enterostomy or colostomy 48 JFG53 Revision of ileal pelvic pouch 49 JFG56 Revision of colonic pelvic pouch 50 51 JFG60 Conversion of conventional ileostomy to continent ileostomy 52 JFG70 Conversion of continent ileostomy to conventional ileostomy 53 JFG73 Excision of ileal pelvic pouch 54 JFG76 Excision of colonic pelvic pouch with colorectal or coloanal anastomosis 55 56 JFG80 Excision of ileal pouch with construction of new continent ileostomy 57 JFG83 Excision of colonic pelvic pouch and construction of new pouch 58 JFG86 Excision of ileal pelvic pouch and construction of new pouch 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 28 of 45

9 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JFG96 Other operation on intestinal stoma or pouch 5 6 JFH00 Total colectomy and ileorectal anastomosis 7 JFH10 Total colectomy and ileostomy 8 JFH20 Proctocolectomy and ileostomy 9 JFH30 Total colectomy, mucosal proctectomy and ileoanal anastomosis without ileostomy 10 11 JFH33 Total colectomy, mucosal proctectomy, ileoanal anastomosis and ileostomy 12 JFH40 Proctocolectomy and continent ileostomy 13 JFH96 Other total colectomy 14 JFJ00 Coecopexy 15 16 JFJ96 Other enteropexy or colopexy 17 JFK00 Division of adhesive band in intestinal obstruction 18 JFK10 Freeing of adhesionsFor in intestinalpeer obstruction review only 19 JFK20 Freeing of adhesions and plication of small intestine 20 21 JFK96 Other operation on adhesions in intestinal obstruction 22 JFL00 Open reduction of intussusception of intestine 23 JFL10 Laparotomy and manipulation of obstructed intestine 24 JFL20 Laparotomy and manipulation of impacted material 25 26 JFL96 Other operation for intestinal obstruction without resection or freeing of adhesions 27 JFW96 Other operation on intestine 28 JGA00 Proctotomy 29 JGA60 Suture of rectum 30 31 JGA70 Proctotomy and excision of lesion of rectum 32 JGA96 Other proctotomy or local operation on rectum 33 JGB00 Partial proctectomy and colorectal or coloanal anastomosis 34 JGB03 Partial proctectomy with partial excision of mesorectum 35 http://bmjopen.bmj.com/ 36 JGB06 Total mesorectal excision 37 JGB10 Partial proctectomy and end colostomy 38 JGB20 Partial rectosigmoidectomy and abdominoperineal pull-through anastomosis 39 JGB30 Abdominoperineal excision of rectum 40 41 JGB33 Abdominoperineal excision of rectum and intersphincter resection 42 JGB36 Wide excision of rectum 43 JGB40 Excision of rectum and end ileostomy on October 1, 2021 by guest. Protected copyright. 44 JGB50 Mucosal proctectomy and ileoanal anastomosis 45 46 JGB60 Excision of rectum and ileoanal anastomosis 47 JGB96 Other proctectomy or excision of rectum 48 JGC00 Rectopexy 49 JGC30 Excision and suture of rectal mucosa with imbrication of muscular layer 50 51 JGC96 Other reconstructive operation on rectum 52 JGW96 Other operation on rectum 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 29 of 45 BMJ Open

10 1 2 3 Table 11. NCSP-N codes for procedures on the liver BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Code Title 6 JJA00 Exploration of liver 7 JJA10 Hepatotomy 8 9 JJA20 Open biopsy of liver 10 JJA23 Open needle biopsy of liver 11 JJA30 Fenestration of cyst of liver 12 JJA40 Excision of lesion of liver 13 14 JJA43 Destruction of lesion of liver 15 JJA50 Suture of liver 16 JJA96 Other local operation on liver 17 JJB00 Wedge resection of liver 18 For peer review only 19 JJB10 Atypical resection of liver 20 JJB20 Excision of single segment of liver 21 JJB30 Excision of two segments of liver 22 JJB40 Excision of segments II, III and IV of liver 23 24 JJB50 Excision of segments V, VI, VII and VIII of liver 25 JJB53 Excision of segments IV,V, VI, VII and VIII of liver 26 JJB60 Other excision of three or more segments of liver 27 JJB96 Other resection of liver 28 29 JJC00 Allogenic transplantation of liver 30 JJC10 Allogenic partial transplantation of liver 31 JJC20 Allogenic partial transplantation of liver from living donor 32 JJC30 Xenogenic transplantation of liver 33 34 JJC40 Xenogenic partial transplantation of liver 35 JJC50 Resection of transplanted liver http://bmjopen.bmj.com/ 36 JJC60 Total excision of transplanted liver 37 JJC96 Other transplantation of liver or related operation 38 39 JJW96 Other operation on liver 40 41 42 Table 12. NCSP-N codes for procedures on biliary tract 43 on October 1, 2021 by guest. Protected copyright. 44 Code Title 45 JKA00 Cholecystotomy 46 47 JKA10 Cholecystostomy 48 JKA20 Cholecystectomy 49 JKA96 Other operation on gallbladder 50 JKB00 Incision of bile duct 51 52 JKB20 Intraoperative cholangioscopy 53 JKB30 Percutaneous transhepatic biliary drainage 54 JKB40 Suture of bile duct 55 JKB96 Other incision or related operation on bile duct 56 57 JKC00 Incision of bile duct and local excision of lesion 58 JKC10 Partial excision and anastomosis of bile duct 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 30 of 45

11 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JKC20 Partial excision of bile duct and anastomosis to duodenum 5 6 JKC30 Partial excision of bile duct and anastomosis to jejunum 7 JKC40 Partial excision of right or left hepatic duct and anastomosis to jejunum 8 JKC50 Excision of papilla of Vater and anastomosis of bile duct to duodenum or jejunum 9 JKC96 Other excision of bile duct 10 11 JKD00 Anastomosis of gallbladder to jejunum 12 JKD10 Anastomosis of bile duct to duodenum 13 JKD20 Anastomosis of bile duct to jejunum 14 JKD30 Extrahepatic anastomosis of right or left hepatic duct to jejunum 15 16 JKD40 Anastomosis of intrahepatic bile duct to jejunum 17 JKD50 Hepatoportoenterostomy 18 JKD96 Other biliodigestiveFor anastomosis peer without excisionreview only 19 JKE00 Transduodenal papillotomy 20 21 JKE06 Transduodenal sphincteroplasty 22 JKE96 Other transduodenal open operation on bile duct or ampulla of Vater 23 JKF00 Excision of cystic duct 24 JKF96 Other secondary operation on biliary tract 25 26 JKW96 Other operation on biliary tract 27 28 29 30 Table 13. NCSP-N codes for procedures on the pancreas 31 32 Code Title 33 JLA00 Exploration of pancreas 34 JLA10 Biopsy of pancreas 35 http://bmjopen.bmj.com/ 36 JLB00 Incision of pancreas 37 JLB10 Pancreaticolithotomy 38 JLB96 Other incision, drainage or dilatation of pancreas 39 JLC00 Excision of lesion of pancreas 40 41 JLC10 Distal pancreatectomy 42 JLC20 Total pancreatectomy 43 JLC30 Pancreatoduodenectomy on October 1, 2021 by guest. Protected copyright. 44 JLC40 Total pancreatoduodenectomy 45 46 JLC50 Atypical pancreatectomy 47 JLC96 Other pancreatectomy 48 JLD00 Pancreaticojejunostomy 49 JLD10 Anastomosis of pancreatic pseudocyst to stomach 50 51 JLD20 Anastomosis of pancreatic pseudocyst to jejunum 52 JLE00 Allogenic total transplantation of pancreas with pancraticocystostomy 53 JLE03 Allogenic total transplantation of pancreas with pancreaticoenterostomy 54 JLE10 Allogenic segmental transplantation of pancreas 55 56 JLE16 Allogenic segmental transplantation of pancreas from living donor 57 JLE20 Allogenic islet cell transplantation 58 JLE30 Xenogenic islet cell transplantation 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 31 of 45 BMJ Open

12 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JLE40 Total excision of transplanted pancreas 5 6 JLE50 Occlusion of duct of transplanted pancreas 7 JLE56 Conversion of pancreaticocystostomy to pancreaticoenterostomy 8 JLE96 Other transplantation of pancreas or related operation 9 JLW96 Other operation on pancreas 10 11 12 13 14 Table 14. NCSP-N codes for procedures on the spleen 15 16 Code Title 17 JMA00 Partial splenectomy 18 JMA10 TransabdominalFor total splenectomy peer review only 19 JMA20 Transthoracic total splenectomy 20 21 JMB00 Biopsy of spleen 22 JMB10 Repair of spleen 23 JMW96 Other operation on spleen 24

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27 28 Table 15. NCSP-N codes for other digestive system procedures 29 30 Code Title 31 JAA10 Excision of lesion of abdominal wall 32 JAA13 Wide excision of extensive necrotising conditions of abdominal wall 33 JAA96 Other local operation on abdominal wall 34

JAK00 Laparotomy and drainage of peritoneal cavity http://bmjopen.bmj.com/ 35 36 JAK03 Laparotomy and peritoneal irrigation 37 JAK10 Laparotomy and insertion of peritoneal dialysis catheter 38 JAL00 Biopsy of peritoneum 39 JAL10 Laparotomy and removal of foreign body 40 41 JAL20 Excision or destruction of lesion of peritoneum 42 JAL23 Excision of local lesion of pelvic wall 43 JAL30 Omentectomy on October 1, 2021 by guest. Protected copyright. 44 JAL50 Intraabdominal revision of shunt of ventricle of brain 45 46 JAL96 Other excision of lesion of peritoneum 47 JAM00 Transposition of omentum 48 JAM10 Operation for malrotation of intestine 49 JAN00 Creation of peritoneovenous shunt 50 51 JAN10 Revision of peritoneovenous shunt 52 JAN20 Removal of peritoneovenous shunt 53 JAP00 Freeing of adhesions in the peritoneal cavity 54 JAQ00 Extensive excision of peritoneum 55 56 JAQ10 Intraoperative hypertermic chemotherapeutic perfusion of abdominal cavity 57 JAW96 Other operation on abdominal wall, peritoneum, mesentery or omentum 58 JBA00 Transabdominal repair of diaphragm for rupture 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 32 of 45

13 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 JBA10 Transabdominal biopsy or excision of lesion of diaphragm 5 6 JBA20 Transabdominal partial excision of diaphragm 7 JBW96 Other transabdominal operation on diaphragm or operation for gastro-oesophageal reflux 8 9 Table 16. NCSP-N codes for procedures on kidney and pelvis of kidney 10 11 Code Title 12 KAA00 Exploration of kidney 13 14 KAA20 Exploratory nephrotomy 15 KAA30 Exploratory pyelotomy 16 KAA96 Other exploration of kidney or pelvis of kidney 17 KAB00 Biopsy of kidney or pelvis of kidney 18 For peer review only 19 KAC00 Nephrectomy 20 KAC20 Nephroureterectomy 21 KAD00 Partial nephrectomy 22 KAD10 Heminephrectomy 23 24 KAD40 Partial excision of pelvis of kidney 25 KAD50 Destruction of tumour of pelvis of kidney 26 KAD56 Destruction of lesion of renal parenchyma 27 KAD60 Percutaneous destruction of lesion of renal parenchyma 28 29 KAD96 Other partial excision of kidney or pelvis of kidney 30 KAE00 Nephrolithotomy 31 KAE10 Pyelolithotomy 32 KAE96 Other removal of calculus from kidney or pelvis of kidney 33 34 KAF00 Removal of foreign body from kidney 35 KAF10 Removal of foreign body from pelvis of kidney http://bmjopen.bmj.com/ 36 KAH00 Suture of kidney 37 KAH10 Suture of pelvis of kidney 38 39 KAH30 Pyeloureteroplasty without division of ureteropelvic junction 40 KAH40 Pyeloureteroplasty with division of ureteropelvic junction 41 KAH50 Ureterocalyceal anastomosis 42 KAH70 Freeing of adhesions of ureteropelvic junction 43 on October 1, 2021 by guest. Protected copyright. 44 KAH80 Nephropexy 45 KAH96 Other reconstruction of kidney or pelvis of kidney 46 KAS00 Autotransplantation of kidney 47 KAS10 Allogenic transplantation of kidney from cadaver donor 48 49 KAS13 Allogenic transplantation of kidney from cadaver donor 50 KAS20 Allogenic transplantation of kidney from living donor with minimally invasive technique 51 KAS23 Allogenic transplantation of kidney from living donor with minimally invasive technique 52 KAS40 Excision of transplanted kidney 53 54 KAS50 Nephrocystostomy in transplanted kidney 55 KAS60 Operation for lymphocele of transplanted kidney 56 KAS96 Other transplantation of kidney or related procedure 57 KAW96 Other operation on kidney or pelvis of kidney 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 33 of 45 BMJ Open

14 1 2 3 Table 17. NCSP-N codes for procedures on other urinary and male genital organs: ureter, bladder, BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 urethra, prostate and seminal vesicles 5 6 Code Title 7 KBA00 Exploration of ureter 8 9 KBA10 Exploratory ureterotomy 10 KBA96 Other exploration of ureter 11 KBB00 Biopsy of ureter 12 KBC00 Ureterectomy 13 14 KBD00 Partial excision of ureter 15 KBD20 Destruction of tumour of ureter 16 KBD30 Excision of stump of ureter 17 KBD96 Other partial excision of ureter or destruction of tumour of ureter 18 For peer review only 19 KBE00 Ureterolithotomy 20 KBE96 Other operation for calculus of ureter 21 KBF00 Removal of foreign body from ureter 22 KBH00 Suture of ureter 23 24 KBH06 Ureteroureterostomy 25 KBH10 Connection of ureter to contralateral ureter 26 KBH20 Replantation of ureter 27 KBH30 Ileal replacement of ureter 28 29 KBH40 Plastic repair of ureter 30 KBH50 Ureterolysis 31 KBH96 Other repair or connection of ureter 32 KBJ00 Cutaneous ureterostomy 33 34 KBJ10 Cutaneous ureteroenterostomy 35 KBJ20 Cutaneous ureteroenterostomy with reservoir http://bmjopen.bmj.com/ 36 KBJ40 Ureteroenterostomy 37 KBJ60 Anastomosis of ureter to urethra with interposition of ileum 38 39 KBJ70 Removal of calculus from ileal conduit or reservoir 40 KBJ80 Operation for malfunction of urinary diversion 41 KBJ96 Other urinary diversion from ureter or related operation 42 KBV00 Insertion of stent into ureter 43 on October 1, 2021 by guest. Protected copyright. 44 KBV10 Removal of stent from ureter 45 KBV40 Incision or excision of ureterocele 46 KBW96 Other operation on ureter 47 KCA00 Exploratory cystotomy 48 49 KCB00 Biopsy of bladder 50 KCC00 Cystectomy 51 KCC10 Cystoprostatectomy 52 KCC20 Cystoprostatourethrectomy 53 54 KCC30 Cystectomy with excision of female internal genital organs 55 KCC96 Other cystectomy 56 KCD10 Partial cystectomy 57 KCD20 Excision of diverticulum of bladder 58 59 KCD30 Destruction of tumour of bladder 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 34 of 45

15 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 KCD40 Excision of urachus or other vesicocutaneous fistula 5 6 KCD96 Other partial excision or destruction of tumour of bladder 7 KCE00 Cystolithotomy 8 KCF00 Cystotomy and removal of foreign body from bladder 9 KCH00 Suture of bladder 10 11 KCH10 Enterocystoplasty 12 KCH20 Reduction cystoplasty 13 KCH30 Closure of vesicointestinal fistula 14 KCH40 Incision or resection of bladder neck 15 16 KCH96 Other reconstructive operation on bladder 17 KCJ00 Cystostomy 18 KCJ10 Cutaneous cystoenterostomyFor peer review only 19 KCJ20 Continent cutaneous cystoenterostomy 20 21 KCJ96 Other cystostomy 22 KCV10 Denervation of bladder 23 KCV20 Freeing of bladder 24 KCW96 Other operations on bladder 25 26 KDC00 Urethrectomy 27 KDD00 Partial excision of urethra 28 KDD10 Excision of diverticulum of urethra 29 KDD30 Destruction of tumour of urethra 30 31 KDD40 Resection of external sphincter of urethra 32 KDD50 Excision of urethral valve 33 KDD80 Partial excision of urethra and repair using graft or flap 34 KDD96 Other partial excision of urethra 35 http://bmjopen.bmj.com/ 36 KDG00 Retropubic suspension of urethra 37 KDG20 Abdominal colposuspension 38 KDG30 Suprapubic sling urethrocystopexy 39 KDG40 Suprapubic urethrocystopexy 40 41 KDG43 Transobturatorial sling urethrocystopexy 42 KDG50 Transabdominal plastic repair of pelvic floor for urinary incontinence 43 KDG60 Implantation of adjustable expander around bladder neck on October 1, 2021 by guest. Protected copyright. 44 KDG70 Exploration of urethra 45 46 KDG96 Other operation on urethra or bladder neck for incontinence 47 KDH00 Suture of urethra 48 KDH10 Meatoplasty of urethra 49 KDH30 Closure of urethrocutaneous fistula 50 51 KDH50 Closure of urethrointestinal fistula 52 KDH70 Plastic repair of stricture of urethra 53 KDH96 Other reconstructive operation on urethra 54 KDJ00 Urethrostomy 55 56 KDK00 Implantation of artificial urinary sphincter around bladder neck 57 KDK10 Implantation of artificial urinary sphincter around bulbar urethra 58 KDK30 Revision of artificial urethral sphincter 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 35 of 45 BMJ Open

16 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 KDK40 Removal of artificial urethral sphincter 5 6 KDW96 Other operation on urethra 7 KEA00 Exploration of prostate 8 KEA10 Prostatotomy 9 KEA20 Incision of seminal vesicle 10 11 KEB00 Biopsy of prostate 12 KED96 Other partial excision of prostate 13 KEE00 Prostatalithotomy 14 KEE10 Removal of foreign body from prostate 15 16 KEW96 Other operation on prostate or seminal vesicle 17 18 For peer review only 19 Table 18- NCSP-N codes for procedures on female genital organs: ovary, fallopian tube, uterus and 20 uterine ligaments 21 22 Code Title 23 LAA00 Puncture of ovarian cyst 24 LAB00 Ovariotomy 25 26 LAB10 Biopsy of ovary 27 LAB96 Other incision or biopsy of ovary 28 LAC00 Excision of ovarian cyst 29 LAC10 Fenestration of ovarian cyst 30 31 LAC20 Destruction of lesion of ovary 32 LAC30 Excision of paraovarian cyst 33 LAC96 Other excision or destruction of lesion of ovary 34 LAD00 Partial excision of ovary 35 http://bmjopen.bmj.com/ 36 LAE10 Unilateral oophorectomy 37 LAE20 Bilateral oophorectomy 38 LAF00 Unilateral salpingo-oophorectomy 39 LAF10 Bilateral salpingo-oophorectomy 40 41 LAF20 Unilateral transvaginal salpingo-oophorectomy 42 LAF30 Bilateral transvaginal salpingo-oophorectomy 43 LAG00 Freeing of adhesions of ovary on October 1, 2021 by guest. Protected copyright. 44 LAG10 Oophoropexy 45 46 LAG20 Detorsion of ovary 47 LAG96 Other reconstructive operation on ovary 48 LAW96 Other operation on ovary 49 LBB00 Biopsy of Fallopian tube 50 51 LBB96 Other biopsy of Fallopian tube 52 LBC10 Removal of products of conception from Fallopian tube 53 LBC20 Salpingotomy and removal of products of conception 54 LBC96 Other tube conserving operation for tubal pregnancy 55 56 LBD00 Partial excision of Fallopian tube 57 LBE00 Salpingectomy 58 LBF00 Perfusion of Fallopian tube 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 36 of 45

17 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 LBF03 Perfusion of Fallopian tube after reconstruction 5 6 LBF20 Transcervical catheter salpingoplasty 7 LBF30 Salpingolysis 8 LBF40 Fimbrioplasty 9 LBF50 Salpingostomy 10 11 LBF60 Partial excision and anastomosis of Fallopian tube 12 LBF70 Partial excision and reimplantation of Fallopian tube 13 LBF96 Other operation on Fallopian tube for infertility 14 LBW96 Other operation on Fallopian tube 15 16 LCA00 Biopsy of uterus or uterine ligaments 17 LCB00 Hysterotomy 18 LCB10 MyomectomyFor peer review only 19 LCB96 Other excision of lesion of uterus 20 21 LCC00 Partial excision of uterus 22 LCC10 Supravaginal hysterectomy 23 LCC20 Vaginal supravaginal hysterectomy 24 LCC96 Other partial excision of uterus 25 26 LCD00 Hysterectomy 27 LCD10 Vaginal hysterectomy 28 LCD30 Radical hysterectomy 29 LCD40 Radical vaginal hysterectomy 30 31 LCD96 Other hysterectomy 32 LCE00 Anterior exenteration of female pelvis 33 LCE10 Posterior exenteration of female pelvis 34 LCE20 Total exenteration of female pelvis 35 http://bmjopen.bmj.com/ 36 LCE96 Other exenteration of female pelvis 37 LCF00 Excision of lesion of parametrium 38 LCF10 Excision of female varicocele 39 LCF96 Other excision of lesion of parametrium 40 41 LCG10 Suture of uterus 42 LCG20 Hysteropexy 43 LCG30 Resection or transcision of sacrouterine ligaments on October 1, 2021 by guest. Protected copyright. 44 LCG40 Reconstruction of uterus 45 46 LCG96 Other reconstructive operation on uterus 47 LCW96 Other operation on uterus and uterine ligaments 48 49 50 51 52 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 37 of 45 BMJ Open

18 1 2 3 Table 19. NCSP-N codes for procedures on the peripheral vessels of the abdomen BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 5 Code Title 6 PCB20 Ligature of coeliac trunk and branches 7 PCB30 Ligature of superior mesenteric artery 8 9 PCB40 Ligature of renal artery 10 PCB99 Ligature of other visceral artery 11 PCC10 Suture of suprarenal or juxtarenal abdominal aorta 12 PCC20 Suture of coeliac trunk and branches 13 14 PCC30 Suture of superior mesenteric artery 15 PCC40 Suture of renal artery 16 PCC99 Suture of other visceral artery 17 PCE30 Thrombectomy or embolectomy of superior mesenteric artery 18 For peer review only 19 PCE40 Thrombectomy or embolectomy of renal artery 20 PCE99 Thrombectomy or embolectomy of other visceral artery 21 PCF20 Thrombendarterectomy of coeliac trunk and branches 22 PCF30 Thrombendarterectomy of superior mesenteric artery 23 24 PCF40 Thrombendarterectomy of renal artery 25 PCF99 Thrombendarterectomy of other visceral artery 26 PCG10 Operation for aneurysm of supracoeliac or juxtarenal abdominal aorta 27 PCG20 Operation for aneurysm of coeliac trunk and branches 28 29 PCG30 Operation for aneurysm of superior mesenteric artery 30 PCG40 Operation for aneurysm of renal artery 31 PCG99 Operation for aneurysm of other visceral artery 32 PCH10 Bypass from supracoeliac or juxtarenal abdominal aorta 33 34 PCH20 Bypass to/from coeliac trunk and branches 35 PCH30 Bypass from superior mesenteric artery http://bmjopen.bmj.com/ 36 PCH40 Bypass from renal artery 37 PCH99 Bypass from other visceral artery 38 39 PCJ30 Transposition of superior mesenteric artery 40 PCJ40 Transposition of renal artery 41 PCJ99 Transposition of other visceral artery 42

PCK20 Reimplantation of coeliac trunk and branches on October 1, 2021 by guest. Protected copyright. 43 44 PCK30 Reimplantation of superior mesenteric artery 45 PCK40 Reimplantation of renal artery 46 PCK50 Reimplantation of inferior mesenteric artery 47 PCK99 Reimplantation of other visceral artery 48 49 PCN20 Plastic repair of coeliac trunk and branches 50 PCN30 Plastic repair of superior mesenteric artery 51 PCN40 Plastic repair of renal artery 52 PCN99 Plastic repair of other visceral artery 53 54 PCU70 Exploration of previous reconstruction of suprarenal abdominal aorta or visceral arteries 55 PCU74 Thrombectomy or embolectomy in bypass from suprarenal abdominal aorta and visceral arteries 56 PCU81 Closure of persisting arteriovenous fistula of bypass from suprarenal abdominal aorta and visceral arteries 57 PCU82 Plastic repair in bypass from suprarenal abdominal aorta and visceral arteries 58 59 PCU99 Other repair after previous reconstruction of suprarenal abdominal aorta and visceral arteries 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 38 of 45

19 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 PCW99 Other operation on suprarenal abdominal aorta and visceral arteries 5 6 PDA10 Exploration of infrarenal abdominal aorta 7 PDA30 Exploration of iliac artery 8 PDC10 Suture of infrarenal abdominal aorta 9 PDC30 Suture of iliac artery 10 11 PDE10 Thrombectomy or embolectomy of infrarenal abdominal aorta 12 PDE30 Thrombectomy or embolectomy of iliac artery 13 PDF10 Thrombendarterectomy of infrarenal abdominal aorta 14 PDF30 Thrombendarterectomy of iliac artery 15 16 PDG10 Operation on infrarenal abdominal aorta for aneurysm 17 PDG20 Bypass from aorta to iliac artery for aneurysm 18 PDG21 Bypass from Foraorta to bilateral peer iliac arteries review for aneurysm only 19 PDG22 Bypass from aorta to iliac and contralateral femoral artery for aneurysm 20 21 PDG23 Bypass from aorta to femoral artery for aneurysm 22 PDG24 Bypass from aorta to bilateral femoral arteries for aneurysm 23 PDG30 Operation on iliac artery for aneurysm 24 PDG35 Bypass from iliac to femoral artery for aneurysm 25 26 PDG99 Other operation for aneurysm of infrarenal abdominal aorta and iliac arteries 27 PDH10 Bypass from infrarenal abdominal aorta 28 PDH20 Bypass from aorta to iliac artery 29 PDH21 Bypass from aorta to bilateral iliac arteries 30 31 PDH22 Bypass from aorta to iliac and contralateral femoral artery 32 PDH23 Bypass from aorta to femoral artery 33 PDH24 Bypass from aorta to bilateral femoral arteries 34 PDH30 Bypass from iliac artery 35 http://bmjopen.bmj.com/ 36 PDH35 Bypass from iliac to femoral artery 37 PDH99 Other bypass from abdominal aorta or iliac artery 38 PDN10 Plastic repair of infrarenal abdominal aorta 39 PDN30 Plastic repair of iliac artery 40 41 PDU70 Exploration of previous reconstruction of infrarenal abdominal aorta or iliac arteries and distal connections 42 PDU74 Thrombectomy or embolectomy in bypass from infrarenal abdominal aorta or iliac artery 43 PDU81 Closure of persisting arteriovenous fistula of bypass from infrarenal abdominal aorta or iliac artery on October 1, 2021 by guest. Protected copyright. 44 PDU82 Plastic repair of bypass from infrarenal abdominal aorta or iliac artery 45 46 PDU99 Other repair after previous reconstruction of infrarenal abdominal aorta and iliac arteries and distal 47 PDW99 Other operation on infrarenal abdominal aorta and iliac arteries and distal connections 48 PHB23 Ligature of iliac vein 49 PHB30 Ligature of inferior vena cava 50 51 PHB31 Ligature of renal vein 52 PHB32 Ligature of portal vein 53 PHB33 Ligature of v. mesenterica superior 54 PHB34 Ligature of v. mesenterica inferior 55 56 PHB36 Ligature of v. spermatica 57 PHC23 Suture of iliac vein 58 PHC30 Suture of inferior vena cava 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 39 of 45 BMJ Open

20 1 2 3 Code Title BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 4 PHC31 Suture of renal vein 5 6 PHC32 Suture of portal vein 7 PHC33 Suture of v. mesenterica superior 8 PHC34 Suture of v. mesenterica inferior 9 PHD30 Resection of inferior vena cava 10 11 PHD32 Resection of portal vein 12 PHD33 Resection of v. mesenterica superior 13 PHD34 Resection of v. mesenterica inferior 14 PHD36 Resection of v. spermatica 15 16 PHE23 Thrombectomy of iliac vein 17 PHE30 Thrombectomy of inferior vena cava 18 PHE31 ThrombectomyFor of renal veinpeer review only 19 PHH25 Bypass from iliac vein 20 21 PHH30 Bypass from inferior vena cava 22 PHN30 Plastic repair of inferior vena cava 23 PHN32 Plastic repair of portal vein 24 PHN33 Plastic repair of v. mesenterica superior 25 26 PHN34 Plastic repair of v. mesenterica inferior 27 PHW35 Portosystemic shunt or bypass 28 29 30 31 32 33 34 35 http://bmjopen.bmj.com/ 36 37 38 39 40 41 42 43 on October 1, 2021 by guest. Protected copyright. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Postoperative wound dehiscence after laparotomy: a useful health care quality indicator? A cohort study based on Norwegian hospital administrative data For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from Page 40 of 45

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, numbers potentially potentially , numbers For peer review only e.g. Cohort study Cohort outcome events or summary or events outcome time over measures study Case-control exposure in each numbers measures or summary category, exposure of study Cross-sectional Cohort study Cohort individuals at each stage the stage of each at individuals ( study for eligibility, examined eligible, included in eligible, confirmed follow-up, completing study, the analysed) and for non- reasons Give (b) of flow a use Consider (c) diagram clinical, social) and information and social) clinical, potential and exposures on confounders of number the (b) Indicate of interest variable each (c) follow-up time ( time follow-up amount) total participation at each stage. each at participation participants with missing data for for missing with data participants participants ( participants

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For peer review only For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml numbers of outcome events outcome or of numbers measures summary interpretation of results of interpretation objectives, considering of limitations, multiplicity from similar results analyses, relevant other and studies, evidence taking into account sources of of sources into account taking and direction both Discuss potential of bias any magnitude reference to study objectives to study reference analyses of subgroups subgroups and of analyses sensitivity and interactions, analyses and, if applicable, confounder- applicable, if and, their and estimates adjusted which clear Make interval). adjusted for were confounders included were they why and boundaries category Report (b) were variables continuous when categorized consider relevant, If (c) relative of estimates translating a for risk into absolute risk period time meaningful potential bias or imprecision. or bias potential precision (e.g., 95% confidence 95% confidence (e.g., precision

Interpretation Interpretation 20 cautious overall a Give Limitations Limitations 19 study, the limitations of Discuss Key results Key 18 withresults key Summarise Discussion Other analyses Other 17 done—e.g., analyses other Report Main results results Main 16 estimates unadjusted Give (a) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 BMJ Open: first published as 10.1136/bmjopen-2018-026422 on 3 April 2019. Downloaded from 2015; 2015; Contact the the Contact corresponding author

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programming code. programming http://bmjopen.bmj.com/ BMJ Open ) license. license. ) Discussion, l 214- Discussion, 218 was received received was No specific funding funding specific No CC BY on October 1, 2021 by guest. Protected copyright.

For peer review only For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml the role of the funders for the for the funders the of role the on study original which the for is based article present the (external validity) of the study of the study validity) (external results present study and, if applicable, applicable, if and, study present .. provide should Authors 22.1: RECORD

in press. press. in Commons ( Attribution Creative under isprotected *Checklist Working RECORD SM, the von HT, Elm E, Sørensen Langan I, Petersen D, Moher K, Harron A, SmeethGuttmann L, EI, Benchimol *Reference: Statement. health (RECORD) Data Routinely-collected Observational using Conducted studies of REporting The Committee. Accessibility of of Accessibility and data, code Funding Funding 22 and funding of source the Give Other Information Other Generalisability Generalisability 21 generalisability the Discuss protocol, raw raw protocol, programming 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 45 of