Randomized Comparison of the Pentax Airway Scope and Macintosh Laryngoscope for Tracheal Intubation in Patients with Obstructive Sleep Apnoea

British Journal of Anaesthesia 111 (4): 662–6 (2013) Advance Access publication 9 June 2013 . doi:10.1093/bja/aet201

RESPIRATION AND THE AIRWAY Randomized comparison of the Pentax AirWay Scope and Macintosh laryngoscope for tracheal intubation in patients with obstructive sleep apnoea

M. K. Kim1,S.W.Park1 and J. W. Lee2,3*

Department of Anesthesiology and Pain Medicine, School of Medicine, Kyung Hee University, 23 Kyungheedae-ro, Dongdaemun-gu, Seoul Downloaded from https://academic.oup.com/bja/article/111/4/662/240396 by guest on 29 September 2021 130-872, Republic of Korea 2 Division of Anesthesiology and Pain Medicine, Cardiovascular Hospital, Seoul, Republic of Korea 3 Department of Anesthesiology and Pain Medicine, College of Medicine, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea * Corresponding author: Department of Anesthesiology and Pain Medicine, College of Medicine, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea. E-mail: [email protected]

Background. Patients with obstructive sleep apnoea (OSA) can often present difficulties in Editor’s key points intubation. This study aimed to compare the efficacy of the Pentax AirWay Scope (AWS) with † Tracheal intubation may that of the Macintosh laryngoscope for tracheal intubation in patients with OSA. be difficult in patients with Methods. Forty-six patients undergoing uvulopalatopharyngoplasty were randomly allocated obstructive sleep apnoea. to tracheal intubation with either the Macintosh laryngoscope or the Pentax AWS. In all † This study compared the patients, intubation was performed by one of two anaesthetists experienced with both ease of tracheal devices. The primary and secondary endpoints of this study were the intubation difficulty intubation using either scale (IDS) score and success/failure and duration of the first successful intubation attempt. the Pentax AirWay Scope Results. With the Pentax AWS, tracheal intubation was successful on the first attempt in all (AWS) or a Macintosh patients whereas four patients required repeated attempts at intubation with the Macintosh laryngoscope. laryngoscope. The IDS score was significantly lower using the Pentax AWS and glottic † The investigators found exposure was better (the Cormack and Lehane grade 1 in all patients vs grade 2 or higher in better views at all patients, P,0.0001). Average duration of successful intubation was shorter (12.9 vs 29.9 laryngoscopy overall s, P¼0.0002), and fewer manoeuvres were needed to improve the glottic exposure (0 in all using the Pentax AWS. patients vs 1 or more in 16 patients, P,0.0001) with the Pentax AWS, compared with the † The study has some Macintosh laryngoscope. limitations and further Conclusions. In this study of patients with OSA, tracheal intubation by experienced data are needed to anaesthetistswasfacilitated usingthe Pentax AWS comparedwiththe Macintosh laryngoscope. confirm these findings. Keywords: intubation, intratracheal; laryngoscopes; sleep apnoea, obstructive Accepted for publication: 26 April 2013

The diagnosis of obstructive sleep apnoea (OSA) is often pre- and an external display, have been developed. With video- sumed to be a risk factor for difficult airway.1 – 4 In fact, the in- laryngoscopes, anaesthetists can theoretically get a better cidence of difficult intubation is reportedly higher in patients glottic exposure and thus make a more straightforward in- with OSA than in patients without OSA.5 Conversely, patients tubation compared with conventional laryngoscopes.6 The who presented with difficult intubation were more likely to Pentax AirWay Scope (AWS; AWS-S100w, Pentax Corporation, have OSA.2 Therefore, patients with diagnosed OSA should be Tokyo, Japan) is a videolaryngoscope with a disposable trans- deemed to have difficult airway during anaesthesia, which is parent blade (ITL-Sw) thatincorporates achannel to pass a tra- associated not only with narrowing of the upper airway, but cheal tube down to the glottic opening. For tracheal intubation, also with morphologic abnormalities, such as small mandible, the AWS is reportedly more valuable than the Macintosh laryn- short and thick neck, and large tongue.1 goscope in various conditions, such as normal airway,7 pre- Direct laryngoscopy using a curved Macintosh blade dicted difficult airway,89and in patients with restricted neck remains the gold standard technique. However, various video- motion.6 However, the efficacy of the AWS has not been evalu- laryngoscopes, equipped with a camera eye near the blade tip ated in a single group of patients with OSA.

This clinical trial aimed to compare the efficacy of the AWS maintained with sevoflurane in a mixture of oxygen and air and the Macintosh laryngoscope when an experienced anaes- at a 1:1 ratio. Further anaesthetic management was at the dis- thetist performed tracheal intubation in patients with OSA. cretion of the anaesthetist assigned to each patient. The hypothesis was that the AWS would provide an easier in- An independent, but unblinded observer collected all data in tubation condition in terms of the intubation difficulty scale every case of this trial. The primary endpoint was the IDS score, (IDS) score, success rate, and duration for successful intubation which was developed by Adnet and colleagues10 as a quantita- attempt compared with the Macintosh laryngoscope. tive scale incorporating multiple parameters of intubation diffi- cultyandthushasbeenadoptedtoenableobjectivecomparison of the complexity of tracheal intubation.971112The secondary Methods endpoints were success/failure and the duration of the first or After approval from the local Institutional Review Board on firstsuccessfulintubationattempt.Failureoftrachealintubation humanstudiesandregistrationinclinicaltrials.gov(UniqueIden- was determined as an attempt in which the trachea was not

tifier: NCT01428570), written informed consent was obtained intubated or an attempt that took .60 s to complete. Up to Downloaded from https://academic.oup.com/bja/article/111/4/662/240396 by guest on 29 September 2021 from all the patients enrolled. Patients, who were aged 20 yr or three attempts at intubation were permitted. The duration of more, and undergoing uvulopalatopharyngoplasty (UPPP) the first attempt and that of the successful attempt were under general anaesthesia, were included. These patients were recorded. Other endpoints were: number of intubation diagnosed as having OSA, which was confirmed by polysomno- attempts, number of optimization manoeuvres required for a graphy, but otherwise healthy (ASA physical status I–II). A better glottic exposure (use of a gum elastic bougie, external total of 46 patients were recruited. Patients who had loosened manipulation of larynx, and a requirement of second assistant), teethoramouthopeningof ,18mm,whichisaminimumclear- the Cormack and Lehane grade of glottic exposure,13 the lowest ance for the ITL-Sw, were excluded from the study. Patients with oxygen saturation recorded during or immediately after intub- any pathology in the neck, pharynx or larynx, a risk factor for as- ation attempts, and complications such as visible trauma to lip piration of gastric contents, or a history of hypersensitivity to an or oral mucosa, bleeding, or dental trauma. anaesthetic drug, were also excluded. To prevent an intubation failure in patients with potential risk Patients were randomly allocated into either the Macintosh for difficult airway, back-up plans were put in place as follows: group or AWS group using the sealed envelope method. Base- first, if intubation attempts with one device failed twice con- line airway parameters, including Mallampati classification secutively, the third intubation attempt with another device without phonation, thyromental distance, and interincisor dis- would be permitted. Secondly, if intubation attempts had tance, were measured before operation at the pre-anaesthesia failed with both devices, the failed intubation algorithm of the evaluation clinic by blinded senior residents in rotation. Stand- Difficult Airway Society Guidelines was followed.14 ard monitoring devices, including electrocardiography, non- Statistical analysis invasive arterial pressure, pulse oximetry, and end-tidal concentrations of carbon dioxide and volatile anaesthetic The sample size was calculated based on the IDS score, begin- agent, were applied when a patient arrived in the operating ning with zero, an ideal condition for intubation, and then in- theatre. Patients were preoxygenated for 3 min using a face creasing with progressively more difficult conditions for 915 mask and 100% oxygen. Anaesthesia was induced with i.v. ad- intubation. Based on previous studies, we considered a re- ministration of fentanyl (1–1.5 mgkg21) and propofol (1.5–2 duction of .2.0 in the mean IDS score, which is approximately mg kg21). Rocuronium (0.6 mg kg21) was given to facilitate tra- half of the expected mean IDS score with the Macintosh laryn- cheal intubation. Sevoflurane (2–3 vol%) in 100% oxygen was goscope, as clinically important. Power analyses suggested given via a face mask. After loss of all four twitches on the that the inclusion of 21 patients per group would be required train-of-four obtained by ulnar nerve stimulation, the patient with an expected standard deviation of 2.25 (a¼0.05, 15 was placed in the sniffing position, and then laryngoscopy b¼0.2). The size of study was finally determined to be 23 and tracheal intubation were performed by one of the two patients per group to account for drop-outs. anaesthetists (M.K.K. and S.W.P.). Before this study, both All analyses were performed with SAS 9.2 (SAS Institute, anaesthetists experienced .3 yr of clinical anaesthesia, and Inc., Cary, NC, USA). Data are presented as mean (SD), median had performed .500 and at least 100 tracheal intubations (interquartile range), and numbers (proportion) for continu- with the Macintosh laryngoscope and the AWS in patients, re- ous, ordinal and categorical variables, respectively. The dur- spectively. The cuffed tracheal tubes with an internal diameter ation of intubation attempt was analysed with a t-test. (ID) of 7.0 and 7.5–8.0 mm were used in females and males, Fisher’s exact test and Wilcoxon’s rank-sum test were used to respectively. The size selection was at the discretion of the analyse categorical and continuous data, respectively. Where anaesthetist who performed the laryngoscopy, based on the appropriate, 95% confidence interval of difference between patient’s build. When the Macintosh laryngoscope was used, the groups is presented. A P-value of ,0.05 was considered a gum elastic bougie was allowed for use. With the AWS, a well- to be significant for all analyses. lubricated tracheal tube was attached into a channel on the right side of the ITL-Sw before insertion. After the confirmation Results of successful intubation, the lungs were mechanically venti- In a total of 46 patients enrolled, one patient in the AWS group lated throughout the surgery, and anaesthesia was was excluded because of a change in surgical plan. No

663 BJA Kim et al. significant differences in patient characteristic or baseline laryngoscope (Table 2). All 23 patients in the Macintosh group airway parameters were found between the two groups had an IDS score of ≥1 while only three patients in the AWS (Table 1). Mean doses of anaesthetic drugs, including propofol, group did. Furthermore, 14 patients in the Macintosh group fentanyl, and rocuronium, and end-tidal concentrations of had an IDS score of ≥4, indicating more than moderate sevoflurane measured just before the tracheal intubation degree of intubation difficulty, but no patient in the AWS were comparable between the two groups. group did (Fig. 1). The duration of intubation attempt was sig- In all patients in the AWS group, tracheal intubation was nificantly shorter in the AWS group (Table 2). In the AWS successfully performed on the first attempt (Table 2). In the group, significantly fewer manoeuvres were required to Macintosh group, however, the first attempt was unsuccessful improve the glottic exposure compared with the Macintosh in four patients. Tracheal intubation was then successfully group (Table 2). No significant differences in the lowest done on the second attempt in these four patients. When the oxygen saturation during intubation attempts and in the inci- AWS was used, the median IDS score was significantly dence of complications, including the appearance of blood

reduced and the Cormack and Lehane grade of the glottic on the laryngoscope blade or minor trauma to the airway, Downloaded from https://academic.oup.com/bja/article/111/4/662/240396 by guest on 29 September 2021 exposure was improved, compared with the Macintosh were found between the two groups (Table 2). No dental

Table 1 Patient characteristic data and baseline airway parameters in patients with OSA. Values are mean (SD), median (interquartile range), or numbers (proportion), as appropriate, except for age as mean (range). CI, conﬁdence interval

Macintosh (n523) Pentax AWS (n522) 95% CI of difference between groups Sex (male/female) 19/4 16/6 Age (yr) 43.7 (19–64) 45.8 (23–62) 29.64 to 5.46 Body mass index (kg m22) 25.8 (3.2) 25.6 (3.5) 21.99 to 2.09 ASA status (I/II) 9/14 11/11 Apnoea-hypopnea index 25.8 (5.9–34.4) 14.9 (4.3–43.1) 211.37 to 16.35 Airway measurements Thyromental distance (cm) 5.3 (0.7) 4.9 (0.7) 20.02 to 0.83 Interincisor distance (cm) 4.6 (0.6) 4.5 (0.5) 20.16 to 0.54 Mallampati classiﬁcation 1 4 (17.4%) 0 (0%) 2 9 (39.1%) 5 (22.7%) 3 6 (26.1%) 10 (45.5%) 4 4 (17.4%) 7 (31.8%)

Table 2 Data on tracheal intubation with the Macintosh laryngoscope and the Pentax AWS in patients with OSA. Values are mean (SD), median (interquartile range), or numbers (proportion), as appropriate. *P,0.01, Wilcoxon’s rank-sum test; †P,0.01, Fisher’s exact test; ‡P,0.01; t-test, between groups

Macintosh (n523) Pentax AWS (n522) 95% CI of difference between the groups Overall success 23 (100%) 22 (100%) IDS score 4 (3–4) 0 (0–0)* 2.9–4.2 Cormack and Lehane grades 1/2/3/4 (number of patients) 0/8/14/1 22/0/0/0† Duration of ﬁrst intubation attempt (s) 24.3 (16.6) 12.9 (6.0)‡ 5.19–16.93 Duration of successful intubation attempt (s) 29.9 (28.5) 12.9 (6.0)‡ 7.73–29.18 Number of intubation attempts 1 19 (82.6%) 22 (100%) 2 4 (17.4%) 0 (0%) Number of optimization manoeuvres† 0 7 (30.4%) 22 (100%) 1 14 (60.9%) 0 (0%) 2 2 (8.7%) 0 (0%) Lowest Sp (%) 99.5 (0.7) 99.5 (0.7) 20.37 to 0.51 O2 Incident of complications 1 (4.4%) 0 (0%)

664 Pentax AWS for OSA BJA

oedema. In our patients, the best glottic exposure (Cormack 22 and Lehane grade 1) was provided with the AWS in all patients (100%) in spite of the higher Mallampati classiﬁcation in the 20 19 18 Macintosh AWS group compared with the Macintosh group. In fact, no 16 Pentax AWS patients had a Cormack and Lehane grade 1 exposure with 14 the Macintosh laryngoscope (Table 2). Secondly, the limited 12 head extension observed in patients with OSA resembles the intubation conditions in patients with restricted neck move- 10 9 ment. Enomoto and colleagues6 reported that a better glottic 8 exposure was produced by the AWS in patients with restricted Number of patients 6 5 4 4 neck movement, resulting in faster intubation with an in- 4 3 creased success rate compared with the conventional Macin- 2 1

tosh laryngoscope. The AWS was also shown to be superior to Downloaded from https://academic.oup.com/bja/article/111/4/662/240396 by guest on 29 September 2021 0123456 otherdevicesincludingAirtraqwandtheLMACTrachwinasimu- Intubation difficulty scale score lated model and patients with cervical immobilization.921 In addition, the AWS was shown to cause less cervical move- Fig 1 Distribution of IDS score for the Macintosh laryngoscope and ments during tracheal intubation than the Macintosh or the Pentax AWS in patients with OSA. The number of patients is McCoyw laryngoscopes.22 Better glottic exposure with the shown above each bar. P,0.01, between groups. AWS in this study could be attributed to the fact that the AWS causes less cervical movement, and requires no additional effort to align the oral, pharyngeal, and laryngeal axes. trauma or major trauma to the airway occurred with either Even when an anaesthetist has a clear glottic exposure with laryngoscope. a videolaryngoscope, it would be difficult to direct the tracheal tube into the trachea because the pharyngeal space is occu- Discussion pied by the relatively larger blade of the videolaryngoscope We found that tracheal intubation was facilitated with signifi- with the integrated camera eye.23 24 In contrast, such a weak- cantly lower IDS scores in patients with OSA when the AWS ness can be overcome with the AWS. The tip of the tracheal was used by experienced anaesthetists, compared with the tube, which is inserted into the channel in the ITL-Sw,is Macintosh laryngoscope. In addition, glottic exposure was already seen on the LCD screen before insertion, and the target better, average duration of successful intubation attempt symbol on the LCD screen enables the operator to optimally was shorter, and fewer manoeuvres to improve the glottic ex- direct the loaded tracheal tube into the glottic opening. Further- posure were used with the AWS, compared with the Macintosh more,the designofthe ITL-Swallows guidingthe loaded tracheal laryngoscope. tube toward the glottis when the tube is advanced down the A number of videolaryngoscopes have been developed to channel of the ITL-Sw. In spite of a clear glottic exposure, the compensate for the shortcomings of the Macintosh laryngo- AWS reportedly has a certain difficulty in advancing the tracheal scope. Compared with other laryngoscopes, the AWS has tube into the glottic opening, because the tip of the tracheal certain structural and functional features that improve the tube impinged on the arytenoids.78In our patients, however, glottic view in patients with OSA. First, patients with OSA impingement of the tracheal tube on the arytenoid cartilages oc- have a larger tongue with a relatively smaller pharyngeal curredinonly1of22patientsintheAWSgroupandwaseasily space surrounded by the skeletal structures of jaws.2 Further- overcome with adjusting the direction of the ITL-Sw. more, the mid to lower face is elongated to compensate for This study has several limitations. First, randomization of the decreased space for larger tongue. These features limit this study was not fully achieved. Even though the best mouth opening and require more anterior displacement of efforts of randomization were made, more patients with the tongue during direct laryngoscopy,16 – 18 because such a higher Mallampati classification were included in the AWS compensation would increase the posterior displacement of group. This could be attributed to the limited number of the tongue, especially with mouth opening.2 By virtue of ana- patients recruited. However, the AWS was shown to overcome tomical design which conforms to the pharyngeal structures, such a disadvantage. Furthermore, it was impossible to blind the ITL-Sw can be passed down just over the tongue, and both the operator and the observer to the device being used. thereby enables the operator to see the tongue base continu- Secondly, this study was carried out in a limited number of ously.19 Moreover, the ITL-Sw is wide and rigid enough to patients by anaesthetists experienced with both devices. The push away the structures around the airway.7 As a result, the results might be different if the users were less experienced. operator can easily place the ITL-Sw in the adequate position Therefore, the interpretation or extrapolation of the results of and have a sufficient room to visualize the glottis without ex- this study must be cautious. Finally, the IDS score has a limita- cessive displacement of the tongue and other soft tissues in tion in evaluating the efficacy of videolaryngoscope because the pharynx. Kariya and colleagues20 demonstrated that the the IDS score adopts the Cormack and Lehane grade, which AWS had an advantage over the Macintosh laryngoscope in a was originally developed for the direct laryngoscope and is in- simulated model of pharyngeal obstruction with tongue evitably subjective.13 However, the IDS score can be a more

665 BJA Kim et al. objective quantitative measure byincorporating multiple para- Macintosh laryngoscopes in predicted difficult intubation. Br meters. Many investigators adopted the IDS score as a primary J Anaesth 2009; 103: 761–8 endpoint to compare the AWS with other videolaryngoscopes 10 Adnet F, Borron SW, Racine SX, et al. The intubation difficulty scale or Macintosh laryngoscope, 71112and verified index of intub- (IDS):proposalandevaluationofanewscorecharacterizingthecom- plexity of endotracheal intubation. Anesthesiology 1997; 87: 1290–7 ation difficulty is not available other than the IDS score. Fur- 11 Malik MA, Subramaniam R, Churasia S, Maharaj CH, Harte BH, thermore, the success rate of tracheal intubation was not Laffey JG. Tracheal intubation in patients with cervical spine immo- reported to be significantly different between the AWS and bilization: a comparison of the Airwayscope, LMA CTrach, and the 25 – 27 Macintosh laryngoscope in various clinical settings. For Macintosh laryngoscopes. Br J Anaesth 2009; 102: 654–61 these reasons, we adopted the IDS as a primary endpoint 12 Malik MA, Maharaj CH, Harte BH, Laffey JG. Comparison of Macin- instead of success rate or elapsed time for tracheal intubation. tosh, Truview EVO2, Glidescope, and Airwayscope laryngoscope In conclusion, in this study involving a small number of use in patients with cervical spine immobilization. Br J Anaesth patients with experienced anaesthetists, the Pentax AWS 2008; 101: 723–30 13 Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. was shown to be more useful for tracheal intubation in patients Downloaded from https://academic.oup.com/bja/article/111/4/662/240396 by guest on 29 September 2021 with OSA, compared with the conventional Macintosh laryngo- Anaesthesia 1984; 39: 1105–11 scope. The unique structural and functional features of the 14 Henderson JJ, Popat MT, Latto IP, Pearce AC. Difficult Airway Society guidelines for management of the unanticipated difficult intub- AWS would contribute to overcoming the anatomical charac- ation. Anaesthesia 2004; 59: 675–94 teristics in patients with OSA, which are well known to be asso- 15 Maharaj CH, Costello JF, Harte BH, Laffey JG. Evaluation of the ciated with difficult intubation. Airtraq and Macintosh laryngoscopes in patients at increased risk for difficult tracheal intubation. Anaesthesia 2008; 63: 182–8 Authors’ contributions 16 Bellhouse CP, Dore´ C. Criteriaforestimating likelihood of difficultyof M.K.K.: study design, performance of laryngoscopy, writing up endotracheal intubation with the Macintosh laryngoscope. Anaesth Intensive Care 1988; 16: 329–37 of the first draft of the paper. S.W.P.: performance of laryngos- 17 DeBerry-Borowiecki B, Kukwa A, Blanks RH. Cephalometric analysis copy, correction of the manuscript of the paper. J.W.L.: data col- for diagnosis and treatment of obstructive sleep apnoea. 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Handling editor: J. P. Thompson

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