Can Pulse Oximetry Select Patients for Screening Spirometry?

Primary Care Respiratory Journal (2004) 13, 155—158

ORIGINAL RESEARCH Can pulse oximetry select patients for screening spirometry?

Eduardo Garcia-Pachon*

Department of Internal Medicine, Hospital Vega Baja, Orihuela-Alicante, Spain

KEYWORDS Summary Aim: To investigate whether the measurement of arterial oxygen saturation

Chronic obstructive (SpO2) with pulse oximetry can identify those patients for whom spirometric screening pulmonary disease; for COPD wouldbe useful, andthose patients for whom spirometric assessment would Oximetry; not be useful. Methods: Twohundredandtenpatients, agedover 40, without significant dyspnoea, Screening; referredby their primary care physicians to the outpatient pulmonary clinic. The value Spirometry of SpO2 was recorded with a finger clip pulse oximeter sensor. Diagnostic values were obtained in order to diagnose COPD (defined as an FEV1/FVC ratio <0.70), andin order to detect patients with an FEV1 <80% of predicted value. Results: With SpO2 <98%, sensitivity for detecting COPD was 79% and specificity 37%. Similar values were obtainedfor detectingpatients with FEV 1 <80%. When only patients with FEV1 <50% were considered, using a value of <98% for SpO2, sensitivity was 77%. Conclusion: Pulse oximetry is not a useful test for selecting patients for screening spirometry in order to diagnose COPD. © 2003 General Practice Airways Group. Published by Elsevier Ltd. All rights reserved.

Introduction Hankinson [3] statedthat the indiscriminateuse of office spirometry shouldbe reconsideredbecause Many patients with COPD remain undiagnosed, and of the potential impact of poor quality spirometric expertsCopyright agree that it wouldbeReproduction General desirableto have Practicerecordings. Prohibited Nevertheless,Airways it is clearlyGroup necessary some test or intervention that wouldallow early to improve the early recognition of COPD in order identification of COPD. A consensus statement to initiate preventable andtherapeutic measures from the National Lung Health Education Program [2,4]. In addition, an important component of the in the USA recommended the widespread use of economic costs of COPD is considered to be due to spirometry by primary care physicians in order non-diagnosis or late diagnosis [5]. to identify those patients at high risk of devel- The measurement of arterial oxygen saturation oping COPD [1]. However, controversy remains may be an aidin the identificationof these pa- as to whether spirometry is the ideal test [2] tients since arterial hypoxaemia in COPD occurs fre- since spirometry is time-consuming, relatively ex- quently andrelatively early in the natural history pensive, andneedstrainedoperators. Moreover, of the disease. The PaO2 in patients with COPD cor- relates with the forcedexpiratory volume in 1 s [6], and, in patients with asthma of varying severity ∗ Present address: Section of Pneumology, Hospital General hypoxaemia was relatedto the degreeof obstruc- Universitario, E-03203 Elche, Alicante, Spain. Tel.: +34-96-667-9000; fax: +34-96-667-9108. tion [7]. The portability and‘easy to use’ nature of E-mail address: [email protected] (E. Garcia-Pachon). pulse oximeters make them potentially attractive

1471-4418/$30.00 © 2003 General Practice Airways Group. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.pcrj.2003.11.006 156 E. Garcia-Pachon for primary care workers [8]. The objective of this latedat several values of oxygen saturation for the study was to investigate whether the measurement following: of arterial oxygen saturation with a simple andinex- (1) Diagnosing COPD (FEV /FVC < 70%) in all the pensive method(pulse oximetry) can identifythose 1 patients; and independently in the group of pa- patients in whom spirometric screening for COPD tients with a history of smoking more than 20 wouldbe useful, andthose patients in whom it pack–years. wouldbe less useful. (2) For detecting significant COPD (FEV1 <50% of predicted, stage IIB and III in the GOLD classifi- cation [12]). Materials andmethods (3) For detecting patients with FEV1 <80% of predicted value. Two hundredandtenconsecutive patients aged over 40 who attended the Outpatient Pulmonary Clinic were included in the study. All patients Results were referredto the clinic from their primary care physicians for evaluation of respiratory problems One hundredandfifty-fourpatients were men including sleep-disordered breathing. Patients with (73%), and56 were women (27%), mean age 62 any of the following criteria were excluded: refer- years (S.D. 11years). One hundredandtenhada ral because of dyspnoea; patients presenting with history of smoking of more than 20 pack–years. basal dyspnoea score higher than 1 in the Medical Fifty-eight patients hadCOPD (prevalence, 28%); Research Council Scale [9]; patients unable to per- 26 of them hadan FEV 1 <50% of predicted. Of the form spirometry; andpatients with haemoptysis, 210 patients, 103 (49%) hadan FEV 1 value <80% of or with suspicion of tuberculosis. predicted value. There was a significant (P < 0.001 During the visit, while sitting, the patients had in all cases) correlation between the oxygen sat- an adult articulated finger clip pulse oximeter sen- uration andthe spirometric variables (FEV 1 per- sor attached (model 8000 AA, Nonin Medical, Inc.; centage of predicted, r = 0.41; FVC percentage of Plymouth, MN, USA) for at least 3 min. The value of predicted, r = 0.40; andFEV 1/FVC, r = 0.34). oxygen saturation was recorded when stabilized, The diagnostic value of oxygen saturation at sev- andwhen it oscillatedbetween two values the eral values (from 95 to 99%) for diagnosing COPD is lower one was considered. Immediately after the detailed in Table 1. Using a cut-off value of <98% visit the patients underwent spirometry performed oxygen saturation, sensitivity for COPD diagnosis by a trainedtechnician (blindedtoany other data) was 79% andspecificity 37%. In orderto ensure 100% in a separate room, according to standard crite- detection of all cases of COPD the SpO2 cut-off value ria [10] with a portable spirometer (PonyGraphic, shouldbe <99%, but then the specificity is only 7%. CosmedSRL, Rome, Italy). Reference values for the The calculations in the 110 smoking patients showed Mediterranean population were used [11]. COPD similar findings; with a cut-off value of <98% oxy- was definedasa ratio of forcedexpiratory volume gen saturation, sensitivity of COPD diagnosis was in 1 s (FEV1) to forcedvital capacity (FVC) of less 76% andspecificity 31%. All of the 45 smokers with than 0.7, andpatients were classifiedaccordingto COPD hadan oxygen saturation level <99% but so a recent international consensus [12]. did 64 of the 65 smokers without COPD (sensitivity CopyrightPearson’s correlationReproduction testGeneral was calculatedbe- Practice100%, Prohibited specificity Airways 2%). When more Group severe COPD was tween oxygen saturation andthe spirometric vari- considered (FEV1 <50%), for an oxygen saturation ables. Sensitivity, specificity, positive likelihood <98% sensitivity of COPD diagnosis was 77%; conse- ratio, andnegative likelihoodratio were calcu- quently 6 of the 26 patients with severe COPD were

Table 1 Diagnostic value of oxygen saturation for detecting obstructive airway disease (FEV1/FVC < 0.70).

Arterial oxygen Sensitivity (%) Speciﬁcity (%) Positive Negative saturation (%) likelihoodratio likelihoodratio <95 31 89 2.77 0.77 <96 50 76 2.05 0.66 <97 64 53 1.36 0.67 <98 79 37 1.25 0.56 <99 100 7 1.07 0.00 Can pulse oximetry select patients for screening spirometry? 157

Table 2 Diagnostic value of oxygen saturation for detecting FEV1 <80% of predicted.

Arterial oxygen Sensitivity (%) Speciﬁcity (%) Positive Negative saturation (%) likelihoodRatio likelihoodratio <95 28 93 4.20 0.76 <96 45 80 2.27 0.68 <97 53 60 1.32 0.77 <98 74 38 1.19 0.68 <99 98 8 1.07 0.23

not detected with this method. The diagnostic val- predicted) remain undetected when using a cut-off ues of oxygen saturation for detecting FEV1 <80% value for SpO2 of 98%. When pulse oximetry was are shown in Table 2. Results were similar to those usedfor detectingthose patients with FEV 1 <80% for diagnosing COPD in terms of the FEV1FVC ratio. predicted (both of obstructive or non-obstructive origin) results were similarly poor. These results shouldbe consideredinthe context Discussion of other means for selecting patients for screening spirometry. Several physical signs have been evalu- The prevalence of COPD in several studies [13–18] atedfor the detectionof COPD, andsome of them has been foundto be between 4.5 and9.9%. In a alone or in association with medical history data large study [13] the prevalence of COPD in peo- may be very useful for this purpose [20–23]. In fact, ple aged40–70 years, non-selectedfor respiratory by using an overall clinical impression for diagnos- symptoms or tobacco exposition, was 9.1%. Impor- ing COPD, reportedvalues [21–24] of sensitivity tantly, 78% of COPD patients hadnot been previ- (50–64%) andspecificity (64–93%), andlikelihood ously diagnosed, including 50% of those with more ratios (positive 1.4–7.3, negative 0.4–0.8) are of severe disease [13]. For early identification of COPD interest. Although these studies were performed patients the widespread use of office spirometry with different inclusion criteria, their results are no by primary care physicians has been recommended worse than ours obtainedby using pulse oximetry. [1]. Nevertheless, this strategy is controversial In conclusion, although arterial oxygen saturation because spirometry needs experienced operators levels correlate with FEV1, pulse oximetry is not a andthere can be difficultyin obtaining goodspiro- useful test for the selection of patients for screen- metric recordings in general practice even after ing spirometry. training workshops [19]. The objective of this study was to evaluate whether the measurement of arterial oxygen sat- References uration by pulse oximetry (a simple, rapid, and inexpensive methodthat doesnot require expe- [1] Ferguson GT, Enright PL, Buist AS, Higgins MW. Office riencedoperators) can select patients who are spirometry for lung health assessment in adults: a consen- suitableCopyright for screening spirometryReproduction General with a view Practice to susProhibited statement Airways from the National LungGroup Health Education improving diagnosis rates of COPD. These results Program. Chest 2000;117:1146—61. show that, in order to detect all patients with COPD [2] Enright PL, Crapo RO. Controversies in the use of spirometry for early recognition anddiagnosisof chronic obstruc- it is necessary to have a cut-off value for SpO2 at tive pulmonary disease in cigarette smokers. Clin Chest <99%, a value so high that we can avoidperform- Med2000;21:645—52. ing spirometry in only 6.5% of those patients who [3] Hankinson JL. Office spirometry. Does poor quality render do not have COPD. With a lower cut-off value (oxy- it impractical? [Editorial]. Chest 1999;116:276—7. gen saturation <98%) we can detect 79% of COPD [4] Van Schayck O, Rabe KF, Rudolf M. COPD: the role of primary care in effective diagnosis, treatment and manage- patients, with a specificity of 37%. When smokers ment. Prim Care Resp J 2003;12:16—20. alone are considered, results in terms of sensitivity [5] Miravitlles M, Figueras M. The cost of chronic obstruc- andspecificity are no better. tive pulmonary disease in Spain: options for optimising A possible use of pulse oximetry might be to de- resources [in Spanish]. Arch Bronconeumol 2001;37:388— tect patients with more severe COPD, who are fre- 93. quently undiagnosed. However, from these results, [6] Lim S, MacRae KD, SeedWA, Roberts CM. The value of forcedexpiratory volume i n1sinscreening subjects with pulse oximetry does not achieve this objective. 23% stable COPD for PaO2 < 7.3 kPa qualifying for long-term of the patients with significant COPD (FEV1 < 50% oxygen therapy. Respir Med1998;92:1122—6. 158 E. Garcia-Pachon

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