Abstract
Nocturnal hypoxemia and obstructive sleep apnea (OSA) are common comorbidities in patients with chronic obstructive pulmonary disease (COPD). The authors sought to develop a strategy to interpret nocturnal pulse oximetry and assess its capacity for detection of OSA in patients with stage 3 to stage 4 COPD. A review of consecutive patients with COPD who were clinically prescribed oximetry and polysomnography was conducted. OSA was diagnosed if the polysomnographic apnea-hypopnea index was >15 events⁄h. Comprehensive criteria were developed for interpretation of pulse oximetry tracings through iterative validation and interscorer concordance of ≥80%. Criteria consisted of visually identified desaturation 'events' (sustained desaturation ≥4%, 1 h time scale), 'patterns' (≥3 similar desaturation⁄saturation cycles, 15 min time scale) and the automated oxygen desaturation index. The area under the curve (AUC), sensitivity, specificity and accuracy were calculated. Of 59 patients (27 male), 31 had OSA (53%). The mean forced expiratory volume in 1 s was 46% of predicted (range 21% to 74% of predicted) and 52% of patients were on long-term oxygen therapy. Among 59 patients, 35 were correctly identified as having OSA or not having OSA, corresponding to an accuracy of 59%, with a sensitivity and specificity of 59% and 60%, respectively. The AUC was 0.57 (95% CI 0.55 to 0.59). Using software-computed desaturation events (hypoxemia ≥4% for ≥10 s) indexed at ≥15 events⁄h of sleep as diagnostic criteria, sensitivity was 60%, specificity was 63% and the AUC was 0.64 (95%CI 0.62 to 0.66). No single criterion demonstrated important diagnostic utility. Pulse oximetry tracing interpretation had a modest diagnostic value in identifying OSA in patients with moderate to severe COPD.
Highlights
Nocturnal hypoxemia and obstructive sleep apnea (OSA) are common comorbidities in patients with chronic obstructive pulmonary disease (COPD)
Nocturnal hypoxemia can be severe in patients with COPD due to upper airway obstruction typical of obstructive sleep apnea (OSA) combined with hypoventilation due to obesity, COPD or both
Clinicians do not have a standardized strategy for selecting patients for PSG when OSA is suspected using nocturnal oximetry because there are few physiological markers recorded in this procedure that have been found to be reliable predictors of a patient with advanced COPD to be likely diagnosed with OSA
Summary
Nocturnal hypoxemia and obstructive sleep apnea (OSA) are common comorbidities in patients with chronic obstructive pulmonary disease (COPD). The presence of nocturnal oxygen desaturation is associated with cardiovascular risks (fatal and nonfatal) as well as the evolution of pulmonary hypertension [4,5] For these reasons, the prevalence of OSA in COPD is similar to that of the general population, it is the overlap of both conditions that creates a greater opportunity for comorbidity and a negative prognosis [6]. Nocturnal pulse oximetry to assess oxygen saturation patterns throughout the usual sleep period has been extensively studied in the diagnostic evaluation of patients typically encountered in sleep clinics, is relatively simple to execute and is, as a result, inexpensive. The objective of the present study was to develop criteria for visual inspection by nonexpert scorers to interpret nocturnal pulse oximetry tracings and assess its capacity for detection of OSA in patients with advanced COPD. Figure 2) An example of a desaturation ‘event’ from an oxygen saturation oximetry tracing with a time frame of 1 h
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