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.