ACCURACY OF OXIMETRY FOR DETECTION OF RESPIRATORY DISTURBANCES IN SLEEP-APNEA SYNDROME

Study objective: The cost and inconvenience of polysomnography make si mplified techniques of screening desirable in the strategy of diagnosi s of sleep apnea syndrome (SAS). We have evaluated, in a prospective s tudy of 301 consecutive patients referred for suspected sleep disorder s, an index (Delta index) that detects apneic events by quantifying ar terial oxygen saturation (SaO(2)) variability. Setting: Regional sleep laboratory taking referrals from general practitioners and specialist s. Design: Classic polysomnography was the gold standard, with 15 apne as plus hypopneas per hour (RDI) being used as a threshold for definit ion of obstructive sleep apnea (OSA). Oximetry was recorded over the s ame night. Signal variability was quantified as a function of time, us ing digital processing of oximetric data. Sensitivity, specificity, an d positive and negative predictive values of oximetry testing were cal culated. A receiver operating characteristic (ROC) curve was construct ed representing the comparative courses of sensitivity and 1-specifici ty at different thresholds of Delta index. Results: Three hundred one patients were included (age, 56+/-12 years). Their RDI was 30+/-24. Fo r a Delta threshold at 0.6, the sensitivity of oximetry for the diagno sis of OSA was 98% and the specificity was 46%. The positive and negat ive predictive values for diagnosing SAS were 77% and 94%, respectivel y. The three false-negative cases had a relatively high awake SaO(2) ( 97 vs 93.9+/-2.8%), a moderate RDI (23.3+/-1.6), and were less obese t han the other patients (body mass index: 25+/-3 vs 33+/-8). The 58 fal se-positive cases had an RDI of 8+/-4, an awake SaO(2) of 93.1+/-3.6 v s 94.1+/-2.6 for the rest of the population (p=0.01). Finally, the fal se-positive cases had more airways obstruction (FEV(1)/VC=72+/-13 vs 7 7+/-15%; p=0.026). Using a Delta value of 0.8 leads to a sensitivity o f 90% with 19 false-negative cases but with a higher specificity of 75 %. Conclusions: A nocturnal oximetry test with a Delta index below 0.6 is helpful in ruling out the diagnosis of SAS in patients being scree ned for this condition, as this yielded only three negative test resul ts in 301 screening procedures.