BACKGROUND: Obstructive Sleep Apnea (OSA) is a condition characterized by repeated episodes of apnea and hypopnea. There has been increasing recognition of OSA with increasing prevalence estimates. It has brought about several clinical consequences most of which are preventable upon treatment of OSA. Given the prevalence of OSA in the population and its dire outcomes, accurate screening for positive cases is being done. The aim of this study is to assess the accuracy of nocturnal pulse oximetry as a confirmatory test in the diagnosis of OSA as against polysomnography (PSG) which is the gold standard
DESIGN: Cross-sectional Study
SETTING: St. Lukes Medical Center Comprehensive Sleep Disorders Center Materials and Methods: Patients referred to the Comprehensive Sleep Disorders Center for PSG with symptoms suggestive of OSA were investigated. Full night diagnostic polysomnography with oximetry was performed at the sleep center. Baseline characteristics were taken. Respiratory Disturbance Index (RDI) and Lowest O2 Saturation (LSAT) levels were determined for each patient. Five LSAT threshold values (/- 75 percent, /- 80 percent, /- 85 percent, /- 90 percent and /- 95 percent) were obtained for analysis. Sensitivity, specificity, false positive rate, positive predictive values (PPV) and negative predictive values were computed for each threshold level. Receiver operating characteristic (ROC) curve was constructed to measure the diagnostic performance of LSAT.
RESULTS: 416 were included in the present study after meeting the inclusion criteria. The group consisted of 315 (75 percent) men and 101 (25 percent) women. Mean age t SD was 46.02 +/- 12.07. The average BMI +/- SD, was 29.04 +/- 6.10. The mean RDI was 33.27 +/- 36.37. 284 patients had an RDI of /- 5/hour. Of these 244 (86 percent) were men and 40 (14 percent) were women. When compared statistically, there was a significant difference in the BMI and LSAT. Correlation of RDI /- 5/hour with LSAT was statistically significant at p-0.000 with an r=-0.662. Using LSAT threshold of /- 85 percent gave a sensitivity of 83 percent, specificity of 90 percent with FPR of 10 percent, PPV of 95 percent and NPV of 72 percent. AUC-0.93.
CONCLUSION: LSAT level of /- 85 percent may suggest that patients with symptoms referrable to OSAS has OSA For adults who are unlikely to have OSA clinically, a negative oximetry result may be sufficient to exclude the diagnosis; for adults who are likely to have OSA clinically, a positive oximetry result may be sufficient to confirm the diagnosis of OSA.