Nocturnal oximetry for the diagnosis of the sleep apnoea hypopnoea syndrome: a method to reduce the number of polysomnographies?

Background-Polysomnography (PSG) is currently the "gold standard" for the d iagnosis of the sleep apnoea hypopnoea syndrome (SAHS). Nocturnal oximetry (NO) has been used with contradictory results. A prospective study was perf ormed to determine the accuracy of NO as a diagnostic tool and to evaluate the reduction in the number of PSGs if the diagnosis of SAHS had been estab lished by this method. Methods-Two hundred and seventy five patients with a clinical suspicion of SAHS were admitted to undergo, in the same night, full PSG and NO. Desatura tion was defined as a fall in the haemoglobin saturation level (SaO(2)) to lower than 4% from the baseline level and an oxygen desaturation index per hour (ODI) was obtained in each patient with three cut off points: greater than or equal to 5 (ODI-5), greater than or equal to 10 (ODI-10), and great er than or equal to 15 (ODI-15). Results-SAHS was diagnosed in 216 patients (194 men). After withdrawing pat ients with abnormal lung function (forced expiratory volume in one second ( FEV1) lower than 80% predicted), sensitivity (SE), specificity (SP), positi ve and negative predictive values (PPV and NPV) of NO were: ODI-5 (80%, 89% , 97%, 48%); ODI-10 (71%, 93%, 97%, 42%); ODI-15 (63%, 96%, 99%, 38%). The accuracy for each ODI was 0.81, 0.75, and 0.70, respectively. If NO had bee n considered as a diagnostic tool and PSG had been performed only in patien ts with a negative NO (false negative and true negative) and those with a p ositive NO and abnormal pulmonary function tests, 135/275 (ODI-5), 156/275 (ODI-10), and 170/275 (ODI-15) PSGs would have been performed, a reduction of 140, 119, and 105, respectively. Conclusion-Nocturnal oximetry in patients with suspected SAHS and normal sp irometric values permits the institution of therapeutic measures in most pa tients.