Prediction of sleep‐disordered breathing by unattended overnight oximetry

SummaryBetween January 1994 and July 1997, 793 patients suspected of having sleep‐disordered breathing had unattended overnight oximetry in their homes followed by laboratory polysomnography. From the oximetry data we extracted cumulative percentage time at SaO2 < 90% (CT90) and a saturation variability index (ΔIndex, the sum of the differences between successive readings divided by the number of readings – 1). CT90 was weakly correlated with polysomnographic apnea/hypopnea index (AHI), (Spearman ????=0.36, P< 0.0001) and with ΔIndex (????=0.71, P< 0.0001). ΔIndex was more closely correlated with AHI (????=0.59, P< 0.0001). In a multivariate model, only ΔIndex was significantly related to AHI, the relationship being AHI=18.8 ΔIndex +7.7. The 95% CI for the coefficient were 16.2, 21.4, and for the constant were 5.8, 9.7. The sensitivity of a ΔIndex cut‐off of 0.4 for the detection of AHI≥15 was 88%, for detection of AHI≥20 was 90% and for the detection of AHI≥25 was 91%. The specificity of ΔIndex ≥0.4 for AHI≥15 was 40%. In 113 further patients, oximetry was performed simultaneously with laboratory polysomnography. Under these circumstances ΔIndex was more closely correlated with AHI (????=0.74, P< 0.0001), as was CT90 (????=0.58, P< 0.0001). Sensitivity of ΔIndex ≥0.4 for detection of AHI≥15 was not improved at 88%, but specificity was better at 70%. We concluded that oximetry using a saturation variability index is sensitive but nonspecific for the detection of obstructive sleep apnea, and that few false negative but a significant proportion of false positive results arise from night‐to‐night variability.