IMPORTANCE OF THE PULSE OXIMETER AVERAGING TIME WHEN MEASURING OXYGENDESATURATION IN SLEEP-APNEA

The accuracy of pulse oximeters in measuring transient changes in oxyg en saturation (SaO(2)) may be affected by the oximeter time response. The aim of this study was to assess the effect of modifying the pulse oximeter averaging time (T) on the measurement of SaO2 in patients wit h the sleep apnea-hypopnea syndrome (SAHS). Twelve patients with sever e SAHS were studied during a nap with conventional oximeters: Ohmeda 3 740 and Criticare 501. We compared the readings of each patient's oxyg en desaturation measured simultaneously with two identical pulse oxime ters. One oximeter was the control (T=3 seconds), and in the other T w as set from 3 seconds to 21 seconds. No significant differences in SaO (2) were found when both oximeters were set to the same T (3 seconds). In contrast, increasing T to 12 seconds and 21 seconds in one of the oximeters resulted in considerable and significant differences in the measured SaO2: oxygen desaturation was underestimated by up to 60% whe n compared with the control. The misestimation of SaO(2) induced by se ttings of T which are within the range selectable in conventional oxim eters may be of epidemiological significance when pulse oximetry is us ed as a complementary diagnostic tool to classify sleep events in SAHS .