The effect of averaging time on oximetry values in the premature infant.

BACKGROUND: The effect of a pulse oximeter's averaging time on time spent by premature infants in established saturation ranges, as well as on desaturation events, has not previously been reported.

OBJECTIVE: Our goal for this pilot study was to evaluate the effect of 2 distinct averaging times on the amount of time spent outside target oxygen saturation (SPo(2)) as well as the types and durations of desaturation events.

METHODS: Neonates <32 weeks' gestation requiring respiratory support were included. Each infant was studied with 2 simultaneous pulse oximeters: 1 with a short averaging time (2 seconds) and 1 with a longer averaging time (16 seconds). Time spent within different saturation ranges and the number, duration, and severity of desaturation events for each averaging time were compared by using Student's 2-tailed t test, and a P value of <.05 was considered significant.

RESULTS: The number of desaturations was greater with the 2-second averaging time; however, it did not reach significance when only desaturations of clinically significant duration were included (22.3 vs 19.4 significant events were detected by 2- and 16-second averaging time; P = .1). There was a trend for the longer averaging time to underestimate brief desaturation lasting <30 seconds (16 vs 41). Longer averaging time also tended to overestimate events of long duration that lasted >300 seconds (40 vs 20 long events). Longer averaging time tended to underestimate desaturation events of greater severity when SPo(2) was <70% (P = .01). Averaging time did not affect the time spent within various target SPo(2) ranges (P > .05).

CONCLUSIONS: These preliminary results suggest that use of longer averaging time reduces the detection of brief periodic desaturation events and of greater severity. It may also interpret a cluster of shorter events as a single, prolonged episode and, thus, potentially overestimate the frequency of long events. The significance of these findings lies in the potential impact on neurodevelopmental outcomes and growth, which will need additional study.