Comparison of four methods of automated recording of physiologic data at one minute intervals.

INTRODUCTION: This study aims to evaluate possible differences between the maximum, minimum, and mean value over each epoch, or the instantaneous value at the end of the interval, when recording physiological data at 1-minute intervals.
METHODS: The mean arterial pressure (MAP), heart rate derived from the radial pulse (PULSE), end-tidal CO2 (etCO2), and the arterial O2 saturation by pulse oximeter (SpO2) were measured continuously in 10 patients during general anesthesia. Anesthesia was induced and maintained using the same technique for the first 10 minutes. At 1-minute intervals for each parameter, the maximum, minimum, and mean value (over the preceding minute), as well as the instantaneous value at the end of the recording epoch, were automatically downloaded to an electronic spreadsheet. The differences between the maximum and minimum, the maximum and mean, the mean and minimum, and the instantaneous and mean values were calculated for each patient.
RESULTS: We found differences between the maximum and minimum values recorded over each interval, between the maximum and mean values, between the mean and minimum values, and between the mean and instantaneous values recorded at the end of each minute interval for all physiological parameters examined.
CONCLUSIONS: From the data presented, we conclude that during the first 10 minutes of a general anesthetic, including anesthesia induction and endotracheal intubation, the values of physiologic parameters derived from different summary indices, namely the maximum, minimum, and mean values over the 1-minute interval or instantaneous at the end of the interval differ from each other. This source of error must be considered when designing systems for computerized recordkeeping of anesthesia charts and when interpreting the data stored in electronic databases.