Sampling intervals to record severe hypotensive and hypoxic episodes in anesthetised patients.

OBJECTIVE: To define the longest sampling interval which will faithfully record the time course of episodes of severe hypotension and hypoxia in anesthetised patients. METHODS: Electronic anesthetic records of 1501 patients were analyzed retrospectively for hypotension where measured systolic blood pressure fell to 60 mmHg or less, and for hypoxia where SpO2 fell to 80% or less. The onset and offset times, maximum rate of change and spectral content were calculated for each episode. RESULTS: These episodes commonly were rapid in onset and offset. The longest sampling interval to accurately represent these data was calculated to be 36 s for invasive blood pressure and 13 s for pulse oximetry. CONCLUSIONS: Our current anesthetic record is inadequate to record many of the severe changes that we observed. One minute recording intervals, such as used in many electronic record keeping systems, are too slow to capture the rapid rates of change seen, and may lead to the assumption that an episode was not recognized promptly or that treatment was not administered in a timely manner.