Influence of pulse oximeter settings on the frequency of alarms and detection of hypoxemia: Theoretical effects of artifact rejection, alarm delay, averaging, median filtering or a lower setting of the alarm limit.

OBJECTIVE: The potential benefit of a reduced frequency of false pulse oximeter low oxyhemoglobin saturation (SpO2) alarms is that the attention of personnel is only directed to patients who experience hypoxemia. The present study was undertaken to better understand the effects of different settings of the pulse oximeter on false (artifact) and true (hypoxemia) alarms.
METHODS: Using the original SpO2 data of 200 postoperative patients, we calculated off-line the effects of five methods (artifact rejection, alarm delay (2-44 s, 2 s increments), averaging (10-90 s), median filtering (10-90 s) and decreasing the alarm limit from 90% to 85%) on the number of (true- and false) alarms.
RESULTS: 830 episodes of hypoxemia (SpO2 < or = 90%) and 73 episodes of severe hypoxemia (SpO2 < or = 85%) occurred. With a SpO2 alarm limit of 90%, the alarm was triggered 1535 times (830 true, 705 false). Artifact rejection reduced alarms by almost 50%. An alarm delay of 6 s or an averaging or median filtering epoch of 10 s resulted in an alarm reduction of almost 50%. No differences were found in the reduction of alarms between averaging and median filtering. Changing the alarm limit to 85% reduced the number of alarms by 82%. A similar reduction of alarms was obtained with either an alarm delay of 18 s or an averaging or median filtering epoch of 42 s. However, an alarm limit of 85% reduced the number of false alarms less than the other three algorithms (p < 0.01).
CONCLUSIONS: The data from the present study suggest that in order to effectively suppress false alarms caused by pulse oximeter artifacts, it may be preferable to use a longer filtering epoch of approximately 40 s, rather than to decrease the lower alarm limit.