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 (SpO(2)) alarms is that the att ention of personnel is only directed to patients who experience hypoxe mia. The present study was undertaken to better understand the effects of different settings of the pulse oximeter on false (artifact) and t rue (hypoxemia) alarms. Methods. Using the original SpO(2) data of 200 postoperative patients, we calculated off-line the effects of five me thods (artifact rejection, alarm delay (2-44 s, 2 s increments), avera ging (10-90 s), median filtering (10-90 s) and decreasing the alarm li mit from 90% to 85%) on the number of (true- and false) alarms. Result s. 830 episodes of hypoxemia (SpO(2) less than or equal to 90%) and 73 episodes of severe hypoxemia (SpO(2) less than or equal to 85%) occur red. With a SpO(2) alarm limit of 90%, the alarm was triggered 1535 ti mes (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 w ere found in the reduction of alarms between averaging and median filt ering. Changing the alarm limit to 85% reduced the number of alarms by 82%. A similar seduction of alarms was obtained with either an alarm delay of 18 s or an averaging or median filtering epoch of 42 s. Howev er, 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 ala rms 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.