Objective: To measure and compare the response times to audibly or visually presented alarms in the operating theatre.
Methods: The time taken by anaesthetists to cancel randomly generated visual and audible false alarms was measured during maintenance of routine anaesthesia. Alarms were generated and times recorded by a laptop computer on the anaesthetic machine. The visual signal was a 15 mm diameter red light positioned next to the physiological monitor mounted on top of the machine. The audible alarm was a Sonalert buzzer of the type incorporated into many medical devices.
Results: Nineteen anaesthetists provided a total of seventy-two hours of data (887 alarm events). The response times to visual alarms was significantly longer than to audible alarms (P = 0.001 Mann Whitney U test). [Table: see text]
Conclusions: The ability of anaesthetists to appreciate changes in patient physiology may be limited by delays in noticing information presented by monitors. The rapid response to the vast majority of alarms indicates a high level of vigilance among the anaesthetists studied. However, this study suggests that it is safer to rely on audible rather than visual alarms when time-critical information such as oxygenation, heart beat and ventilator disconnection is concerned. Visual alarms would appear to be more appropriate for conveying less urgent information.