Objective To measure and compare the response times to audibly or visu
ally presented alarms in the operating theatre. Methods The time taken
by anaesthetists to cancel randomly generated visual and audible fals
e alarms was measured during maintenance of routine anaesthesia. Alarm
s were generated and times recorded by a laptop computer on the anaest
hetic machine. The visual signal was a 15mm diameter red light positio
ned next to the physiological monitor mounted on top of the machine. T
he audible alarm was a Sonalert(R) buzzer of the type incorporated int
o many medical devices. Results Nineteen anaesthetists provided a tota
l 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). [GRAPHICS] Conclusions The ability of anaest
hetists to appreciate changes in patient physiology may be limited by
delays in noticing information presented by monitors. The rapid respon
se 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-critic
al information such as oxygenation, heart bent and ventilator disconne
ction is concerned. Visual alarms would appear to be more appropriate
for conveying less urgent information.