Identification of Medical Alarm Source and Reason

The recognition accuracy of medical alarms within the operating room is quite low. When presented with alarm sounds and asked to identify the source, anesthesiologists, operating room technicians, and operating room nurses correctly identify the device producing the alarm only 33 to 53.8% of the time.23-25 Furthermore, experiments suggest that humans have difficulty reliably recognizing more than 6 alarms at one time.26 The sheer number of different medical devices with alarms can make it difficult to discern one medical alarm from another and studies within the human factors literature have documented the inability of medical providers to discern between high priority and low priority alarms.27 While this is a known problem in operating rooms and intensive care units, how well alarms are recognized in other settings has not been described.
Some effort has been made to improve Medical alarm systems through redesign.28 One non-medical study examined ways to improve the recognition of auditory alarms by comparing abstract alarm sounds with specially designed alarms using speech and auditory icons.29 Other studies within the human factors literature have revealed certain acoustical properties that are more likely to result in a higher sense of perceived urgency by the operator.

In a series of experiments, Edworthy required subjects to rank the level of urgency associated with different alarms.30 The acoustical properties of the alarms were altered for the different subjects. Level of urgency was then correlated with a specific alarm sound. After ranking a set of acoustic parameters based on perceived urgency, the experimenters predicted what urgency ranking the alarm would receive and played the alarms for a new set of subjects. The correlation between the subjects' urgency rating and the investigators' predicted ratings was 93% (p<0.0001). Acoustical properties such as fundamental frequency, harmonic series, and delayed harmonics all affected the users perceived urgency.

Another study looked at the redesign of a Medical alarm to improve detectability within the operating room.31 An alarm that was spectrally rich, frequency-modulated, and contained small amounts of interpolated silence was detectable with at least 93% accuracy over background operating room noise. However, both of these alarm experiments have only been done in laboratory settings. In addition, Burt and colleagues found that when subjects were required to urgently perform a task, the prior acoustically manipulated perception of urgency was ignored in order to attend to the situational urgency of the task.32 Furthermore, with both alarms and clinical tasks competing for an operator's attention, the newly designed alarm might not be as discernible. It has continued to be a challenge to create the best auditory alarm sound to indicate an emergency.

From www.ahrq.gov