AAMI News November 2018

Standards for Auditory Alarm Signals Put on Fast Track

Key committees are fast-tracking new standards for auditory alarm signals, a tacit recognition of the growing number and types of alarm sounds in clinical settings—and the associated challenge in making sense of them to best support patient safety.

An amendment to ANSI/AAMI/IEC 60601-1-8, Medical electrical equipment—General requirements for basic safety and performance—Collateral standard: General requirements, tests and guidance for alarm systems in medical electrical equipment and medical electrical systems, will be completed in 2020. “This is a narrowly focused amendment addressing the issues that two-thirds of International Electrotechnical Commission (IEC) national committees agreed were important enough to address immediately, as opposed to waiting until 2024 or later, when the next edition of this family of standards is planned,” said Dave Osborn, senior manager of global regulations and standards, Philips, and secretary of International Organization for Standardization Technical Committee (TC) 121/Subcommittee 3.

This amendment will address:

  • Changes required to stay current with the state of the art.
  • Unaddressed safety aspects in the general standard and any collateral standards.
  • Inconsistencies or ambiguities between the general standard and any collateral standards, or among individual collateral standards. “We hope that both manufacturers and clinicians will benefit from these standards, which thereby improves patient safety and, hence, patients,” Osborn said.

Judy EdworthyCreating New Auditory Alarm Signals

Current auditory alarm signals were standardized almost 20 years ago. “At the time, the types of sounds that could be used as alarm signals were rather limited,” said Judy Edworthy, director of the Cognition Institute and professor of applied psychology at the University of Plymouth, UK, and a member of AAMI’s Medical Device Alarms standards committee, AAMI’s Alarm Management Committee, and the AAMI Foundation’s National Coalition for Alarm Management Safety. The abstract tonal melodies at that time had the same rhythm, making it difficult to distinguish the melodies, as well as making them difficult to learn and retain, she said.

The AAMI committee commissioned Edworthy, whose expertise is the applied cognitive psychology of sound and the psychology of music, to create and validate new auditory alarm signals using modern psychoacoustic principles for medical equipment. The proposed new audio alarm signals are very different from those in the current standard, Edworthy said, and make use of digital sound. Her work covers the conception of potential new alarm sound designs and testing the sounds for:

  • Learnability (how easy they are to learn and remember).
  • Localizability (listeners’ ability to detect where the sound is coming from in 3D space).
  • Performance in a more realistic, simulated environment and in other more realistic settings that use typical noise and/or involve a clinician or other participant doing other tasks at the same time.

Edworthy works with collaborators from the University of Miami, Delft University of Technology (The Netherlands), Vanderbilt University, Trinity Health, Ohio State University, and the State University of New York at Buffalo. “The science shows that the proposed new alarm signals outperform the current ones by spectacular amounts,” she said. For example, in a University of Miami study, the proposed new alarm signals perform 26 times better than the current ones.

“It is known that people’s ability to learn and retain the meaning of a sound is related to the extent to which the listener is able to make a link between the sound and the situation it is representing,” Edworthy said. “The degree to which an alarm sound’s meaning is intuitive is important in how easy it will be to learn. So in the development of potential new sounds for testing, we were very careful to develop various sets of sounds within which individual sounds acted as metaphors in some way or other for the hazards they are signaling. As predicted, those with the most direct metaphors were most learnable.”

Another key element in a good alarm sound is localizability. “Psychoacoustic theory enables a designer to predict with some degree of accuracy which types of sounds will be more localizable than others,” Edworthy said. “Our predictions about localizability were also borne out in our designs.” Edworthy sees parallels in addressing clinical alarm signals, management, and fatigue with her previous work developing alarm and track signaling systems for the rail industry.

 “The problems in most safety-critical systems are pretty much the same,” she said, including sounds that are too loud, hard to localize, with no connection between the sound and the meaning, and with many “false” alarm signals.