The classic belief that hospital alarms should be loud might be a mistake, a new study suggests.
The overabundance and high volume of hospital alarms can have deleterious effects on patients and providers, impairing clinician performance and possibly compromising patient safety (Crit Care 2009;13:208; Anesth Analg 2014;118:1249-1253).
“They’re already an annoying sound,” said Joseph J. Schlesinger, MD, study author and assistant professor of anesthesiology in the Division of Critical Care at Vanderbilt University Medical Center, in Nashville, Tenn. “But do they have to be annoying and loud?”
Dr. Schlesinger found that clinician performance is maintained with alarms that are softer than background noise. This finding is “revolutionary because it completely goes against the supposition of alarmism,” according to Dr. Schlesinger.
“Alarms are designed to be louder than background noise,” he said. “We’ve shown that clinician performance, measured in response time and accuracy to a clinical task, is preserved even when alarms are softer than background noise. … Implementation of these results could help decrease overall sound-level exposure.”
As Dr. Schlesinger reported, there are several issues concerning alarms in the ICU, including loudness, high number of false alarms and multiplicity of alarm types. Since false alarm rates can reach 80% to 99%, he noted, practitioners can distrust alarms, lose confidence in their significance and manifest so-called “alarm fatigue,” a phenomenon of diminished response due to desensitization (Anaesthesia 2015;70:1215).
Moreover, the jarring sound of alarms could be a risk factor for delirium in the ICU and post-traumatic stress disorder anchored to critical illness in all patients (Am J Respir Crit Care Med 2016;193:1373-1381; Crit Care 2009;13:208).
How Low Can You Go?
For the study, Dr. Schlesinger utilized an anechoic chamber, a room designed to absorb reflections of sound, to control auditory stimuli to a single decibel and localize those stimuli throughout the room. He also was able to measure response time and accuracy to the millisecond, propelling this line of research from qualifiable results from previous researchers to granular, quantifiable results that can inform future research and alarm redesign.
“I wanted to study whether alarms could be softer than background noise and not contribute to this feed-forward cycle of acoustic noise pollution in the hospital,” Dr. Schlesinger said.
He enrolled 31 physician participants because “they have a much more visceral, emotional, reflexive response to alarms compared to the typical undergraduate student research participant,” and assessed their near-threshold auditory perception of alarms.
“I wanted to know how soft we could get,” he said. “Taking hospital background noise normalized at 60 dB, I found that 27 dB below the background noise is the threshold where most people can barely perceive the sound of an alarm.”
The study then used clinical scenarios to determine the stimulus–response relationships for changes in auditory alarm intensity, spanning negative to positive signal-to-noise ratios.
“I tested different alarm levels, ranging from softer than background noise to louder than background noise, while physicians performed an auditory and visual secondary task designed to tax attentional and decisional resources,” he said.
Hospital alarms are typically louder than background noise, a positive signal-to-noise ratio, but results showed that clinician performance measured in response time and accuracy was preserved when alarms were softer than background noise, a negative signal-to-noise ratio. This shows that alarms can be softer than background noise, Dr. Schlesinger noted.
According to Dr. Schlesinger, these results may inform future work on components of novel psychoacoustic alarm presentations in concordance with existing standards for medical electrical equipment (e.g., IEC 60601-1-8) (Cereb Cortex 2007;17:1147-1153; Anesth Analg 2008;106:357-359), and may have an influence beyond medicine.
“These results can redefine alerts and alarms in high-consequence industries including, but not limited to, aviation, nuclear power, rail transport, automobile and construction,” he said.
Dr. Schlesinger is collaborating with experts in music perception and cognition to analyze other acoustic features of alarms, such as amplitude envelope, sharpness, roughness and sonification. He also is working with psychologists to develop auditory icons that exploit natural auditory associations to convey information more effectively in hospitals (Anesth Analg 2016;122:1253-1255).
The findings were presented at the 2016 World Congress of Anaesthesiologists (abstract PR124).