Enhancing the Sounds of Urgency: Lessons From Music and Aviation on Human Response to Critical Auditory Stimuli

See Article, p GLOSSARY OR = operating room; PO = pulse oximeter; Spo2 = oxygen saturation Auditory warnings are used to convey important information in a variety of settings, in particular high-consequences industries like health care and aviation. The anesthesiologist has to perform multiple tasks simultaneously in the operating room (OR), including monitoring the patient's vital signs and data entry in a setting that is often very noisy and full of sensory information. If something changes indicating deterioration with regard to oxygen saturation (Spo2), it is important that the anesthesiologist can recognize the change via the auditory display only because vision may be engaged in other tasks, or the monitor may be out of the visual stream. However, the acoustic properties that convey changes in Spo2 vary depending on the manufacturer, and the display of information is not always effective.1 This heterogeneity, in addition to the fact that the majority of individuals are not able to identify pitch in an absolute way,2 renders the anesthesiologist unable to precisely identify the absolute level of Spo2 without visual input. The accompanying article by Paterson et al3 assessed the ability to identify changes in Spo2 parameters comparing enhanced pulse oximeter (PO) auditory displays with standard ones. This builds on the work of Janata and Edwards,4 who studied the effect of enhanced sonification to identify changes in heart rate and Spo2 levels. They found that the ability to recognize and categorize changes improved when the quality of the sounds conveying those vital signs were modified to map physiological variations with acoustic changes. Paterson et al3 determined 3 predefined ranges: target (100%–97%), low (96%–90%), and critical (89%–80%). The standard model was based on POs commercially available and included pitch pulse tones and an alarm. The auditory-enhanced version did not have an alarm but added a tremolo when Spo2 decreased to low and critical values, and sound brightness when the range of Spo2 was <89% (critical). The tremolo generated a vibrating effect, whereas the brightness produced a "sharper" tone without raising the volume. Clinicians and nonclinicians had to monitor the Spo2 while performing 2 tasks (arithmetic verification and detection of keywords) with background noise that aimed to simulate the cognitively demanding environment that an anesthesiologist experiences in the OR. The researchers found that auditory enhancement with tremolo and brightness enabled participants to detect transitions between the 3 predefined ranges more accurately (87%) than using standard PO with an alarm only (57%). Enhanced auditory displays also enabled more accurate identification of the specific Spo2 range (86%) than the standard display (76%). Both clinicians and nonclinicians performed equally well when using the enhanced equipment, suggesting that the cues related to identifying Spo2 ranges are easy to recognize and interpret even without being a medically trained professional. While the study was conducted in a quiet and controlled environment rather than in the dynamic OR, and the distractor tasks were likely less demanding than the actual workload that anesthesiologists handle in the OR, the researchers showed that auditory-enhanced POs help identification of Spo2 parameters. If the equipment were to be implemented in the OR, the findings by Paterson et al3 suggest that the clinician would be able to notice a decline in the patient's vital signs quickly, enabling prompt intervention and more effective care. LESSONS ABOUT SOUND PERCEPTION FROM MUSIC AND THE AVIATION INDUSTRY An understanding of how individuals process environmental acoustic stimuli where the cognitive and visual loads are high is important to improve performance in the OR. In aeronautics, auditory alarms convey information to pilots without requiring visual interaction, but the inability to detect "changes" in alarms is a recognized safety problem in the aviation industry that has led to a number of accidents.5 Culture also plays a role: the inquiry into the causes that led to higher-than-normal rates of crashes by Korean Air in the 1990s suggested that adherence to strict hierarchical social norms can be a barrier to speaking up when interpreting critical auditory and visual information, an issue that has also been reported in medicine. For example, failure of nurses to convey clinically relevant information to anesthesiologists due to the hierarchy between themselves and the doctors contributed to the death of Elain Bromiley during what was initially a "routine operation."6 Moreover, alarms in the cockpit are more likely to sound during busy times such as takeoff and landing,5 leading to a potential overload of warning signals. Macdonald and Lavie7 found that high visual burden leads to a reduction in the ability to perceive auditory stimuli: a phenomenon they called "inattentional deafness" under visual load. They reported that when vision was highly engaged, inattentional deafness of tones that were unrelated to the visual task occurred in up to 79% of cases. Therefore, when involved in tasks that require high perceptual load, the ability to process auditory stimuli decreases. After this, Dehais et al8 studied the response to critical auditory warnings in a simulated cockpit to assess whether inattentional deafness occurs when flying. Testing pilots in a flight simulator, the researchers found that in 39.3% of cases, alarms were unintentionally missed in the setting of high cognitive workload and stress. Failure to hear important auditory stimuli in a highly demanding situation is believed to happen due to a combination of central limited cognitive resources, leading to transient impairment of attention,9 and the idea that when the task requires interpretation of key visual cues, vision is prioritized over audition. Dehais et al10 suggested in another study that accuracy in detecting auditory alarms significantly varied depending on the cognitive load of the situation. When pilots were put under difficult scenarios, including flying with poor visibility, a simulated cabin fire with a flashing red light, and an experienced fighter pilot acting as an observer to add social pressure, 57.7% of auditory alarms were missed. In contrast, when pilots were asked to fly the plane in autopilot, with their only task being to respond to the auditory target stimuli, the alarm was missed in only 0.33% of cases. The dominance of vision over audition predicted the miss rate in the cognitively demanding situation, suggesting that when vision and audition compete, vision engagement functions as a distractor, leading the pilot to miss the auditory alarms. Inattentional deafness has been shown to occur when listening to music, too, suggesting that involvement in a cognitively demanding task (without visual engagement) can also lead to lack of auditory awareness. Koreiman et al11 found that participants were unable to perceive an unexpected stimulus when focused on a certain aspect of the musical piece. The control group listened to the first minute and 50 seconds of Richard Strauss' Thus Spoke Zarathustra, while the intervention group was tasked with counting the number of timpani beats. An electric guitar solo was blended into the musical fragment, disrupting several bars of the piece. Compared to the control group, the majority of participants who had to count the timpani beats did not notice the intrusion of the electric guitar during the fragment. An added problem to inattentional deafness is that being able to hear the alert itself is not always enough to trigger an effective response. In the health care setting, the majority of alarms have little or no clinical relevance, leading to unwanted distraction without conveying successfully the message of urgency.12 In aeronautics, Mumaw13 showed that failure to understand the auditory alerts contributed (to some extent) to 42 of the 46 aviation accidents analyzed. This knowledge is significant for the field of anesthesia, particularly because the way POs transmit changes in Spo2 is not standardized. Loeb et al14 reviewed 21 commercially available POs and studied their sonification. They found that there was a wide variation in the way Spo2 was conveyed, and not all POs behaved equally when Spo2 diminished: some decreased the pulse tone pitch at every 1% change in Spo2, whereas others decreased the pitch at certain Spo2 thresholds. These variations occurred between POs that looked almost identical to one another. The fact that in aviation, lack of understanding of auditory alerts is a known factor that contributes to accidents suggests that standardization of POs would be desirable to avoid erroneous interpretation of Spo2 values, even when the anesthesiologist is able to hear the alarm and is not experiencing inattentional deafness. An additional difficulty to this lack of standardization is the variability of the anesthesiologists' work environment. A pilot who is trained to fly one type of plane (eg, a Boeing 787) can do so irrespective of the company he/she works for because both models will be almost identical. In contrast, anesthesiologists have to constantly adapt to variations in the layout and equipment from one OR to another, often within the same hospital. And as shown by Loeb et al,14 even equipment that looks alike conveys vital parameters differently. Achieving the degree of standardization that characterizes the aviation industry is not possible in health care, but we believe that an effort should be made to minimize unnecessary variations. In aeronautics, alerts are ranked and convey critical information using >1 sense (tactile, visual, and/or aural). The Boeing 737 and the early 747–400s initially forewarned pilots of low altitude using a horn only, but in 2011, a light was added to better convey the danger.13 The alert that indicates "approach to stall" has always been a 2-modality alert (tactile and aural) and is now further enhanced with visual indications13 due to its critical nature. In addition, to avoid alarm fatigue, the cockpit is built with a hierarchy of warnings. That means that noncritical alerts are less enhanced than higher-level warning: red lights, text, and voice alarm convey "warning," with added tactile information in the form of stick shaker only when the situation is critical. "Cautions" and "advisories" use one sensory modality only (vision) because the pilot needs to be aware of the problem, but action is not required imminently (according to the Capitan of an Airbus 380). These lessons from aviation have an enormous potential in health care, especially for environments in which the risk of alarm fatigue is high. For that reason, the author (J.J.S.) is currently working with an international team of researchers to build vibrotactile feedback for medical equipment. Preliminary work15 has shown that perception of changes in alarms monitoring vital signs improved when tactile stimulus were added to the auditory alarm. The ultimate aim is to create equipment that is truly multisensory, like in aviation. The findings of the article by Paterson et al3 in this issue of Anesthesia & Analgesia are a step forward in ensuring that patient monitoring with auditory alarms can be improved with auditory-enhanced POs. The fact that both clinicians and nonclinicians performed better with the enhanced equipment highlights the importance of incorporating what is known about music perception and cognition into the design of critical alarms because outcomes appear to be related to the way human beings process sound rather than to medical training.12 The lessons from music and aviation about processing the sounds of urgency, in particular, the phenomenon of inattentional deafness, the competition between hearing and vision, and the fact that under stressful conditions, alarms are sometimes misunderstood, contributing to accidents, are important points that need to be taken into account when designing monitors that utilize sound to alert the clinician. Moreover, ideas such as the use of multisensory enhancement of alarms and hierarchy of sounds can help us better create equipment without overwhelming the cognitive capacity of the individual, contributing to the delivery of safer patient care. Finally, the preliminary inquiries after the recent crashes of the Boeing 737 Max, which led to grounding the model around the world, highlight 3 key lessons from the aviation industry that are relevant to medicine: the importance of always prioritizing "safety;" the significance of studying the interaction between humans and machines "in the environment" in which that interaction is actually meaningful (ie, in the OR or hospital setting, not just in the laboratory); and the provision of regular and excellent "training" so that we can always offer the best possible care. DISCLOSURES Name: Barbara Salas, BA. Contribution: This author helped draft and critically revise the manuscript. Name: Joseph J. Schlesinger, MD. Contribution: This author helped draft and critically revise the manuscript. This manuscript was handled by: Maxime Cannesson, MD, PhD.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.