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 Figure 3. Relationship between quiet time and L Amax occurrence rate. Reproduced from Bliefnick et al., 2019.
[OR(90)max] is the fraction of the time the maximum sound pressure level in a space exceeds 90 dB(A) By definition, the OR starts at 100% at low levels and decreases monotonically to 0% as the sound level increases. An example is shown in Figure 3, which reveals reductions in occurrences of the maximum A-weighted sound levels (LAmax) in three US adult hospital units during set quiet time hours (Bliefnick et al., 2019).
The OR(N) was first used as an acoustic measure by Ryherd et al. (2008) and Williams et al. (2007) to describe the environ- ments of adult and neonatal intensive care units, respectively. It was more formally defined by Okcu et al. (2011, 2012) who examined the nursing staff in two different hospital units with similar staff activities and acuity levels. These authors showed that the unit with a higher peak OR(90) [OR(90)peak] was judged more harshly than the unit with nearly identical Leq values but a lower OR(90)peak. More recently, papers have linked staff perceptions to the OR(N). For instance, Sbihi et al. (2011) found that occurrence rates were correlated with the staff perception of noise-related health effects including distraction, stress, fatigue, and tension headaches. Bliefnick (2018) found correlations between the occurrence rate range in hospitals and patient satisfaction.
Alarm Noise
Ask people who have been hospital patients what sound they most associate with hospital stays. The likely answer is clinical alarms. As shown in an analysis by Busch-Vishniac (2015), alarms sound on average over 135 times per day per patient in the hospital, with soundings over 500 times per patient per day not unusual in intensive care units. Alarms sound so often that the staff becomes desensitized to them,
a process referred to as alarm fatigue. Alarms result in no action being taken over 90% of the time (Cvach, 2012). Nonetheless, alarm failures (failure to sound or failure by staff to respond in a timely fashion) have led to deaths or loss of function, leading the Emergency Care Research Institute (ECRI; 2013) to list clinical alarms as the top medi- cal technology hazard in 2013.
The impact of alarms is different for the staff and patients and their visitors. For the staff, alarms add to the stress level because each alarm demands a response. For patients and their visitors, alarms disrupt conversation and sleep and are routinely listed as one of the most disturb- ing noises.
Hospital soundscapes could be improved by changing the way we manage alarms, and there are many aspects of alarms that merit further study. For instance, alarms currently sound to indicate that a physiological measure has gone out of bounds. Instead, we could integrate sensors from various medical devices and alarms when they collectively indicate a medical problem such as a trend toward a cardiac arrest. Addition- ally, alarms provide very little information. They tend to be difficult to localize and hard to recognize. An early study by Lawless (1994) showed that no group of staff were able to identify more than half of the alarms. Work on alarm sounds that would be more effective in transmitting information is currently underway, with a paper by Edworthy and Hellier (2006) leading the way. More fundamentally, because there is never a reason for patients or visitors to hear alarms, there is a question as to when an alarm should sound as opposed to providing a visual or vibratory alert.
Speech Communication
The problem of speech communication in hospitals has been understudied and underappreciated. Speech communication in hospitals is a dual-edged sword: we want communication to be uninhibited by noise, but we also want to preserve patient pri- vacy. These dual needs are challenging to meet simultaneously.
Studies of speech communication in hospitals indicate that they are very challenging venues for clear conversations. Kwon et al. (2007), Godfrey et al. (2011), and Ryherd et al. (2013) measured the speech intelligibility index (SII) in rooms and hallways of seven hospitals between 2007 and 2013. In not one of these hospitals did the SII indicate good speech communication was possible at normal voice levels. Instead, they were found to be fair or poor for speech communication.
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