Variability of environmental sound levels: An observational study from a general adult intensive care unit in the UK
Darbyshire JL., Duncan Young J.
Background Intensive care units are significantly louder than WHO guidelines recommend. Patients are disturbed by activities around them and frequently report disrupted sleep. This can lead to slower recovery and long-term health problems. Environmental sound levels are usually reported as LAeq24, a single daily value that reflects mean sound levels over the previous 24-h period. This may not be the most appropriate measure for intensive care units (ICUs) and other similar areas. Humans experience sound in context, and disturbance will vary according to both the individual and acoustic features of the ambient sounds. Loudness is one of a number of measures that approximate the human perception of sound, taking into account tone, duration, and frequency, as well as volume. Typically sounds with higher frequencies, such as alarms, are perceived as louder and more disturbing. Methods Sound level data were collected from a single NHS Trust hospital general adult intensive care unit between October 2016 and May 2018. Summary data (mean sound levels (LAeq) and corresponding Zwicker calculated loudness values) were subsequently analysed by minute, hour, and day. Results The overall mean LAeq24 across the study duration was 47.4 dBA. This varied by microphone location. We identified a clear pattern to sound level fluctuations across the 24-h period. Weekends were significantly quieter than weekdays in statistical terms but this reduction of 0.2 dB is not detectable by human hearing. Peak loudness values over 90 dB were recorded every hour. Conclusions Perception of sound is sensitive to the environment and individual characteristics and sound levels in the ICU are location specific. This has implications for routine environmental monitoring practices. Peak loudness values are consistently between 90 and 100 dB. These may be driven by alarms and other sudden high-frequency sounds, leading to more disturbance than LAeq24 sound levels suggest. Addressing sounds with high loudness values may improve the ICU environment more than an overall reduction in the 24-h mean decibel value.