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Hospitalized patients frequently report poor sleep, partly due to the inpatient environment. In-hospital sound and light levels are not well described on non-intensive care unit (non-ICU) wards. Although non-ICU wards may have lower average and peak noise levels, sound level changes (SLCs), which are important in disrupting sleep, may still be a substantial problem.To compare ambient sound and light levels, including SLCs, in ICU and non-ICU environments.Observational study.Tertiary-care hospital.Sound measurements of 0.5 Hz were analyzed to provide average hourly sound levels, sound peaks, and SLCs ≥17.5 decibels (dB). For light data, measurements taken at 2-minute intervals provided average and maximum light levels.The ICU rooms were louder than non-ICU wards; hourly averages ranged from 56.1 ± 1.3 dB to 60.3 ± 1.7 dB in the ICU, 47.3 ± 3.7 dB to 55.1 ± 3.7 dB on the telemetry floor, and 44.6 ± 2.1 dB to 53.7 ± 3.6 dB on the general ward. However, SLCs ≥ 17.5 dB were not statistically different (ICU, 203.9 ± 28.8 times; non-ICU, 270.9 ± 39.5; P = 0.11). In both ICU and non-ICU wards, average daytime light levels were <250 lux, and peak light levels occurred in the afternoon and early evening.Quieter, non-ICU wards have as many SLCs as ICUs do, which has implications for quality improvement measurements. Efforts to further reduce average noise levels might be counterproductive. Light levels in the hospital (ICU and non-ICU) may not be optimal for maintenance of a normal circadian rhythm for most people.