Original articleThe influence of white noise on sleep in subjects exposed to ICU noise
Introduction
Sleep disruption is common in the hospital setting, especially in the intensive care unit (ICU) and leads to poor quality of sleep that subjectively is non-restorative and may be associated with important morbidity [1], [2], [3], [4], [5]. Multiple factors may contribute to sleep disruption in hospitalized patients, including underlying illness, uncomfortable therapeutic or monitoring interventions, mechanical ventilation and environmental factors including light or noise [1], [6], [7], [8], [9]. Several previous reports have demonstrated evidence of alterations in sleep architecture in ICU patients, including reduced nocturnal total sleep time, slow wave sleep, rapid eye movement (REM) sleep, and increased stage 1–2 sleep [10], [11]. In addition, sleep fragmentation (increased arousals) and alterations in sleep distribution have been observed in hospitalized patients [1], [4], [12]. There is significant debate in the literature regarding the impact of environmental noise on arousals from sleep in the ICU. A previous report from this laboratory suggests that environmental noise levels in the ICU setting are regularly elevated with an average of 150–200 sound peaks that are >80 weighted decibels (DB) between midnight and 6:00 AM [9]. Such increased noise levels have been variably associated with sleep disruption, leading up to 10–40% of the arousals recorded in the ICU [6]. Interventions aimed at reducing sleep disruption from noise, such as behavioral modification of critical care nursing staff [13] or use of earplugs [14] can decrease peak ICU noise levels and may reduce arousals from sleep. However, the absolute sound reductions from these interventions are often small, suggesting that a threshold level of sound change (from baseline to peak), rather than simply peak noise, may be the most important sound quality that leads to sleep disruption [15], [16]. Reducing the change in sound from baseline to peak may influence amplitude and latency of brain (cortical)—evoked potentials [17], such that in the presence of added background noise, a large acoustic stimulus may cause less intense cerebral cortical activation during sleep. In this study, we aimed to determine the influence of added ambient (white) noise (62 DB of mixed frequency sound) on sleep fragmentation in normal individuals who were exposed to recorded ICU noise during sleep in a sleep laboratory setting. We hypothesized that white noise added to the room would increase baseline levels of sound but would substantially increase arousal thresholds (reduce arousals), improve sleep architecture and improve subjective sleep quality. By removing subjects from the ICU setting we sought to isolate the effects of sound on sleep disruption, recognizing that other factors such as ventilator interactions, underlying illness, medications or nursing interventions may also contribute to sleep disruption in ICU patients.
Section snippets
Subjects
Subjects (age 18–65 years, body mass index (BMI) <26 kg/m2), recruited from the Brown medical community, had no history of medical or sleep problems and took no medications. Once recruited, subjects had audiology testing and were excluded for abnormal test results. Each subject underwent a total of three overnight polysomnograms (PSG) separated by at least 2 weeks including: (1) baseline; (2) recorded ICU noise exposure (N), and (3) recorded ICU noise and mixed-frequency white noise exposure
Results
Eight healthy volunteers were recruited. Three were excluded due to evidence of significant obstructive sleep apnea (mean apnea/hypopnea index 22.3 events/h sleep). A total of five subjects (2 males and 3 females, 27.0±1.7 years) had baseline PSG, followed by subsequent studies, while exposed to previously recorded ICU noise levels. Four of the five subjects (2 males and 2 females) had an additional PSG while exposed to the same ICU noise levels in addition to continuous background of white
Discussion
The major finding in this study is that in normal individuals exposed to recorded ICU noise, the addition of mixed frequency white noise substantially reduced arousals from sleep and returned sleep architecture to baseline values. In addition, in normal individuals a threshold increase in baseline noise was identified for tone-induced arousals to occur during sleep.
Acknowledgements
The authors would like to thank Charleen Pysz for help with the preparation of this manuscript and Steven Ambrose, of Sound Eng. who provided us with the white noise recording used in this study.
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