• Melissa Knauert, Sangchoon Jeon, Terrence E Murphy, H Klar Yaggi, Margaret A Pisani, and Nancy S Redeker.
• Section of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT. Electronic address: melissa.knauert@yale.edu.
• J Crit Care. 2016 Dec 1; 36: 1-7.

PurposeSound levels in the intensive care unit (ICU) are universally elevated and are believed to contribute to sleep and circadian disruption. The purpose of this study is to compare overnight ICU sound levels and peak occurrence on A- vs C-weighted scales.Materials And MethodsThis was a prospective observational study of overnight sound levels in 59 medical ICU patient rooms. Sound level was recorded every 10 seconds on A- and C-weighted decibel scales. Equivalent sound level (Leq) and sound peaks were reported for full and partial night periods.ResultsThe overnight A-weighted Leq of 53.6 dBA was well above World Health Organization recommendations; overnight C-weighted Leq was 63.1 dBC (no World Health Organization recommendations). Peak sound occurrence ranged from 1.8 to 23.3 times per hour. Illness severity, mechanical ventilation, and delirium were not associated with Leq or peak occurrence. Equivalent sound level and peak measures for A- and C-weighted decibel scales were significantly different from each other.ConclusionsSound levels in the medical ICU are high throughout the night. Patient factors were not associated with Leq or peak occurrence. Significant discordance between A- and C-weighted values suggests that low-frequency sound is a meaningful factor in the medical ICU environment.Copyright © 2016 Elsevier Inc. All rights reserved.

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