Circadian Hygiene in the ICU Environment (CHIE) study

Objective: To investigate the environment and care in the intensive care unit (ICU) and its relationship to patient circadian temperature disruption. Design: 30-day, prospective period prevalence study. Setting: 27-bed tertiary ICU. Participants: Patients expected to remain in the ICU for at least 24 hours. Main outcome measures: Temperature, relative humidity, light and sound intensity in the ICU; nursing interventions (using the Therapeutic Intervention Scoring System-28); and core body temperature of ICU patients. Results: Of 28 patients surveyed, 20 (71%) were mechanically ventilated. Median (interquartile range [IQR]) light intensity peaked at 07:00 at 165 (12–1218) lux with a trough at 23:00 of 15 (12–51) lux and was consistently < 100 lux between 21:00 and 06:00. Peak median (IQR) sound intensity was at 07:00 (62.55 [57.87–68.03] dB) while 58.84 (54.81–64.71) dB at 02:00. Ambient temperature and humidity varied with median (IQR) peaks of 23.11°C (22.74–23.31°C) at 16:00 and 44.07% (32.76–51.08%) at 11:00 and median troughs of 22.37°C (21.79–22.88°C) at 05:00 and 39.95% (31.53–47.95%) at 14:00, respectively. Disturbances to sleep during the night occurred due to care activities including linen changes (15 patients, 54%) and bathing (13, 46%). On the day before and the day of the study, 13 patients (47%) and 10 patients (36%), respectively, had a circadian rhythm on core body temperature without an association with illness severity, nursing intervention or environmental measures. Conclusions: The ICU has low light intensity with relative humidity and ambient temperature not aligned to normal human circadian timing. Noise levels are commonly equivalent to conversational speech while patient care procedures interrupt overnight sleep. The contribution of these factors to disrupted CBT rhythmicity is unclear.