Abstract Introduction Circadian disruption is common in the intensive care unit (ICU) and is associated with adverse outcomes. ICU light patterns are frequently abnormal (e.g., dim daytime and bright nighttime light levels). Our objective was to understand what factors are associated with the observed light patterns. We hypothesized that individual patient factors, such as patient age, sex, severity of illness (SOFA score), mechanical ventilation status, room direction, and season of admission, are associated with variation in light levels. Methods This observational cohort study was conducted in a medical ICU (MICU) from 2/2021-2/2022. Thirteen of 56 MICU rooms were preselected for light measurement during the 1-year study period. Patients admitted to light measurement rooms who were in their first ICU admission of hospitalization and remained for 48 hours were included in the cohort. Patient demographic and clinical data were recorded. Light intensity (lux) was recorded every 1 minute via HOBO-MX2202 light meters mounted to the wall just above the head of the bed to approximate angle of gaze. Mean lux, proportion of time250 lux (gt250), and proportion of time 10 lux (le10) were calculated for day (05:00-22:59) and night (23:00-04:59) periods. We selected the above-listed between-individual patient factors that we hypothesized could influence light levels. We then analyzed the proportion of variance due to between-individual factors via estimation of the intraclass correlation coefficient for unconditional models. Results 339 patients (50% female) were enrolled in the study; mean(SD) age was 66(15) years and SOFA score 6.8(3.5). Mean day and night light intensity was 173(177) lux and 62(119) lux, respectively. Daytime gt250 was 28%(42%) and le20 was 16%(33%). Nighttime gt250 was 10%(28%) and le20 was 62%(45%). The selected factors explained 9-26% of daytime light variation and 47-54% of nighttime light variation, depending on the light outcome being tested. Conclusion There was a high degree of variation in MICU light levels. Differences in between-individual factors explained a notable proportion of the variation. This was especially pronounced during the night period. Further analysis will assess the degree to which each of the patient factors contributes to light variation and thus facilitate intervention in adverse MICU light patterns. Support (if any) K23-HL138229
Intihar et al. (Fri,) studied this question.