Sleep and light in the ICU
We note that, consistent with other studies, sleep in the ICU was quite poor at night. Assuming actigraphy may overestimate sleep time in the ICU, especially for those moving little after major surgery, we note that sleep time decreased each day post-extubation. This decrease is probably due to increased activity/movement that helps better estimate sleep duration (i.e. less time thought to be sleep due to inactivity). Additionally, sleep fragmentation as assessed by sleep bout length remained high throughout. By the end of the ICU stay, total nighttime sleep duration was only about 350 min per patient. Regarding the light data, while we found no between-group differences, we did find that the light levels were very low (generally below 100 lx). Low light levels are desirable at nighttime to help with sleep (high light levels at nighttime can suppress melatonin production, which is important for the maintenance of sleep), but should be much higher during the daytime as it is a major circadian rhythm cue (zeitgeber). This suggests a potential area of improvement for in critical care medicine.