The importance of improving the quality and quantity of sleep for critically ill patients is increasingly recognised 1-7. Sleep is a physiological state that permits the maintenance and healing of the human body. The sleep cycle is divided into rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep 2-7. A normal sleep cycle lasts approximately 90 minutes, cycling continuously between REM and NREM sleep. NREM sleep is subdivided into four stages, 1 through 4, scaled according to increasing depth of sleep. The more restful sleep of stages 3 and 4 is slow wave sleep (SWS) and generally comprises about 15 to 20% of sleep in healthy, middle-aged individuals 2,3. REM sleep, also considered to be restful sleep, comprises about 20 to 25% of sleep in healthy subjects 2,3. In intensive care units (ICU) mechanically ventilated patients often exhibit sleep fragmentation and a suppression of REM sleep and SWS 1-7. Some investigators have demonstrated that the sleep of mechanically ventilated patients is frequently disrupted, with as many as 63 arousals and awakenings per hour 5 , decreased SWS (0 to 9% of sleep) and less REM sleep (0 to 14% of sleep) 8-11. These sleep disturbances have been associated with neurocognitive dysfunction 1-4,6,7 , abnormalities in host defence mechanisms 1-4,6,7,12 , alterations in protein catabolism 1-4,6,7,13 and respiratory dysfunction 2,6,14,15. The causes of sleep disruption in critically ill patients include the ICU environment itself, medical illness, psychological stress, mechanical ventilation, medications and treatments 1-11. Sedatives and analgesics are indispensable for the treatment of critically ill patients, however many commonly used drugs have adverse effects on sleep
