Review Article INTRODUCTION Since their introduction about 30 years ago, intensive care units have been invaluable for the treatment of acute organ failure. However, it is immediately obvious to the casual observer that intensive care has a price in physical and emotional discomfort to the patient. Sleep is commonly disrupted in intensive care unit patients. Tremendous advances have been made in the past three decades in our knowledge of normal and abnormal sleep physiology. Sleep is a basic biological function in humans as important to continued health as eating. Nevertheless, clinicians are much more likely to consider nutrition as an important concern for critically ill patients than they are to consider patients’ sleep. This review will first describe normal sleep. Next, the sleep disruption common to critical care units, and the consequences of poor sleep will be reviewed. Finally, the impact on sleep disorders and medical disorders on the care of critically ill patients will be discussed, along with treatment guidelines for improving sleep in this environment. NORMAL SLEEP Sleep is much more than simple decreased consciou- sness. Since the work of Rechtschaffen and Kales in 1968, 1 sleep has been divided into two types: rapid eye movement (REM) and non-REM, with non-REM further divided into four stages. Stages of sleep are distinguished on the basis of electroencephalographic patterns (EEG), muscle activity (EMG), and eye Correspondence and reprint requests: Dr Arunabh Talwar, 300 Community Drive, Manhasset, NY 11030, USA; Phone: 516 562-4217; Fax: 516 562-4908; E-mail: arun1@optonline.net. Sleep in the Intensive Care Unit Arunabh Talwar 1 , Baba Liman 1 , Harley Greenberg 1 , Steven H. Feinsilver 1 and V.K. Vijayan 2 Division of Pulmonary Critical Care and Sleep Medicine, North Shore Long Island Jewish Health System 1 , USA and Vallabhbhai Patel Chest Institute 2 , University of Delhi, Delhi, India ABSTRACT Sleep is commonly disrupted in intensive care unit patients. The causes of this sleep disruption include the underlying medical illness itself, intensive care unit (ICU) environment, psychological stress, and effects of many medications and other treatments used to help those who are critically ill. The purpose of this review is to discuss the relevant literature in this regard, in order to improve the knowledge and recognition of this problem by health care providers. Also general and specific integrative steps to improving sleep of patients in the ICU is also described. [Indian J Chest Dis Allied Sci 2008; 50: 151-162] Key words: Sleep, Respiratory, Cardiac, Stress, Intensive care, Oximetry, Breathing, Apnea, Obesity, Hypertension, Arrhythmia, Hypoxemia, Narcolepsy. movements, in 30 second periods called epochs. The normal subject during relaxed wakefulness with eyes closed exhibits alpha activity (8-12 Hz) on EEG. During stage 1 non-REM alpha activity disappears, and the subject is in a very light sleep and can easily be awakened. Stage 2 is characterised by the appearance of characteristic K-complexes (large, biphasic waves) and sleep spindles (12-14 Hz activity lasting at least 0.5 sec). During stage 3 and 4 sleep, the EEG becomes increasingly dominated by delta or slow waves (large amplitude waves of 2 Hz or slower). These stages are referred to together as delta sleep or slow wave sleep, and constitute the “deepest” sleep in terms of arousal threshold and restorative properties. The percentage of delta sleep declines with age. During REM sleep, EEG resembles wakefulness in many ways, but muscle activity is greatly reduced. Typical very rapid eye movements are seen, allowing for easy identification of REM sleep. It is generally thought that REM sleep represents dreaming activity; during dreaming muscle hypotonia prevents the dreamer from acting out their dreams. The period of REM sleep is associated with the greatest instability of respiratory and cardiac function during the night. The way these stages of sleep are put together during the sleep period is known as sleep architecture, and the graphic display of sleep is known as a sleep histogram or hypnogram. Although highly variable both among different individuals and on different nights, some generalisations can be made about typical sleep architecture. Normal subjects will fall asleep within about 20 minutes, and enter successively deep stages of non-REM sleep, with a REM period occurring in about