States related to or confused with coma.

c CONSCIOUSNESS Consciousness is a state characterised by awareness of self and environment and an ability to respond to environmental factors. Normal consciousness can be regarded as having two separate but closely interrelated components. The first of these is the arousal component of wakefulness. It is this that keeps the patient awake and which relates to the physical manifestations of awakening from sleep—for example, eyes being open, motor activity. The second component is the content of consciousness or the awareness of self and environment. This consists of the sum of psychological functions of sensations, emotions, and thoughts. A detailed description of the pathophysiology of consciousness is beyond the scope of this article. In simple terms, normal consciousness requires an interaction between the reticular activating system of the brain stem and the cerebral cortex. The reticular activating system is responsible for arousal or alertness and the cerebral cortex is responsible for the content of consciousness or the awareness of self and environment. It should be recognised that an individual’s awareness of self can only be recognised by an observer on the basis of the responses made to external stimuli, especially verbal or motor responses. Inability to respond may not only result from abnormalities of consciousness but also from paralysis (such as the locked in state). This may be a particular problem in the intensive care unit where patients have often received sedative drugs and paralytic agents. Issues relating to the common patterns of altered consciousness, sleepiness, delirium, and coma are dealt with elsewhere in this supplement. This article will introduce some of the less commonly seen states.