Consciousness is a complex phenomenon comprising arousal and awareness. These functions are mediated by the reticular activating system that begins in the brainstem and projects to higher cortical structures. Abnormalities directly or indirectly affecting this system may produce coma. Detailed neurologic assessment consists of evaluation of history, skeletal motor response, pupillary size and reactivity, eye movement, and respiratory patterns. Information obtained may be useful in localizing the contributory lesion, predicting outcome, and determining brain death. Several scales have been used to quantify coma, each with limitations. In the United States, the most widely used scale is the Glasgow Coma Scale.
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