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Coma is among the most common neurologic emergencies encountered general medicine and requires an organized approach. It accounts for a substantial portion of admissions to emergency wards and occurs on all hospital services.
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There exists a continuum of states of reduced alertness, the most severe form being coma, defined as a deep sleeplike state with eyes closed from which the patient cannot be aroused. Stupor refers to a higher degree of arousability in which the patient can be transiently awakened by vigorous stimuli, accompanied by motor behavior that leads to avoidance or withdrawal from uncomfortable or aggravating stimuli. Drowsiness simulates light sleep and is characterized by easy arousal and the persistence of alertness for brief periods. Stupor and drowsiness are usually accompanied by some degree of confusion (Chap. 24). A precise narrative description of the level of arousal and of the type of responses evoked by various stimuli as observed at the bedside is preferable to use of ambiguous terms such as lethargy, semicoma, or obtundation.
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Several conditions that render patients unresponsive and simulate coma are considered separately because of their special significance. The vegetative state signifies an awake-appearing but nonresponsive state often in a patient who has emerged from coma. In the vegetative state, the eyelids may open periodically, giving the appearance of wakefulness. Respiratory and autonomic functions are retained. Yawning, coughing, swallowing, and limb and head movements persist, but there are few, if any, meaningful responses to the external and internal environment. There are always accompanying signs that indicate extensive damage in both cerebral hemispheres, e.g., decerebrate or decorticate limb posturing and absent responses to visual stimuli (see below). In the closely related but less severe minimally conscious state, the patient displays rudimentary vocal or motor behaviors, often spontaneous, but some in response to touch, visual stimuli, or command. Cardiac arrest with cerebral hypoperfusion and head trauma are the most common causes of the vegetative and minimally conscious states (Chap. 301).
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The prognosis for regaining mental faculties once the vegetative state has supervened for several months is very poor, and after a year, almost nil; hence the term persistent vegetative state. Most reports of dramatic recovery, when investigated carefully, are found to yield to the usual rules for prognosis, but there have been rare instances in which recovery has occurred to a severely disabled condition and, in rare childhood cases, to an even better state. Patients in the minimally conscious state carry a better prognosis for some recovery compared to those in a persistent vegetative state, but even in these patients, dramatic recovery after 12 months is unusual.
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The possibility of incorrectly attributing meaningful behavior to patients in the vegetative and minimally conscious states creates inordinate problems and anguish for families and physicians. On the other hand, the question of whether these patients lack any capability for cognition has been reopened by functional MRI ...