Coma is a state of complete unresponsiveness. The patient exhibits only minimal reflex responses to stimuli. Consciousness depends on the interaction of the two cerebral hemispheres of the brain where neurological processes of awareness occur and on part of the upper brain stem and midbrain called the reticular activating substance which is responsible for activation of the hemispheres. A coma can occur when either the cerebral hemispheres or these activating centers are damaged.
Brain damage may be caused by tumors, shock, lack of oxygen, poisoning, infections, or concussion. Direct trauma, especially head injury, is the most common cause. When a severe blunt force is applied to the skull, as in a car accident, communication pathways between the cortex and brainstem are disrupted, resulting in loss of consciousness. Bleeding and tissue damage lead to brain swelling, which, if not relieved quickly, can lead to further brain damage and death.
Levels of alertness fall along a spectrum, with coma the greatest degree of unconsciousness. A useful assessment of consciousness in trauma cases is derived from the Glasgow Coma Scale. Patients who fail to open their eyes in response to voice and who respond to pain with weak flexion and grunting noises are regarded as being in coma. This scale has been modified for use with infants and small children.
A person in terminal coma may lack all reflexes, including those involved in breathing. In such cases a mechanical respirator is necessary to keep the patient alive. Difficult ethical questions arise concerning the continuing maintenance of such patients on life-support systems when they have no hope of recovery. When patients continue in a comatose state for much longer than a month, the condition is described as a persistent vegetative state and is usually considered irreversible.
Recovery proceeds by stages, each of which may vary in duration by several days depending on the extent of brain damage. In general, the patient first enters a state called stupor, a state of unconsciousness that can be only temporarily interrupted by vigorous stimulation. The next phase is a state of delirium and extreme agitation. Eventually the patient becomes quieter but is in a state of mental confusion. Later, in the automatism phase, the patient can respond to questions but perform only simple tasks in an automatic way. Gradually, the highest brain functions return. The longer a person is in a coma, the less likely that complete recovery will occur.
No comments:
Post a Comment