COMA

complete lack of consciousness, characterized by loss of reaction to external stimuli and absence of spontaneous nervous activity, usually associated with diffuse injury to the cerebrum. Unconsciousness may accompany a number of metabolic disorders or physical injuries to the brain from disease or trauma. Different patterns of coma depend on the origin of the injury. Simple concussions cause losses of consciousness of short duration; in contrast, lack of oxygen (anoxia) may result in a coma that lasts for several weeks and is often fatal. Stroke, a rupture or blockage of vessels supplying blood to the brain, can cause sudden loss of consciousness in some patients, while comas caused by metabolic abnormalities or cerebral masses such as tumours are characterized by more gradual onset, passing through stages of lethargy and stupor before reaching true coma. Metabolic comas are also more likely to have associated brain seizures and usually leave pupillary light reflexes intact, whereas comas with physical causes usually eradicate this reflex. Common causes of metabolic coma include diabetes, alcohol, and barbiturate poisoning. In diabetes, low insulin levels allow the buildup of ketones, breakdown products of fat tissue that destroy the osmotic balance in the brain, damaging brain cells. Ingestion of large quantities of alcohol over a short period can precipitate a coma that may be treated by gastric lavage (stomach pump) in its early stages; alcohol combined with barbiturates is a common cause of coma in suicide attempts. Large doses of barbiturates alone will also produce coma by suppressing cerebral blood flow, thus causing anoxia. Gastric lavage soon after the drug is taken may remove sufficient barbiturate to allow recovery. For most metabolic comas, the first step in treatment is to protect the brain cells and attempt to eliminate the cause of coma. In some psychiatric conditions, such as catatonic schizophrenia, a comalike state may also occur.