Coma

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For other meanings of the word "coma", especially in astronomy, see coma (disambiguation)

In medicine, a coma (from the Greek koma, meaning deep sleep) is a profound state of unconsciousness. A comatose patient cannot be awakened, fails to respond normally to pain or light, does not have sleep-wake cycles, and does not take voluntary actions. Coma may result from a variety of conditions, including intoxication, metabolic abnormalities, central nervous system diseases, and hypoxia.

1 Causes
2 Contrasts to other conditions
3 Outcome
4 Controversy
5 Diagnosis and treatment
6 References

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Causes

Brain trauma, the most common cause of comas, accounts for 60% of cases. Unless the brain has correct temperature, pressure, pH, oxygenation, chemical balance and nutrients, comas may occur. Head trauma associated with an increased intracranial pressure can lead to comas by compressing delicate brain tissue, as can subarachnoid hemorrhage. Various toxins can also lead to coma, including poisons, alcohol, barbiturates, opiate narcotics, sedatives, amphetamines, cocaine and aspirin. Metabolic abnormalities (such as diabetes) altering blood glucose levels beyond safe levels, can cause comas, as can liver or kidney failure, hypoxia (poor oxygenation), and electrolyte imbalances. Seizure disorders and central nervous system infections, such as meningitis and encephalitis, are further examples.

Comas can also be caused by focal lesions or strokes affecting only a small part of the brain and may be either supratentorial or infratentorial. Focal supratentorial injuries account for 30% of coma cases, and can be caused by problems with blood vessels or by expansive lesions such as neoplasia or hydrocephalus.

Focal infratentorial lesions account for the remaining 10% of comas, and can be of vascular nature, expansive or demyelinating lesions.

Medical professionals may intentionally induce a coma with drugs to reduce swelling of the brain after injury.

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Contrasts to other conditions

Some conditions share characteristics with coma and must be ruled out in a differential diagnosis before coma is conclusively diagnosed. These include locked-In syndrome, akinetic mutism and catatonic stupor.

The difference between coma and stupor is that a patient with coma cannot give a suitable response to either noxious or verbal stimuli, whereas a patient in a stupor can give a crude response, such as screaming, to an unpleasant stimulus.

Some psychiatric diseases appear similar to coma. Some forms of schizophrenia, catatonia, and extremely severe major depression are responsibile for behaviour that appears comatose.

Coma is also to be distinguished from the persistent vegetative state which may follow it. This is a condition in which the individual has lost cognitive neurological function and awareness of the environment but does have noncognitive function and a preserved sleep-wake cycle. Spontaneous movements may occur and the eyes may open in response to external stimuli, but the patient does not speak or obey commands. Patients in a vegetative state may appear somewhat normal and may occasionally grimace, cry, or laugh.

Likewise, coma is not the same as brain death, which is the irreversible cessation of all brain activity. One can be in a coma but still exhibit spontaneous respiration; one who is brain-dead, by definition, cannot.

Coma is different from sleep; sleep is always reversible.

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Outcome

There are several levels of coma, through which patients may or may not progress. As coma deepens, responsiveness of the brain lessens, normal reflexes are lost, and the patient no longer responds to pain. The chances of recovery depend on the severity of the underlying cause. A deeper coma alone does not necessarily mean a slimmer chance of recovery, because some people in deep coma recover well while others in a so-called milder coma sometimes fail to improve.

The outcome for coma and vegetative state depends on the cause, location, severity and extent of neurological damage: outcomes range from recovery to death. People may emerge from a coma with a combination of physical, intellectual and psychological difficulties that need special attention. Recovery usually occurs gradually, with patients acquiring more and more ability to respond. Some patients never progress beyond very basic responses, but many recover full awareness. Gaining consciousness again is not instant: in the first days, patients are only awake for a few minutes, and duration of time awake gradually increases.

Coma generally lasts a few days to a few weeks, and rarely lasts more than 2 to 4 weeks. After this time, some patients gradually come out of the coma, some progress to a vegetative state, and others die. Many patients who have gone into a vegetative state go on to regain a degree of awareness. Others may remain in a vegetative state for years or even decades. Predicted chances of recovery are variable due to different techniques used to measure the extent of neurological damage. All the predictions are statistical rates with some level of chance for recovery present: a person with a low chance of recovery may still awaken. Time is the best general predictor of a chance for recovery, with the chances for recovery after 3 months of brain damage induced coma being low (less than 10%), and full recovery being very low. [1] [2]

The most common cause of death for a person in a vegetative state is secondary infection such as pneumonia which can occur in patients who lie still for extended periods.

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Controversy

There have been controversies and legal cases over whether to keep comatose patients alive for long periods using life support equipment. Two such cases are those of Karen Ann Quinlan and Terri Schiavo. However, these individuals were not in a coma per se but were in a persistent vegetative state.

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Diagnosis and treatment

Diagnosis has the following steps: Medical History, Physical Exam & Neurological Evaluation, Eye Examination, Laboratory Tests, Imaging Studies(CT,MRI), EEG.

The Glasgow Coma Scale is used to quantify the severity of a coma. There are three components to the score: Eye opening response, Verbal response, and Motor response.

In Germany, music therapy is used to attempt to arouse patients from coma.

In Belgium a project is being set up to train dogs and cats to warn patients and medical staff that a coma patient has awakened.

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