Coma

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

In medicine, a coma (from the Greekkoma, meaning deep sleep) is a profound state of unconsciousness. A comatose patient cannot be awakened, fails to respond properly or at all to stimuli such as pain or light, does not have sleep-wake cycles, and does not take voluntary actions (BAIUSA). Coma may result from a variety of conditions, including intoxication, metabolicabnormalities, central nervous system diseases, and hypoxia.

Causes

An impairment that affects a large part of the brain, called diffuse pathology, is the most common cause of coma, accounting for about 60% of the cases. To maintain consciousness, the brain requires the correct temperature, pressure, pH, oxygenation, and nutrients; denying the brain any of these necessities will lead to coma. A variety of common causes of coma can be classified as diffuse pathologies. For example, head trauma associated with an increased intracranial pressurecan lead to coma by compressing delicate brain tissue, as can subarachnoid hemorrhage. Various toxins can also lead to coma, including poisons, alcohol, barbiturates, opiatenarcotics, sedatives, amphetamines, cocaineand aspirin. Metabolic abnormalities that lead to either elevated or reduced glucose levels in the blood, liver or kidney failure, hypoxia(poor oxygenation), and electrolyteimbalances can also produce unconsciousness. Seizuredisorders and central nervous systeminfections, such as meningitisand encephalitis, are further examples.

Coma can also be caused by focal lesions, those that affect only a small part of the brain and may be either supratentorial or infratentorial. Focal supratentorialinjuries account for 30% of coma cases, and can be caused by problems with blood vesselsor by expansive lesions such as neoplasiaor hydrocephalus.

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

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

Contrasts to other conditions

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

The difference between coma and stuporis 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 depressionare responsibile for behaviour that appears comatose.

Coma is also to be distinguished from the persistent vegetative statewhich 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 eyesmay 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.

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 statisticalrates 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 damageinduced 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 infectionsuch as pneumoniawhich can occur in patients who lie still for extended periods.

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 Quinlanand Terri Schiavo. However, these individuals were not in a coma per se but were in a persistent vegetative state.

Diagnosis and treatment

The Glasgow Coma Scaleis 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 quicken the awakening traject.

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

Reference

• Brain Injury Association of America (BIAUSA). Types of Brain Injury.

• This article contains text from the NINDS public domain pages on TBI at:

1. http://www.ninds.nih.gov/health_and_medical/disorders/tbi_doc.htm
2. http://www.ninds.nih.gov/health_and_medical/pubs/tbi.htm

• Some of the information in this section is from the public domain resourceprovided by the National Institute of Neurological Diseases and Stroke.bs:coma

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It uses material from the http://en.wikipedia.org/wiki/Coma Wikipedia article Coma.