A state of unconsciousness in which a person’s responses to stimuli are absent or reduced
- Age, gender, genetics, and lifestyle are not significant factors
Coma is an unconscious state in which a person does not respond to outside stimuli such as sound, light, or touch. There are varying depths of coma. In less severe forms, a person may still respond to certain stimuli, move his or her eyes, cough, and murmur occasionally. A person who is deeply comatose does not make any movements or respond to any form of stimulation.
In the past, being in a state of coma was usually fatal within a short time. Nowadays, recovery is possible because vital functions, such as breathing, can be sustained with life-support machines (see Intensive therapy unit).
In severe cases of coma, some people lose all automatic functions irreversibly (see Brain death). Other people still retain these basic functions but are otherwise unresponsive. This condition is called a persistent vegetative state.
What are the causes?
A state of coma is caused by damage to the brain. Although such damage is often treatable, very severe damage may be irreversible and is sometimes fatal.
A serious head injury or a disorder that prevents blood flow to the brain, such as a stroke or cardiac arrest, may damage enough brain tissue to result in a state of coma. Other causes of coma include infections that affect the brain, such as meningitis and viral encephalitis.
Excessively high or low levels of certain substances in the blood may result in a state of coma. For example, a person with diabetes mellitus may become comatose if his or her blood glucose (sugar) level rises or falls excessively. In such circumstances, it is usually possible to reverse the condition with appropriate treatment. A state of coma may also be caused by a drug overdose (see Drug overdose and accidental ingestion) or by drinking an excessive amount of alcohol or be associated with kidney or liver failure.
How is it diagnosed?
A person who is unconscious on admission to hospital will be examined for evidence of injury and to assess nervous system function. Family members and friends will be asked about possible causes. Coma is diagnosed when a person is persistently unconscious. The depth of coma is assessed against a standard scale (such as the Glasgow Coma Scale) by measuring the person’s response to stimuli such as pain. For example, the doctor may rub the sternum (breastbone) or press hard at the base of a nail bed. Blood tests are used to look for an underlying cause, such as a drug overdose, high levels of alcohol, or abnormal levels of glucose. Imaging tests, such as MRI or CT scanning, may be carried out to look for brain damage.
If meningitis is suspected, a lumbar puncture may be performed. In this test, a sample of fluid from around the spinal cord is taken and tested for evidence of an infection.
What is the treatment?
A person who is comatose is likely to need care in an intensive therapy unit, and mechanical ventilation may be necessary if breathing is impaired. If possible, underlying causes are treated immediately. For example, antibiotics are given for an infection. The level of consciousness is assessed at regular intervals. Monitoring the pressure inside the skull may also be necessary because a state of coma may be associated with raised pressure. If the pressure rises, drugs can be given to reduce it.
What is the prognosis?
If brain damage is minor or reversible, a person may come out of a state of coma and make a full recovery. However, sometimes it is difficult for doctors to predict the likelihood of a complete recovery. Deep coma caused by severe head trauma often leads to long-term neurological problems. Problems may include muscle weakness or changes in behaviour for which long-term treatments such as physiotherapy or occupational therapy may be needed. If the damage to the brain is severe and irreversible, particularly if the brainstem has been affected, the person is unlikely to recover, and death may be the eventual outcome.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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