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Coma: Types, causes, treatments, outlook

What is a coma?

A person in a coma remains unconscious for a period of time during which they cannot be woken up, and do not respond to anything around them.

Causes of coma include accidents and head injuries, stroke and extremes of diabetes blood sugar levels.

What causes a coma?

Problems that can lead to coma include:

  • Trauma: Head injuries can cause the brain to swell and/or bleed. When the brain swells as a result of trauma, the fluid pushes up against the skull. The swelling may eventually cause the brain to push down on the brain stem, which can damage the reticular activating system (RAS), a part of the brain that's responsible for arousal and awareness.
  • Swelling: Swelling of brain tissue can occur even without distress. Sometimes a lack of oxygen, electrolyte imbalance, or hormones can cause swelling.
  • Bleeding: Bleeding in the layers of the brain may cause coma due to the compression on the injured side of the brain. This compression causes the blood to shift to the unaffected side of the brain, thereby causing both cerebral hemispheres to be affected. High blood pressure, cerebral aneurysms, and tumours are non-traumatic causes of bleeding in the brain.
  • Stroke: When there is no blood flow to a major part of the brain stem or loss of blood accompanied with swelling, coma can occur.
  • Blood sugar: In people with diabetes, coma can occur when blood sugar levels stay very high. That's a condition known as hyperglycaemia. Hypoglycaemia, or blood sugar that's too low, can also lead to a coma.
  • Oxygen deprivation: Oxygen is essential for brain function. Cardiac arrest causes a sudden cut-off of blood flow and oxygen to the brain. After cardiopulmonary resuscitation ( CPR), survivors of cardiac arrest are often in comas. Oxygen deprivation can also occur with drowning or choking.
  • Infection: Infections of the central nervous system, such as meningitis or encephalitis, can also cause coma.
  • Toxins: Substances that are normally found in the body can accumulate to toxic levels if the body fails to dispose of them correctly. As an example, ammonia due to liver disease, carbon dioxide from a severe asthma attack or urea from kidney failure can accumulate to toxic levels in the body. Drugs and alcohol in large quantities can also disrupt neuron functioning in the brain.
  • Seizures: A single seizure rarely produces coma. But continuous seizures, called status epilepticus, can. Repeated seizures can prevent the brain from recovering in between seizures. This may cause prolonged unconsciousness and coma.

What are the different types of coma?

Types of coma can include:

  • Toxic- metabolic encephalopathy. This is an acute condition of brain dysfunction with symptoms of confusion and/or delirium. The condition is usually reversible. The causes of toxic- metabolic encephalopathy are varied. They include systemic illness, infection, organ failure, and other conditions.
  • Anoxic brain injury. This is a brain condition caused by total lack of oxygen to the brain. Lack of oxygen for a few minutes causes cell death to brain tissues. Anoxic brain injury may result from heart attack (cardiac arrest), head injury or trauma, drowning, drug overdose, or poisoning.
  • Persistent vegetative state. This is a state of severe unconsciousness. The person is unaware of his or her surroundings and incapable of voluntary movement. With a persistent vegetative state, someone may progress to wakefulness but with no higher brain function. With persistent vegetative state, there is breathing, circulation and sleep-wake cycles.
  • Locked-in syndrome. This is a rare neurological condition. The person is totally paralysed except for the eye muscles, but remains awake and alert and with a normal mind.
  • Brain death. This is an irreversible cessation of all brain function. Brain death may result from any lasting or widespread injury to the brain.

WebMD Medical Reference

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