coma

coma in medicine, deep state of unconsciousness from which a person cannot be aroused even by painful stimuli. The patient cannot speak and does not respond to command. Coma is the result of damage to the brain stem and cerebrum that may be caused by severe head or brain injury, cardiac arrest, stroke , diabetes , drug overdose, shock , or hemorrhage . It occurs just before death in many diseases. There are various depths of coma; the nature of the injury determines the level of supportive treatment necessary (see artificial life support ). Survival and prognosis depend upon the cause, extent of damage, and duration of the coma.

The term persistent vegetative state was coined in 1972 to describe an unconscious state in which sleep and wake cycles remain and eyes may open, but there is no thinking, feeling, or awareness of one's surroundings (although one may react reflexive to certain stimulations). The brain stem is usually relatively intact but the cerebral cortex is severely impaired. It is this state that sometimes results from resuscitation and life support of people who otherwise would have died; partial emergence from such a state sometimes occurs with a year or two, but not after that.

coma All persons in coma are unconscious, but not all who are unconscious are in coma. Sleep is a state of unconsciousness from which a person can be roused. The vegetative state is unconsciousness with the eyes open, the person being awake but not aware. Coma is a state of unrousable, sleep-like (eyes closed) unconsciousness. Although asleep and unaware, only those in the deepest states of coma are unresponsive. Most patients in coma respond reflexly — the pupils react to light and the limbs move in response to a painful stimulus (such as pinching the skin or pressing the nailbed). A person in coma may move restlessly and make sounds, but utters no words.

Different levels of coma, and of impaired consciousness not severe enough to be called coma, are defined by the Glasgow Coma Scale or Score — often referred to internationally as the GCS. This grades three items of behaviour: eye opening, motor responses (limb movements on command or in response to a painful stimulus), and verbal activity. For each of these there is a score of 1 to 5 according to how good the response is, with higher numbers indicating the more normal responses. At a combined score of 15 the eyes open spontaneously, commands are obeyed, and the patient can say who he is and where he is and when it is. A patient is considered to be in coma if the eyes remain closed, there are no motor responses on command, and no recognizable words are uttered — if all three of these conditions are satisfied, as well as the total score being 8 or less. At the lowest score of 3 the eyes are closed, the limbs show no response even to pain, and no sounds at all are made.

Coma is associated with loss of function in the arousal centre in the brain stem which is responsible both for eye opening and for activating the cerebral cortex, which has to be functioning for a person to be aware of self and surroundings. Some causes of coma temporarily affect the arousal mechanisms alone. These include normal doses of anaesthetic agents, overdoses of sedative drugs or alcohol, and a generalized epileptic seizure. Toxic body chemicals can also cause coma, due to disease in other organs, as a complication of diabetes, or of failure of kidney or liver function. More often coma is a feature of major structural insults in various parts of the brain, such as those resulting from severe head injury, brain haemorrhage, infection, tumour, or oxygen lack (either in part of the brain from a blocked blood vessel (stroke), or in the brain as a whole due to stoppage of the heart or the breathing). In all these conditions the development of coma is a sign that the condition is very serious and that there is much less likelihood of recovery than if coma had not occurred.

The person in coma is at immediate risk of obstruction of the airway, as the normal coughing reflex is depressed. Obstruction may come from the tongue falling back or from inhalation of vomited stomach contents. This complication, which can be fatal, is less likely to occur if as a first-aid measure the person is turned over with the face down — the so-called coma position. Paramedics or doctors will later deal more effectively with this threat by passing a tube through the nose or mouth into the trachea (endotracheal intubation), and artificial ventilation may be set up. Since a person in coma is unable to take food and fluids normally, if coma lasts more than 24 hours artificial feeding will be necessary to ensure survival. This may be by a tube in the stomach (passed through the mouth or nose), or by a infusion into a vein.

Recovery from coma depends on the cause. Chemically-caused coma with no other brain damage or complications can be followed by complete recovery. When there has been a major structural insult the rapidity of recovery and the degree of residual disability will depend on how much permanent brain damage has been caused. How long the coma lasts is often a good indication of how severe this damage is, but a good recovery is still possible when coma has lasted 2 or 3 weeks. On the other hand, severe brain damage can occur without the patient ever being in coma, for example after a severe stroke. In survivors of even the most severe brain damage, however, coma seldom lasts more than 3–4 weeks; the eyes then open and the patient passes into another state of reduced responsiveness such as the vegetative state. Press reports of patients in ‘coma’ for months or years are therefore misleading.

Bryan Jennett

Bibliography

Teasdale, G. and and Jennett, B. (1976). Assessment of coma and impaired consciousness. A practical scale. Lancet, 1, 1031.

coma State of unconsciousness brought about by head injury, brain disease, drugs, or lack of blood supply to the brain.