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In whatever disease sleep is laborious, it is a deadly symptom; but if sleep does good, it is not deadly.
HIPPOCRATES
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The state of arousal is determined by the function of the central reticular formation, which extends from the brain stem to the thalamus. Coma occurs when this centre is damaged by a metabolic abnormality or by an invasive lesion that compresses this centre. Coma is also caused by damage to the cerebral cortex.1
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The word ‘coma’ is derived from the Greek koma, which means deep sleep. The deeply unconscious patient is not in a deep sleep. Coma is best defined as ‘lack of self-awareness’.2
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The various levels of consciousness are summarised in TABLE 75.1; the levels vary from consciousness, which means awareness of oneself and the surroundings in a state of wakefulness,3 to coma, which is a state of unrousable unresponsiveness. Rather than using these broad terms in clinical practice it is preferable to describe the actual state of the patient in a sentence.
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Key facts and checkpoints
Always consider hypoglycaemia or opioid overdose in any unconscious patient, especially of unknown background.
If a patient is unconscious and cyanosed, consider upper airway obstruction until proved otherwise.
The commonest causes of unconsciousness encountered in general practice are reflex syncope, especially postural hypotension, concussion and cerebrovascular accidents (CVAs). The main causes are presented in TABLE 75.2.
Do not allow the person who accompanies the unconscious patient to leave until all relevant details have been obtained.
Record the degree of coma as a baseline to determine improvement or deterioration.