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Unconsciousness may occur as the result of traumatic brain injury, brain hypoxia (inadequate oxygen, possibly due to a brain infarction or cardiac arrest), severe intoxication with drugs that depress the activity of the central nervous system (e.g., alcohol and other hypnotic or sedative drugs), severe fatigue, pain, anaesthesia, and other causes.
In medicine, a coma (from the Greek κῶμα koma, meaning deep sleep) is a state of unconsciousness, lasting more than six hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light, sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions.
Lack of blood to cells in the brain prevents oxygen from getting to the neurons, and consequently causes cells to become disrupted and die. As brain cells die, brain tissue continues to deteriorate, which may affect the functioning of the ARAS, causing unconsciousness and coma. [19]
Prolonged unconsciousness is understood to be a sign of a medical emergency. [3] A deficit in the level of consciousness suggests that both of the cerebral hemispheres or the reticular activating system have been injured. [4] A decreased level of consciousness correlates to increased morbidity (sickness) and mortality (death). [5]
If hypoxia results in coma, the length of unconsciousness is often indicative of long-term damage. In some cases coma can give the brain an opportunity to heal and regenerate, [34] but, in general, the longer a coma, the greater the likelihood that the person will remain in a vegetative state until death. [9]
Causes range from non-serious to potentially fatal. [1] There are three broad categories of causes: heart or blood vessel related; reflex, also known as neurally mediated; and orthostatic hypotension. [1] Issues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common. [1]
Reflex syncope can occur in otherwise healthy individuals, and has many possible causes, often trivial ones such as prolonged standing with the legs locked. [citation needed] The main danger of vasovagal syncope (or dizzy spells from vertigo) is the risk of injury by falling while unconscious.
The researchers found that in many nursing homes and hospitals unheated oxygen is given to non-responsive patients via tracheal intubation. This bypasses the warming of the upper respiratory tract and causes a chilling of aortic blood and chilling of the brain which the authors believe may contribute to the person's nonresponsive state.