Causes
Video of the man still nonresponsive to stimuli.Coma may result from a variety of conditions, including intoxication (such as drug abuse, overdose or misuse of over the counter medications, prescribed medication, or controlled substances), metabolic abnormalities, central nervous system diseases, acute neurologic injuries such as strokes or herniations, hypoxia, hypothermia, hypoglycemia or traumatic injuries such as head trauma caused by falls or vehicle collisions. It may also be deliberately induced by pharmaceutical agents in order to preserve higher brain functions following brain trauma, or to save the patient from extreme pain during healing of injuries or diseases.
Forty percent of comatose states result from drug poisoning. Drugs damage or weaken the synaptic functioning in the ARAS and keep the system from properly functioning to arouse the brain. Secondary effects of drugs, which include abnormal heart rate and blood pressure, as well as abnormal breathing and sweating, may also indirectly harm the functioning of the ARAS and lead to a coma. Seizures and hallucinations have shown to also play a major role in ARAS malfunction. Given that drug poisoning causes a large portion of patients in a coma, hospitals first test all comatose patients by observing pupil size and eye movement, through the vestibular-ocular reflex.
The second most common cause of coma, which makes up about 25% of comatose patients, occurs from lack of oxygen, generally resulting from cardiac arrest. The Central Nervous System (CNS) requires a great deal of oxygen for its neurons. Oxygen deprivation in the brain, also known as hypoxia, causes neuronal extracellular sodium and calcium to decrease and intracellular calcium to increase, which harms neuron communication. Lack of oxygen in the brain also causes ATP exhaustion and cellular breakdown from cytoskeleton damage and nitric oxide production.
Twenty percent of comatose states result from the side effects of a stroke. During a stroke, blood flow to the brain ceases. An ischemic stroke or hemorrhage may cause such cessation of blood flow. Lack of blood to cells in the brain prevents nutrients and oxygen from getting to the neurons, and consequently causes cells to die. As brain cells die, brain tissue continues to deteriorate, which may affect functioning of the ARAS.
The remaining 15% of comatose cases result from trauma, bleeding, malnutrition, hypothermia or hyperthermia, abnormal glucose levels, and many other biological disorders.
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