What causes coma? 32 possible conditions
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A coma is a prolonged state of unconsciousness. A coma occurs when a part of the brain is damaged, either temporarily or permanently. This damage results in unconsciousness, an inability to awake, and unresponsiveness to stimuli such as pain, sound, and light. The word “coma” is derived from the Greek word “koma,” which means “deep sleep” (Koehler & Wijdicks, 2008).
Comas may be caused by an injury, an illness, a stroke, tumors, drugs, alcohol abuse, and other damage to the brain. A person who is in a coma is alive but is unable to move at will, think, speak, or respond to his or her environment. Important functions, such as breathing and blood circulation, remain intact.
A coma is a medical emergency. Doctors need to work quickly to preserve brain life and function, and to keep the patient healthy during the course of his or her coma. A coma may be challenging to diagnose and treat. A coma usually does not last for more than four weeks, and recovery occurs gradually. However, some patients have remained in comas for years or even decades.
Comas are caused by damage to the brain—specifically, either the diffused bilateral cerebral hemisphere cortex or the reticular activating system, which controls arousal and awareness (Adukauskiene et al, 2008). Comas can be caused by many factors, including head injuries, loss of oxygen, bleeding or pressure in the brain, infections, metabolic problems, and toxic factors. Some examples include:
- traumatic brain injuries, such as those caused by traffic accidents or violent fights
- stroke (reduced blood supply to the brain)
- tumors in the brain or brainstem
- lack of oxygen to the brain, such as when the patient is rescued from drowning or from a heart attack
- diabetes, when blood sugar levels become too high (hyperglycemia) or too low (hypoglycemia), which can lead to swelling in the brain
- overdosing on drugs or alcohol
- carbon monoxide poisoning
- buildup of toxins in the body, such as ammonia, urea, or carbon dioxide
- lead poisoning
- infections such as meningitis or encephalitis
- repeated seizures
- electrolyte imbalance
A coma is a medical emergency and requires immediate medical attention. Signs of a coma include:
- closed eyes
- irregular breathing
- no response of limbs, except for reflexes
- no response to pain, except for reflexes
- pupils not responding to light
People in a coma cannot speak or express themselves in other ways. Doctors must rely on information from loved ones or witnesses, and on any physical signs that may give information about what caused the coma.
A doctor will ask friends and family about any events or symptoms that led up to the coma, details about recent changes in the patient’s life, medical history, and drug-use, including prescription drugs and over-the-counter drugs, as well as recreational drugs.
A doctor will then conduct a physical exam. This might include:
- checking reflexes
- observing breathing patterns
- checking for signs of bruises on the skin that may have been caused by trauma
- determining the patient’s response to painful stimuli
- observing pupil size
Blood tests and other laboratory tests will be used to test for the following:
- blood count
- thyroid and liver function
- electrolyte levels
- carbon monoxide poisoning
- drug overdose
- alcohol overdose
- infections of the nervous system
Doctors may order tests that create images of the brain (brain scans), to locate areas of brain injury and look for signs of brain hemorrhage, tumors, strokes and seizures. These tests include:
- computerized tomography (CT) scans, which use X-rays to create a detailed image of the brain
- magnetic resonance imaging (MRI), which uses radio waves and magnets to view the brain; and
- electroencephalography (EEG), which measures electrical activity inside the brain
Doctors will work first to preserve brain life and function. Antibiotics may be given right away, in case there is an infection in the brain. If the cause of the coma is known, such as in the case of a drug overdose, doctors will administer proper medications to treat the underlying condition. Surgery may be required to reduce swelling in the brain.
Once the patient stabilizes, a team of medical professionals will work with the comatose patient to prevent infections, bedsores, and contractures of the muscles. The team will also make sure to provide the patient with balanced nutrition during his or her coma.
A coma usually does not last for more than four weeks. However, some people may remain in a coma for years. Long-term outcomes depend on what caused the coma and the site of damage to the brain. Prognosis is good for people whose comas are caused by a drug overdose. If the patient has suffered severe brain damage, he or she may never come out of the coma.
Some people emerge from a coma with physical, intellectual, or psychological problems. Patients who remain in a coma for more than a year are unlikely to come out of that state (Mayo, 2012). For these people, the most common cause of death is infection (NIH, 2013).
- Adukauskiene, D., Budryte, B. & Karpec, D. (2008). Coma: etiology, diagnosis, and treatment. Medicina (Kaunas), 44(10): 812-819. PMID: 19001840
- Coma. (2013). National Institutes of Health. Retrieved August 11, 2013, from http://www.nlm.nih.gov/medlineplus/coma.html
- Coma. (2012). The Mayo Clinic. Retrieved August 12, 2013, from http://www.mayoclinic.com/health/coma/DS00724
- Koehler, P.J., Wijdicks, E.F.M. (2008). Historical study of coma: looking back through medical and neurological texts. Brain, 131:877-889, doi:10.1093/brain/awm332
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