A coma is a state of prolonged unconsciousness that can be caused by a wide variety of problems — traumatic head injury, stroke, brain tumor, or even an underlying illness, such as diabetes or an infection.
A coma is a medical emergency. Swift action is needed to preserve life and brain function. Doctors typically order a battery of blood tests and brain scans to try to determine what’s causing the coma so that proper treatment can begin.
Comas seldom last longer than a few weeks. People who are unconscious for longer than that are usually reclassified as being in a persistent vegetative state. People who are in a persistent vegetative state for more than a year are extremely unlikely to awaken.
The signs and symptoms of a coma commonly include:
- Closed eyes
- No responses of limbs except for reflex movements
- No response to painful stimuli, except for reflex movements
Many types of problems can cause a coma. Some examples are:
- Traumatic brain injuries. Brain injuries that result from traffic collisions or acts of violence are the most common cause of comas.
- Stroke. Acute loss of blood flow to the brain followed by swelling or no blood flow to a major part of the brainstem can result in a coma.
- Diabetes. Blood sugar levels that get too high (hyperglycemia) and stay too high or get too low (hypoglycemia) and stay too low can cause coma.
- Lack of oxygen. People who have escaped drowning or been resuscitated after a heart attack may not awaken due to lack of blood flow and oxygen to the brain.
- Infections. Encephalitis and meningitis are infections that cause inflammation of the brain, spinal cord or the tissues that surround the brain. Severe cases of either encephalitis or meningitis can result in a coma.
- Toxins. Exposure to toxins, such as carbon monoxide or drug overdoses, can cause brain damage and coma.
Because people in a coma cannot express themselves, doctors must rely on physical clues and information provided by families and friends. Questions may include:
- Did the coma start abruptly or gradually?
- Were there problems with vision, dizziness or numbness beforehand?
- Any history of diabetes, seizures or strokes?
- What prescription or nonprescription drugs were used?
Doctors will check your reflexes, response to painful stimuli and pupil size. Squirting ice cold or warm water into the ear canals also can be informative. In unconscious people, these tests will cause reflexive eye movements of different types, depending on the cause of unconsciousness.
Blood samples will be taken to check for:
- Complete blood count
- Electrolytes, glucose and liver function
- Carbon monoxide poisoning
- Drug overdose
A spinal tap (lumbar puncture) can check for signs of infections. During a lumbar puncture procedure, a doctor inserts a needle into your spinal canal, measures the pressure and collects fluid for analysis. The entire procedure usually takes about 10 minutes.
Imaging tests help doctors pinpoint areas of brain injury. Tests may include:
- CT. A CT scan uses a sophisticated X-ray machine linked to a computer to produce detailed images of your brain. This is the best imaging test for assessing brain injuries because it can show a hemorrhage or brain tissue swelling. The scan takes only a few minutes.
- MRI. This scan uses magnetic fields and radio waves to generate images of the brain. You lie inside a cylindrical machine for 15 minutes to an hour. MRI scans are particularly useful for examining the brainstem and deep brain structures. Sometimes a special dye is injected into your bloodstream during the procedure. The dye can help distinguish damaged brain tissue from healthy tissue.
An EEG measures the electrical activity inside the brain. Small electrodes are attached to the scalp with paste or an elastic cap. The electrodes pick up the brain’s electrical impulses, which are recorded on the EEG machine. This test can determine if the person is having nonconvulsive seizures, which can cause comas.
A coma usually lasts only a few days or weeks. Although many people gradually recover, others enter a vegetative state or die.
Complications that may develop during a coma include pressure sores, bladder infections and pneumonia.
A coma is a medical emergency, and attention first is given to maintaining respiration and circulation. Assistance with breathing, administration of fluids and blood, and other supportive care may be necessary.
Emergency personnel may administer glucose or antibiotics intravenously, even before blood test results return, on the chance that the person is in diabetic shock or has an infection affecting the brain.
Treatment varies, depending on what’s causing the coma. Sometimes surgery is needed to relieve the pressure due to brain swelling. Other treatments may focus on addressing an underlying disease, such as diabetes, kidney failure or liver disease.
Sometimes the cause of a coma can be completely reversed, and the person will regain normal function. But if the brain damage is severe, the person may sustain permanent disabilities or may never regain consciousness.