Coma is a state of prolonged unconsciousness that can be caused by a variety of problems — traumatic head injury, stroke, brain tumor, drug or alcohol intoxication, or even an underlying illness, such as diabetes or an infection.

Coma is a medical emergency. Swift action is needed to preserve life and brain function. Doctors normally order a series of blood tests and a brain scan to try to determine what's causing the coma so that proper treatment can begin.

A coma seldom lasts longer than several weeks. People who are unconscious for a longer time might transition to a persistent vegetative state or brain death.

The signs and symptoms of a coma commonly include:

• Closed eyes
• Depressed brainstem reflexes, such as pupils not responding to light
• No responses of limbs, except for reflex movements
• No response to painful stimuli, except for reflex movements
• Irregular breathing

When to see a doctor

A coma is a medical emergency. Seek immediate medical care for the person in a coma.

Many types of problems can cause a coma. Some examples are:

• Traumatic brain injuries. These are often caused by traffic collisions or acts of violence.
• Stroke. Reduced or interrupted blood supply to the brain (stroke), can result from blocked arteries or a burst blood vessel.
• Tumors. Tumors in the brain or brainstem can cause a coma.
• Diabetes. Blood sugar levels that become too high (hyperglycemia) or too low (hypoglycemia) can cause a coma.
• Lack of oxygen. People who have been rescued from drowning or those who have been resuscitated after a heart attack might not awaken due to lack of oxygen to the brain.
• Infections. Infections such as encephalitis and meningitis cause swelling of the brain, spinal cord or the tissues that surround the brain. Severe cases of these infections can result in brain damage or a coma.
• Seizures. Ongoing seizures can lead to a coma.
• Toxins. Exposure to toxins, such as carbon monoxide or lead, can cause brain damage and a coma.
• Drugs and alcohol. Overdosing on drugs or alcohol can result in a coma.

Although many people gradually recover from a coma, others enter a vegetative state or die. Some people who recover from a coma end up with major or minor disabilities.

Complications can develop during a coma, including pressure sores, urinary tract infections, blood clots in the legs and other problems.

Because people in a coma can't express themselves, doctors must rely on physical clues and information provided by families and friends. Be prepared to provide information about the affected person, including:

• Events leading up to the coma, such as vomiting or headaches
• Details about how the affected person lost consciousness, including whether it occurred suddenly or over time
• Noticeable signs or symptoms before losing consciousness
• The affected person's medical history, including other conditions he or she may have had in the past, such as a stroke or transient ischemic attacks
• Recent changes in the affected person's health or behavior
• The affected person's drug use, including prescription and over-the-counter medications as well as unapproved medications and illicit recreational drugs

Physical exam

The exam is likely to include:

• Checking the affected person's movements and reflexes, response to painful stimuli, and pupil size
• Observing breathing patterns to help diagnose the cause of the coma
• Checking the skin for signs of bruises due to trauma
• Speaking loudly or pressing on the angle of the jaw or nail bed while watching for signs of arousal, such as vocal noises, eyes opening or movement
• Testing reflexive eye movements to help determine the cause of the coma and the location of brain damage
• Squirting cold or warm into the affected person's ear canals and observing eye reactions

Laboratory tests

Blood samples will be taken to check for:

• Complete blood count
• Electrolytes, glucose, thyroid, kidney and liver function
• Carbon monoxide poisoning
• Drug or alcohol overdose

A spinal tap (lumbar puncture) can check for signs of infections in the nervous system. During a spinal tap, a doctor or specialist inserts a needle into the spinal canal and collects a small amount of fluid for analysis.

Brain scans

Imaging tests help doctors pinpoint areas of brain injury. Tests might include:

• CT scan. This uses a series of X-rays to create a detailed image of the brain. A CT scan can show a brain hemorrhage, tumors, strokes and other conditions. This test is often used to diagnose and determine the cause of a coma.
• MRI. This uses powerful radio waves and magnets to create a detailed view of the brain. An MRI can detect brain tissue damaged by an ischemic stroke, brain hemorrhages and other conditions. MRI scans are particularly useful for examining the brainstem and deep brain structures.
• Electroencephalography (EEG). This measures the electrical activity inside the brain through small electrodes attached to the scalp. Doctors send a low electrical current through the electrodes, which record the brain's electrical impulses. This test can determine if seizures might be the cause of a coma.

A coma is a medical emergency. Doctors will first check the affected person's airway and help maintain breathing and circulation. Doctors might give breathing assistance, intravenous medications and other supportive care.

Treatment varies, depending on the cause of the coma. A procedure or medications to relieve pressure on the brain due to brain swelling might be needed. Emergency personnel might administer glucose or antibiotics intravenously, even before blood test results return, in case of diabetic shock or an infection affecting the brain.

If the coma is the result of drug overdose, doctors will give medications to treat the condition. If the coma is due to seizures, doctors will use medications to control seizures. Other treatments might focus on medications or therapies to address an underlying disease, such as diabetes or liver disease.

Sometimes the cause of a coma can be completely reversed, and the affected person will regain normal function. Recovery usually occurs gradually. A person with severe brain damage might have permanent disabilities or never regain consciousness.

A coma is an emergency medical condition. If you are with a person who develops signs and symptoms of a coma, call 911 or your local emergency number immediately.

When you arrive at the hospital, emergency room staff will need as much information as possible from family and friends about what happened to the affected person before the coma. You might be asked the following questions while riding in the ambulance:

• Did the coma start abruptly or gradually?
• Were there problems with vision, dizziness or weakness beforehand?
• Does the affected person have a history of diabetes, seizures or strokes?
• Did you notice changes in the affected person's health in the time leading up to the coma, such as a fever or worsening headache?
• Did you notice changes in the affected person's ability to function in the time leading up to the coma, such as frequent falls or confusion?
• Did the affected person use prescription or nonprescription drugs?