Coma (Medical)

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Hypoglycemic coma

All cells in the body need glucose and oxygen to perform their functions by aerobic (oxygen requiring) metabolism. While other parts of the body can continue for short periods of time without these two nutrients (anaerobically), the brain cannot. Without glucose, brain function stops almost immediately.

Hypoglycemia (low blood sugar) most often occurs in people with diabetes who have given themselves too much insulin or have not taken in enough food.

In normal physiology, the pancreas produces insulin and balances the amount it produces with the amount of glucose in the blood stream. People with diabetes need to inject insulin into their body, or take medication to stimulate the pancreas to make insulin. If too much insulin is injected, glucose levels in the blood stream decrease, and not enough glucose is delivered for the brain cells to function. While tight control of blood glucose levels is important to prevent the long term complications of diabetes, including heart disease, peripheral vascular disease, blindness, and kidney failure; close monitoring is also required to prevent hypoglycemic coma.

People who do not have diabetes also may have low blood sugar because of situation where too much insulin is abnormally secreted by the pancreas when it is not needed.


There are two sources of poisons that can affect the brain, those that we take into the body (through ingestion or inhaling), and those that the body generates and cannot dispose of in some way.

If the body can be considered a factory, it needs to have the ability to get rid of the waste products that are made when the body generates energy. These waste products can cause different organs in the body to fail, including the brain.

The liver performs many functions including glucose and protein manufacturing. It also breaks down and metabolizes chemicals in the body. When the liver fails, different chemicals like ammonia can accumulate and are potentially toxic to the brain cell function. Hepatic encephalopathy or hepatic coma occurs when the liver fails because of an acute or chronic injury. The most common cause is cirrhosis due to chronic alcohol abuse.

The kidneys filter blood to rid the body of waste products. When the kidneys fail, a variety of waste products can accumulate in the bloodstream and cause direct or indirect damage to the brain. Direct causes include uremia, where blood urea levels rise and are directly toxic to brain cells. Common causes of kidney failure include poorly controlled diabetes or poorly controlled high blood pressure.

The thyroid acts as the thermostat for the body, producing thyroid hormone to regulate the speed at which the body functions. If thyroid hormone levels gradually drop too low over a period of time myxedema coma can occur because of the profound hypothyroidism.

Ingestions can cause the brain to slow down, speed up or alter its perception of the world. Some ingestions may cause coma in an indirect way. Acetaminophen overdose has a delayed effect. It is directly toxic to the liver, but takes a few days before liver failure occurs, leading to hepatic coma and the potential of death.

Alcohol is probably the most common cause of ingested poison or toxin, leading to altered mental status and coma. In acute alcohol intoxication, the brain is directly poisoned. Blood alcohol levels fall when the alcohol is metabolized by the liver, but depth of intoxication can be so great it shuts off many of the involuntary brain activities that control breathing and maintain muscle function. Opiates like pain pills or heroin, and other sedatives like sleeping pills can cause similar slowing of brain function to the point that the person stops breathing.

Cocaine and amphetamines are the common "uppers" or brain stimulants. These brain stimulants cause an adrenaline-like body response that causes a rise in blood pressure and heart rate, increasing the risk of heart attack, heart rhythm disturbances, or bleeding in the brain.

Medically Reviewed by a Doctor on 3/11/2016

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