Coma (cont.)

Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

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.

View Full Profile

Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

View Full Profile

In this Article

• What is a "coma"?
• What is the Glasgow Coma Scale?
• What are the causes of a coma?
• Trauma
• Bleeding (Hemorrhage)
• Epidural, subdural, and subarachnoid hemorrhages
• Tumors
• Swelling
• Infection
• Lack of oxygen
• Hypoglycemic coma
• Poisons
• How is coma assessed?
• What tests are there for coma?
• What is the outcome and prognosis for a patient in a coma?
• Induced Coma
• Patient Comments: Coma - Cause
• Coma Index

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

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 makes insulin and balances the amount it produces with the amount of glucose in the blood stream. Diabetics need to inject insulin into their body, or take medication to stimulate the pancreas to make insulin. Monitoring blood sugars is critical to avoid hypoglycemic coma.

There are two sources of poisons that can affect the brain, those that we take in (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 can cause brain cells to stop functioning. Hepatic encephalopathy (hepatic=liver + encephalo=brain + pathy=disease) or hepatic coma occurs when the liver fails because of an acute or chronic injury. The most common cause is cirrhosis due to alcoholism.

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. An example of indirect causes would be an elevated potassium level affecting heart electrical activity. 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 and high blood pressure.

The thyroid acts as the thermostat for the body and regulates the speed at which the body functions. If thyroid levels gradually drop too low over a period of time myxedema coma can occur because of 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 potentially 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 can cause similar slowing of brain function.

Cocaine and amphetamines are the common "uppers" or brain stimulants. These brain stimulants cause an adrenaline-like body response, thus blood pressure and heart rate spiral out of control and the risk of heart attack, heart rhythm disturbances, or bleeding in the brain are increased.