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

Just as blood takes up space within the skull and can cause coma, so may brain tumors. Brain tumors may be associated with localized swelling edema, inflammation and bleeding. Seizures, stroke-like symptoms, decreased mental status, and change in behavior may be the initial symptom.

While trauma can make the brain swell, other types of injury or insult can cause brain swelling (cerebral edema). Whether the insult is lack of oxygen, abnormal electrolytes, or hormones, it may ultimately result in edema of the brain tissue. As with bleeding, the skull limits the space available for brain swelling to occur. As a result, the brain tissue is damaged and its function decreases the more it is compressed against the bones of the skull.

Infection and inflammation, such as encephalitis and meningitis of the brain and surrounding tissues may be associated with coma. Encephalitis is an infection of the brain tissue itself, while meningitis is an infection of the linings surrounding the brain. Infections may also be associated with abscesses or collections of pus within the brain.

The brain requires oxygen to function; and without it the brain shuts down. There is a very short time to get oxygen back to brain tissue before there is permanent damage. Most research suggests that the time window is four to six minutes.

The body provides oxygen to the brain through the lungs. The lungs extract oxygen from the air, hemoglobin in red blood cells pick up the oxygen, and the heart pumps blood through normal blood vessels to cells in the body. If any part of the system fails, the oxygen supply to the brain can be interrupted.

The most common failure occurs with heart rhythm disturbances. The coordinated electrical beat of the heart is lost and the heart muscle doesn't squeeze blood adequately; no blood is pumped to the brain and it stops functioning almost immediately.

Lungs can also fail; examples include pneumonia, emphysema, or asthma. In each case, inflammation in the lung tubes (bronchi or bronchioles) or lung tissue makes it difficult for oxygen to get into the lungs and transferred into the blood stream. Hemoglobin also takes carbon dioxide, the waste product of metabolism, and returns it to the lungs to be exhaled. Elevated levels of carbon dioxide in the blood can affect brain function to cause coma.

Anemia, or low red blood cell count, can cause the brain to fail directly, or more likely it causes other organs like the heart to fail. The heart, like any other muscle requires oxygen to function. Anemia can occur chronically or it can be due to an acute blood loss (examples include trauma, bleeding from the stomach). If the blood loss is slow, the body is better able to adapt and tolerate low hemoglobin levels; if the bleeding occurs quickly, the body may be unable to compensate, the result being inadequate oxygen supply to tissues such as the brain.