Coma (cont.)
Swelling
While trauma can make the brain swell, other types of injury or insult can
cause cerebral edema (cerebral=brain + edema=swelling due to increased fluid).
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; thus the brain tissue is damaged
and its function decreases the more it is compressed against the bones of the
skull.
Lack of oxygen
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, a molecule in the red blood cell, attaches oxygen from the lungs
and delivers it to cells for use in metabolism. 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.
Next: Hypoglycemic coma »
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