Coma

Coma is the result of something which interferes with the functioning of the cerebral cortex and/or the functioning of the structures which make up the RAS. The number of conditions which could result in coma is mind-boggling. A good way of categorizing these conditions is to consider the anatomic and the metabolic causes of coma. Anatomic causes of coma are those conditions which disrupt the normal physical architecture of the brain structures responsible for consciousness. Metabolic causes of coma consist of those conditions which change the chemical environment of the brain and thereby adversely affecting function.

Anatomic causes of coma include brain tumors, infections, and head injuries. All three types of condition can affect the brain's functioning by actually destroying brain tissue. They may also affect the brain's functioning by taking up too much space within the skull. The skull is a very hard, bony structure which is unable to expand in size. If something within the skull begins to require more space (for example an expanding tumor or an injured/infected area of the brain which is swelling) other areas of the brain are compressed against the hard surface of the skull, which results in damage to these areas.

There are many metabolic causes of coma, including the following: (1) A decrease in the delivery of substances necessary for appropriate brain functioning, such as oxygen, glucose, and sodium. (2) The presence of certain substances disrupting the functioning of neurons. Drugs or alcohol in toxic quantities can result in neuronal dysfunction, as can some substances normally found in the body, but which accumulate at toxic levels due to some disease state. Accumulated substances which might cause coma include ammonia due to liver disease, ketones due to uncontrolled diabetes, or carbon dioxide due to a severe asthma attack. (3) The changes in chemical levels in the brain due to the electrical derangements caused by seizures.

The four brain conditions that result in coma. Illustration by Hans & Cassidy. Courtesy of Gale Group.