Coma, from the Greek word koma, meaning deep sleep, is a state of extreme unresponsiveness, in which an individual exhibits no voluntary movement or behavior. Furthermore, in a deep coma, even painful stimuli (actions which,when performed on a healthy individual, result in reactions) are unable to effect any response, and normal reflexes may be lost.

Coma lies on a spectrum with other alterations in consciousness. The level ofconsciousness required by, for example, someone reading this passage lies atone extreme the spectrum, whereas complete brain death lies at the other end. In between are such states as obtundation (dullness), drowsiness, and stupor. All of these are conditions which, unlike coma, still allow the person torespond to stimuli, although such a response may be brief and require stimulus of greater than normal intensity.

Consciousness is defined by two fundamental elements: awareness and arousal.Awareness allows people to take in and process all the information communicated by the five senses, and thus relate to themselves and to the outside world. Awareness has both psychological and physiological components. The psychological component is governed by a person's mind and mental processes. The physiological component refers to the functioning of a person's brain, and therefore that brain's physical and chemical condition. Awareness is regulated by cortical areas within the cerebral hemispheres, the outermost layer of the brain which separates humans from other animals by allowing for greater intellectual functioning.

Arousal is regulated solely by physiological functioning and consists of moreprimitive responsiveness to the world, for example, reflex (involuntary) responses to stimuli. Arousal is maintained by the reticular activating system (the RAS). This is not an anatomical area of the brain, but rather a network of structures (including the brainstem, the medulla, and the thalamus) and nerve pathways, which function together to produce and maintain arousal.

Coma is the result of something that interferes with the functioning of the cerebral cortex or the functioning of the structures which make up the RAS. Infact, a huge and varied number of conditions can result in coma. A good wayof categorizing these conditions is to consider the anatomic and metabolic causes of coma. Anatomic causes of coma are conditions that damage the brain structures responsible for consciousness, either at the level of the cerebal cortex or the brainstem, whereas metabolic causes of coma consist of those conditions that change the chemical environment of the brain, thereby adversely affecting function.

Metabolic causes of coma include a decrease in the delivery to the brain of substances necessary for appropriate brain functioning, such as oxygen, glucose (sugar), and sodium.

Drugs or alcohol in toxic quantities can disrupt the functioning of neurons,as can substances normally found in the body, but that, due to some diseasedstate, accumulate at toxic levels. Accumulated substances that might cause coma include ammonia due to liver disease, ketones due to uncontrolled diabetes, or carbon dioxide due to a severe asthma attack.

Coma may also be caused by changes in chemical levels in the brain due to theelectrical derangements caused by seizures (sudden attacks).

As in any neurologic condition (one that originates in the nervous system), history and examination form the cornerstone of diagnosis when the patient isin a coma; however, history must be obtained from family, friends, or mentalstatus examination. The Glasgow Coma Scale provides a means of examining a comatose patient. It assigns a different number of points for exam results in three different categories: opening the eyes, verbal response (using words orvoice to respond), and motor response (moving a part of the body). When performed as part of the admission examination, a Glasgow score of 3 to 5 points (out of a total of 15) often suggests that the patient has likely suffered fatal brain damage, whereas 8 or more points indicates that the patient's chances for recovery are good. Metabolic causes of coma are diagnosed from blood work and urinalysis to evaluate blood chemistry, drug screen, and blood cell abnormalities that may indicate infection. Anatomic causes of coma are diagnosed from CT (computed tomography scans) or MRI (magnetic resonance imaging) scans.

Coma is a medical emergency, and attention must first be directed to maintaining the patient's respiration and circulation, using intubation and ventilation, administration of intravenous fluids or blood as needed, and other supportive care. If head trama has not been excluded, the neck should be stablizedin the event of fracture. It is obviously extremely important for a physicianto determine quickly the cause of a coma, so that potentially reversible conditions are treated immediately. For example, an infection may be treated with antibiotics; a brain tumor may be removed; and brain swelling from an injury can be reduced with certain medications. Various metabolic disorders can beaddressed by supplying the individual with the correct amount of oxygen, glucose, or sodium; by treating the underlying disease in liver disease, asthma,or diabetes; and by halting seizures with medication. Because of their low incidence of side effects and potential for prompt reversal of coma in certainconditions, glucose, the B-vitamin thiamine, and Narcan (to counteract any narcotic-type drugs) are routinely given.

Some conditions that cause coma can be completely reversed, restoring the person to his or her original level of functioning. However, if areas of the brain have been sufficiently damaged due to the severity or duration of the condition which led to the coma, the person may recover from the coma with permanent disabilities, or may even never regain consciousness. Patients who have suffered head injuries tend to do better than do patients whose coma was caused by other types of medical illnesses. Leaving out those people whose coma followed drug poisoning, only about 15% of patients who remain in a coma for more than just a few hours make a good recovery. Adult patients who remain in acoma for more than four weeks have almost no chance of eventually regainingtheir previous level of functioning. On the other hand, children and young adults have regained functioning even after two months in a coma.

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