Coma

Definition

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

Description

The important characteristics of the conscious state is defined by two fundamental elements: awareness and arousal.

Awareness allows one to receive and process all the information communicated by the five senses. Awareness has both psychological and physiological components. The psychological component refers to an individual's mind and mental processes. The physiological component refers to the functioning of an individual's brain, and the physical and chemical condition of the brain. Awareness is regulated by cortical areas within the cerebral hemispheres, the outermost layer of the brain.

Arousal is regulated solely by physiological functioning and consists of more primitive responsiveness to the world, as demonstrated by predictable reflex (involuntary) responses to stimuli. Arousal is maintained by the reticular activating system (RAS), a network of brain structures, including the brainstem, the medulla, and the thalamus, and nerve pathways that function together to produce and maintain arousal.

Causes and symptoms

Coma is the result of something that interferes with the functioning of the cerebral cortex and/or the functioning of the structures that comprise the RAS. Several conditions can result in coma. Anatomic causes of coma are those conditions that disrupt the brain structures responsible for consciousness, either at the level of the cerebral cortex or the brainstem, while metabolic causes of coma consist of those conditions that change the chemical environment of the brain, thereby adversely affecting function.

There are many metabolic causes of coma, including:

• a decrease in the delivery to the brain of substances necessary for appropriate brain functioning, such as oxygen, glucose (sugar), and sodium
• hyperglycemia, a condition in which blood sugar levels rise too high and remain dangerously high or hypoglycemia, in which blood sugar levels are too low and remain that way for a prolonged period of time.
• the presence of certain substances such as drugs, alcohol, carbon dioxide, and ketones that disrupt the functioning of neurons
• changes in chemical levels in the brain caused by seizures

Anatomic causes of coma include:

• Physical trauma to the brain as a result of a motor vehicle or sports related accident or a near drowning can result in coma. Such injuries usually involve trauma to the brain including fractures or lack of oxygen.
• A stroke or brain tumor. Although these conditions are not the result of physical trauma they nonetheless affect the brainstem. For instance, a coma often results when an individual suffers a stroke at the base of the brain.

Common signs and symptoms of a coma include:

• failure to be aroused
• eyes remain closed, however, in some cases the eyes move peculiarly
• no response to external stimuli

Diagnosis

History and examination form the cornerstone of diagnosis when an individual is in a coma. However, history must be obtained from family, friends, or emergency medical service personnel.

The Glasgow Coma Scale is a system of examining a comatose person. It evaluates the depth of the coma, tracks the person's progress, and predicts the ultimate outcome of the coma. The Glasgow Coma Scale assigns a different number of points for exam results in three different categories: opening the eyes, verbal response, and motor response (moving a part of the body). Fifteen is the largest possible number of total points, indicating the highest level of functioning, which would be demonstrated by individuals who spontaneously open their eyes, give appropriate answers to questions about their situations, and can carry out a command such as moving a specific limb when ordered. Three is the least possible number of total points, and would be given to a person for whom not even a painful stimulus is sufficient to provoke a response. In the middle are those people who may be

able to respond, but who require an intense or painful stimulus, and whose response may demonstrate some degree of brain malfunctioning. When performed as part of the admission examination, a Glasgow score of three to five points often suggests that an individual has likely suffered fatal brain damage, while eight or more points indicates that the person's chances for recovery are good.

Expansion of the pupils and respiratory pattern are also important. 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 computed tomography (CT), magnetic resonance imaging (MRI), or electroencephalography (EEG) scans.

Treatment

Coma is a medical emergency, and attention must first be directed to maintaining an individual's respiration and circulation, using intubation and ventilation, administration of intravenous fluids or blood as needed, and other supportive care. If head trauma has not been excluded, the neck should be stabilized in the event of fracture. It is extremely important for a physician to quickly determine the cause of a coma, so that potentially reversible conditions are immediately treated. These conditions may include an infection that can be treated with antibiotics , a brain tumor that can be removed, or brain swelling that can be reduced with certain medications.

Various metabolic disorders can be addressed by supplying an individual with the correct amount of oxygen, glucose, or sodium , by treating the underlying problem 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 certain conditions, glucose, the B-vitamin thiamine, and Narcan (to counteract any narcotic-type drugs) are routinely given.

Prognosis

Some conditions that cause coma can be completely reversed, restoring an individual to an original level of functioning. However, if areas of the brain have been sufficiently damaged due to the severity or duration of the condition that led to the coma, an individual may recover with permanent disabilities, either physical or mental, or may never regain consciousness. Short of death , the most severe types of brain injury result in states in which an individual loses all ability to function and remains deeply unresponsive. An individual who has suffered such a severe brain injury may remain in a coma indefinitely. This condition is termed a persistent vegetative state .

KEY TERMS

Anatomic —Related to the physical structure of an organ or organism.

Metabolic —Refers to the chemical processes of an organ or organism.

Narcan —A drug that reverses the effects of narcotics.

Neuron —The cells within the body which comprise the nervous system.

Reticular activating system (RAS) —A network of structures, including the brainstem, medulla, and thalamus, and nerve pathways, which function together to produce and maintain arousal.

Stimulus —Action performed on an individual that predictably provokes a reaction.

Outcome from a coma is therefore quite variable and depends a great deal on the cause and duration of the coma. In the case of drug poisonings, extremely high rates of recovery can be expected following prompt medical attention. Persons who have suffered head injuries tend to do better than do those whose coma was caused by medical illness. Besides those people whose coma results from drug poisoning, only about 15% of individuals who remain in a coma for more than just a few hours make a good recovery. Adult patients who remain in a coma for more than four weeks have almost no chance of eventually regaining their previous level of functioning. On the other hand, children and young adults have regained functioning after two months in a coma.

Caregiver concerns

Emergency medical team members are often first on the scene to provide a preliminary assessment of unconsciousness. In the hospital, a physician makes the diagnosis of coma, often with assistance from radiologists and laboratory technicians. Nurses provide supportive care throughout the duration of a coma. Physical therapists provide range of motion and other therapeutic movements designed to preserve normal muscular functioning.

Prevention

Medical conditions known to cause comas should be monitored and promptly treated. Applicable safety precautions and rules should be followed when engaging in any activity that has the potential for serious head injury .

Resources

periodicals

Dowdy, Mickey “A Comfortable Old Couch. (reflections) (Treating a patient from diabetic coma).” Diabetes Forecast 60.6 (May 2007): 80.

Mcauliffe, Kathleen “The Will To Live.” Prevention 59.8(August 2007): 182.

“Research Brief: Slow Therapy Best in Diabetic Coma. (Brief article).” GP (April 6 2007): 02.

organizations

American Academy of Neurology, 1080 Montreal Ave., St. Paul, MN, 55116, (651) 695–1940, (651) 695–2791, [email protected], http://www.aan.org.

Brain Injury Association, 105 North Alfred St., Alexandria, VA, 22314, (703) 236–6000, (800) 444–6443, [email protected], http://www.biausa.org/Sportsfs.htm.

Brain Trauma Foundation, 523 East 72nd St.,8th Floor, New York, NY, 10021, (212) 772–0608, http://www.braintrauma.org.

Coma Recovery Association, Republic Airport, Ste. 106, Farmingdale, NY, 11735, (631) 756–1826, http://www.comarecovery.org.

International Brain Injury Association, 1150 South Washington St., Ste. 210, Alexandria, VA, 22314, (703) 683–8400, [email protected], http://www.internationalbrain.org.

NIH Neurological Institute, PO Box 5801, Bethesda, MD, 20824, (800) 352–9424, http://www.ninds.nih.gov.

L. Fleming Fallon Jr., M.D., Dr.P.H.

Lisa M. Piazza M.A.