Coma

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Coma

The ethical dilemma presented by persistent coma

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. In a deep coma, stimuli, even painful stimuli, are unable to effect any response. Normal reflexes may be lost.

Coma lies on a spectrum with other alterations in consciousness. The level of consciousness that readers of this article are currently enjoying is at one end of the spectrum, while complete brain death is at the other end of the spectrum. In between are such states as obtundation, drowsiness, and stupor, which all allow the individual to respond to stimuli, though such response may be brief and require a stimulus of greater than normal intensity.

Consciousness

In order to understand the loss of function suffered by a comatose individual, consider the important characteristics of the conscious state. Consciousness is defined by two fundamental elements: awareness and arousal.

Awareness allows humans to receive and process information communicated by the five senses and thereby relate to themselves and the rest of the world.

Awareness has psychological and physiological components. The psychological component is governed by an individual’s mind and its mental processes. The physiological component refers to the functioning— the physical and chemical condition—of an individual’s brain. Awareness is regulated by areas within the cerebral hemispheres, the outermost layer of the brain, which separates humans from other animals because it allows greater intellectual functioning.

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

Causes of coma

Coma is the result of something which interferes with the functioning of the cerebral cortex and/or the functioning of the structures that make up the RAS. The number of conditions that 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 that disrupt the normal physical architecture of the brain structures responsible for consciousness. Metabolic causes of coma consist of those conditions that change the chemical environment of the brain and thereby adversely affect 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 that 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 that 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, that accumulate at toxic levels due to some disease state. 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. (3) The changes in chemical levels in the brain due to the electrical derangements caused by seizures.

Outcome

It is extremely important for a physician to quickly determine 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. Furthermore, various metabolic disorders can be addressed 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.

Some conditions that cause coma can be completely reversed, restoring the individual to his or her original level of functioning. However, if areas of the brain have been sufficiently damaged because of the severity or duration of the condition that led to the coma, the individual may recover from the coma with permanent disabilities, or may never regain consciousness. Take the situation of someone whose coma was caused by brain injury in a car accident. Such an injury can result in one of three outcomes. In the event of a less severe brain injury, with minimal swelling, an individual may indeed recover consciousness and regain all of his or her original abilities. In the event of a more severe brain injury, with swelling that results in further pressure on areas of the brain, an individual may regain consciousness, but with some degree of impairment. The impairment may be physical, such as paralysis of a leg, or result in a change in the individual’s intellectual functioning and/or personality. The most severe types of brain injury result in states in which the individual loses all ability to function and remains deeply unresponsive. An individual who has suffered such a brain injury may remain in a coma indefinitely.

Outcome from a coma depends on its cause and duration. In drug poisonings, extremely high rates of recovery can be expected, following prompt medical attention. Patients who have suffered head injuries tend to do better than patients whose coma was caused by other types of medical illnesses. Excluding drug-poisoning induced comas, only about 15% of patients who remain in a coma for more than a few hours make a good recovery. Adult patients who remain in a coma for more than four weeks have almost no chance of regaining their previous level of functioning. However, children and young adults have regained functioning after two months in a coma.

Glasgow coma scale

The Glasgow Coma Scale, a system of examining a comatose patient, can be helpful for evaluating the depth of the coma, tracking the patient’s progress, and possibly predicting ultimate outcome of the coma. The Glasgow Coma Scale assigns a different number of points for examination results in three different categories: opening the eyes, verbal response (using words or voice to respond), and motor response (moving a part of the body). Fifteen indicates the highest level of functioning. An individual who spontaneously opens his or her eyes, gives appropriate answers to questions about his or her situation, and can follow a command (such as “move your leg,” “nod your head”) has the highest level of functioning. Three is the smallest possible number of points, and would be given to a patient who is unresponsive to a painful stimulus. In the middle range are those patients 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 suggests that the patient likely has suffered fatal brain damage, while eight or more points indicates that the patient’s chances for recovery are good.

The ethical dilemma presented by persistent coma

When a patient has not suffered brain death (the complete absence of any electrical activity within the brain) but has been in a deep coma for some time, a change in condition may occur. This condition is called a persistent vegetative state. The patient may open his or her eyes and move his or her limbs in a

KEY TERMS

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

Ethical— Referring to a system of values that provides the criteria for right behavior.

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

Neuron— The cells within the body that make up the nervous system.

Physiological— Pertaining to the functioning of an organ, as governed by its physical and chemical condition.

Psychological— Pertaining to the mind and its mental processes.

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

primitive fashion, demonstrating some degree of arousal. However, the patient lacks any element of awareness and is unable to have any measurably meaningful interactions with the surrounding world. This condition may last for years. The care of these patients has sparked some of the most heated debates within the field of medical ethics. The discovery of medical advances that allow various disease states to be arrested, without restoration of lost brain function, and the fact that medical resources are limited, have led to debates regarding when medical help should be withdrawn from an individual who has no hope of recovery.

See also Brain; Nervous system; Neuron; Psychology; Stimulus.