coma

coma,

in medicine, deep state of unconsciousness from which a person cannot be aroused even by painful stimuli. The patient cannot speak and does not respond to command. Coma is the result of damage to the brain stembrain stem,
lower part of the brain, adjoining and structurally continuous with the spinal cord. The upper segment of the human brain stem, the pons, contains nerve fibers that connect the two halves of the cerebellum.
..... Click the link for more information. and cerebrum that may be caused by severe head or brain injury, cardiac arrest, strokestroke,
destruction of brain tissue as a result of intracerebral hemorrhage or infarction caused by thrombosis (clotting) or embolus (obstruction in a blood vessel caused by clotted blood or other foreign matter circulating in the bloodstream); formerly called apoplexy.
..... Click the link for more information. , diabetesdiabetes
or diabetes mellitus
, chronic disorder of glucose (sugar) metabolism caused by inadequate production or use of insulin, a hormone produced in specialized cells (beta cells in the islets of Langerhans) in the pancreas that allows the body to use and store
..... Click the link for more information. , drug overdose, shockshock,
any condition in which the circulatory system is unable to provide adequate circulation to the body tissues, also called circulatory failure or circulatory collapse. Shock results in the slowing of vital functions and in severe cases, if untreated, in death.
..... Click the link for more information. , or hemorrhagehemorrhage
, escape of blood from the circulation (arteries, veins, capillaries) to the internal or external tissues. The term is usually applied to a loss of blood that is copious enough to threaten health or life.
..... Click the link for more information. . It occurs just before death in many diseases. There are various depths of coma; the nature of the injury determines the level of supportive treatment necessary (see artificial life supportartificial life support,
systems that use medical technology to aid, support, or replace a vital function of the body that has been seriously damaged. Such techniques include artificial pacemakers, internal defibrillators, dialysis machines (see kidney, artificial), and
..... Click the link for more information. ). Survival and prognosis depend upon the cause, extent of damage, and duration of the coma.

The term persistent vegetative state was coined in 1972 to describe an unconscious state in which sleep and wake cycles remain and eyes may open, but there is no thinking, feeling, or awareness of one's surroundings (although one may react reflexive to certain stimulations). The brain stem is usually relatively intact but the cerebral cortex is severely impaired. It is this state that sometimes results from resuscitation and life support of people who otherwise would have died; partial emergence from such a state sometimes occurs with a year or two, but not after that.

coma,

in astronomy: see cometcomet
[Gr.,=longhaired], a small celestial body consisting mostly of dust and gases that moves in an elongated elliptical or nearly parabolic orbit around the sun or another star. Comets visible from the earth can be seen for periods ranging from a few days to several months.
..... Click the link for more information. .

Coma due to concave mirror

coma

(koh -mă) 1. The most obvious part of a comet when it is close to the Sun. It consists of a diffuse luminous nebulous cloud of gas and dust that surrounds the comet's nucleus and is formed by the sublimation of ices and ejection of dust particles from the nucleus. The brightest part of the coma is the central region nearest the surface of the nucleus, where the density of material being released is at its highest; the gas density in this region is typically 10¹³ molecules per cm³. The visual boundary of the coma merges with the sky background. A coma's size varies with the comet's distance from the Sun and with the amount of material being released from the nucleus but can grow to typically 10⁴ to 10⁵ km in diameter. The luminosity of the coma is mainly produced by fluorescence from a variety of carbon, nitrogen, hydrogen, and oxygen radicals and reflection of sunlight by dust particles. The shape seems roughly circular but fan-shaped comas have been reported. The material comprising the coma is extremely rarefied: even faint stars shine through.

Coma

a life-threatening condition characterized by loss of consciousness, severe decrease or absence of reaction to external stimuli, extinction of reflexes (to the point of complete disappearance), disturbance of the depth and frequency of respiration, change in vascular tonus, acceleration or deceleration of the pulse, and upset of temperature regulation.

Coma is a consequence of deep inhibition in the cerebral cortex extending to the subcortex and lower sections of the central nervous system, as a result of acute disruption of blood circulation in the brain, head injury, inflammation (encephalitis, meningitis, malaria), intoxication (barbiturates, carbon monoxide), diabetes mellitus, uremia (urémic coma), and hepatitis (hepatic coma). In addition, there is disruption of the acid-base equilibrium in nervous tissue, oxygen starvation, disturbances of ion exchange, and energy starvation in the nerve cells. A precomatose state, during which the symptoms indicated develop, precedes coma. The condition can be treated by eliminating the primary causes of the coma and taking measures aimed at restoring the acid-base balance, reversing collapse, restoring respiration, and combating oxygen starvation.

Coma

an aberration of optical systems in which each part of the system at a distance d (circular zone) from the axis gives the image of a luminous point as a ring with a radius that increases as d increases; the centers of the rings are not coincident, so that their superposition, that is, the image of the point produced by the system as a whole, takes the form of an asymmetrical, diffuse spot (see Figure 1).

Figure 1. Coma in a simple optical system passing a beam of parallel rays: (a) beam, passing through the center of the system at angle w, intersects the focal plane FF’ at point O; rays traversing the system at points A₁, A₁, A₂, A₂, . . . , which are symmetrical with respect to the axis, are not collected by the system at point O in plane FF’, but rather at points O₁ O₂, . . . , at a distance from O proportional to dP (d being the distance from the axis at which a ray intersects the system); (b) the diffuse spot observed in the focal plane instead of point image O

The size of this spot is proportional to the square of the aperture angle of the system and the distance of the point-object from the system’s axis. The coma is very large with parabolic mirrors; it is, in fact, the principal factor limiting their visual field (see Figure 2). In complicated optical systems, coma is usually corrected together with spherical aberration by matching lenses. If one of the lens surfaces is off-center when a system is assembled, coma will also distort the images of points located on the system’s axis.

Figure 2. Coma effect with a parabolic mirror

Coma

a tuft of simple or pinnate hairs at the apex or base of the seeds of certain plants, for example, the willow herb. The coma is an outgrowth of the seed coat, or testa. It promotes distribution of seeds and fruits by means of wind, water, and animals.

coma

[′kō·mə] (astronomy) The gaseous envelope that surrounds the nucleus of a comet. Also known as head. (electronics) A cathode-ray tube image defect that makes the spot on the screen appear comet-shaped when away from the center of the screen. (medicine) Unconsciousness from which the patient cannot be aroused. (optics) A manifestation of errors in an optical system, so that a point has an asymmetrical image (that is, appears as a pear-shaped spot).

coma

¹ a state of unconsciousness from which a person cannot be aroused, caused by injury to the head, rupture of cerebral blood vessels, narcotics, poisons, etc.

coma

²1. Astronomy the luminous cloud surrounding the frozen solid nucleus in the head of a comet, formed by vaporization of part of the nucleus when the comet is close to the sun 2. Botanya. a tuft of hairs attached to the seed coat of some seeds b. the terminal crown of leaves of palms and moss stems 3. Optics a type of lens defect characterized by the formation of a diffuse pear-shaped image from a point object

coma

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 behavior. Furthermore, in a deep coma, even painful stimuli (actions which, when performed on a healthy individual, result in reactions) are unable to affect any response, and normal reflexes may be lost.

Description

Coma lies on a spectrum with other alterations in consciousness. The level of consciousness required by, for example, someone reading this passage lies at one extreme end of the spectrum, while complete brain death lies at the other end of the spectrum. In between are such states as obtundation, drowsiness, and stupor. All of these are conditions which, unlike coma, still allow the individual to respond to stimuli, although such a response may be brief and require stimulus of greater than normal intensity.In order to understand the loss of function suffered by a comatose individual, it is necessary to first understand the important characteristics of the conscious state. Consciousness is defined by two fundamental elements: awareness and arousal.Awareness allows one to receive and process all the information communicated by the five senses, and thus relate to oneself and to the outside world. Awareness has both psychological and physiological components. The psychological component is governed by an individual's mind and mental processes. The physiological component refers to the functioning of an individual'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 that separates humans from other animals by allowing for greater intellectual functioning.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). 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.

Causes and symptoms

Coma, then, is the result of something that interferes with the functioning of the cerebral cortex and/or the functioning of the structures which make up the RAS. In fact, a huge and varied number of conditions can result in coma. 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, either at the level of the cerebal 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.
The presence of certain substances that disrupt the functioning of neurons. Drugs or alcohol in toxic quantities can result in neuronal dysfunction, as can substances normally found in the body, but that, due to some diseased state, 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.
The changes in chemical levels in the brain due to the electrical derangements caused by seizures.

Diagnosis

As in any neurologic condition, history and examination form the cornerstone of diagnosis when the patient is in a coma; however, history must be obtained from family, friends, or EMS. The Glasgow Coma Scale is a system of examining a comatose patient. It is helpful for evaluating the depth of the coma, tracking the patient's progress, and predicting (somewhat) 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 (using words or voice to respond), and motor response (moving a part of the body). Fifteen is the largest possible number of total points, indicating the highest level of functioning. The highest level of functioning would be demonstrated by an individual who spontaneously opens his/her eyes, gives appropriate answers to questions about his/her situation, and can carry out a command (such as "move your leg" or "nod your head"). Three is the least possible number of total points and would be given to a patient for whom not even a painful stimulus is sufficient to provoke a response. In the middle 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 (such as a person whose only response to pain in a limb is to bend that limb in toward the body). When performed as part of the admission examination, a Glasgow score of three to five points often suggests that the patient has likely suffered fatal brain damage, while eight or more points indicates that the patient'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 CT (computed tomography) or MRI (magnetic resonance imaging) scans.

Treatment

Coma is a medical emergency, and attention must first be directed to maintaining the patient's respiration and circulation, using intubation aand ventilation, administration of intravenous fluids or blood as needed, and other supportive care. If head trama has not been excluded, the neck should be stablized in the event of fracture. It is obviously extremely important for a physician to 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 be addressed by supplying the individual

The four brain conditions that result in coma. (Illustration by Hans & Cassady.)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 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 the individual 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 individual may recover from the coma with permanent disabilities, or may even never regain consciousness. Take, for example, 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 resulted in further pressure on areas of the brain, an individual may regain consciousness, but may have some degree of impairment. The impairment may be physical (such as paralysis of a leg) or may even result in a change in the individual's intellectual functioning and/or personality. The most severe types of brain injury, short of death, result in states in which the 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 persistent vegetative state.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. 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. Those adult patients who remain in a coma for greater 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 even after two months in a coma.

Resources

Organizations

American Academy of Neurology. 1080 Montreal Ave., St. Paul, MN 55116. (612) 695-1940. http://www.aan.com.Coma Recovery Association, Inc. 570 Elmont Rd., Suite 104, Elmont, NY 11003. (516) 355-0951.

Key terms

Anatomic — Related to the physical structure of an organ or organism.Metabolic — Refers to the chemical processes of an organ or organism.Neuron — The cells within the body which make up the nervous system, specifically those along which information travels.Physiological — Pertaining to the functioning of an organ, as governed by the interactions between its physical and chemical conditions.Psychological — Pertaining to the mind, its mental processes, and its emotional makeup.Stimulus/stimuli — Action or actions performed on an individual which predictably provoke(s) a reaction.

coma

[ko´mah] a state of unconsciousness from which the patient cannot be aroused, even by powerful stimuli. Traumatic brain injuries are the most frequent cause; other causes include severe uncontrolled diabetes mellitus, liver disease, kidney disease, and neurologic conditions. Evaluation of a patient in a coma is comprehensive. The underlying cause should be identified so that appropriate treatment can be initiated. magnetic resonance imaging, electroencephalography, and potentials" >brainstem auditory evoked potentials give information about electrical activity of the brain in a patient who is comatose, although the results are not predictive of recovery. Some patients are able to emerge from a coma. In others, the coma may progress to a state" >persistent vegetative state in which the functions of the brainstem and circulation remain relatively intact or may be supported with assistive technologies. Patients in irreversible coma may meet the criteria of brain death.

Schematic representation of major brain stem reflexes used in coma examination. From Marx et al., 2002.Patient Care. Assessment of the patient in a coma includes an evaluation of vital signs, determination of level of consciousness, neuromuscular responses, and reaction of the pupils to light. In most hospitals a standard form is used to measure and record the patient's responses to stimuli in objective terms. The glasgow coma scale is a standardized tool that aids in assessing a comatose patient and eliminates the use of ambiguous and easily misinterpreted terms such as unconscious and semicomatose. Additional assessment data are gathered relating to the underlying cause and the patient's immobility; these include evaluation of the gag and corneal reflexes. In the absence of gag reflex, regurgitation and aspiration are potential problems.
Abnormal rigidity and posturing in response to noxious stimuli are motor responses to coma. Decorticate rigidity is abnormal flexor posturing, with the arms, wrists, and fingers drawn up. The legs may be extended with plantar flexion. This type of rigidity usually indicates a lesion in the cerebral hemispheres or a disruption of the corticospinal tracts. Decerebrate rigidity is abnormal extensor posturing: in response to painful stimuli the extremities extend rigidly and the palms turn outward. This type of rigidity is indicative of damage to the brainstem and as a rule is a sign of greater cerebral impairment than is decorticate rigidity.
Comatose patients are predisposed to all the hazards of immobility, including impairment of skin integrity and development of pressure ulcers and contractures. A multidisciplinary, coordinated plan of care is essential. Families should be encouraged to be actively involved in care of the patient. The health care team should also recognize the family's need for support; the emotional and financial impacts of coma are usually significant.alcoholic coma coma accompanying severe alcoholic intoxication.alpha coma coma in which there are electroencephalographic findings of dominant alpha-wave activity.diabetic coma the coma of severe acidosis" >diabetic acidosis; see also diabetes mellitus.hepatic coma coma accompanying cerebral damage resulting from degeneration of liver cells, especially that associated with cirrhosis of the liver.hyperglycemic hyperosmolar nonketotic coma (hyperosmolar nonketotic coma) see hyperglycemic hyperosmolar nonketotic coma.irreversible coma brain death.Kussmaul's coma the coma and air hunger of acidosis" >diabetic acidosis.myxedema coma an often fatal complication of long-term hypothyroidism in which the patient is comatose with hypothermia, depression of respiration, bradycardia, and hypotension; usually seen in elderly patients during cold weather.coma vigil locked-in syndrome.

co·ma

(kō'mă), 1. A state of profound unconsciousness from which one cannot be roused; may be due to the action of an ingested toxic substance or of one formed in the body, to trauma, or to disease. 2. An aberration of spheric lenses; occurring in cases of oblique incidence (for example, the image of a point becomes comet shaped). 3. Synonym(s): coma aberration

coma

(kō′mə)n. pl. co·mas A state of deep, often prolonged unconsciousness, usually the result of injury, disease, or poison, in which an individual is incapable of sensing or responding to external stimuli and internal needs.

(1) COMA
Combining Monteplase with Angioplasty. A trial comparing direct PTCA to PTCA + prior mutant t-PA-monteplase in patients with acute MI
Conclusion Angiographic restenosis rates were significantly lower with monteplase in this very small study
(2) Coma
A state of unarousable unconsciousness; a sleep-like state
Aetiology Head injury, neurologic disease, acute hydrocephaly, intoxication or metabolic derangement or hypoglycemia

coma

Neurology A state of unarousable unconsciousness; a sleep-like state; not conscious Etiology Head injury, neurologic disease, acute hydrocephaly, intoxication or metabolic derangement or hypoglycemia. See Barbiturate coma, Diabetic coma, Induced pentobarbital coma, Pseudocoma.

co·ma

(kō'mă) 1. A state of profound unconsciousness from which one cannot be roused; may result from trauma, disease, or the action of an ingested toxic substance or of one formed in the body. [G. kōma, deep sleep] 2. An aberration of spheric lenses; occurring in cases of oblique incidence (e.g., the image of a point becomes comet-shaped). [G. komē, hair] 3. Synonym(s): coma aberration. [G. kōma, deep sleep, trance]

coma

A state of deep unconsciousness from which the affected person cannot be aroused even by strong stimulation. Coma can result from head injury, oxygen lack, interruption of the blood supply to the brain, poisoning and various disease states such as those occurring in uncontrolled diabetes, liver failure and kidney failure.

coma

a tuft of hairs attached to the testa of a seed and used in wind dispersal.

coma

Monochromatic aberration of an optical system produced when the incident light beam makes an angle with the optical axis. The image appears like a comet with the tail pointing towards the axis. See aplanatic lens; sine condition.

co·ma

(kō'mă) Profound unconsciousness from which one cannot be roused; may be due to the action of an ingested toxic substance or of one formed in the body, to trauma, or to disease. [G. kōma, deep sleep, trance]

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Definition

Description

Causes and symptoms

Diagnosis

Treatment

Prognosis

Resources

Organizations

Key terms

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Synonyms for coma

noun unconsciousness

Synonyms

Synonyms for coma

noun a state of deep and often prolonged unconsciousness

Synonyms

Related Words

noun (botany) a usually terminal tuft of bracts (as in the pineapple) or tuft of hairs (especially on certain seeds)

Related Words

noun (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet

Related Words

co·ma¹

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coma²