Stupor is unresponsiveness from which a person can be aroused only by vigorous, physical stimulation. Coma is unresponsiveness from which a person cannot be aroused.
Normally, the brain can quickly adjust its own levels of activity and consciousness as needed. The brain makes these adjustments based on information it receives from the eyes, ears, skin, and other sensory organs. For example, the brain can decrease its metabolic activity and induce sleep.
Whether a person is awake (wakefulness) is controlled by the upper part of the brain stem through a system of nerve cells and fibers (the reticular activating system—see Brain Stem). The cerebrum (the largest part of the brain) interacts with the upper part of the brain stem to maintain consciousness and alertness. The cerebrum consists of two parts (the right and left hemispheres). At least one hemisphere, as well as the reticular activating system, must be functioning normally to maintain consciousness.
The brain's ability to adjust its activity and consciousness levels can be impaired in several ways:
Periods of impaired consciousness can be short or long. The degree of impairment can range from slight to severe:
The various levels of impaired consciousness—lethargy, obtundation, stupor, and coma—have the same causes, of which there are many. Most commonly, the cause is a
Some of these causes interfere with the delivery of needed substances to the brain or the body's ability to use them. Examples are a very low or high level of sugar in the blood (hypoglycemia or hyperglycemia), a very low level of oxygen in the blood, and the sudden stopping of the heart's pumping (cardiac arrest). For example, having diabetes increases the risk of stupor or coma because diabetes can cause the blood sugar level to become too low or too high.
Disorders such as liver or kidney failure, an underactive thyroid gland (hypothyroidism), or a very low or high body temperature (hypothermia or hyperthermia) can cause cells throughout the body to malfunction. Often, brain cells are affected the most.
Commonly, consciousness is impaired by drinking too much alcohol or taking too much of certain drugs, such as sedatives (see Sidebar 2: Prescription Sleep Aids: Not to Be Taken Lightly) and opioids (narcotics—see Opioid Analgesics). In addition to making brain cells function slowly, alcohol and some drugs can damage brain cells indirectly. They can slow breathing so much that the oxygen level in blood becomes low enough to cause brain damage. Occasionally, taking certain antipsychotic drugs results in an unresponsive state called neuroleptic malignant syndrome (see Sidebar 2: What Is Neuroleptic Malignant Syndrome?).
In older people, reactions to drugs, dehydration, and infections are common causes of impaired consciousness.
Other common causes are disorders that affect the areas of the brain that control consciousness. For example, a head injury may jar but not physically damage these areas, directly damage them, or indirectly damage them by causing bleeding (hemorrhage) in or around the brain. Strokes and tumors can also directly damage areas of the brain that control consciousness.
Any disorder that increases pressure within the skull (intracranial pressure) can impair consciousness. A mass in the brain, such as an accumulation of blood (hematoma), a tumor, or an abscess, can impair consciousness indirectly by putting pressure on the areas of the brain that control consciousness. A large mass can push the brain against the relatively rigid structures inside the skull, damaging brain tissue. If the areas of the brain that control consciousness are affected, stupor or coma results. If the pressure is high enough, the brain may be forced through a small natural opening in the relatively rigid sheets of tissue that separate the brain into compartments. This life-threatening disorder is called brain herniation (Fig. 1: Herniation: The Brain Under Pressure). Herniation can further damage brain tissue, making an already dire condition worse.
Occasionally, people with a psychiatric disorder seem to have impaired consciousness. That is, they do not respond normally when they are spoken to or touched. Doctors can usually distinguish these disorders from true impaired consciousness during the examination.
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Consciousness is impaired to varying degrees. People in a stupor are usually unconscious but can be aroused with vigorous stimulation. People in a coma are unconscious and cannot be aroused.
The brain damage or dysfunction that causes stupor and coma affects other parts of the body. The pattern of breathing is usually abnormal. People may breathe too rapidly, too slowly, too deeply, or irregularly. Or they may alternate between these abnormal patterns.
Muscles may remain contracted in unusual positions. For example, the head may be tilted back with the arms and legs extended—a position called decerebrate rigidity. The arms may be flexed—a position called decorticate rigidity. Or the entire body may be limp. Sometimes muscles contract sporadically or involuntarily.
One or both pupils of the eyes may be widened (dilated) and not react to changes in light. Or the pupils may be tiny. The eyes may not move or may move in abnormal ways.
The disorder that is impairing consciousness may cause other symptoms. For example, if the cause is meningitis (infection of the fluid-filled space within the layers of tissue covering the brain and spinal cord), symptoms may include fever, vomiting, headache, and a painful, stiff neck that makes lowering the chin to the chest difficult or impossible.
Doctors can usually tell that consciousness is impaired based on observation and examination. Doctors try to identify the parts of the brain that are impaired and the cause of impairment because treatment differs and because impairment may progress, leading to coma and brain death. Stupor is diagnosed when vigorous, repeated attempts arouse the person only briefly. Coma is diagnosed when the person cannot be aroused at all and the eyes remain closed.
People who become stuporous or comatose must be taken to the hospital immediately because either state may be caused by a life-threatening disorder. Health care practitioners try to identify the cause and provide emergency medical care at the same time. For example, a quick test is done to estimate the blood sugar level. Then if people have a low blood sugar level (which can quickly and permanently damage the brain), it can be treated immediately.
People with disorders that put them at risk of stupor or coma (such as diabetes or a seizure disorder) should carry medical identification or wear a Medic Alert identification bracelet or necklace. Thus, if they lose consciousness, the probable cause can be quickly identified.
Because a stuporous or comatose person cannot communicate, the doctor asks any witnesses of the change in consciousness about the circumstances in which it occurred. The doctor also talks to family members and friends, who should honestly provide emergency medical personnel or the doctor with any relevant information about the person, which includes the following:
If a drug or toxic substance was ingested, family members or friends should give a sample of that substance or its container to the doctor. Information from the family and friends is usually valuable and is more likely to lead to the correct diagnosis than examination or testing. For example, no test can rule out all possible drug overdoses. Thus, information about empty pill containers or drug paraphernalia near the person is extremely important.
Body temperature is checked. An abnormally high temperature may indicate infection, heatstroke, or an overdose of a drug that stimulates the body (such as cocaine or an amphetamine). An abnormally low temperature may indicate prolonged exposure to cold, an underactive thyroid gland, alcohol intoxication, a sedative overdose or, in older people, infection.
Doctors examine the head, face, and skin for clues to the cause, such as the following:
A neurologic examination is done as thoroughly as possible. This examination helps doctors determine how severely consciousness is impaired, whether the brain stem is functioning normally, what part of the brain is damaged, and what the cause may be.
If people are unconscious, doctors try to rouse them first by speaking to them, then by touching the person's limbs, chest, or back. If these measure do not work, doctors use stimuli that cause discomfort or pain, such as a pinch. If people open their eyes or grimace when a painful stimulus is applied or if they purposefully withdraw from it, consciousness is not severely impaired.
Abnormal breathing patterns can provide clues to which parts of the brain are malfunctioning.
Checking reflexes can help determine whether parts of the brain and spinal cord are malfunctioning. When coma is present, using painful stimuli may trigger unusual body positions, such as decerebrate or decorticate rigidity, which may indicate substantial brain dysfunction. Sometimes the dysfunction results from a mass (such as a brain abscess or tumor) that increases pressure within the skull and causes brain herniation. Limpness of the entire body and no reflexes are the worst possible response. They may indicate widespread dysfunction in all parts of the central nervous system, including the brain stem, the cerebrum, and the nerve fibers that connect the cerebrum to the spinal cord. All reflexes are normal if unresponsiveness is caused by a psychiatric disorder.
The eyes also provide important clues about how well the brain stem is functioning and what may be impairing consciousness. The position of the pupils, their size, their reaction to bright light, their ability to follow a moving object (in people who are not comatose), and the appearance of the retina are checked. Normally, pupils widen (dilate) when light is dim and become smaller (constrict) when light is bright. If a pupil remains dilated and does not constrict in response to bright light, the cause may be a tumor, a hematoma, or another large mass. The mass may be putting pressure on the 3rd cranial nerve (which helps control eye movement) or on the brain stem. If coma is deep but both pupils constrict in response to light, the cause is more likely to be a metabolic abnormality (such as a low blood sugar level or low blood oxygen level) or the effect of a drug. To accurately evaluate the person, doctors need to know whether the person's pupils are normally different sizes and whether the person takes a drug to treat glaucoma, which can affect pupil size.
Doctors also examine the inside of the eye with an ophthalmoscope for signs that the pressure within the skull is increased. Increased pressure suggests that the cause is a mass in the brain, such as a tumor, a hematoma, or an abscess.
The person's response to certain maneuvers can provide additional information:
These tests provide further clues about the possible cause of stupor or coma. Blood levels of substances such as sugar, sodium, alcohol, oxygen, and carbon dioxide are measured. Red and white blood cell counts are determined. Blood tests to check liver function are done. Urine is analyzed to determine whether any commonly used or suspected toxic substances are present.
Doctors measure the oxygen level in blood with a sensor placed on a finger (called pulse oximetry). They also measure levels of oxygen, carbon dioxide, and sometimes other gases in a sample of blood withdrawn from an artery (arterial blood gas tests). These tests are done to check for heart and lung disorders and for possible carbon monoxide poisoning.
Electrocardiography (ECG) is done to check for heart disorders.
If no cause has been quickly identified, computed tomography (CT) or magnetic resonance imaging (MRI) of the head is done to check for a mass or for other structural brain damage.
If the cause is unclear after imaging tests or if meningitis or bleeding between the layers of tissue covering the brain (subarachnoid hemorrhage) is possible, a spinal tap (lumbar puncture) is done to withdraw a sample of cerebrospinal fluid (see Fig. 2: How a Spinal Tap Is Done). The fluid is examined and analyzed to check for various causes. CT or MRI of the head is often done before the spinal tap to determine whether pressure inside the skull is increased—for example, by a tumor or bleeding within the brain (intracerebral hemorrhage). If pressure is increased, a spinal tap could make the brain shift downward by rapidly reducing the pressure below the brain and thus, at least theoretically, cause or worsen brain herniation.
If the cause is still unclear, electroencephalography (EEG) may be done to check the brain's electrical activity. Occasionally, EEG indicates that the person is having a seizure even though the limbs are not jerking (a disorder called nonconvulsive status epilepticus).
In general, if people start to respond within 6 hours, they are more likely to recover. Recovery is likely if one or more of the following occur within the first days:
The likelihood of recovery also depends on the cause and duration of impaired consciousness, as in the following:
After cardiac arrest, full recovery is rare if people have any of the following:
However, if doctors have used cooling (called hypothermia) to treat people after cardiac arrest, they usually wait an extra 3 days for these responses to occur. Cooling the body tends to preserve brain function after cardiac arrest, but it also tends to slow recovery of brain function.
Sometimes doctors use a test called evoked responses to determine whether the brain stem is functioning. This test can accurately predict a poor prognosis after only 24 hours. Usually, electrodes, which produce a mild electrical signal, are placed on parts of the body, and EEG is used to detect and record how long the electrical signal takes to reach the brain.
Doctors may also do blood tests to measure the level of neuron-specific enolase, a substance that occurs mainly in nerve cells. A high level in the blood may result from brain damage due to lack of oxygen and may indicate a worse prognosis after cardiac arrest.
Children and sometimes young adults recover more fully than older people because brain cells repair themselves more quickly and completely in the young.
For people who remain in a deep coma longer than a few weeks, decisions about continued use of a ventilator, feeding tube, and drugs should be made. Family members should discuss these issues with the doctors. If people have advance medical directives (see Advance Directives), such as a living will or durable power of attorney for health care, the directives should guide decisions about continuing care.
If a person is rapidly becoming less alert and more difficult to arouse, immediate treatment is required, sometimes even before a diagnosis is made. This rapid deterioration in consciousness is considered a medical emergency. The first steps in treatment, sometimes done by emergency medical personnel, are to check whether the airway is open, whether breathing is adequate, and whether pulse, blood pressure, and heart rate are normal (to make sure blood is reaching the brain). If possible, any problems present are corrected.
People are treated first in an emergency department and then admitted to a hospital intensive care unit. In both places, nurses can monitor heart rate, blood pressure, temperature, and the oxygen level in the blood. Any abnormalities in these measurements are immediately corrected to prevent further damage to the brain. Oxygen is often given immediately, and an intravenous line is put in place so that drugs can be given quickly. Any other disorders (such as heart or lung disorders), if present, are treated.
The cause is treated when possible. For example, for a low blood sugar level, glucose (a sugar) is immediately given intravenously. Giving glucose often results in instant recovery if the coma is caused by a low blood sugar level. Thiamin is always given with glucose because if people are undernourished (usually because of alcohol abuse), glucose alone can trigger or worsen a brain disorder called Wernicke encephalopathy (see Wernicke's Encephalopathy).
If doctors suspect that the cause is an opioid, the antidote naloxone may be given. Recovery may be almost instantaneous if the opioid is the only cause of impaired consciousness.
If the cause is a head injury, the neck must be immobilized until doctors can check for damage to the spine. People in a deep stupor or a coma after a head injury sometimes benefit from treatment with amantadine (a drug that interacts with certain receptors in the brain). Such treatment may help them regain some level of conscious more quickly. However, such treatment may not make any difference in improvement over the long term.
People in a deep stupor or a coma typically require a breathing tube and mechanical ventilation. The breathing tube prevents people from inhaling stomach contents after vomiting and facilitates mechanical ventilation if their breathing is too slow or shallow.
Rarely, when doctors suspect that certain toxic substances have been ingested within about 1 hour, they may insert a large tube through the mouth and into the stomach so that the stomach can be pumped. Pumping the stomach is done to identify its contents and to prevent more of the substances from being absorbed. Activated charcoal may also be given through the tube or through a smaller tube inserted through the nose (nasogastric tube). The charcoal prevents the stomach from absorbing more of the substances.
If findings suggest that the pressure within the skull is increased, particularly if doctors suspect brain herniation, doctors may drill a small hole in the skull and insert a pressure-monitoring device into one of the fluid-filled spaces (ventricles) in the brain. If the pressure is increased, the following measures may be taken to lower it:
If the cause is a brain tumor or abscess, corticosteroids, such as dexamethasone, may help reduce pressure. However, corticosteroids are not used when increased pressure is caused by certain other disorders, such as intracerebral hemorrhage or a stroke, because corticosteroids may make these conditions worse.
People in a coma require comprehensive care. They are fed through a tube inserted through the nose and into the stomach. Sometimes they are fed through a tube (called a percutaneous endoscopic gastrostomy tube, or PEG tube) inserted directly into the stomach through an incision in the abdomen (see Tube feeding). Drugs may also be given through this tube.
Many problems result from being unable to move, and measures to prevent them are essential. For example, lying in one position can cut off the blood supply to some areas of the body, causing skin to break down and pressure sores to form. Caregivers must turn people very frequently. Lack of movement can also lead to permanent stiffening of muscles (contractures) and make blood clots more likely to form in leg veins. To prevent these problems, physical therapists gently move the person's joints in all directions (passive range-of-motion exercises) and may splint joints in certain positions.
Because people cannot blink, their eyes may become dry. Eye drops can help.
If people are incontinent, care should be taken to keep the skin clean and dry. If the bladder is not functioning and urine is being retained, a tube (catheter) may be placed in the bladder to drain urine.
Last full review/revision March 2013 by Kenneth Maiese, MD