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. In coma, the person's eyes remain closed.
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.
Consciousness is controlled by the lower part of the brain (brain stem) through a system of nerve cells and fibers (the reticular activating system, also known as the ascending arousal system (see Biology of the Nervous System: Brain Stem). The upper part of the brain (cerebrum) helps maintain consciousness and alertness. The cerebrum is divided into two halves (cerebral 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 level 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 toxic substance, drug, metabolic abnormality, or another disorder that makes nerve cells throughout the brain function slowly. 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).
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 many types of 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 Sleep Disorders: 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 Schizophrenia and Delusional Disorder: What Is Neuroleptic Malignant Syndrome?).
In older people, reactions to drugs, dehydration (which results in a high sodium level), 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 (stun) such 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.
A mass in the brain, such as an accumulation of blood (hematoma), a tumor, or an abscess, can impair consciousness indirectly. 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. The pressure may affect the entire cerebrum or the brain stem. 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 (see Head Injuries:Overview of Head Injuries). Herniation can further damage brain tissue, making an already dire condition worse.
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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.
Doctors can usually tell that consciousness is impaired based on observation and examination. Doctors try to identify the level and 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.
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.
People with disorders that put them at risk of stupor or coma (such as diabetes, which can result in a low blood sugar level) 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, family members and friends must 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 usually is 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.
Emergency medical personnel or doctors first check whether the airway is open, whether breathing is adequate, and whether blood pressure and pulse are normal. Body temperature is checked. For example, 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. The skin is examined for signs of injury, drug injections, illnesses, and allergic reactions, and the scalp is examined for cuts and bruises. The tongue is examined to see if it has been bitten—a finding that suggests seizures.
A neurologic examination is done as thoroughly as possible. This examination helps doctors determine how severe stupor or coma is, whether the brain stem is functioning normally, and what part of the central nervous system is damaged.
Doctors may use stimuli that cause discomfort or trigger reflexes. If the eyes open or the person grimaces or purposefully withdraws from a painful stimulus, consciousness is not severely impaired.
Doctors look for signs of brain damage or impaired brain function. For example, abnormal breathing patterns can provide clues to the depth of coma. Checking reflexes can help determine whether parts of the brain and spinal cord are malfunctioning. Unusual body positions, such as decerebrate or decorticate rigidity, may indicate substantial brain damage. Absence of reflexes and limpness of the entire body are worrisome. 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.
The eyes also provide important clues. 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. If a pupil remains dilated and does not react to bright light, there may be pressure on the 3rd cranial nerve, which helps control eye movement, or on the brain stem. Such a reaction sometimes indicates a large mass in the brain causing herniation. If coma is deep and both pupils do not remain dilated but react to light, this type of a mass is unlikely. 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.
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. The 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. The blood sugar level is also estimated using a quick test done at the person's bedside, so that a low blood sugar level can be treated immediately.
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 (such as a hematoma, a tumor, or an abscess), or for other structural brain damage.
If the cause is unclear after imaging tests or if meningitis or subarachnoid hemorrhage is possible, a spinal tap (lumbar puncture) is done to withdraw and examine a sample of cerebrospinal fluid (see Symptoms and Diagnosis of Brain, Spinal Cord, and Nerve Disorders: Tests for Brain, Spinal Cord, and Nerve Disorders). Emergency 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 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) is 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).
A rapidly deteriorating level of consciousness is a medical emergency requiring immediate treatment, sometimes even before a diagnosis is made.
People are admitted to a hospital intensive care unit, where nurses can monitor heart rate, blood pressure, temperature, and the oxygen level in the blood. Any abnormalities in these levels 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) present are treated.
The cause is treated when possible. For example, for a low blood sugar level (hypoglycemia), glucose, a sugar, is immediately given intravenously. Giving glucose often results in instant recovery if the coma is caused by hypoglycemia. Thiamin is always given with glucose because in malnourished people (such as alcoholics), glucose alone can trigger or worsen a brain disorder called Wernicke's encephalopathy. If taking an opioid is the suspected cause, the antidote naloxone may be given. Recovery may be almost instantaneous if the opioid is the only cause of impaired consciousness.
People with deep stupor or in a coma may require a breathing tube, particularly if a feeding tube is to be inserted into the stomach. 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, a large tube may be inserted 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) to prevent further absorption of the substances.
If findings suggest that the pressure inside the skull is increased, 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, measures are taken to lower it:
People in a coma require comprehensive care. They are fed through a tube inserted through the nose and into the stomach. Sometimes a tube (called a percutaneous endoscopic gastrostomy tube or PEG tube) is inserted through an incision in the abdomen directly into the stomach.
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. Caretakers must turn people into different positions 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 that tend to prevent contractures. Because people cannot blink, their eyes may become dry. Eye drops can help.
People who are incontinent should be kept clean from urine and stool. If the person's bladder is not functioning and urine is being retained, then doctors prefer using intermittent urinary catheterization over placing an indwelling catheter to reduce the risk of infection.
The likelihood of recovery can be predicted by the cause, duration, and rate of recovery from coma:
Sometimes doctors use evoked responses to determine whether the brain stem is functioning. This test can accurately predict a poor prognosis after only 24 hours. The brain stem is stimulated, and EEG is used to detect the response.
Results of a physical examination can also help predict prognosis. Recovery is likely if one or more of the following occur within the first days:
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 Legal and Ethical Issues: Advance Directives), such as a living will or durable power of attorney for health care, the directives should guide decisions about continuing care.
Last full review/revision February 2008 by Kenneth Maiese, MD