Merck Manual

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Some Causes of Stupor and Coma

Some Causes of Stupor and Coma

Condition

Process

Effects

Brain disorders

Seizures that recur frequently or last a long time can

  • Overstimulate brain tissue, disrupting normal transmission of nerve impulses

  • Occasionally cause a high fever, which may add to the brain malfunction

Such seizures can damage brain tissue.

Consciousness is often impaired during a seizure.

After a seizure, most people feel sluggish (lethargic) and confused, and some feel weak or are paralyzed. They may remain that way for minutes to hours after the seizure.

Strokes occur when blood flow to parts of the brain, including to the brain stem, are blocked.

If blood flow to the upper brain stem is blocked, consciousness may be suddenly lost, and coma can result. If blood flow to the entire brain stem is blocked and not restored within several minutes, most or all of the brain stem is damaged, and death may result.

Strokes may result from bleeding in the brain (intracerebral hemorrhage) or between the layers of the tissue covering the brain (subarachnoid hemorrhage).

Blood can directly damage or increase pressure on brain tissue.

Consciousness may be impaired, and coma may result. Seizures may also occur. Even a small amount of bleeding in the brain stem can cause coma.

A large tumor or abscess can push the brain against the relatively rigid structures inside the skull and put pressure on brain tissue, causing it to malfunction. Sometimes the pressure pushes brain tissue through a natural opening in the relative rigid sheets of tissue that divide the brain into parts. This abnormal protrusion of brain tissue is called brain herniation.

Tumors can directly invade and damage brain tissue and cause swelling that disrupts communication between different areas of the brain.

If the areas of the brain that control consciousness are affected, coma results.

Other disorders

Cardiac arrest or respiratory arrest

In cardiac arrest, the heart stops pumping. As a result, not enough blood reaches the brain, and the brain is deprived of oxygen because blood delivers oxygen to the body's tissues.

In respiratory arrest, the person stops breathing. As a result, not enough oxygen enters the blood and the brain is deprived of oxygen.

Usually, cardiac and respiratory arrest occur together.

Consciousness is lost within a minute or two. If people are deprived of oxygen for even 4 to 5 minutes, the lack of oxygen triggers death of nerve cells in certain parts of the brain. Coma results and may quickly become irreversible.

Heart or lung disorders if severe

Severe heart disorders (such as heart failure) can reduce blood flow to the brain.

Severe lung disorders (such as chronic obstructive pulmonary disease, pulmonary edema, pulmonary embolism, and severe and long-lasting asthma attacks) can reduce the amount of oxygen in the blood.

With either type of disorder, the brain may not receive enough oxygen. Lack of oxygen can cause delirium or coma, depending on how much oxygen is in the blood.

If the kidneys or liver cannot remove toxic waste products from the blood as they normally do, waste products accumulate in the blood and cause the brain to malfunction.

Over time, high blood pressure damages blood vessels in the brain.

Treating chronic kidney or liver failure can usually reverse the coma that they cause.

If coma results from acute, severe liver failure, the brain swells because fluid accumulates in brain cells. Death often results.

If blood vessels in the brain are damaged, blood flow and oxygen supply to the brain are reduced. Also, damaged blood vessels may burst, resulting in a stroke (due to bleeding in the brain).

Metabolic abnormalities

Diabetes may cause the blood sugar level to become too high (hyperglycemia) or, when treatment is too aggressive, too low (hypoglycemia—see below).

Also, when there is not enough insulin (as may occur in type 1 diabetes), the body breaks fat cells down to produce energy. During this process, ketones are produced. Ketones make the blood too acidic (a condition called diabetic ketoacidosis).

Stupor or coma can result.

Without treatment, diabetic ketoacidosis or hypoglycemia can result in coma and death.

The blood sugar level is abnormally high. High blood sugar levels can cause dehydration, drawing fluid from the brain and causing it to shrink.

Stupor or coma can result.

The blood sugar level is abnormally low. The brain malfunctions or is damaged if it is deprived of sugar, which is its main source of energy in combination with oxygen.

Coma can result. People with hypoglycemia must be treated immediately to prevent permanent brain damage or death. Treatment consists of giving them glucose (a sugar) intravenously

The blood sodium level is high. Hypernatremia is usually due to dehydration and can reduce the amount of water in brain cells.

An abnormal amount of water in brain cells interferes with chemical reactions there. Stupor or coma may result.

The blood sodium level is low. Hyponatremia may be due to the following:

  • Drinking too much water (for example, during college fraternity rituals)

  • Retaining too much water (as can occur in certain heart, kidney, liver, and hormone disorders)

  • Losing too much sodium in urine or in the digestive tract (as when diarrhea occurs)

Hyponatremia can increase the amount of water in brain cells and cause the brain to swell.

An abnormal amount of water in brain cells interferes with chemical reactions there. Whether the brain is damaged and how badly it is damaged depends on how quickly the amount of water in brain cells increases. If the amount increases slowly. the brain may be able to adjust, and damage is usually avoided.

The thyroid gland is underactive.

Untreated hypothyroidism may cause mental confusion and slowed thinking.

The confusion may progress to stupor and coma.

Deficiency of a nutrient, such as thiamin or certain electrolytes or minerals (such as magnesium)

Deficiency of the vitamin thiamin or a mineral such as magnesium causes nerve cells in the brain to malfunction. Some minerals (including magnesium) are also electrolytes. Electrolytes help regulate nerve and muscle function and maintain acid-base balance in the body.

Thiamin deficiency may result in confusion, stupor, and coma. The eye muscles may not work normally, resulting in double vision.

Very low or high levels of certain electrolytes or minerals (such as magnesium) can cause sleepiness, weakness, and, rarely, seizures and coma.

Infections

Encephalitis (infection of the brain)

Meningitis (infection of the layers of tissue covering the brain and spinal cord)

Sepsis (a serious bodywide response to a bloodstream infection)

Urinary tract infections in older people

If brain tissue becomes infected, the brain may malfunction.

Other infections, such as sepsis, can cause high fevers, which may make the brain malfunction or may damage brain tissue.

Age-related changes in the brain make older people more susceptible to disturbances in mental function caused by minor disorders, such as urinary tract infections.

Coma may result.

In older people, urinary tract infections can cause confusion, disorientation, and delirium.

Accidents and injuries

Asphyxiation

The brain is deprived of oxygen.

Consciousness is quickly lost, and coma and death may follow.

Head injuries may damage the brain in the following ways:

  • Jar the brain, possibly disrupting communication between brain cells but not causing any obvious physical damage (as in a concussion)

  • Damage small blood vessels in the brain (as in a bruise or contusion)

  • Cut or crush brain tissue

  • Cause severe bleeding in the brain (as occurs in an intracerebral hemorrhage) or between the tissues covering the brain (as occurs in a subarachnoid hemorrhage)

Blood may directly irritate brain tissue or may accumulate as a mass (hematoma), which puts pressure on the brain (as in epidural or a subdural hematoma).

Depending on the injury, coma may develop immediately or gradually over several hours. Seizures may also result, particularly if a large amount of blood leaks from blood vessels and comes into direct contact with brain tissue, irritating it.

A body temperature above 104° F (40° C), as occurs in high fevers or heatstroke, can damage the brain.

Coma can result. Nerve cells die much more quickly when body temperature is very high.

A body temperature below 96.8° F (36° C) slows brain function. A body temperature below 80° F (26.7° C) causes coma.

However, low temperatures can sometimes protect the brain by slowing the damage caused by lack of blood or oxygen. Also, nerve cells die much more slowly when body temperature is very low. For example, a child may fully recover after being submersed for 30 minutes in an icy lake. Being submersed that long in warm water is usually fatal.

Stupor or coma can result, but if people survive, there is usually no permanent damage.

Substances

Alcohol slows brain function. Consumed in large amounts, it may affect brain tissue directly or indirectly by slowing breathing so much that the oxygen level in blood becomes low enough to cause brain damage.

A high blood alcohol level, especially when it exceeds 0.2%, can cause stupor or coma.

Carbon monoxide or similar substances inhaled in large amounts

Carbon monoxide attaches to the hemoglobin in red blood cells. It takes the place of oxygen and prevents red blood cells from carrying oxygen to tissues, including the brain.

Severe carbon monoxide poisoning can cause coma or irreversible brain damage because the brain does not receive enough oxygen.

Drugs

Many drugs, even if not given in high doses, can slow brain function, sometimes by slowing breathing. They include

  • High doses of barbiturates

  • Opioids (including morphine)

  • Sedatives (such as diazepam)

  • A combination of these drugs with each other or with alcohol

  • Overdose of marijuana, including medical marijuana

Coma can result. If treated early, this type of coma can be completely reversed.