Seizures that recur frequently or last a long time can
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 Intracerebral Hemorrhage An intracerebral hemorrhage is bleeding within the brain. Intracerebral hemorrhage usually results from chronic high blood pressure. The first symptom is often a severe headache. Diagnosis is... read more ) or between the layers of the tissue covering the brain (subarachnoid hemorrhage Subarachnoid Hemorrhage (SAH) A subarachnoid hemorrhage is bleeding into the space (subarachnoid space) between the inner layer (pia mater) and middle layer (arachnoid mater) of the tissues covering the brain (meninges)... read more ).
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.
Tumor Overview of Brain Tumors A brain tumor can be a noncancerous (benign) or cancerous (malignant) growth in the brain. It may originate in the brain or have spread (metastasized) to the brain from another part of the body... read more or abscess Abscess of the Brain A brain abscess is a pocket of pus in the brain. An abscess may form in the brain when bacteria from an infection elsewhere in the head or in the bloodstream or from a wound enter the brain... read more
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 Herniation: The Brain Under Pressure Head injuries that involve the brain are particularly concerning. Common causes of head injuries include falls, motor vehicle crashes, assaults, and mishaps during sports and recreational activities... read more .
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.
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 Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more ) can reduce blood flow to the brain.
Severe lung disorders (such as chronic obstructive pulmonary disease Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease is persistent narrowing (blocking, or obstruction) of the airways occurring with emphysema, chronic obstructive bronchitis, or both disorders. Cigarette... read more , pulmonary edema, pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism is the blocking of an artery of the lung (pulmonary artery) by a collection of solid material brought through the bloodstream (embolus)—usually a blood clot (thrombus) or... read more , and severe and long-lasting asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more 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.
Kidney failure Overview of Kidney Failure This chapter includes a new section on COVID-19 and acute kidney injury (AKI). Kidney failure is the inability of the kidneys to adequately filter metabolic waste products from the blood. Kidney... read more
Liver failure Liver Failure Liver failure is severe deterioration in liver function. Liver failure is caused by a disorder or substance that damages the liver. Most people have jaundice (yellow skin and eyes), feel tired... read more
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 Intracerebral Hemorrhage An intracerebral hemorrhage is bleeding within the brain. Intracerebral hemorrhage usually results from chronic high blood pressure. The first symptom is often a severe headache. Diagnosis is... read more (due to bleeding in the brain).
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 Diabetic Ketoacidosis Diabetic ketoacidosis is an acute complication of diabetes that occurs mostly in type 1 diabetes mellitus. Symptoms of diabetic ketoacidosis include nausea, vomiting, abdominal pain, and a characteristic... read more ).
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:
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 Thiamin Deficiency Thiamin deficiency (causing beriberi and other problems) is most common among people whose diet mainly consists of white rice or highly processed carbohydrates in developing countries and among... read more or certain electrolytes or minerals (such as magnesium Overview of Magnesium's Role in the Body Magnesium is one of the body's electrolytes, which are minerals that carry an electric charge when dissolved in body fluids such as blood, but the majority of magnesium in the body is uncharged... read more )
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 Overview of Electrolytes Well over half of the body's weight is made up of water. Doctors think about the body's water as being restricted to various spaces, called fluid compartments. The three main compartments are... read more . 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.
Encephalitis Encephalitis Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved... read more (infection of the brain)
Meningitis Introduction to Meningitis Meningitis is inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid space). Meningitis can be... read more (infection of the layers of tissue covering the brain and spinal cord)
Sepsis Sepsis and Septic Shock Sepsis is a serious bodywide response to bacteremia or another infection plus malfunction or failure of an essential system in the body. Septic shock is life-threatening low blood pressure ... read more (a serious bodywide response to a bloodstream infection)
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
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:
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.
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 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.
Many drugs, even if not given in high doses, can slow brain function, sometimes by slowing breathing. They include
Coma can result. If treated early, this type of coma can be completely reversed.