Fainting

Fainting (syncope) is a sudden and temporary loss of consciousness. A person who has fainted cannot be aroused for several seconds to several minutes.

Fainting can be frightening. People who have fainted open their eyes and find themselves slumped in a chair or sprawled on the floor, just moments after they had been going about their business. They may find themselves surrounded by a throng of concerned people.

Some people faint only once. Others faint over and over again. Anyone can faint, but older people are much more likely to do so. Sometimes symptoms related to the cause of fainting occur before, during, or after fainting. People who have fainted may limit their daily activities because their doctor has advised them to so or because they are afraid of fainting again. Fainting often results in a fall, which increases the risk of injuries and disability. In older people, a fall is more likely to result in a fracture. Fainting can also be a symptom of a life-threatening disorder.

See the sidebar Before, During, and After Fainting.

Causes

Most commonly, fainting occurs because the brain does not get enough oxygen or sugar (glucose). The brain needs oxygen and sugar to function. These vital fuels are carried to the brain by the blood. If the brain does not get enough blood, the brain may not get enough oxygen and sugar, causing fainting. Or if the level of oxygen or sugar in the blood decreases, the brain may not get enough of them. Many disorders interfere with getting enough oxygen and sugar to the brain and thus can cause fainting. A less common reason for fainting is temporary interruption of consciousness by a seizure.

As the body ages, blood flow to the brain and the amount of oxygen available to the brain decrease. These changes alone are not enough to cause fainting. But because of them, other problems—certain disorders, certain drugs, and sudden stressful events—are more likely to cause fainting. For most older people, fainting results from several problems, not just one.

Certain disorders and situations can cause blood pressure to fall. As a result, the brain may not get enough blood, and fainting may occur. Blood pressure may fall after standing up quickly (orthostatic hypotension) or after eating a meal (postprandial hypotension). Coughing strenuously, straining while having a bowel movement, or urinating under certain circumstances (for example, when straining) can cause a fall in blood pressure. Blood pressure may fall when a person becomes dehydrated.

Fainting can result from overstimulation of the vagus nerve, which helps control heart rate and blood pressure. Stimulating the vagus nerve causes the heart rate to slow and blood pressure to fall. This type of fainting is sometimes called a vasovagal attack or vasovagal (neurocardiogenic) syncope. It can result when a person is having trouble swallowing something, is startled, is in a stressful situation, suddenly has severe pain, or becomes nauseated.

Some disorders keep the brain from getting enough blood. For example, a heart attack, an abnormal heart rhythm (arrhythmia), or a heart valve disorder can interfere with the heart's ability to pump blood. In a stroke, an artery that carries blood to the brain may be blocked.

The two large arteries in the front of the neck (carotid arteries)—one on each side—have a specialized area that helps control blood pressure. This area, called the carotid sinus, can become overly sensitive to pressure caused by movements of the neck or by a tight collar. This disorder is called carotid sinus syndrome. In people with this disorder, pressure on the carotid sinus can cause the heart rate to slow dramatically or blood pressure to fall. Fainting can result.

Blood flow through the arteries that carry blood to the back of the brain may be decreased because atherosclerosis has narrowed the arteries or because bony outgrowths due to osteoarthritis press on them. People with either disorder may faint when they tilt the head backward or turn it sharply to the side. This disorder is called vertebrobasilar insufficiency.

A low number of red blood cells (anemia) increases the risk of fainting. Red blood cells carry oxygen. Thus, anemia reduces the amount of oxygen the blood carries to the brain. Fainting sometimes results from a fall in the level of sugar in the blood, which may happen in people with diabetes.

Many prescription drugs may contribute to fainting, particularly when a drug is first started. They include drugs used to treat heart disorders and high blood pressure, such as beta-blockers (which slow the heart), diuretics (which cause the kidneys to excrete more water and salt), and angiotensin-converting enzyme (ACE) inhibitors (which lower blood pressure by widening arteries). Other drugs that can cause fainting include some antidepressants and alpha-blockers (often used to treat an enlarged prostate gland).

Diagnosis

Fainting is easy to recognize. A doctor focuses on identifying the cause, particularly whether the cause could be life threatening, such as an abnormal heart rhythm or a heart valve disorder. The doctor begins by asking questions and by performing a physical examination. Often, these steps are enough to identify possible causes of fainting.

The doctor asks what the person was doing before fainting. For example, if the person had eaten a large meal within an hour before fainting, the cause may be postprandial hypotension. The doctor also asks what the person felt like before fainting and what the person remembers immediately after regaining consciousness. The symptoms that occurred before, during, or after may suggest a possible cause. The doctor asks whether the person has started taking any new prescription or nonprescription drugs and whether the dosage of any drug has been changed.

The physical examination includes measuring blood pressure after the person has been lying down for about 5 minutes and immediately after the person stands up. Sometimes it is measured again after 3 minutes. If blood pressure falls excessively when the person stands, orthostatic hypotension may have contributed to fainting.

If blood pressure falls occasionally, a person may be asked to measure blood pressure at home with an automatic device. The person measures and records blood pressure at specific times when fainting has previously occurred. The doctor can then review the blood pressure record to determine how often and when it falls too low.

The doctor listens to the heart with a stethoscope. If the sound of turbulent blood flow (a heart murmur) is heard, a heart valve disorder may have caused the fainting. The doctor checks the functioning of the brain and nerves. This check (called a neurologic examination) can determine whether sensation or muscle control was lost. Such a loss may indicate that a stroke caused the fainting.

Blood tests are usually done. The number of red blood cells is determined to check for anemia. The sodium and urea nitrogen levels in the blood are measured to check for dehydration. The sugar level in the blood is measured to check for diabetes.

More complex procedures are done only if evidence suggests a specific cause that needs to be confirmed.

Electrocardiography (ECG), which records the electrical activity of the heart, is done to check for a heart disorder. Sometimes the person is asked to wear a small, portable ECG device (Holter monitor) for 1 or 2 days. If the monitor detects an abnormal heart rhythm just before or at the same time as a fainting episode, the abnormal heart rhythm is likely to have caused or contributed to the fainting. Another type of monitor is used when the person must be monitored longer. This monitor is similar to the Holter monitor except it records the heart's rhythm only when the person or someone assisting the person pushes a button. The button is pushed when the person feels he is about to faint or immediately after regaining consciousness after fainting.

Echocardiography, which uses sound waves to produce a picture of the heart, can show whether the heart has an abnormality that may decrease blood pressure or blood flow to the brain.

If seizures may be the cause, electroencephalography (EEG) may be done. In this procedure, small adhesive sensors (electrodes) are placed on the person's scalp. The electrodes are connected by wires to a machine that records the electrical activity of the brain.

To confirm a suspected cause, the doctor may try to re-create a fainting episode under safe conditions. For example, while monitoring the heartbeat with electrocardiography, a doctor may gently press on the person's neck over the carotid sinus. This pressure temporarily increases blood pressure inside the carotid sinus. Thus, the body is tricked into thinking that blood pressure has increased throughout the body. A signal is then sent to the brain to reduce blood pressure. If the brain's response is exaggerated, blood pressure may fall excessively, and the person may feel faint or even faint.

Another procedure, called tilt table testing, involves tilting a person who is lying flat to an almost standing position. Tilt table testing is used to confirm a diagnosis of vasovagal syncope. For the procedure, the person is strapped to a padded motorized table. The table is then tilted until the person is nearly upright. The person is kept in position for up to 45 minutes. Blood pressure and heart rate are continuously monitored. If blood pressure does not decrease, the person is given a drug that stimulates the heart, and the procedure is repeated. Use of this drug makes the procedure more likely to detect a problem. During the procedure, the person should report any feelings of faintness or light-headedness to the doctor or nurse.

Prevention

Learning about and then avoiding conditions that can cause fainting can help prevent fainting. For example, older men who have felt faint or have fainted while urinating can sit down when they urinate. Avoiding straining during a bowel movement can help prevent fainting. If needed, a stool softener can be used, or the fiber content of the diet can be increased.

For people who must continue taking a drug that increases the risk of fainting, lying down after taking the drug—for example, taking the drug before going to bed—can help.

If fainting sometimes occurs after eating a large meal, eating smaller, more frequent meals that are low in carbohydrates and lying down after eating can help. Antihypertensive drugs, if being used, should not be taken immediately before a meal. For people whose blood pressure falls when they stand up, drinking plenty of fluids and increasing the amount of salt consumed helps. These measures increase the amount of fluid in the bloodstream and thus help keep blood pressure from falling. However, consuming too much salt may be dangerous for people who have heart failure. People should consult a dietitian or doctor about how much salt to consume.

Sitting up and flexing the feet before getting out of bed can also help. This maneuver improves blood flow to the heart and thus helps maintain blood pressure. In general, older people should sit or stand up slowly, particularly when getting out of bed in the middle of the night.

To prevent dehydration and thus reduce the risk of fainting, older people should drink plenty of fluids, particularly during hot weather or an illness. People who take diuretics (used to treat high blood pressure or heart failure) should ask their doctor about discontinuing the drug temporarily during very hot weather or an illness. These drugs cause the kidneys to excrete more water. The increased loss of body fluids lowers blood pressure. Thus, diuretics may increase the risk of fainting. People who have fainting episodes should not drink alcohol because it tends to make them lose body fluids and lowers blood pressure.

Exercising the legs to keep the muscles toned can help prevent fainting. Strong leg muscles are needed to help move blood from the legs back to the heart.

People who have fainted can take steps to prevent serious injury and accidents if they faint again. For example, people can learn to recognize the warning symptoms of fainting and to lie down immediately when these symptoms occur. If the cause of the fainting cannot be identified and corrected, they should not drive for at least 6 months after the last fainting episode.

Treatment

Treatment focuses on several areas. Any injuries due to fainting are treated. If a potentially life-threatening disorder, such as an abnormal heart rhythm, a heart attack, or rapid bleeding is suspected, hospitalization and immediate treatment are needed. However, for most people, hospitalization is not needed and diagnosis can be done more slowly.

Measures are taken to correct or control other possible conditions that may contribute to or cause fainting. If the cause of fainting appears to be orthostatic hypotension, increasing the amount of salt consumed, wearing waist-high support stockings (compression stockings), and raising the head of the bed may help. If orthostatic hypotension occurs after a long period of bed rest, the person may be instructed to sit on the side of the bed a few times to get used to being upright again before trying to stand. Occasionally, a tilt table is used. It helps reprogram the body to adjust blood pressure in response to changes in position. If orthostatic hypotension persists despite these measures, drugs such as fludrocortisone or midodrine may help.

If a potentially life-threatening disorder is the cause, surgery is sometimes necessary. The type of surgery depends on the disorder. For example, a pacemaker may be implanted to correct an abnormal heart rhythm. After a heart attack, coronary angioplasty or coronary artery bypass surgery can improve blood flow to the heart. After a stroke, surgery to improve blood flow through arteries in the neck (carotid endarterectomy) may be needed. A heart valve may need to be repaired or replaced.

If the cause is carotid sinus syndrome, a pacemaker may be implanted or a drug such as midodrine may be used.

If anemia is detected, vitamins, iron supplements, drugs that stimulate the production of red blood cells, or transfusions may be given.

Drugs that may increase the risk of fainting are discontinued whenever possible or replaced with another drug less likely to cause fainting. When a potentially harmful drug cannot be discontinued or replaced, the dose is reduced to the lowest effective dose.

People who have fainted several times can get a personal emergency response system (a medical alert device). Most of these systems include an alert button worn on a necklace. Pressing the button calls for help.

Outlook

Most people who faint recover completely within minutes to hours. However, fainting can cause injuries when a person suddenly falls to the floor. Older people may bump their head or break a bone. Sometimes the fracture is a serious one, such as a hip fracture.

When fainting is due to a life-threatening heart disorder, the person's outlook depends on whether the heart disorder can be treated effectively.