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Alternate Names

  • passing out
  • syncope
  • syncopal episode


Fainting is a temporary loss of consciousness and muscle tone, caused by not having enough blood flow to the brain.

What is going on in the body?

When there is not enough blood flow to the brain, passing out protects the brain from damage. People who faint generally lose muscle tone and fall to the ground. When someone is lying on the ground, the blood being pumped out of the heart does not have to fight gravity to get to the brain. Those who faint have a relaxed body, which uses less energy. This also makes it easier for the heart to pump blood to the brain.


What are the causes and risks of the condition?

The cause of fainting may be minor or it may be life-threatening. Often, however, no cause can be found.
The following diseases and conditions may cause fainting:
  • anemia, a low red blood cell count
  • arrhythmias, which are irregular heartbeats
  • carotid stenosis, which is narrowing of the arteries supplying the brain
  • myocardial infarction, a heart attack
  • congestive heart failure, a condition in which a weakened heart fails to pump enough blood to body organs
  • hypoglycemia, a low blood sugar that occurs most often in people with diabetes
  • low oxygen in the blood from any cause
  • orthostatic hypotension, or low blood pressure that is caused by standing up too quickly
  • pulmonary embolus, which is a blood clot in the arteries supplying the lungs
Additional factors that can cause fainting include:
  • dehydration
  • extreme fatigue
  • low blood pressure as a side effect of medications for high blood pressure
  • marked fear
  • pain, such as an acute injury
  • prolonged or severe coughing
  • side effects of certain medications, such as sedatives
  • straining to urinate or have a bowel movement
  • stressful events such as receiving an injection at the health care professional's office
  • standing for a long period of time without moving one's legs, as in a choral concert
  • standing or moving too fast after donating a unit of blood
There may be precipitating events as well. In some cases, no cause is found.


What can be done to prevent the condition?

It is usually not possible to prevent fainting. An individual should seek treatment for underlying conditions, such as anemia or diabetes. Drinking enough fluids is important in preventing dehydration. A diet high in fiber and fluids can help prevent straining to have a bowel movement. A person with a history of fainting should stand up slowly. Those who feel as though they may faint should sit or lie down. This simple step often prevents fainting.


How is the condition diagnosed?

Diagnosis of fainting starts with a medical history and physical exam. This may be all that is needed to make the diagnosis and determine the cause.
The healthcare professional may order one or more of the following tests:
  • blood tests, including a blood glucose test
  • a cardiac catheterization, which shows blood flow through the heart
  • a cerebral angiogram, which shows the blood flow to the brain
  • a chest X-ray
  • a cranial CT scan, which can show abnormalities in the brain
  • an electrocardiogram (ECG), which shows the electrical activity of the heart
  • a tilt table test, which detects drops in blood pressure when a person stands up

Long Term Effects

What are the long-term effects of the condition?

People who faint may hurt themselves when they fall. Long-term effects are mainly related to the underlying cause of the fainting. Those who have heart disease often have an increased risk of complications and death.

Other Risks

What are the risks to others?

Fainting is not contagious in the true sense, although watching a person faint has been known to predispose others to faint as well.


What are the treatments for the condition?

First aid for a person who has fainted includes the following steps:
  • Check for signs of circulation by checking the carotid pulse in the neck and look for normal breathing, coughing, or movement in response to stimulation.
  • Contact the emergency medical system immediately if these signs are absent.
  • Start cardiopulmonary resuscitation (CPR) if the person stops breathing and has no pulse.
If the person has signs of circulation and is breathing, he or she has probably fainted. The individual should be left on the ground and both legs should be elevated. This helps improve blood flow to the brain. The person should remain lying down for at least 10 minutes, even if he or she wakes up.
After that, he or she should get up slowly and sit in a chair for a few minutes. The person should have help when trying to stand up. Someone who gets up too fast and without help may faint again. Most of the time, no further treatment is needed for fainting. If the person faints repeatedly or has other symptoms, more treatment may be needed.
Some of the common treatments include:
  • blood transfusions for anemia
  • fluids for dehydration
  • medications for arrhythmias
  • medications to raise the blood pressure
  • oxygen
  • stopping medications that are causing low blood pressure

Side Effects

What are the side effects of the treatments?

All medications have possible side effects. These may include allergic reactions, stomach upset, and headaches. Surgery can be complicated by bleeding, infection, or an allergic reactions to the anesthetic. Blood transfusions may be complicated by allergic reactions or infections.

After Treatment

What happens after treatment for the condition?

Those who have simple fainting usually need no further monitoring or treatment. Those who have heart disease may need ongoing treatment for many years. Most people are able to return to normal activities after treatment. Those with frequent fainting may need to avoid certain activities, such as climbing ladders or driving.


How is the condition monitored?

Specific monitoring depends on the underlying cause of the fainting. It may range from none at all to intense monitoring and follow-up. Any new or worsening symptoms should be reported to the healthcare professional.


Harrison's Principles of Internal Medicine, 1998, Fauci et al.

Instructions for Patients, 1994, Griffith et al.

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