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Syncopal Episode - Fainting

Overview, Causes, & Risk Factors

Fainting is a temporary loss of consciousness and muscle tone. It is 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 doesn't 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, no cause can be found. The following diseases and conditions may cause fainting:

  • anemia, or a low red blood cell count
  • arrhythmias, or irregular heartbeats
  • carotid stenosis, which is narrowing of the arteries supplying the brain
  • congestive heart failure, a condition in which a weakened heart fails to pump enough blood to body organs
  • hypoglycemia, which is 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 are as follows:

  • 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
  • There may be other causes as well. In some cases, no cause is found.

    Symptoms & Signs

    What are the signs and symptoms of the condition?

    A person who faints usually becomes quite pale and may sweat heavily. The individual may be nauseated. Most people who pass out wake up in less than 2 minutes. There are several things a healthcare provider may want to know after a person has fainted, such as:

  • how long the person was unconscious
  • how quickly the person felt normal again after waking up
  • what position the person was in before fainting
  • whether the person felt dizzy or light-headed before passing out
  • whether the person has fainted before
  • whether there was any strong emotion, pain, or fatigue before the person fainted
  • The healthcare provider will also ask about other medical conditions. The provider will want to know what medications the person is taking. All of these things can be clues as to the cause of the fainting.

    Diagnosis & Tests

    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 provider 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, or ECG, which shows the electrical activity of the heart
  • a tilt table test, which detects drops in blood pressure when a person stands up

  • Prevention & Expectations

    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.

    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.

    What are the risks to others?

    Fainting is not contagious and poses no risk to others.

    Treatment & Monitoring

    What are the treatments for the condition?

    First aid for a person who has fainted includes the following steps:

  • Check for signs of circulation, such as normal breathing, coughing, or movement in response to stimulation.
  • Contact the emergency medical system immediately if these signs are absent.
  • Start cardiopulmonary resuscitation or CPR if the person stops breathing.
  • If the person has signs of circulation, 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. Following are some of the common treatments:

  • 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
  • What are the side effects of the treatments?

    All medications have possible side effects. These may include allergic reactions, stomach upset, and headaches. Surgery carries a risk of bleeding, infection, and allergic reactions to anesthesia. Blood transfusions may cause allergic reactions or infections.

    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 provider.


    Author:Adam Brochert, MD
    Date Written:
    Editor:Crist, Gayle P., MS, BA
    Edit Date:05/31/01
    Reviewer:Eileen McLaughlin, RN, BSN
    Date Reviewed:09/24/01


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

    Instructions for Patients, 1994, Griffith et al.