passing out, syncope, syncopal episode
Fainting is a temporary loss of consciousness. It is caused by not having enough blood flow to the brain.
What is going on in the body?
Fainting, or passing out, is thought to be a reflex response of the body when there is not enough blood flow to the brain. A reflex response is one that happens automatically, without a person thinking about it. When there is not enough blood flow to the brain, passing out protects the brain from damage. People who faint generally 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. Also, those who faint have relaxed bodies, which use less energy. This also makes it easier for the heart to pump blood to the brain.
The cause of fainting may be minor or it may be life-threatening. Often, no cause can be found.
What are the signs and symptoms of the condition?
A person who faints usually becomes quite pale and may sweat heavily. Most people who pass out wake up in less than 2 minutes. There are several things a doctor may want to know after a person has fainted. These include:
The doctor will also ask about any other symptoms, other medical conditions, and what medications a person is taking. All of these things can be clues as to the cause of the fainting.
- whether there was any strong emotion, pain, or fatigue before the person fainted
- whether the person has fainted before
- 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
What are the causes and risks of the condition?
The following conditions may cause fainting:
There may be other causes as well. In some cases, no cause is found.
- vasovagal response, a type of fainting that occurs with strong emotion, fear, pain or injury, or extreme fatigue. It is by far the most common cause of fainting.
- low blood pressure, which can be due to dehydration, problems with the nervous system, or taking certain medications that can lower blood pressure. Medications used for high blood pressure and other medications, such as sedatives, may cause a low blood pressure.
- postural hypotension, or low blood pressure that is caused by standing up too quickly
- decreased pumping ability of the heart, which may be due to fluid around the heart, irregular heartbeats known as arrhythmias, or congestive heart failure
- a blood clot in the lung, known as a pulmonary embolism
- anaemia, or a low red blood cell count
- low oxygen in the blood from any cause
- hypoglycaemia, which is a low blood sugar which occurs in people with diabetes or certain types of cancer
- blockage in the arteries that supply blood to the brain, known as carotid stenosis
- prolonged straining, such as from severe coughing or attempted bowel movements when constipated
What can be done to prevent the condition?
It is usually not possible to prevent fainting. Avoiding dehydration and treating anaemia, heart disease , and other conditions may prevent some cases of fainting. Someone with a history of fainting or a person who takes blood pressure medications 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?
The role of the doctor is to find out if the person did actually faint and then to figure out why. Other conditions, such as seizures, can make a person think she has fainted when in fact something else is going on. Diagnosis starts with a history and physical examination. This may be all that is needed to make the diagnosis and determine the cause.
Other tests may be done if certain causes are suspected. For example, if heart disease is suspected, an electrocardiogram, or ECG, may be done as well as an echocardiogram or ultrasound of the heart. A special x-ray of the heart, known as a cardiac catheterisation, may also be taken. In other cases, blood tests or special x-ray tests of the arteries that supply blood to the brain, known as a cerebral angiogram, may be done. Sometimes, people are put on a special table and tilted up and down to see if this causes another episode of fainting. Other tests are also possible in certain settings.
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. For example, those with vasovagal fainting generally have no long-term effects. Those with heart disease as the cause of their fainting 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.
What are the treatments for the condition?
First aid for a person who has fainted includes:
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 he tries to stand up. Someone who gets up too fast and without help may faint again.
- 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. Use 15 chest compressions for every 2 mouth-to-mouth rescue breaths.
- If the person starts breathing, place him or her in a side-lying position and monitor closely.
This may be the only treatment if the cause is thought to be vasovagal fainting. If the person has fainted for another reason, he or she may need fluids for dehydration, medications to raise the blood pressure, or oxygen. Other possible treatments include: What are the side effects of the treatments?
All medications have possible side effects. These may include allergic reactions, stomach upset, and headaches. All surgery carries a risk of bleeding, infection, and allergic reactions to anaesthesia. Blood transfusions may cause allergic reactions or infections.
What happens after treatment for the condition?
Those with vasovagal fainting usually need no further monitoring or treatment. Those with 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 doctor.
Author: Adam Brochert, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request