Passing out (syncope) can be caused by dehydration, standing up fast, low blood pressure, heart rhythm problems, or stress. Get medical care after fainting.
What it is
Fainting (syncope) is a temporary loss of consciousness from reduced blood flow to the brain.
Common causes
- Dehydration.
- Standing up fast.
- Vasovagal reaction to pain, heat or stress.
- Low blood sugar.
- Heart rhythm problems.
- Medicines.
What to do
Lie down with legs raised.
See a doctor
For first-time or repeated fainting.
Emergency
Fainting with chest pain, shortness of breath or injury. Call 911.
Mechanism
Fainting (syncope) is a brief loss of consciousness from reduced blood flow to the brain. The most common type is vasovagal syncope, triggered by pain, standing for a long time, heat, stress or the sight of blood. Heart rate and blood pressure drop suddenly. About 40 percent of people faint at least once in their lifetime.
- Orthostatic hypotension, dehydration and medicines cause fainting on standing.
- Cardiac causes such as arrhythmias and aortic stenosis are more serious.
- Fainting during exercise or without warning needs evaluation.
What to do
Lay the person flat and raise the legs. Recovery typically occurs within a minute or two. To prevent, drink fluids, avoid triggers, and sit or lie down if you feel lightheaded. See a doctor for faints with chest pain, palpitations, injury, a family history of sudden death, or fainting in older adults. Call emergency services if the person does not wake within a minute or has breathing problems.
Mechanism
Fainting (syncope) is a temporary loss of consciousness from reduced blood flow to the brain. The most common type is vasovagal syncope triggered by standing, pain, heat or emotion. About 3 percent of men and 3.5 percent of women faint at some point.
What to do
Lie down with legs raised, hydrate and avoid triggers. See a doctor if fainting happens without warning, during exercise, with chest pain or palpitations, since cardiac causes can be serious.
Types of fainting
Vasovagal syncope accounts for about 60 percent of faints. Orthostatic hypotension and cardiac syncope are other causes. Cardiac syncope has the highest risk and is associated with arrhythmias, aortic stenosis and hypertrophic cardiomyopathy. About 1 to 3 percent of emergency visits are for syncope.
Evaluation and prevention
Doctors perform an ECG, orthostatic blood pressures and sometimes an echocardiogram or heart monitor. Counter pressure maneuvers, such as crossing the legs and clenching fists, can abort vasovagal faints. Hydration of 2 to 3 liters, salt as advised and avoiding triggers help. Pass out during exercise or with a family history of sudden death needs prompt cardiology evaluation.
Based on data from the American Heart Association and the American College of Cardiology
