Encyclopedia / S / Syncope (Fainting)

Syncope (Fainting)


Syncope is the medical term for fainting. This is a brief lapse in consciousness caused by transient cerebral hypoxia (diminished oxygen).

Syncope usually is preceded by a sensation of light-headedness and may often be prevented by lying down or by sitting with the head between the knees. It may be caused by many different factors including emotional stress, vagal (nerve) stimulation, pooling of blood in the legs, or sudden change in environmental temperature or body position.

Syncope must be separated from seizures and other states of altered consciousness such as dizziness, vertigo, coma, and narcolepsy.


Fainting (syncope) occurs when the blood supply in the brain is temporarily inadequate and is restored in a minute or so. There are many causes of fainting, ranging from benign to serious. A fainting episode can have no medical significance or it can be a symptom of a serious disorder.

Some people faint at the sight of blood, after intense pain, emotional shock, or as a result of severe anxiety or fatigue. This is due to reflexes that slow the heart and dilate blood vessel resulting in a fall in blood pressure.

Fainting is not uncommon during the early stages of pregnancy. Cardiovascular, neurological, and metabolic problems (such as hypoglycemia), and adverse drug reactions are also causes of fainting. Anyone who experiences a fainting episode or "blackout" should see a doctor to determine the cause.

Loss of consciousness is reported by 12 to 48 percent of young adults. Approximately one-third of these are related to trauma or ingestion of ethanol and the remaining are syncope.

Syncope also is a common presenting complaint accounting for 1 to 6 percent of hospital admissions and 3 percent of emergency room visits. Syncope is also common in the elderly.


The basic causes of syncope are:

  • Abnormalities of regulation of blood pressure and blood flow
  • Cardiac reasons, including mechanical or electrophysiologic abnormalities
  • Underlying neurologic disorders such as seizure disorders
  • Abnormalities of metabolic or endocrine function
  • Psychiatric disturbances


Medical history and a physical examination are particularly helpful in the evaluation of patients with syncope or near-syncope.


Treatment of syncope is based upon the cause and can be aimed at everything from improving blood flow or volume, to improving the ability of the heart to pump blood, to treating underlying neurologic disorders.


What is the cause of the fainting?

How serious is the condition?

What treatment will you be recommending?

Should a specialist be consulted?

Are there any signs or symptoms that I should pay particular attention to?