What is neurally mediated syncope?

Adapted from materials by Joel Hardin, M.D.

What is syncope?

"Syncope" refers to a brief loss of consciousness, usually related to temporarily insufficient blood flow to the brain: a fainting spell. It may be caused by many different things, including emotional stress, sudden pain, sudden changes in body position, or dehydration (e.g. after heavy sweating.) Rarely, syncope can be caused by heart disorders, but fortunately these are very rare in children and young adults.

 What is neurally mediated syncope?

Neurally mediated syncope (NMS) is a harmless form of fainting that is common in children and teenagers. In fact, it's the most common cause of fainting, or near fainting, in young people. It seems to be particularly common in tall, slim teenage girls, although boys and girls of all body types can have it.

 NMS happens when blood pressure or heart rate drops, reducing circulation to the brain. It can cause dizziness, lightheadedness, or loss of consciousness. Children having an episode of NMS often describe it as feeling weak or dizzy, "seeing white" or seeing spots, feeling shaky or trembling. Parents or other people watching the episode often comment that the child seemed to be pale and sweaty appearing before passing out. If the fainting is prolonged, it can even trigger a seizure. (Placing the child in a reclining position will restore blood flow to the brain, resulting in return of consciousness and an end to the seizure.) Over two-thirds of children with NMS will have it more than once. NMS is not caused by a weak heart or heart problems.

 What can I do for NMS?

Most of the time, NMS can be avoided by:

  • Lying down before losing consciousness. Fortunately, most children have symptoms which signal a spell is about to happen: nausea or vomiting, turning pale, lightheadedness, dizziness, visual disturbances, sweating, and shortness of breath. These let the young person know that it's time to lie down and take a break.
  • Wearing elastic hose or tights to prevent venous pooling in the legs.
  • Increasing salt and water intake. Adding an extra gram of salt per day and an extra liter of fluids per day help maintain good blood volume.
  • Eating regularly. Poor diet also precipitates a "faint" feeling. Anemia from poor diet can also be a contributing factor.
  • Avoiding noxious stimuli that precipitate syncope, such as pain, fear, exhaustion, hunger, prolonged standing, or crowded/poorly ventilated rooms. Acute illness (colds, "flu," etc.) is also a stimulus.
  • Intermittently contracting leg muscles when standing to increase venous return.
  • Avoiding drugs that can increase the likelihood of NMS, like alcohol, beta-blockers, and tricyclic antidepressants.

In cases where NMS continues to be common and disruptive in spite of doing the above, medications like hydrofluorocortisone or pseudoephedrine can be given to raise blood pressure. Fortunately, though, this is pretty unusual.