Why shouldn't both sides of the neck be massaged simultaneously during a carotid sinus massage?

No need dangerous. This maneuver works based on stimulating the carotid sinus nerve. Only one side needs to be stimulated. Vigorous massage could conceivably reduce blood flow through the carotid artery. Although rare, if this happened on both sides it could be dangerous. Therefore simultaneous bilateral carotid massage is no more effective and potentially dangerous than unilateral or sequential massage.

Related Questions

Why is it that both sides of the neck should never be massaged simultaneously during carotid sinus massage?

Carotid massage. When you massage the carotid sinus you can cut down flow to the brain, if you are pushing on both carotids you can cut that flow enough to cause serious trouble. Read more...