Fainting

Fainting (Syncope): Sudden loss of consciousness

Fainting, or syncope, is a sudden, brief loss of consciousness and muscle tone, followed by rapid and complete recovery. The underlying cause is a temporary, global reduction in cerebral blood flow. Although the appearance of a person who has fainted can be very frightening, in the vast majority of cases the causes are benign. However, any episode of loss of consciousness requires medical evaluation to rule out dangerous, especially cardiac, causes.

Mechanism of fainting: Why does the brain "shut down"?

The brain requires a constant supply of oxygen and glucose via the blood to function. If blood flow to the brain suddenly drops for 6-8 seconds, that is enough for a temporary "shutdown" of consciousness. Most often this occurs due to a sudden drop in blood pressure and/or a slowing of the heart rate.

Most common types of fainting

• Vasovagal (reflex) syncope: This is the most common type. It occurs due to an excessive reaction of the autonomic nervous system to a certain trigger: severe pain, fear, sight of blood, prolonged standing in a stuffy environment. In response to the trigger, there is a sudden vasodilation and slowing of the heartbeat, leading to a drop in pressure.
• Orthostatic syncope: Fainting that occurs when moving abruptly to an upright position. Gravity "pulls" blood to the legs, and the vessels do not constrict quickly enough to maintain pressure. Often associated with dehydration or medication use.
• Cardiac syncope: The most dangerous type. The cause is heart disease that prevents it from pumping blood effectively, such as arrhythmias or structural defects.

It is important to distinguish fainting from seizures, in which loss of consciousness is accompanied by tonic-clonic movements. Read about fainting in children in the article "Fainting in children".