Hypoglycemia as a possible factor in the induction of vasovagal syncope.

Glucose level was estimated in capillary blood of 16 patients, who had vasovagal syncope during exodontia with local anaesthesia. One consistent finding was the low blood sugar level in all patients during syncope, as compared with the level 1 hour after recovery. Hypoglycemia can be induced by parasympathetic activation; this may be the product of reflex conditioning. Modest lowering of blood sugar levels can also act in synergy with hypotension and hypocapnea to induce loss of consciousness. Psychogenic syncope may be mediated through a mechanism involving hypoglycemia. Reflex conditioning perhaps accounts for the small but consistent fraction of the adult population who have repeated fainting episodes.