Relative bradycardia: a sign of acute intraperitoneal bleeding.

Acute intraperitoneal bleeding with hypotension may be accompanied by a relatively normal pulse rate instead of the tachycardia usually produced by blood loss. Four cases of intraperitoneal bleeding of diverse, though pelvic, origin, are described. In each patient, symptomatic hypotension occurred with a pulse rate less than 80 per minute, thereby initially confusing the diagnosis of internal bleeding. The hypotension and relative bradycardia responded to atropine followed by fluid replacement. Response to atropine implies that the reflex that produces bradycardia is mediated by the parasympathetic nervous system. It is concluded that relative bradycardia occurring with intraperitoneal haemorrhage may be the cause of both diagnostic difficulty and disproportionately severe hypotension.