Intravenous heparin for cardiopulmonary bypass is an acute vasodilator.

Study Objectives: To investigate the changes in hemodynamic profile during cardiopulmonary bypass, and determine the effect of intravenous (IV) heparin on serum chemistry and acid-base status.
Design: Prospective study.
Setting: Three Canadian hospitals.
Patients: 43 consecutive patients undergoing elective aortocoronary bypass.
Interventions: Anesthetic technique was standarized. Hemodynamic profile, blood gases, and serum electrolytes were measured immediately before IV heparin for cardiopulmonary bypass, and 5 minutes after.
Results: Mean arterial pressure (MAP) decreased by a mean of 11.2 mmHg (12.5%, p = 0.0001) in all patients, of whom 28% were treated with vasoactive drugs to restore MAP. Mean systemic vascular resistance decreased by 418 dyne sec/cm(5) (25%, p = 0.0001), and mean serum potassium increased by 0.14 meq/L (p = 0.0002). The reduction in MAP correlated strongly with the reduction in SVR (p = 0.004), but not with changes in potassium or other variables.
Implications: Mean arterial pressure is significantly affected by IV heparin for cardiopulmonary bypass. The hemodynamic mechanism is systemic vasodilation, implying that treatment with a short-acting vasoconstrictor is appropriate, if necessary. Unlike earlier studies, the increase in serum potassium observed, although reproducible, was trivial.