CALCIUM ATTENUATES EPINEPHRINE BETA-ADRENERGIC EFFECTS IN POSTOPERATIVE HEART-SURGERY PATIENTS

Epinephrine and calcium possess both cardiac inotropic and vasopressor activity. In addition, epinephrine's cardiovascular effects are mediated via increases in intracellular calcium. As a result, many clinicians administer the two agents together in an attempt to augment their effects. Although this approach seems rational, it has never been proven effective. We evaluated the cardiovascular and hyperglycemic actions of epinephrine (10 and 30 ng/kg/min), with and without calcium chloride administration (10 mg/kg bolus followed by 2 mg/kg/hr infusion), in a prospective, randomized, blinded, crossover designed study. Twelve adult patients were studied 1 day after aortocoronary bypass surgery. Calcium chloride raised ionized calcium levels from 1.06±0.03 (mean±SEM) to 1.44±0.05 mM (p<0.05). Calcium raised mean arterial pressure from 85±1 to 94±2 mm Hg (p<0.05) but had no significant effect on cardiac index. Epinephrine alone at 10 and 30 ng/kg/min significantly raised cardiac index from 2.7±0.2 to 3.0±0.2 (p<0.05) and 3.6±0.3 (p<0.05) 1/min/m2. After calcium, epinephrine failed to significantly increase cardiac index. Epinephrine at 30 ng/kg/min significantly increased mean arterial pressure from 87±1 to 95±2 mm Hg (p<0.05). After calcium, epinephrine had no significant effect on blood pressure. In addition, epinephrine's hyperglycemic effect was blunted by calcium. Plasma epinephrine levels were similar during control and calcium infusions. We conclude that calcium blunts epinephrine's β-adrenergic actions in postoperative cardiac surgery patients.