Histamine blockade and cardiovascular changes following heparin administration during cardiac surgery

Large doses of heparin given as a bolus may produce hypotension; however, conflicting reports exist about the mechanisms involved. This study was undertaken to determine the role of histamine in beef lung heparin-induced hypotension and the efficacy of histamine-receptor blockade in attenuating this undesirable side effect in patients undergoing cardiac surgery. Two hundred patients with good ventricular function were studied after they were randomized into four equal groups. Group I (control) received no histamine-receptor blockade, group II received 1 mg/kg of diphenhydramine 30 minutes prior to heparin administration, group III received 5 mg/kg of cimetidine 4 hours and again 30 minutes before heparin administration, and group IV received 1 mg/kg of diphenhydramine 30 minutes prior to heparin administration and 5 mg/kg of cimetidine 4 hours and 30 minutes before heparin administration. Hemodynamic variables, plasma histamine, and ionized calcium levels were measured before and after heparin administration. Significant hypotension occurred in group I patients after heparin administration. Mean arterial pressure decreased from 95 +/- 5 to 67 +/- 1.5 mm Hg (P less than 0.005) after 1 minute and to 85 +/- 2 mm Hg (P less than 0.05) at 4 minutes. Those changes were significantly greater than in group II (P less than 0.025) and Group IV (P less than 0.005) patients, in whom no significant hypotension was found. In group III, mean arterial pressure decreased from 92 +/- 3 to 75 +/- 1 mm Hg (P less than 0.05) after 1 minute and returned toward baseline values after 4 minutes. Histamine levels increased significantly in all groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)