[Vascular effects of urapidil administrated during extracorporeal circulation]

Urapidil exerts a combined central sympathetic and peripheral alpha-1 adrenergic receptor inhibition. Urapidil induces arterial vasodilation but its effects on venous capacitance are more difficult to assess. During cardiopulmonary bypass with constant perfusion index (2.4 l.min-1 x m-2) total peripheral resistance varies similarly as to arterial pressure and, as the apparatus venous reservoir is filled continuously by simple gravity from the right atrium, a decrease in venous blood reservoir level reflects an increased venous capacitance. Twenty-six patients undergoing cardiac surgery were anaesthetized with fentanyl and midazolam and randomly assigned to one of two groups. During normothermic cardiopulmonary bypass, group 1 was administered i.v. urapidil 12.5 mg and group 2 a placebo. In group 1, arterial pressure decreased by 33 +/- 14% (mean +/- SD) at the second minute while total peripheral resistance decreased from 1,384 +/- 255 to 927 +/- 193 dyn.s.cm-5. Then this two parameters regained group 2 values after the eighth minute. Reservoir blood level was lower in group 1 than in group 2 from the second to the eight minute (p < 0.05) with maximum effect at 7 minutes. It is concluded that urapidil exerts arterial and venous dilation. Its arterial effects seem greater during normothermic cardiopulmonary bypass than in normal conditions and its maximum venous effects seem to occur after its maximum arterial effects. The short duration of action may be due to the small dose administered.