Propofol and hypothermic cardiopulmonary bypass. Vasodilation and enhanced metabolic protection?

The effects of propofol during low flow (1.6 l.min-1.m-2) hypothermic (27-29 degrees C) cardiopulmonary bypass on systemic haemodynamic and metabolic variables were studied in 20 patients in a parallel group comparison. Patients in the control group underwent two consecutive control periods, whereas those in the propofol group underwent a control period followed by a 'propofol' period during which they received an intravenous bolus of propofol 5 mg.kg-1 followed by an infusion at a rate of 20 mg.kg-1.h-1. Haemodynamic and metabolic variables were measured at the end of each period. The propofol group showed a significant reduction in both systemic vascular resistance (p less than 0.001) and systemic oxygen uptake (p less than 0.05). There was a small but significant fall in lactate in the control group (p less than 0.02); however, there was no significant change in the propofol group. These findings could indicate impaired tissue perfusion, although they more likely indicate systemic metabolic depression with washout of lactate from previously hypoperfused tissues.