Effects of propofol, etomidate, and pentobarbital on critical oxygen delivery

Objective: To test the hypothesis that propofol, etomidate, and pentobarbit al increase critical oxygen delivery in a dose-dependent manner during prog ressive hemorrhage. Design: Prospective, randomized laboratory investigation. Setting: University laboratory. Subjects: A total of 40 anesthetized, paralyzed, and mechanically ventilate d dogs weighing 29.2 +/- 4.6 kg. Interventions: Dogs were randomly assigned to be anesthetized with propofol (n = 13), etomidate (n = 13), or pentobarbital (n = 14) at either low or h igh dosages. At 30 mins after splenectomy, the dogs underwent progressive h emorrhage by successive withdrawals of 3-5 mL/kg arterial blood. Measurements and Main Results: At each step of hemorrhage, oxygen consumpti on and oxygen delivery were determined. Oxygen consumption was obtained fro m expired gas analysis, and oxygen delivery was determined from thermodilut ion cardiac output and calculated arterial oxygen content. In each animal, critical oxygen delivery and critical oxygen consumption were obtained from a plot of oxygen consumption vs. oxygen delivery as the point of intersect ion of the two best-fit regression lines deter-mined by a least sum of squa res method. Critical oxygen extraction was obtained by dividing critical ox ygen consumption by critical oxygen delivery. In the three groups, animals receiving the higher anesthetic infusion had a significantly higher critica l oxygen delivery (propofol: 10.5 +/- 0.8 vs. 13.9 +/- 2.5 mL/min/m(2), p < .05; etomidate: 10.1 +/- 0.7 vs. 13.4 +/- 3.0 mL/min/m(2), p < .05; pentob arbital: 7.8 +/- 1.0 vs, 12.3 +/- 2.5 mL/min/m(2), p < .01) attributable to a lower critical oxygen extraction ratio (propofol: 41.1 +/- 6.4% vs. 54.2 +/- 2.5%, p < .01; etomidate: 42.7 +/- 10.2% vs. 60.6 +/- 7.1%, p < .01; p entobarbital: 42.2 +/- 7.2% vs. 64.3 +/- 8.8%, p < .01). Conclusions: This study indicates that propofol, etomidate, and pentobarbit al increased critical oxygen delivery in a dose-dependent manner. This effe ct was mainly related to a decrease in tissue oxygen extraction capabilitie s.