Normovolemic hemodilution improves oxygen extraction capabilities in endotoxic shock

We studied the effects of normovolemic hemodilution on tissue oxygen extrac tion capabilities in a canine model of endotoxic shock. Eighteen anesthetiz ed and mechanically ventilated dogs underwent normovolemic hemodilution wit h 6% hydroxyethyl starch solution to reach hematocrit (Het) levels around 4 0, 30, or 20% before the administration of 2 mg/kg of Escherichia coli endo toxin. Cardiac tamponade was then induced by repeated injections of normal saline into the pericardial sac to reduce cardiac output and study whole bo dy oxygen extraction capabilities. Whole body critical oxygen delivery was lower in the Hct 20% and 30% groups (8.4 +/- 0.4 and 10.4 +/- 0.7 ml.kg(-1) .min(-1), respectively) than in the Hct 40% group (12.8 +/- 0.8 ml.kg(-1).m in(-1)) (both P < 0.005). The whole body critical oxygen extraction ratio w as higher in the Het 30% and 20% groups (49.1 +/- 8.2 and 55.2 +/- 4.6%, re spectively) than in the Het 40% group (37.1 +/- 4.4 %) (both P < 0.05). Liv er critical oxygen extraction ratio was also higher in the Het 30% and 20% groups than in the Het 40% group. The arterial lactate concentrations and t he gradient between ileum mucosal PCO2 and arterial PCO2 were lower in the Hct 20% and 30% groups than in the Hct 40% group. We conclude that, during an acute reduction in blood flow during endotoxic shock in dogs, normovolem ic hemodilution is associated with improved tissue perfusion and increased oxygen extraction capabilities.