Detection of tissue hypoxia by arteriovenous gradient for PCO2 and pH in anesthetized dogs during progressive hemorrhage.

The present study tested the hypothesis that, during acute bleeding, the development of tissue hypoxia might be reflected by an abrupt widening in arteriovenous gradient for Pco 2 (AV Pco 2 ) and for pH (AV pH) as accurately as by an increase in blood lactate levels. Twenty-four anesthetized (isoflurane 1.4% endtidal), paralyzed, and mechanically ventilated dogs submitted to progressive hemorrhage were studied. Oxygen uptake (Vo 2 ) was derived from expired gas analysis and oxygen delivery (Do 2 ) was calculated by the product of the thermodilution cardiac index and the arterial O 2 content. During the first part of the protocol, Vo 2 remained stable as the progressive reduction in Do 2 was associated with a corresponding increase in O 2 extraction (O 2 ER). Blood lactate increased slightly but not significantly. AV Pco 2 and AV pH increased significantly, essentially related to venous respiratory acidosis. The critical value of Do 2 below which Vo 2 decreased was 8.95±1.60 mL.min -1 .kg -1 . Below this value, there was a marked increase in blood lactate and an abrupt widening in AV Pco 2 and AV pH gradients. The critical value of Do 2 obtained from blood lactate, AV Pco 2 and AV pH were similar to those obtained from Vo 2 (8.6±1.12; 8.73±1.40; 8.78±1.37, respectively; P=not significant). A significant correlation was found, during the hemorrhage protocol, between blood lactate and AV Pco 2 (r=0.84; P<0.001) or AV pH (r=0.78; P<0.001). THEREFORE, AV PCO 2 and AV pH represent simple but reliable indicators of tissue hypoxia during hemorrhagic shock