DETECTION OF TISSUE HYPOXIA BY ARTERIOVENOUS GRADIENT FOR PCO(2) AND PH IN ANESTHETIZED DOGS DURING PROGRESSIVE HEMORRHAGE

The present study tested the hypothesis that, during acute bleeding, t he development of tissue hypoxia might be reflected by an abrupt widen ing 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. Oxyg en uptake (Vo(2)) was derived from expired gas analysis and oxygen del ivery (Do(2)) was calculated by the product of the thermodilution card iac index and the arterial O-2 content. During the first part of the p rotocol, Vo(2) remained stable as the progressive reduction in Do(2) w as associated with a corresponding increase in O-2 extraction (O(2)ER) . Blood lactate increased slightly but not significantly. AV Pco(2) an d AV pH increased significantly, essentially related to venous respira tory 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) (8.60 +/- 1.12; 8.73 +/- 1.40; 8.78 +/- 1.37, respectively; P = not s ignificant). A significant correlation was found, during the hemorrhag e 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 represe nt simple but reliable indicators of tissue hypoxia during hemorrhagic shock.