THE EFFECTS OF PROGRESSIVE ANEMIA ON JEJUNAL MUCOSAL AND SEROSAL TISSUE OXYGENATION IN PIGS

Anemia may promote intestinal hypoxia. We studied the effects of progr essive isovolemic hemodilution on jejunal mucosal (Po(2)muc), and sero sal tissue oxygen tension (Po(2)ser, Clark-type surface electrodes), m ucosal microvascular hemoglobin oxygen saturation (Hbo(2)muc), and hem atocrit (Hctmuc; tissue reflectance spectophotometry) in a jejunal seg ment. Twelve domestic pigs were anesthetized, paralyzed, and mechanica lly ventilated. Laparatomy was performed, arterial supply of a jejunal segment isolated, and constant pressure pump perfused. Seven animals were progressively hemodiluted to systemic hematocrits (Hctsys) of 20% , 15%, 10%, and 6%. Baseline for Po(2)muc, Po(2)ser and Hbo(2)muc was 23.5 +/- 2.1 mm Hg, 57.5 +/- 4 mm Hg, and 47.0% +/- 6.4% which were no t different from the five controls. Despite a significant increase in jejunal blood flow, jejunal oxygen delivery decreased and oxygen extra ction ratio increased significantly at Hctsys 10% and 6%. Po(2)ser dec reased significantly below or at Hctsys of 15%, whereas Po(2)muc and H bo(2)muc were maintained to Hctsys of 10%, but less than 10% Hbo(2)muc and mesenteric venous pH decreased significantly, implying that physi ological limits of jejunal microvascular adaptation to severe anemia w ere reached. Decrease of Hctmuc was less pronounced than Hctsys. In co nclusion, redistribution of jejunal blood flow and an increase in the ratio of mucosal to systemic hematocrit are the main mechanisms mainta ining mucosal oxygen supply during progressive anemia.