Preservation of intestinal microvascular PO2 during normovolemic hemodilution in a rat model

Abstract The effect of hemodilution on the intestinal microcirculatory oxygenation is not clear. The aim of this study was to determine the effect of moderate normovolemic hemodilution on intestinal microvascular partial oxygen pressure (P o 2 ) and its relation to the mesenteric venous P o 2 (P mv o 2 ). Normovolemic hemodilution was performed in 13 anesthetized male Wistar rats. Systemic hemodynamic and intestinal oxygenation parameters were monitored. Intestinal microvascular P o 2 was measured by using the oxygen-dependent quenching of palladium-porphyrin phosphorescence. Hemodilution decreased systemic hematocrit from 45.0% ± 0.1% (average ± SEM) to 24.6% ± 1.6%. The mesenteric blood flow did not change from baseline values, resulting in a linear decrease in intestinal oxygen delivery (from 2.77 ± 0.15 to 1.42 ± 0.11 mL·kg –1 ·min –1 ). The intestinal oxygen extraction ratio increased significantly from 24% ± 1% to 42% ± 4%. P mv o 2 decreased significantly (from 57 ± 2 to 41 ± 2 mm Hg), but intestinal oxygen consumption and microvascular P o 2 remained unaffected. As a result, the difference between microvascular P o 2 and P mv o 2 increased significantly during hemodilution. Intestinal microvascular P o 2 and oxygen consumption were well preserved during moderate normo-volemic hemodilution. These results might be explained by the notion of others that hemodilution induces recruitment of capillaries, resulting in redistribution of the intestinal blood flow in favor of the microcirculation, which allows a more efficient extraction of oxygen. These findings further indicate that the use of venous P o 2 values as indicators of microvascular oxygenation may be misleading. (J Lab Clin Med 2000;135:476-83)