Preservation of intestinal microvascular Po-2 during normovolemic hemodilution in a rat model

The effect of hemodilution on the intestinal micracirculatory oxygenation i s not clear. The aim of this study was to determine the effect of moderate normovolemic hemodilution on intestinal microvascular partial oxygen pressu re (PO2) and its relation to the mesenteric venous PO2 (PmvO2) Normovolemic hemodilution was performed in 13 anesthetized male Wistar rats. Systemic h emodynamic and intestinal oxygenation parameters were monitored, Intestinal microvascular Po, was measured by using the oxygen-dependent quenching of palladium-porphyrin phosphorescence. Hemodilution decreased systemic hemato crit from 45.0% +/- 0.1% (average +/- SEM) to 24.6% +/- 1.6%. The mesenteri c blood flow did not change from baseline values, resulting in a linear dec rease 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 signific antly from 24% 1% to 42% +/- 4%, PmvO2 decreased significantly (from 57 +/- 2 to 41+/-e 2 mm Hg), but intestinal oxygen consumption and microvascular Po, remained unaffected. As a result, the difference between microvascular PO2 and PmvO2 increased significantly during hemodilution. intestinal micro vascular Po, and oxygen consumption were well preserved during moderate nor movolemic hemodilution. These results might be explained by the notion of o thers that hemodilution induces recruitment of capillaries, resulting in re distribution 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 PO2 values as indicators of microvascular oxygenation may be misleading.