Tissue Oxygenation and Microchemodynamics during Endotoxemia in Rat Mesenteric Microcirculation

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Although endotoxemia sometimes leads to serious circulatory shock, the microcirculatory events in endotoxemia are not well understood. This study was undertaken to explore the relationship between systemic and microscopic circulations in endotoxemia, by using a dual microscope system that allows the simultaneous observation of OィイD22ィエD2 distribution and microcirculation in the rat mesentery.In anesthetized spontaneously breathing Wistar rats, endotoxemia was induced by the intravenous injection of lipopolysaccharide (LPS; 20mg/kg). The POィイD22ィエD2 distribution in the vicinity of mesenteric arterioles (〜20-μm diam.) was monitored for 2 hr after LPS administration, and red cell velocity (VィイD2RBCィエD2 and cell-free layer thickness (TィイD2CFLィエD2 were measured. Systemic arterial blood pressure and arterial blood gases were also measured simultaneously. Mesenteric tissue POィイD22ィエD2 (PTOィイD22ィエD2) showed a gradual decrease shortly after LPS injection, suggesting an impaired OィイD22ィエD2 supply from the arteriolar source. In arterioles, a decrease in VィイD2RBCィエD2 and an increase in TィイD2CFLィエD2 were detected at 30 min after LPS injection. In contrast, the systemic parameters except for PaCOィイD22ィエD2 did not show significant changes until 90 min. Change in PTOィイD22ィエD2 was well correlated with those in VィイD2RBCィエD2, TィイD2CFLィエD2, and PaCOィイD22ィエD2. Thus, the tissue hypoxia in the mesentery occurred prior to the systemic circulatory impairments was attributable to the decreased tissue perfusion and the increased rheological resistance to OィイD22ィエD2 transport from red cells. It was also suggested that, under the present experimental condition, PaCOィイD22ィエD2 can be used as a systemic predictor of microcirculatory oxygenation impairment.