Aortic cross-clamping and reperfusion in pigs reduces microvascular oxygenation by altered systemic and regional blood flow distribution

Background: In this study, we tested the hypothesis that aortic cross-clamping (ACC) and reperfusion cause distributive alterations of oxygenation and perfusion in the microcirculation of the gut and kidneys despite normal systemic hemodynamics and oxygenation. Methods: Fifteen anesthetized pigs were randomized between an ACC group (n = 10), undergoing 45 minutes of aortic clamping above the superior mesenteric artery, and a time-matched sham surgery control group (n = 5). Systemic, intestinal, and renal hemodynamics and oxygenation variables were monitored during 4 hours of reperfusion. Microvascular oxygen partial pressure (μPO2) was measured in the intestinal serosa and mucosa and the renal cortex, using the Pd-porphyrin phosphorescence technique. Intestinal luminal PCO2was determined by air tonometry and the serosal microvascular flow by orthogonal polarization spectral imaging. Results: Organ blood flow and renal and intestinal μPO2decreased significantly during ACC, whereas the intestinal oxygen extraction and PCO2gap increased. The intestinal response to reperfusion after ACC was a sustained reactive hyperemia but no such effect was seen in the kidney. Despite a sustained high intestinal O2delivery, serosal μPO2(median [range], 49 mm Hg [41-67 mm Hg] versus 37 mm Hg [27-41 mm Hg]; P < 0.05 baseline versus 4 hours reperfusion) and the absolute number of perfused microvessels decreased along with an increased intestinal PCO2gap (17 mm Hg [10-19 mm Hg] versus 23 mm Hg [19-30 mm Hg]; P < 0.05). In contrast, the kidney showed a progressive O2delivery decrease accompanied by a decrease in renal cortex oxygenation (70 mm Hg [52-93 mm Hg] versus 57 mm Hg [33-64 mm Hg]; P < 0.05). Conclusion: Increased systemic and regional blood flow and oxygen supply after ACC does not ensure adequate regional blood flow and microcirculatory oxygenation in all organs.

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