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 (mu PO2) was measured in the intestinal serosa and mucosa and the renal cortex, using the Pd-porphyrin phosphorescence technique. Intestinal luminal PCO2 was determined by air tonometry and the serosal microvascular flow by orthogonal polarization spectral imaging. RESULTS: Organ blood flow and renal and intestinal mu PO2 decreased significantly during ACC, whereas the intestinal oxygen extraction and PCO2 gap 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 O-2 delivery, serosal mu PO2 (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 PCO2 gap (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 O-2 delivery 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. (Anesth Analg 2010;111:345-53)