Shunting of the microcirculation after mesenteric ischemia and reperfusion is a function of ischemia time and increases mortality

Objective: Shunting of the microcirculation contributes to the pathology of sepsis and septic shock. The authors address the hypothesis that shunting of the microcirculation occurs after superior mesenteric artery occlusion (SMAO) and reperfusion, and explore functional consequences. Methods: Spontaneously breathing animals (rats) ( n = 30) underwent SMAO for 0 (controls), 30 (SMAO_30) or 60 min (SMAO_60) followed by reperfusion (4 h) with normal saline. Leukocyte-endothelial interactions in mesenteric venules were quantified in an exteriorized ileal loop using intravital microscopy. Abdominal blood flow was recorded continuously, and arterial blood gases were analyzed at intervals. The above groups were matched by comparable groups with continuous superior mesenteric artery blood flow measurements and without exteriorizing an ileal loop (controls*, SMAO_30*, SMAO_60*). Results: Adherent leukocytes increased shortly after reperfusion in ischemia groups, and plateaued in these groups. Centerline velocity in the recorded venules was significantly reduced after reperfusion down to low-flow/no-flow in SMAO_60 as compared to SMAO_30 and controls, whereas perfusion of the SMA and ileal vessels persisted. The microcirculatory changes in SMAO_60 were accompanied by progressive metabolic acidosis, substantially larger volumes of intravenous fluids needed to support arterial blood pressure and significantly reduced survival (30%). SMA blood flow increased in relation to abdominal blood flow after reperfusion in SMAO_60*, and remained constant in SMAO_30* and controls*. Survival was 80% in SMAO_60*. Conclusion: Shunting of the microcirculation can be observed after SMAO for 60 min and reperfusion, and contributes significantly to the pathology of mesenteric ischemia and poor outcome.