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Occurrence and functional consequences of shunting of the microcirculation after mesenteric ischemia

Shunting of the microcirculation contributes to the pathology of sepsis and septic shock. In this study, we hypothesize that shunting of the microcirculation occurs after superior mesenteric artery (SMA) ischemia (occlusion) and reperfusion, and we explore functional consequences using intravital microscopy.

Spontaneously breathing animals (rats) (n = 30) underwent occlusion of the SMA for 0 (controls), 30 or 60 minutes followed by reperfusion (4 hours) 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. Continuous SMA blood flow measurements were performed in comparable groups without exteriorizing an ileal loop. Adherent leukocytes increased shortly after reperfusion in ischemia groups, and plateaued in these groups. The centerline velocity and shear rate in the recorded venules were significantly reduced after reperfusion down to low-flow/no-flow in animals undergoing 60 minutes of mesenteric artery occlusion compared with animals with 30 minutes occlusion and controls, whereas perfusion of the SMA and ileal vessels persisted. The microcirculatory changes in animals with 60 minutes occlusion were accompanied by progressive metabolic acidosis, substantially larger volumes of intravenous fluids needed to support arterial blood pressure and significantly reduced survival (30%). In the groups with continuous SMA blood flow measurements, SMA blood flow increased in relation to abdominal blood flow after reperfusion in animals with 60 minutes occlusion, and remained constant in animals undergoing 30 minutes occlusion and controls. Survival was 80% in animals with 60 minutes occlusion without an exteriorized ileal loop. SMA occlusion for 60 minutes and subsequent reperfusion causes perfusion abnormalities in the mesenteric microcirculation as often seen in sepsis and septic shock with increased microcirculation shunting, progressive metabolic acidosis and increased mortality. To detect these significant changes requires prolonged observation periods and might help to find new treatments to improve the poor prognosis of mesenteric ischemia.

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Lauterbach, M., Horstick, G., Plum, N. et al. Occurrence and functional consequences of shunting of the microcirculation after mesenteric ischemia. Crit Care 11 (Suppl 2), P270 (2007).

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