Local blood flow changes in the renal cortex during tourniquet and burn shock in rats

Intermittent patchy ischemia in the renal cortex has been observed in dogs during traumatic shock. In search of a model for further studies of this phenomenon in anesthetized rats, we induced tourniquet shock by bilateral hindlimb occlusion for 3 1/2 h, and burn shock by scalding the hind 50% of body surface for 30 sec in 90 degrees C water. Local cortical blood flow (RCF) was repeatedly measured by the H2-washout technique. After releasing the tourniquets, mean arterial pressure (AP) and RCF decreased by 44 and 68% whereas hematocrit (Hct) rose to 66 vol%. Only two episodes of local ischemia were observed. After scalding, Hct first fell to 49 vol%, probably due to hemolysis, but rose toward 54 vol% in the next 2 h. Following an initial drop to 99 mmHg, AP was relatively well maintained throughout the experiment. The RCF fell to 53% of control within 15 min with a further decrease to 40% during the next 2 h. The cortical vascular resistance was increased by 89%. Increased local flow heterogeneity and episodes of patchy intermittent ischemia were observed in six out of eight rats. During the second hour postburn, 21% of the washout curves showed abrupt shifts of washout rates, indicating local cortical ischemia. The burn shock model seems well suited for studies of the mechanisms causing intermittent local ischemia.