The effect of hemodilution on blood flow regulation in normal and postischemic intestine

We investigated the effect of hemodilution on intestinal blood flow and oxygen consumption ( VO 2) in denervated rat small intestinal preparations. In one series of experiments, intestinal blood flow (IBF) and intestinal oxygen extraction (A- VO 2) were measured during graded decreases in perfusion pressure. Control animals underwent consecutive studies without hemodilution; experimental animals were studied before and after isovolemic hemodilution. In a second series of experiments, normovolemic hemodilution was performed in experimental animals NH while hematocrit was maintained in controls, C. Preparations were then subjected to 30 min of complete ischemia followed by 30 min of reperfusion. Hemodilution (40.5 ± 0.8% to 17.2 ± 2.5%) decreased A- VO 2 (3.9 ± 0.5 to 2.1 ± 0.4 ml/dl; P < 0.05) but increased IBF (77.5 ± 9.8 to 132.1 ± 15.0 ml/min/100 gm; P < 0.01). IBF was maintained to the limit of pressure: flow autoregulation (69 mmHg). Below this point, decreases in IBF were accompanied by increases in A- VO 2 thus maintaining VO 2. At a much lower “critical pressure” (42 mmHg) maximal oxygen extraction was reached and VO 2 decreased with IBF. In the second series of experiments, hemodiluted animals (hematocrit 25 ± 1%) studied during the reperfusion period maintained higher O 2 consumption [30 min values (ml/min/100 gm): 4.8 ± 0.9 NH vs 1.6 ± 0.2 C, P < 0.01] and A- VO 2 difference [30 min values (vol%): 3.9 ± 0.4 NH vs 2.1 ± 0.4 C, P < 0.005] than control animals (hct 33 ± 2%). Hemodilution does not impair the intestine's ability to maintain O 2 consumption during hypotension and hypoperfusion. Hemodilution may be beneficial during reperfusion of postischemic intestine as reperfusion oxygen consumption in hemodiluted animals was significantly higher than control animals subjected to equivalent periods of ischemia.