JA Romand, JV Attewell and MR Pinsky
Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh, Pennsylvania, USA.

Blood flow redistribution away from the gastrointestinal tract and kidney occurs during progressive hemorrhage and stress. However, the effects of remote increases in oxygen demand on a circulation with limited ability to respond have not been described. Thus, we observed the effect of remote increases in oxygen demand on splanchnic and renal blood flow in hemorrhaged dogs. Nine alpha-chloralose-anesthetized, splenectomized dogs were subjected to hemorrhage of 10 ml/kg followed by an additional 5 ml/kg. At each of these two stages, bilateral femoral nerve stimulation was used to increase lower extremity oxygen demand while lower extremity, splanchnic, renal blood flows and arteriovenous oxygen content differences were monitored. Hemorrhage was associated with redistribution of blood flow away from the lower extremities and kidneys and increasing the oxygen extraction ratio of the splanchnic bed. Lower extremity stimulation increased whole-body oxygen consumption (7.3 +/- 2.7 to 11.4 +/- 4.5 ml O2/min/kg, p < 0.01). If arterial pressure remained stable during stimulation (> 90% of baseline value, n = 9), visceral organ blood flow did not change. However, when blood pressure decreased (< 70% of baseline, n = 8), splanchnic (226.3 +/- 143.5 to 140.9 +/- 126.4 ml/min, p < 0.01) and renal (59.6 +/- 30.2 to 28.5 +/- 26.0 ml/min, p < 0.01) blood flow also decreased. Thus, in the anesthetized, hemorrhaged dog, increased peripheral oxygen demand results in further redistribution of blood flow away from the gastrointestinal tract and kidneys only when there is a concurrent decrease in blood pressure.