Regional changes in cerebral blood flow during acute endotoxemia

Summary

Endotoxin has been shown to deteriorate autoregulation of Wood flow in liver, kidney and splanchnic organs. Despite frequently observed early changes in mental status in septic patients, regional cerebral blood flow (rCBF) has not been studied during the initial phase of endotoxemia. In 10 barnraised pigs, hyperdynamic endotoxemia was induced by continuous i.v. infusion of S. abortus equi endotoxin (total dose 13 μg/kg). A fall in pulmonary capillary wedge pressure (PCWP) was prevented by controlled infusion of Dextran 60. Arterial PCO₂ was maintained at 40 mmHg by adapting the tidal volume of the respirator. Central hemodynamics, ventilatory parameters and rCBF (quantified by means of radioactively labeled microspheres ø15 μm) were measured before and 30, 90 and 150 min after endotoxemia. Furthermore, the concentration of endotoxin in the plasma was quantified using chromogenic substrate (Limulus A moebocyte Lysate Test). Despite a significant drop in mean aortic pressure from 128 to 78 mmHg within 90 min of endotoxemia, the blood flow in cerebral cortex, medulla, nucleus caudatus, brain stem lamina quadrigemina and cerebellum remained within the control range. rCBF was independent of the actual concentration of endotoxin in the plasma. In contrast, deterioration of microcirculatory perfusion was observed in myocardium and kidney. We are led to conclude that the autoregulation of rCBF is maintained during the initial phase of endotoxemia. The results of the present study suggest that brain vessels respond differently to endotoxin or endotoxin-released mediators from visceral vessels.