Alteration of vascular capacitance and blood flow distribution during halothane anesthesia

We examined the effect of halothane on systemic vascular capacitance as well as on systemic vascular resistance using cardiopulmonary bypass in dogs. Venous outflows from two different vascular beds, the splanchnic and extrasplanchnic beds, were also measured. Under constant perfusion flow and constant central venous pressure, a change in reservoir blood volume inversely represented a change in systemic blood volume and then in systemic vascular capacitance, and a change in mean arterial pressure directly reflected a change in systemic vascular resistance. Administration of 1% and 2% halothane produced the blood concentrations of 0.58±0.14 mM and 1.34±0.06 mM, respectively. Systemic vascular resistance decreased by 12±6% and 40±4% during 1% and 2% halothane, respecitively. Systemic blood volume increased by 7±2 ml·kg^-1 and 15±4 ml·kg^-1 during 1% and 2% halothane, respectively. Halothane did not cause significant blood flow redistribution between the splanchnic and extrasplanchnic vascular beds. These results suggest that halothane causes an increase in systemic vascular capacitance as well as a decrease in systemic vascular resistance. This increase in vascular capacitance may contribute in part to a decrease in cardiac output during halothane anesthesia.