Effects of phenylephrine and prostaglandin E₁ on ventriculo-arterial matching during halothane anaesthesia

We have investigated the effects of phenylephrine alone and combined with prostaglandin E₁ (PGE₁) on ventriculo-arterial matching during halothane anaesthesia in dogs. The ratio of left ventricular end-systolic elastance (Ees) to effective arterial elastance (Ea) was used as an index of ventriculo-arterial matching. In group 1 (n = 7), measurements were performed at control, 1.5% halothane, halothane + phenylephrine 1-10 μg kg^-1 min^-1, and halothane + phenylephrine + PGE₁ 0.2-1.0 or 1.0-2.0 μg kg^-1 min^-1. In group 2 (n = 5), dobutamine 2 and 5 μg kg^-1 min^-1 was infused during halothane anaesthesia. Halothane 1.5% decreased mean arterial pressure (MAP), cardiac output and Ees. Phenylephrine restored MAP, but further decreased cardiac output. The decrease in Ees produced by halothane was reversed by phenylephrine. PGE₁ increased cardiac output and reversed the increases in Ea and Ea/Ees during phenylephrine infusion. Dobutamine also reversed halothane-induced decreases in MAP, cardiac output and Ees, and improved Ea/Ees. Our results indicate that combined use of PGE₁ with phenylephrine can eliminate the vasoconstrictive property of phenylephrine, resulting in an improvement in ventriculo-arterial matching.