Effect of ephedrine and phenylephrine on cardiopulmonary parameters in horses undergoing elective surgery

Objective To assess the cardiopulmonary effects of ephedrine and phenylephrine for management of isoflurane-induced hypotension in horses. Study design Prospective randomized clinical study. Animals Fourteen isoflurane-anesthetized horses undergoing digital palmar neurectomy. Methods Ephedrine (EPH group; 0.02mgkg-1 minute-1; n=7) or phenylephrine (PHE group; 0.002mgkg-1minute-1; n=7) was administered to all horses when mean arterial pressure (MAP) was <60mmHg. The infusions were ended when the target MAP was achieved, corresponding to a 50% increase over the pre-infusion MAP (baseline). The horses were instrumented with an arterial catheter to measure blood pressure and allow the collection of blood for pH and blood-gas analysis and a Swan-Ganz catheter for measurement of cardiac output using thermodilution. Cardiopulmonary parameters were recorded at baseline and at 5, 30, 60 and 90minutes after achieving the target MAP. Results In both groups, the MAP and systemic vascular resistance (SVR) increased significantly at 5, 30, 60 and 90minutes post infusion compared to baseline (p<0.05). The EPH group had a significant increase in cardiac index (CI) and systemic oxygen delivery index at 5, 30, 60 and 90minutes post infusion compared to baseline (p<0.05) and compared to the PHE group (p<0.05). The PHE group had significantly higher SVR and no decrease in oxygen extraction compared with the EPH group at 30, 60 and 90minutes post infusion (p<0.05). No significant differences in ventilatory parameters were observed between groups after the infusion. Conclusions Ephedrine increased the MAP by increasing CI and SVR. Phenylephrine increased MAP by increasing SVR but cardiac index decreased. Ephedrine resulted in better tissue oxygenation than phenylephrine. Clinical relevance Ephedrine would be preferable to phenylephrine to treat isoflurane-induced hypotension in horses since it increases blood flow and pressure.