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; 0.02 mg kg(-1) minute(-1); n = 7) or phenylephrine (PHE group; 0.002 mg kg(-1) minute(-1); n = 7) was administered to all horses when mean arterial pressure (MAP) was <60 mmHg. 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 90 minutes after achieving the target MAP.
Results: In both groups, the MAP and systemic vascular resistance (SVR) increased significantly at 5, 30, 60 and 90 minutes 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 90 minutes 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 90 minutes 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.