Effects of dopamine, dobutamine, dopexamine, phenylephrine, and saline solution on intramuscular blood flow and other cardiopulmonary variables in halothane-anesthetized ponies

Abstract

Abstract Objective To evaluate the effect on intramuscular blood flow (IMBF) and hemodynamic variables of 4 antihypotensive agents given during anesthesia. Animals 8 ponies. Procedure Halothane-anesthetized ponies (n = 6) positioned in lateral recumbency received, on separate occasions, infusions of each of the following 4 agents in serially increasing dosages or saline solution: phenylephrine hydrochloride (0.25, 0.5, 1, and 2 μg/kg of body weight), dopamine (2.5, 5, 10, and 20 μg/kg), dobutamine (1, 2.5, 5, and 10 μg/kg), and dopexamine (0.5, 1, 5, and 10 μg/kg). Changes in IMBF (by laser-Doppler flowmetry) in nondependent and dependent triceps brachii muscles and cardiopulmonary variables were measured. Results Phenylephrine at all dosages failed to improve IMBF or cardiac index (CI), but increased mean arterial pressure (MAP) and systemic vascular resistance (SVR); 2 ponies had forelimb lameness on recovery. Dopamine (10 μg/kg/min) increased Cl, MAP, and IMBF in the dependant muscle. A higher dose (20 μg/kg/min) caused cardiac arrhythmias and muscular tremor. Dobutamine increased Cl, MAP, and IMBF of both forelimbs, effects being significant for 2.5 μg/kg/min, with further improvement as the dosage increased. In 2 ponies, 10 μg of dobutamine/kg/min caused cardiac arrhythmias. Dopexamine (1 and 5 μg/kg/min) increased Cl, MAP, and IMBF in the nondependent muscle, and 10 μg/kg/min caused muscular tremor, sweating, and arrhythmias. SVR was reduced after infusion of dopamine, dobutamine, or dopexamine. Conclusion During anesthesia of equids, an increase in CI and MAP is necessary to improve IMBF in the dependant forelimb. Clinical Relevance Of the agents investigated, dobutamine proved the most consistent in improving IMBF. (Am J Vet Res 1998;59:1463–1472)