• Y H Lee, K W Clarke, H I Alibhai, and D Song.
• Department of Farm Animal and Equine Medicine and Surgery, Royal Veterinary College, Hatfield, Hertfordshire, United Kingdom.
• Am. J. Vet. Res. 1998 Nov 1;59(11):1463-72.

ObjectiveTo evaluate the effect on intramuscular blood flow (IMBF) and hemodynamic variables of 4 antihypotensive agents given during anesthesia.Animals8 ponies.ProcedureHalothane-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 microg/kg of body weight), dopamine (2.5, 5, 10, and 20 microg/kg), dobutamine (1, 2.5, 5, and 10 microg/kg), and dopexamine (0.5, 1, 5, and 10 microg/kg). Changes in IMBF (by laser-Doppler flowmetry) in nondependent and dependent triceps brachii muscles and cardiopulmonary variables were measured.ResultsPhenylephrine 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 microg/kg/min) increased CI, MAP, and IMBF in the dependent muscle. A higher dose (20 microg/kg/min) caused cardiac arrhythmias and muscular tremor. Dobutamine increased Cl, MAP, and IMBF of both forelimbs, effects being significant for 2.5 microg/kg/min, with further improvement as the dosage increased. In 2 ponies, 10 microg of dobutamine/kg/min caused cardiac arrhythmias. Dopexamine (1 and 5 microg/kg/min) increased CI, MAP, and IMBF in the nondependent muscle, and 10 microg/kg/min caused muscular tremor, sweating, and arrhythmias. SVR was reduced after infusion of dopamine, dobutamine, or dopexamine.ConclusionDuring anesthesia of equids, an increase in Cl and MAP is necessary to improve IMBF in the dependent forelimb.Clinical RelevanceOf the agents investigated, dobutamine proved the most consistent in improving IMBF.

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