Temporal effects of an infusion of dobutamine hydrochloride in horses anesthetized with halothane

Objective-To evaluate temporal hemodynamic effects of dobutamine in horses anesthetized with halothane.

Animals-8 adult Thoroughbreds.

Procedure-Anesthesia was induced by IV administration of romifidine and ketamine and maintained using halothane in oxygen. After 60 minutes, dobutamine was administered IV for 60 minutes at 4 mu g/kg of body weight/min. Measurements of left ventricular function were obtained by transesophageal echocardiography and cardiac catheterization.

Results-Mean, systolic, diastolic, aortic, pulmonary arterial, and left and right ventricular end-diastolic and systolic pressures, maximal rate of increase of intraventricular pressure (LVdp/dt(max)), maximum acceleration (dv/dt(max)) and velocity (V-max) of aortic blood flow, cardiac output, and left ventricular velocity time integral were significantly increased, whereas left ventricular pre-ejection period and ejection time significantly decreased. Cardiac output, LVdp/dt(max), V-max, and dv/dt(max) increased throughout infusion. Heart rate was significantly less after 10 minutes and significantly greater at 60 minutes than before infusion. Supraventricular tachycardia developed in 2 horses. Cardiac output, LVdp/dt(max), V-max dv/dt(max), left ventricular and aortic systolic pressures, and mean aortic pressure had not returned to control values 30 minutes after infusion was discontinued.

Conclusions-At this dosage, dobutamine did not achieve peak effect on many hemodynamic variables within 40 minutes of commencing infusion, and effects of 60-minute infusion persisted after infusion was discontinued.

Clinical Relevance-Dobutamine has a hemodynamic profile suited to treatment of low cardiac output in anesthetized horses; however, sustained administration may be associated with supraventricular tachycardia and a protracted time to peak effect.