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

The study explores how dobutamine, a drug typically used to increase heart performance, affects a horse’s hemodynamic (blood flow-related) functions over time when the horses are under halothane anesthesia.

Research Methodology

• The research involved 8 adult Thoroughbred horses.
• Anesthesia was induced in these horses via an intravenous administration of romifidine and ketamine and was maintained using halothane in oxygen.
• After 60 minutes of anesthetization, dobutamine was administered intravenously to the horses for 60 minutes at 4 micrograms per kilogram of body weight.
• Left ventricular function measurements were taken by employing transesophageal echocardiography and cardiac catheterization techniques.

Results of the Study

• Several blood flow and heart performance-related metrics increased significantly. These include mean, systolic, diastolic, aortic, pulmonary arterial, and left and right ventricular pressures, maximum rate and acceleration of intra-ventricular pressure, velocity of aortic blood flow, cardiac output, and left ventricular velocity time integral.
• Conversely, left ventricular pre-ejection period and ejection time decreased significantly.
• Cardiac output, maximum rate and acceleration of intra-ventricular pressure, and velocity of aortic blood flow increased throughout the dobutamine infusion.
• The heart rate was found to be significantly lower after 10 minutes but significantly higher after 60 minutes of dobutamine infusion compared to heart rate before the infusion.
• Supraventricular tachycardia, a condition where the heart beats abnormally fast, developed in 2 of the horses.
• Certain hemodynamic variables such as cardiac output, maximum rate and acceleration of intra-ventricular pressure, left ventricular and aortic systolic pressures, and mean aortic pressure had not returned to their original values even 30 minutes after the dobutamine infusion was stopped.

Conclusions of the Study

• Many hemodynamic variables didn’t reach their peak effect until 40 minutes after starting the dobutamine infusion. Furthermore, the effects of a 60-minute infusion persisted even after the infusion was discontinued.
• Dobutamine’s hemodynamic profile makes it suitable to treat low cardiac output in anesthetized horses. However, sustained administration may be linked to supraventricular tachycardia and a delayed time to peak effect.