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

The research article describes a study assessing the impact of slowing down the release of a medication called dopexamine in horses under general anesthesia. While beneficial effects were noted, several adverse effects arose that could limit the medication’s clinical use.

Methodology

• The study involved seven adult Thoroughbred horses.
• They were anesthetized using halothane, a general anesthetic mostly used in veterinary medicine.
• Dopexamine was administered to the horses in a controlled, slow manner—in this case, a 60-minute infusion.
• Hemodynamic measurements—factors involved in the circulation of blood—were taken using a technique called transesophageal Doppler echocardiography and cardiac catheterization. This included factors like heart rate, cardiac output, blood flow, left and right ventricular pressures, and various other measurements related to the function of the left ventricle of the heart.

Results

• The slow release of dopexamine led to several significant changes in the horses’ hemodynamics. The effects included increased heart rate, cardiac output, maximal rates of increase and decrease of left ventricular pressure, and maximal acceleration and maximal velocity of aortic blood flow.
• The time taken for the left ventricle to eject blood—the ejection time—also significantly increased.
• Pressure in the right ventricle while it was filling with blood—the end-diastolic pressure—was significantly lower after 20 minutes of the dopexamine infusion, and it continued to decrease as the infusion went on.
• A lot of these changes, including the reduced right ventricular end-diastolic pressure, hadn’t returned to normal levels 30 minutes after the infusion ended.

Adverse Effects

• All the horses sweated heavily during the infusion.
• When coming around from the anesthesia, six of the seven horses showed signs of excitement and violently shivered.
• Within three hours of waking up, two of the horses developed colic—a severe abdominal pain caused by spasms in the horse’s digestive tract.

Conclusion

• Slowing the release of dopexamine doesn’t achieve a peak effect for many hemodynamic factors quickly—instead, the effects continue to arise as the infusion goes on.
• These changes in hemodynamics can last for an extended period after the drug is no longer being administered.
• While the use of dopexamine could be suited to treating low cardiac output in anesthetized horses, several serious side effects were observed, which could potentially reduce its suitability for clinical use.