Effects on cardiopulmonary function and oxygen delivery of doses of romifidine and xylazine followed by constant rate infusions in standing horses.

The research article discusses a study that was conducted to compare the effects of xylazine or romifidine, both α(2)-agonists, on the cardiopulmonary system of horses. The results showed that romifidine had more pronounced effects than xylazine.

Study Methodology and Procedure

• The study involved nine research horses who were treated with either xylazine or romifidine in a randomized, blinded, crossover design. This means that each horse had the treatment switched in different rounds and neither the researcher nor the horse knew which drug was being administered.
• After the horses were prepared, or instrumented, a loading dose of intravenous xylazine or romifidine was administered, immediately followed by a constant rate infusion (CRI) of the same drug for two hours.
• The aspects that were monitored and recorded before, during and after the drug administration included the haemoglobin concentration (tHb), arterial oxygen content (CaO(2)), oxygen delivery (DO(2)), the mixed venous partial pressure of oxygen, heart rate, and cardiac output (Qt).

Results and Findings

• The administration of romifidine or xylazine led to a significant decrease in haemoglobin concentration, arterial oxygen content, oxygen delivery, venous partial pressure of oxygen, heart rate, and cardiac output.
• There were significant increases in blood pressure, systemic vascular resistance, and right atrial pressure after administering each drug. These increases were followed by significant decreases compared to the baseline measurements.
• Other significant changes included an increase in mean pulmonary arterial pressure with the administration of romifidine only.
• There were no significant changes to stroke volume, arterial partial pressure of oxygen, and oxygen consumption.
• During the CRI, haemoglobin and arterial oxygen content were noticed to be significantly higher with romifidine, while oxygen delivery did not differ between the two treatments.

Conclusions of the Study

• The cardiopulmonary effects of the drugs were more pronounced and lasted longer with romifidine as opposed to xylazine.
• There were no differences identified in the oxygen delivery of the two drugs during the CRI stage.
• While the cardiovascular effects of both drugs were most pronounced after the loading dose, they leveled off and stabilized during the constant rate infusion.