Effects of intravenous terbutaline on heart rate, arterial pressure and blood gases in anesthetized horses breathing air.

This research study investigates the effects of using terbutaline, a bronchodilator, by IV on heart rate, blood gases and arterial pressure in anesthetized horses. Findings suggest that while being anesthetized and under the influence of terbutaline, horses experienced decreases in blood oxygen levels, heightened heart rate and reduced arterial pressure.

Research Methodology

In this prospective experimental study:

• Eight healthy adult horses, including four mares and two geldings, were included in the examination, out of which six completed the research.
• For the placement of arterial and venous catheters, horses were sedated with xylazine. Afterwards, two more drugs – midazolam and ketamine – are used to induce anesthesia.
• Anesthesia was maintained through an IV infusion of guaifenesin, ketamine, and xylazine. The animals remained in left lateral recumbency, breathing air spontaneously throughout the procedure.
• Arterial blood samples were collected for pH and blood gas analysis during several stages: during the sedation period, 15 minutes post-anesthesia induction, immediately pre and post-administration of terbutaline (at 5, 15 and 30 minutes), and once the horse was fully recovered from anesthesia.
• Heart rates and arterial pressures (systolic, mean, and diastolic) were recorded at 5-minute intervals during the anesthesia period.
• Various statistical analyses were performed to interpret the data.

Research Findings

Based on the research:

• Findings indicate that the mean PaO, which represents the partial pressure of oxygen in arterial blood, consistently decreased from the baseline to less than 60mmHg (8.0 kPa) throughout anesthesia. This decrease was statistically significant (p < 0.0001).
• The administration of terbutaline did not improve this reduced PaO level.
• Post administration of terbutaline, a significant increase in heart rate was observed (p = 0.002).
• Along with increased heart rate, systolic, mean, and diastolic arterial pressures were observed to decrease, indicating a substantial drop in blood pressure. These changes were greatest just after the administration of terbutaline, and were statistically significant (p < 0.001).

Research Conclusions

The study concluded that intravenous administration of terbutaline did not improve the oxygen levels in blood during anesthesia. Additionally, it was associated with negative cardiovascular effects, manifesting as an increased heart rate and a decrease in systemic arterial pressure in laterally recumbent, anesthetized horses. As such, care ought to be taken in the use of terbutaline in similar clinical situations.