Cardiovascular and respiratory effects of detomidine in isoflurane-anaesthetised horses.

The research investigates the cardiovascular and respiratory effects of administering detomidine to isoflurane-anesthetized horses. It found that detomidine changes several heart and respiration measures, and it suggests that detomidine enhances some of the cardiovascular effects of isoflurane.

Research Methodology

• The research was conducted on six horses. Anaesthesia was induced in these horses using a mixture of thiopentone and guaiphenesin and maintained by breathing a mix of oxygen, air, and isoflurane.
• Using electrocardiography, the researchers evaluated the heart rate and rhythm of the horses. They also directly measured mean systemic arterial pressure (SAPm), pulmonary artery pressure (PAPm), right atrial pressure (RAPm), and pulmonary capillary wedge pressure (PCWP).
• They estimated the blood flow in the upper triceps brachii muscle using a process called laser Doppler flowmetry.
• They checked the blood gas values, pH, and haemoglobin concentration (Hb) in arterial and mixed venous blood.
• A baseline was established after stabilising anaesthesia and the results obtained were statistically compared with those observed after an intravenous bolus of detomidine had been administered. Samples were taken at intervals from 2 to 80 minutes post-injection.

Research Findings

• The data revealed that administering detomidine caused significant reductions in heart rate (HR), cardiac index (CI), and oxygen transport (O2TR). It also led to a significant increase in SAPm, systemic vascular resistance (SVR), and the utilization efficiency of oxygen (O2CU) after 2 minutes.
• Additionally, a significant decline in HR, CI, SAPm, Hb, and the content of oxygen in arterial blood (CaO2), alongside a significant increase in O2CU, were noticed 10-50 minutes after detomidine was given.
• Reducing the end-expiratory concentration of isoflurane to 1.3% led to a progressive improvement in SAPm, CI, and muscle perfusion back towards the baseline. In comparison, there was a further decrease in Hb and CaO2 against the baseline values.

Conclusion

• The research findings suggest that detomidine has the capacity to increase some of the cardiovascular effects of isoflurane in horses. This provides a deeper understanding of the combined impact of detomidine and isoflurane, which could potentially enhance the safety and efficacy of anaesthesia practices in veterinary medicine, especially with horses.