Comparison of respiratory function during TIVA (romifidine, ketamine, midazolam) and isoflurane anaesthesia in spontaneously breathing ponies Part I: blood gas analysis and cardiorespiratory variables.

The research study compares the effects of anaesthesia with isoflurane gas versus anaesthesia induced by a combination of intravenous drugs (TIVA technique) on the respiratory function and gas exchange parameters in ponies. The study concluded that while both techniques remained within acceptable ranges for CO2, oxygenation was significantly more impaired during anaesthesia by the TIVA technique.

Study Design and Procedure

The study was an experimental, cross-over design involving six healthy ponies. The ponies were anesthetized twice using two different methods with a minimum of two weeks apart to avoid any residual effects of anesthesia. The ponies were first sedated with romifidine and then anesthetized with midazolam and ketamine. The anesthesia was then maintained using one of two methods:

• Isoflurane gas (T-ISO)
• An intravenous infusion of romifidine, midazolam, and ketamine (T-TIVA)

The ponies were placed in lateral recumbency (on their sides) and breathed in a mixture of air with 60% oxygen. After a period of 30 minutes meant for instrumentation/stabilization, arterial and venous blood samples were taken every 10 minutes for an hour and analyzed immediately. Various parameters were measured and recorded including tidal volume (TV), minute volume (MV), respiratory rate (f(R)), packed cell volume (PCV), arterial blood pressure, and heart rate (HR).

Results and Analysis

Results were statistically analyzed using a mixed model analysis of variance (ANOVA) method with a significance level of 0.05. The results showed significant differences between the two anesthesia methods. In ponies undergoing T-TIVA anesthesia, arterial and venous oxygen pressures were lower and carbon dioxide pressures were comparably lower than those in ponies undergoing T-ISO anesthesia. The respiratory rate (f(R)) was higher and tidal volume (TV) was significantly lower in the T-TIVA group.

The study also calculated the oxygen extraction ratio (O2 ER) and found it to be significantly higher in the T-TIVA group. The venous admixture (mixture of oxygenated and deoxygenated blood) was, however, found to be unaffected by the type of anesthesia. Arterial pressure was higher and heart rate was lower in ponies under T-TIVA anesthesia.

Conclusion

The study concluded that TIVA technique-involved anesthesia caused more pronounced oxygenation impairment in ponies compared to isoflurane anesthesia, despite carbon dioxide levels remaining within acceptable levels during both procedures.