A clinical comparison of two anaesthetic protocols using lidocaine or medetomidine in horses.

This research study compares the effects of two balanced anaesthetic protocols, one using lidocaine and the other using medetomidine, on the cardiopulmonary performance, isoflurane levels, and quality of recovery in horses undergoing elective surgery.

Study Methodology

• The study involved 69 horses, divided into two groups. Group L (37 horses) were given xylazine and lidocaine, while group M (31 horses) were given medetomidine. These drugs are all types of sedatives or anaesthetics.
• All horses were first premedicated with acepromazine before the induction of anaesthesia. Each horse was then given either xylazine (group L) or medetomidine (group M) for sedation, depending on their assigned group.
• Anaesthesia was then induced with Ketamine and Diazepam, and maintained with isoflurane mixed with oxygen/air. Throughout the anaesthesia process, the horses were also given a continuous infusion (CRI) of either lidocaine (for group L) or medetomidine (for group M).
• If a horse showed signs of movement or eye-related disturbance (nystagmus), additional doses of thiopental or ketamine were administered.
• Various physiological parameters such as heart rate, mean arterial pressure (MAP), end-tidal isoflurane (Fe’ISO), and blood gases were constantly measured. Cardiac output was measured in some horses using the lithium dilution method for every 45 minutes. The recovery process of the horses was also carefully observed and scored.

Study Findings

• The heart rate and cardiac index (a measure of cardiac performance) were significantly higher in the Lidocaine group (group L). In the Medetomidine group (group M), mean arterial pressure was significantly higher in the initial 50 minutes.
• It was observed that horses in group L needed more ketamine and thiopental to maintain a surgical level of anaesthesia. The isoflurane level (Fe’ISO) was also significantly higher from 70 minutes in this group.
• In terms of recovery, horses in the Medetomidine group took longer to recover but the quality of the recovery was observed to be better.

Conclusion

• The researchers concluded that the Medetomidine group had a more stable anaesthetic depth and required less isoflurane to maintain a surgical plane of anaesthesia. Even though their recovery was longer, it was of a better quality than the Lidocaine group.
• On the other hand, the Lidocaine group had a higher cardiac index, but despite this, the cardiovascular function was generally well maintained in both groups.
• Therefore, while both protocols had their advantages and disadvantages, it was acknowledged that different horses may respond better to one protocol over another for various reasons.