Cardiopulmonary effects and anaesthesia recovery quality in horses anaesthetized with isoflurane and low-dose S-ketamine or medetomidine infusions.

The research investigates the effects of using isoflurane with either low-dose S-ketamine or medetomidine infusions on the cardiopulmonary response and quality of anaesthesia recovery in horses. They carried out a clinical trial involving 50 horses and found that using S-ketamine resulted in higher cardiac index, however, the quality of anaesthesia recovery was significantly better with medetomidine.

Methods

The study was a randomized, blinded, prospective clinical trial involving 50 horses that were slated for elective surgery. The horses were premedicated with acepromazine and flunixin meglumine, after which they were given medetomidine. Anaesthesia was induced using midazolam and either racemic ketamine (for the Med group) or S-ketamine (for the S-ket group). The horses’ anaesthesia was then maintained with isoflurane in an oxygen/air mix plus either medetomidine or S-ketamine.

• The researchers measured cardiopulmonary variables such as isoflurane end-tidal concentrations, heart rate, and blood pressure. They also recorded the dobutamine requirements and use of thiopental boli.
• To estimate S-ketamine and S-norketamine concentrations, plasma samples were taken from six horses.

Results

The research found that whilst the mean Fe’Iso (isoflurane end-tidal concentrations) required by both groups was similar, the horses in the S-ket group required more thiopental boli.

• The median intraoperative cardiac index values were higher with S-ket compared to Med.
• Though there were no major differences in heart rate, blood pressure, or dobutamine requirements across the two groups, the S-ket group showed a higher heart rate 30 minutes after the anaesthesia was induced.
• Horses in the S-ket group had decreased PaO and increased pulmonary venous admixture values as estimated by the Fshunt calculation.
• Recovery times were shorter and of lesser quality with S-ket compared to Med, where recoveries were of better quality.
• During the infusion, S-ketamine and S-norketamine plasma concentrations were found to be in the ranges of 0.209-0.917 μg mL and 0.250-0.723 μg mL, respectively.

Conclusions

Despite the higher intraoperative cardiac index associated with S-ket, both protocols were deemed to provide acceptable cardiovascular function. However, the quality of anaesthesia recovery was significantly better in the Med group. This research suggests that for horses undergoing elective surgery, using medetomidine with isoflurane might lead to better anaesthesia recovery compared to using S-ketamine with isoflurane.