# Effect of a Constant Rate Infusion of Ketamine on a Variable Rate Infusion of Xylazine in Standing Horses Undergoing Ventriculocordectomy and Laryngoplasty

## TL;DR

This study tested if adding ketamine to xylazine improves sedation in horses during surgery without increasing risks.

## Contribution

The study provides new clinical evidence on the effects of combining low-dose ketamine with xylazine for equine sedation.

## Key findings

- Adding ketamine did not reduce the xylazine infusion rate needed for sedation.
- Horses receiving ketamine had deeper sedation without increased instability or cardiorespiratory issues.
- No adverse events occurred in either group during the procedures.

## Abstract

Performing surgery on standing horses under sedation helps avoid the high risks of general anesthesia. However, effective sedation is needed to keep the horse still and pain-free without causing harm. Xylazine is a common horse sedative, but higher doses can cause side effects like wobbliness and heart or breathing problems. This study explored whether adding a low dose of ketamine as a continuous infusion could reduce the amount of xylazine rate infusion needed and improve sedation quality during standing throat surgery. Fifty-one horses undergoing these procedures received either xylazine alone or xylazine with a low-dose ketamine infusion. The level of sedation, postural stability, ease of performing surgery, and vital parameters were recorded. Adding ketamine did not noticeably reduce the xylazine required; both groups ended up needing similar amounts. However, horses that received ketamine were slightly more deeply sedated without becoming more unsteady. Heart rate and respiratory rate remained normal in all horses, and no complications occurred. In summary, the addition of a low-dose ketamine infusion to xylazine improved sedation degree while maintaining postural stability and cardiorespiratory safety during upper way surgery.

Standing sedation in horses provides immobilization and analgesia for surgery while avoiding the high risks of general anesthesia. Ketamine at subanesthetic doses may enhance sedation and reduce xylazine requirements, but evidence in clinical settings is limited. In a randomized blinded trial, we evaluated whether adding a low-dose ketamine infusion could reduce the xylazine dose required for effective sedation during standing ventriculocordectomy and laryngoplasty. Fifty-one horses were randomly assigned to sedation with xylazine alone (SX group) or xylazine plus ketamine (KX group) in a continuous rate infusion. The ketamine group received ketamine (0.25 mg/kg intravenous (IV) bolus followed by 0.5 mg/kg/h infusion), while xylazine was administered in both groups via a titrated infusion to effect according to the Ghent Sedation Algorithm. Sedation depth, ataxia, surgical condition scores, and cardiorespiratory parameters were recorded. Data are presented as median (25th–75th percentiles) and estimated effect with 95% confidence intervals (CI). Statistical significance was set at p < 0.05 and at 95% CIs excluding zero. The addition of ketamine did not significantly reduce xylazine requirements (0.9 (0.7–1.3) vs. 0.8 (0.5–1.1) mg/kg/h for SX and KX, respectively; p = 0.139). However, horses receiving ketamine (KX) achieved deeper sedation (Estimate = 2.74; 95% CI: 0.95 to 4.63) with no differences in ataxia or surgical conditions. Cardiorespiratory variables remained stable in both groups, and no adverse events occurred. In conclusion, adding a subanesthetic ketamine infusion improved sedation depth without adverse effects but did not significantly reduce the xylazine requirement.