Xylazine Infusion during Equine Colic Anesthesia with Isoflurane and Lidocaine: A Retrospective Study

Simple Summary Equine colic is a critical and painful illness. Xylazine provides analgesia; sedation and muscle relaxation; and improves anesthetic recoveries in healthy horses. These might be useful for anesthesia in colic patients. This study aimed to retrospectively evaluate the intraoperative effects, and the influence on recovery from anesthesia, of adding a xylazine infusion (group XL) to isoflurane and lidocaine infusion (group L) for anesthesia maintenance. Cardiovascular parameters, blood gas analyses, anesthetic requirements, and time during recovery were retrospectively studied. Minimal and average heart rate, hematocrit, ketamine requirements and days to discharge were significantly lower in group XL than in group L. Time to sternal and first attempt to stand were significantly longer in group XL than in group L. Group XL showed almost twice the number of ‘best possible’ recoveries and no horses with the worst score. The reductions in heart rate and hematocrit were considered clinically irrelevant. The time to finally stand remained similar in both groups. Xylazine infusion might provide a stable anesthesia since less animals required ketamine. Animals in this group went home sooner and none of them had a dangerous recovery. Xylazine infusion might be a good option for anesthesia maintenance in colic patients. Abstract This retrospective study investigated the effect of a xylazine infusion on heart rate; mean arterial pressure; blood gases; anesthetic and dobutamine requirements; recovery quality and duration; percentage of death/survival; and days to die/discharge in horses after colic surgery under partial intravenous anesthesia with isoflurane and lidocaine infusion. Anesthetic records of equine colic surgery were reviewed from similar periods in 2020–2021 and 2021–2022. In both groups, after sedation with xylazine 0.7 mg/kg intravenously (IV) and induction with ketamine 2.2 mg/kg and midazolam 0.06 mg/kg IV, anesthesia was maintained with isoflurane and lidocaine (bolus 1.5 mg/kg IV, infusion 2 mg/kg/h). Group L (2020–2021, n = 45) received xylazine 0.2 mg/kg IV before recovery, group XL (2021–2022, n = 44) received xylazine 0.5 mg/kg/h IV intraoperatively. In group XL, minimal (p = 0.04) and average (p = 0.04) heart rate, intraoperative hematocrit (p = 0.001), minimal (p = 0.002) and maximal (p = 0.04) dobutamine administration rate, animals requiring ketamine top-ups (p = 0.04), and the number of days to discharge (p = 0.02), were significantly lower compared to group L. During recovery in group XL, the time to sternal recumbency (p = 0.03) and time to first attempt (p = 0.04) were significantly longer. This retrospective study suggests that a xylazine infusion may have beneficial effects on horses undergoing colic surgery. Further prospective studies are necessary.