The effects of low-dose medetomidine and butorphanol premedication on anesthetic induction and recovery for intramuscular alfaxalone anesthesia in cats.

This study evaluated effects of premedication with low-dose medetomidine (MED), butorphanol (BTR), or their combination on intramuscular (IM) alfaxalone (ALFX) anesthesia in cats. Five healthy purpose-bred cats were used in a completely randomized crossover study with a minimum 1-week washout period. Cats received three types of premedication: MED (5 µg/kg), BTR (0.3 mg/kg) or their combination via IM injection. After 15 min, anesthesia was induced with low (1.0 mg/kg), medium (2.5 mg/kg) or high (5.0 mg/kg) doses of IM ALFX. Anesthetic depth, tracheal intubation scores, and cardiorespiratory variables were evaluated over 120 min. Dose-dependent anesthetic effects of ALFX were observed across all protocols. Although tracheal intubation was difficult with MED alone, premedication with BTR alone or in combination with MED facilitated successful intubation. Notably, the MED-BTR combination resulted in a significantly greater sedation/anesthetic effect, even with lower doses of ALFX. The MED-BTR combination completely prevented MED-induced emesis. Cardiorespiratory evaluation revealed a decrease in heart rate with MED and MED-BTR premedication, and percutaneous arterial oxygen saturation dropped below 93% temporarily at higher ALFX doses. In summary, premedication combining BTR and low-dose MED facilitates reliable and smooth anesthetic induction with low-dose ALFX (1.0 mg/kg), achieving sufficient anesthetic depth without inducing prolonged or turbulent recovery. However, careful monitoring for bradycardia and hypoxemia is recommended, and its clinical application should be limited to young and healthy cats with sufficient cardiorespiratory reserve.