Minimum infusion rate of alfaxalone for total intravenous anaesthesia after sedation with acepromazine or medetomidine in cats undergoing ovariohysterectomy

Objective: To determine the induction doses, then minimum infusion rates of alfaxalone for total intravenous anaesthesia (TIVA), and subsequent, cardiopulmonary effects, recovery characteristics and alfaxalone plasma concentrations in cats undergoing ovariohysterectomy after premedication with butorphanol-acepromazine or butorphanol-medetomidine. Study design: Prospective randomized blinded clinical study. Animals: Twenty-eight healthy cats. Methods: Cats undergoing ovariohysterectomy were assigned into two groups: together with butorphanol [0.2 mg kg−1 intramuscularly (IM)], group AA (n = 14) received acepromazine (0.1 mg kg−1 IM) and group MA (n = 14) medetomidine (20 μg kg−1 IM). Anaesthesia was induced with alfaxalone to effect [0.2 mg kg−1 intravenously (IV) every 20 seconds], initially maintained with 8 mg kg−1 hour−1 alfaxalone IV and infusion adjusted (±0.5 mg kg−1 hour−1) every five minutes according to alterations in heart rate (HR), respiratory rate (fR), Doppler blood pressure (DBP) and presence of palpebral reflex. Additional alfaxalone boli were administered IV if cats moved/swallowed (0.5 mg kg−1) or if fR >40 breaths minute−1 (0.25 mg kg−1). Venous blood samples were obtained to determine plasma alfaxalone concentrations. Meloxicam (0.2 mg kg−1 IV) was administered postoperatively. Data were analysed using linear mixed models, Chi-squared, Fishers exact and t-tests. Results: Alfaxalone anaesthesia induction dose (mean ± SD), was lower in group MA (1.87 ± 0.5; group AA: 2.57 ± 0.41 mg kg−1). No cats became apnoeic. Intraoperative bolus requirements and TIVA rates (group AA: 11.62 ± 1.37, group MA: 10.76 ± 0.96 mg kg−1 hour−1) did not differ significantly between groups. Plasma concentrations ranged between 0.69 and 10.76 μg mL−1. In group MA, fR, end-tidal carbon dioxide, temperature and DBP were significantly higher and HR lower. Conclusion and clinical relevance: Alfaxalone TIVA in cats after medetomidine or acepromazine sedation provided suitable anaesthesia with no need for ventilatory support. After these premedications, the authors recommend initial alfaxalone TIVA rates of 10 mg kg−1 hour−1