Alfaxalone for total intravenous anaesthesia in dogs undergoing ovariohysterectomy: a comparison of premedication with acepromazine or dexmedetomidine

To describe alfaxalone total intravenous anaesthesia (TIVA) following premedication with buprenorphine and either acepromazine (ACP) or dexmedetomidine (DEX) in bitches undergoing ovariohysterectomy. Prospective, randomised, clinical study. Thirty-eight healthy female dogs. Following intramuscular buprenorphine (20 μg kg−1) and acepromazine (0.05 mg kg−1) or dexmedetomidine (approximately 10 μg kg−1, adjusted for body surface area), anaesthesia was induced and maintained with intravenous alfaxalone. Oxygen was administered via a suitable anaesthetic circuit. Alfaxalone infusion rate (initially 0.07 mg kg−1 minute−1) was adjusted to maintain adequate anaesthetic depth based on clinical assessment. Alfaxalone boluses were given if required. Ventilation was assisted if necessary. Alfaxalone dose and physiologic parameters were recorded every 5 minutes. Depth of sedation after premedication, induction quality and recovery duration and quality were scored. A Student's t-test, Mann–Whitney U and Chi-squared tests determined the significance of differences between groups. Data are presented as mean ± SD or median (range). Significance was defined as p < 0.05. There were no differences between groups in demographics; induction quality; induction (1.5 ± 0.57 mg kg−1) and total bolus doses [1.2 (0 – 6.3) mg kg−1] of alfaxalone; anaesthesia duration (131 ± 18 minutes); or time to extubation [16.6 (3–50) minutes]. DEX dogs were more sedated than ACP dogs. Alfaxalone infusion rate was significantly lower in DEX [0.08 (0.06–0.19) mg kg−1 minute−1] than ACP dogs [0.11 (0.07–0.33) mg kg−1 minute−1]. Cardiovascular variables increased significantly during ovarian and cervical ligation and wound closure compared to baseline values in both groups. Apnoea and hypoventilation were common and not significantly different between groups. Arterial haemoglobin oxygen saturation remained above 95% in all animals. Recovery quality scores were significantly poorer for DEX than for ACP dogs. Alfaxalone TIVA is an effective anaesthetic for surgical procedures but, in the protocol of this study, causes respiratory depression at infusion rates required for surgery.