Intraoperative effect of low doses of ketamine or dexmedetomidine continuous rate infusions in healthy dogs receiving propofol total intravenous anaesthesia and epidural anaesthesia: A prospective, randomised clinical study.

The present study aimed to determine the effect of either ketamine or dexmedetomidine constant rate infusion (CRI) on intraoperative propofol anaesthetic requirements during total intravenous anaesthesia (TIVA) in healthy dogs undergoing hindlimbs orthopaedic procedures receiving epidural anaesthesia. In this randomised, blinded clinical study, thirty-nine healthy client-owned dogs were premedicated intramuscularly (dexmedetomidine 4 μg/kg and methadone 0.3 mg/kg). General anaesthesia was induced to effect with propofol administered as intravenous bolus, and maintained with propofol TIVA (18 mg/kg/h), adjusted to meet the suitable clinical anaesthetic depth (indicatively±20%) based on clinical judgement. Lumbosacral epidural anaesthesia was performed using bupivacaine (1 mg/kg) and morphine preservative free (0.1 mg/kg). Dogs randomly received either saline (SP; loading dose 1 mL/kg, CRI 1 mL/kg/h), or ketamine (KP; loading dose 1.5 mg/kg, CRI 1.5 mg/kg/h), or dexmedetomidine (DP; loading dose 1 μg/kg/, CRI 1 μg/kg/h). Physiological variables were recorded intraoperatively at 5-min intervals using standard-of-care monitoring. Recovery quality and duration were recorded. Treatment groups were compared with parametric and non-parametric tests as appropriate, p < 0.05. Propofol rates and recovery scores were similar between groups. Overall mean and diastolic blood pressures were higher in group DP compared to group KP (12-14 mmHg, p = 0.016 and p = 0.015, respectively). More dogs required mechanical ventilation in group KP (12 dogs) than in either group SP or DP (7 dogs per group, p = 0.037). Ketamine or dexmedetomidine CRIs, at the studied rates, did not reduce propofol TIVA requirements in dogs undergoing orthopaedic surgery with epidural anaesthesia.