Haemodynamic effects of labetalol in isoflurane-anaesthetized dogs that received dexmedetomidine: A randomized clinical trial.

ABSTRACT

OBJECTIVE: To test whether labetalol improved cardiovascular function in anaesthetized dogs injected with dexmedetomidine. STUDY DESIGN: Prospective, randomized, blinded, clinical trial. ANIMALS A group of 20 healthy client-owned dogs undergoing ovariohysterectomy. METHODS: Each dog received dexmedetomidine (5 µg kg-1) and methadone (0.2 mg kg-1) intramuscularly. General anaesthesia was induced with propofol and maintained with isoflurane in oxygen. All dogs were mechanically ventilated, and epidural anaesthesia with lidocaine was performed. Standard anaesthetic monitoring, invasive blood pressure, oesophageal Doppler and near-infrared tissue perfusion/oxygenation were applied. Peak velocity (PV), mean acceleration and stroke distance (SD) from the oesophageal Doppler were recorded. Arterial elastance (Ea) was calculated. Tissue oxygenation (rStO2) was also recorded. Prior to surgery, animals received either 0.1 mg kg-1 of labetalol intravenously (IV) over 60 seconds or the equivalent volume of saline. Data were recorded for 20 minutes. Age, weight and propofol dose were compared with a Wilcoxon rank-sum test. The effects of time, treatment and their interaction with haemodynamic and perfusion variables were analysed with mixed-effect models and Tukey's post hoc tests. RESULTS: Significant effects of the interaction between treatment and time were observed whereby heart rate (HR) was higher in dogs given labetalol (p = 0.01), whereas arterial blood pressure and Ea were lower (p < 0.01). Similarly, PV, SD and rStO2 were higher in the labetalol group, and significant effects were detected for the interaction between treatment and time (p < 0.01). CONCLUSIONS AND CLINICAL RELEVANCE Labetalol at a dose of 0.1 mg kg-1 IV in dogs under general anaesthesia and administered a pre-anaesthetic medication of dexmedetomidine produced mild vasodilation (reduction of Ea), resulting in an increase in HR and left ventricular outflow. Although labetalol could be an effective option to achieve haemodynamic optimization after dexmedetomidine-induced vasoconstriction, future studies are needed to assess long-term effects.