Effect of detomidine or romifidine constant rate infusion on plasma lactate concentration and inhalant requirements during isoflurane anaesthesia in horses.

OBJECTIVE: Influence of detomidine or romifidine constant rate infusion (CRI) on plasma lactate concentration and isoflurane requirements in horses undergoing elective surgery.

STUDY DESIGN: Prospective, randomised, blinded, clinical trial.

ANIMALS: A total of 24 adult healthy horses.

METHODS: All horses were administered intramuscular acepromazine (0.02 mg kg-1 ) and either intravenous detomidine (0.02 mg kg-1 ) (group D), romifidine (0.08 mg kg-1 ) (group R) or xylazine (1.0 mg kg-1 ) (group C) prior to anaesthesia. Group D was administered detomidine CRI (10 μg kg-1 hour-1 ) in lactated Ringer's solution (LRS), group R romifidine CRI (40 μg kg-1 hour-1 ) in LRS and group C an equivalent amount of LRS intraoperatively. Anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. Plasma lactate samples were taken prior to anaesthesia (baseline), intraoperatively (three samples at 30 minute intervals) and in recovery (at 10 minutes, once standing and 3 hours after end of anaesthesia). End-tidal isoflurane percentage (Fe'Iso) was analysed by allocating values into three periods: Prep (15 minutes after the start anaesthesia-start surgery); Surgery 1 (start surgery-30 minutes later); and Surgery 2 (end Surgery 1-end anaesthesia). A linear mixed model was used to analyse the data. A value of p<0.05 was considered significant.

RESULTS: There was a difference in plasma lactate between 'baseline' and 'once standing' in all three groups (p<0.01); values did not differ significantly between groups. In groups D and R, Fe'Iso decreased significantly by 18% (to 1.03%) and by 15% (to 1.07%), respectively, during Surgery 2 compared with group C (1.26%); p<0.006, p<0.02, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE: Intraoperative detomidine or romifidine CRI in horses did not result in a clinically significant increase in plasma lactate compared with control group. Detomidine and romifidine infusions decreased isoflurane requirements during surgery.