Evaluation of the isoflurane-sparing effects of fentanyl, lidocaine, ketamine, dexmedetomidine, or the combination lidocaine-ketamine-dexmedetomidine during ovariohysterectomy in dogs

Objective To evaluate the isoflurane-sparing effects of an intravenous (IV) constant rate infusion (CRI) of fentanyl, lidocaine, ketamine, dexmedetomidine, or lidocaine-ketamine-dexmedetomidine (LKD) in dogs undergoing ovariohysterectomy. Study design Randomized, prospective, blinded, clinical study. Animals Fifty four dogs. Methods Anesthesia was induced with propofol and maintained with isoflurane with one of the following IV treatments: butorphanol/saline (butorphanol 0.4 mg kg(-1), saline 0.9% CRI, CONTROL/BUT); fentanyl (5 mu g kg(-1), 10 mu g kg(-1) hour(-1), FENT); ketamine (1 mg kg(-1), 40 mu g kg(-1) minute(-1), KET), lidocaine (2 mg kg(-1), 100 mu g kg(-1) minute(-1), LIDO); dexmedetomidine (1 mu g kg(-1), 3 mu g kg(-1) hour(-1), DEX); or a LKD combination. Positive pressure ventilation maintained eucapnia. An anesthetist unaware of treatment and end-tidal isoflurane concentration (FE'Iso) adjusted vaporizer settings to maintain surgical anesthetic depth. Cardiopulmonary variables and FE'Iso concentrations were monitored. Data were analyzed using ANOVA (p < 0.05). Results At most time points, heart rate (HR) was lower in FENT than in other groups, except for DEX and LKD. Mean arterial blood pressure (MAP) was lower in FENT and CONTROL/BUT than in DEX. Overall mean +/- SD FE'Iso and % reduced isoflurane requirements were 1.01 +/- 0.31/41.6% (range, 0.75 +/- 0.31/56.6% to 1.12 +/- 0.80/35.3%, FENT), 1.37 +/- 0.19/20.8% (1.23 +/- 0.14/28.9% to 1.51 +/- 0.22/12.7%, KET), 1.34 +/- 0.19/22.5% (1.24 +/- 0.19/28.3% to 1.44 +/- 0.21/16.8%, LIDO), 1.30 +/- 0.28/24.8% (1.16 +/- 0.18/32.9% to 1.43 +/- 0.32/17.3%, DEX), 0.95 +/- 0.19/54.9% (0.7 +/- 0.16/59.5% to 1.12 +/- 0.16/35.3%, LKD) and 1.73 +/- 0.18/0.0% (1.64 +/- 0.21 to 1.82 +/- 0.14, CONTROL/BUT) during surgery. FENT and LKD significantly reduced FE'Iso. Conclusions and clinical relevance At the doses administered, FENT and LKD had greater isoflurane-sparing effect than LIDO, KET or CONTROL/BUT, but not at all times. Low HR during FENT may limit improvement in MAP expected with reduced FE'Iso.