Effect of lidocaine, fentanyl, or dexmedetomidine on minimum infusion rate and cardiorespiratory variables in dogs undergoing ketofol total intravenous anesthesia

BACKGROUND: It has been proposed that dose reduction via co-administration of other agents might ameliorate respiratory depression associated with ketofol. AIMS: The present study was designed to evaluate the effects of adding lidocaine, fentanyl, or dexmedetomidine on the required dose and cardiorespiratory variables in dogs undergoing total intravenous anesthesia (TIVA) with ketofol. METHODS: In phase I, twelve dogs (six per each treatment) were induced and maintained with two out of four anesthetic regimens of (1) ketofol (4 mg/kg and 0.3 mg/kg/min, respectively; KET), (2) ketofol and lidocaine (1.5 mg/kg and 0.25 mg/kg/min, respectively; KLD), (3) ketofol and fentanyl (5 µg/kg and 0.1 µg/kg/min, respectively; KFN), and (4) ketofol and dexmedetomidine (2 µg/kg and 2 mg/kg/h, respectively; KDX) with at least one-week interval. The minimum infusion rate (MIR) of ketofol was determined. In phase II, the other twelve dogs were given the same anesthetic regimens for 60 min with the determined infusion rate of ketofol, and cardiorespiratory variables were recorded. RESULTS: Mean MIR of ketofol for KET, KLD, KFN, and KDX were 0.35, 0.23, 0.15, and 0.08 mg/kg/min, respectively. In phase II, the times of recovery events were shorter in KFN and KDX than KET and KLD. The heart rate was significantly higher than baseline in KET and KLD, which was also significantly lower than KFN and KDX at several time points. In all treatments, respiratory depression was detected. CONCLUSION: Despite the decrease in the dose of ketofol, none of the added drugs attenuated respiratory depression caused by this agent.