To evaluate the effects of a constant rate infusion (CRI) of lidocaine alone or in combination with ketamine on the minimum infusion rate (MIR) of propofol in dogs and to compare the hemodynamic effects produced by propofol, propofol-lidocaine or propofol-lidocaine-ketamine anesthesia.Study design
Prospective, randomized cross-over experimental design.Animals
Fourteen adult mixed-breed dogs weighing 15.8 ± 3.5 kg.Methods
Eight dogs were anesthetized on different occasions to determine the MIR of propofol alone and propofol in combination with lidocaine (loading dose [LD] 1.5 mg kg−1, CRI 0.25 mg kg−1 minute−1) or lidocaine (LD 1.5 mg kg−1, CRI 0.25 mg kg−1 minute−1) and ketamine (LD 1 mg kg−1, CRI 0.1 mg kg−1 minute−1). In six other dogs, the hemodynamic effects and bispectral index (BIS) were investigated. Each animal received each treatment (propofol, propofol-lidocaine or propofol-lidocaine-ketamine) on the basis of the MIR of propofol determined in the first set of experiments.Results
Mean ± SD MIR of propofol was 0.51 ± 0.08 mg kg−1 minute−1. Lidocaine-ketamine significantly decreased the MIR of propofol to 0.31 ± 0.07 mg kg−1 minute−1 (37 ± 18% reduction), although lidocaine alone did not (0.42 ± 0.08 mg kg−1 minute−1, 18 ± 7% reduction). Hemodynamic effects were similar in all treatments. Compared with the conscious state, in all treatments, heart rate, cardiac index, mean arterial blood pressure, stroke index and oxygen delivery index decreased significantly, whereas systemic vascular resistance index increased. Stroke index was lower in dogs treated with propofol-lidocaine-ketamine at 30 minutes compared with propofol alone. The BIS was lower during anesthesia with propofol-lidocaine-ketamine compared to propofol alone.Conclusions and clinical relevance
Lidocaine-ketamine, but not lidocaine alone, reduced the MIR of propofol in dogs. Neither lidocaine nor lidocaine in combination with ketamine attenuated cardiovascular depression produced by a continuous rate infusion of propofol.