Studies to Evaluate the Safety of Constant Rate Infusions of Dexmedetomidine, Ketamine and Lidocaine Alone or in Combination during Isoflurane Anesthesia in Horses

Background: Horses mount a huge stress response to anesthesia when compared to other animals, hence are risky candidates for anesthesia. Inhalant anesthetic agents offer more control to anesthetic depth and facilitate rapid recovery, hence are considered to be safer than intravenous agents for surgical procedures requiring more than an hour, however, newer drug combinations are being explored to minimize the undesired consequences and dose rate of inhalant agents. The present study explored the safety of dexmedetomidine, ketamine and lidocaine constant rate infusion alone or as a combination along with Isoflurane for safer anesthesia in horses. Methods: The study was conducted on 28 horses divided into S, D, DK and DKL groups having 7 animals in each. Xylazine (1 mg/kg) and butorphanol (0.05 mg/kg) were given intravenously for premedication. Ketamine (2 mg/kg) and midazolam (0.2 mg/kg) were used for induction and anesthesia was maintained with isoflurane. Normal saline (1000 ml/hour), Dexmedetomidine (2 mu g/kg/hr), Dexmedetomidine and ketamine (2 mu g/kg/ hr and 2 mg/kg/hr) and Dexmedetomidine, ketamine and lidocaine (2 mu g/ kg/hr, 2 mg/kg/hr and 2 mg/kg/h) were given as CRI in groups S, D, DK and DKL, respectively. Thiopentone sodium (250 mg bolus, 5%) was given as a fast intravenous bolus whenever required. Anesthetic efficacy was evaluated based on clinical, haemato-biochemical, hemodynamic, and endocrine variables. Result: A significant decline in mean arterial pressure was noticed in group DKL but changes in CVP and SpO2 in different groups were non-significant. Higher Blood glucose and low Insulin levels were seen in group DK during 45-60 min. Constant rate infusions of Dexmedetomidine, Ketamine and Lidocaine alone or in combination produced a significant sparing effect on Isoflurane and thiopentone while they improved peri- operative quality of anesthesia in horses.