Effect of intravenous ketamine and lidocaine on isoflurane requirement in sheep undergoing orthopedic surgery

Intravenous ketamine and lidocaine infusions may be useful adjuncts to inhalation anesthesia for sheep undergoing orthopedic surgery. In this study, 50 female sheep underwent experimental stifle surgery (29 received a meniscal implant and 21 received sham surgery). To induce anesthesia in the sheep, the authors intravenously injected ketamine and diazepam. They administered isoflurane in oxygen to maintain anesthesia and used mechanical ventilation to maintain normal arterial carbon dioxide pressure. Some sheep received intravenous infusions of ketamine and lidocaine during surgery, whereas others did not. Sheep that received a meniscal implant without ketamine-lidocaine required similar to 23% greater isoflurane concentrations than sheep that were given ketamine-lidocaine. These findings suggest that intravenous infusion of ketamine and lidocaine decreases the requirement for isoflurane during orthopedic surgery on anesthetized sheep.