P052: HORSE SENSE: ANESTHETIC LESSONS FROM HORSE TO HUMAN
Dalya Elhady, MD, Sindhu Nimma, MD, Fernando Garcia-Pereira, DVM, MVSc, Steven Robicsek, MD, PhD; University of Florida
Human patients undergoing a number of neurosurgical, orthopedic and vascular procedures benefit from intraoperative assessment of the integrity of motor pathways, which may reduce the risk of injury by providing feedback to the operating surgeon. Motor evoked potentials (MEPs) are sensitive to the patient’s underlying neurological condition, the anesthetic technique, and the extent of myelination of the corticospinal pathways. Since these procedures have variable stimulation throughout the procedure, anesthetic management has significant challenges for anesthesia providers since the use of neuromuscular antagonists cannot be used. We offer an analogy to assist in the conceptual understanding of anesthetic management by reviewing equine anesthesia which also avoids neuromuscular antagonists for different reasons.
Movement during equine arthroscopic surgery can pose morbidity to the horse but can also be dangerous to surgical staff. For both of these reasons it is imperative that movement be avoided. A typical anesthetic protocol in equine practice is based on alpha- 2 agonist, opioid, ketamine and diazepam. The routine use of neuromuscular antagonists are avoided due to the potential of vestigial motor blockade, which could be catastrophic during the recovery period, as these animals will try to stand when regaining consciousness. Additionally, antimuscarinic agents used in paralytic reversal can significantly decrease gastrointestinal motility and this species is prone to gastrointestinal stasis, impaction, endotoxemia and potential death. After endotracheal intubation, horses are usually placed under isoflurane anesthesia at 1.5 MAC and positive pressure ventilation. This amount of isoflurane causes significant vasodilation and hypotension; therefore, normotension is achieved by administration of dobutamine and often norepinephrine.
Since MEPs are extremely sensitive to the inhibitory effects of volatile anesthetics a balanced fentanyl-propofol technique is used in place of isoflurane. However the principle of administering a higher amount of anesthetic (>1.5 MAC) that requires pressor support to obtain baseline hemodynamics minimizes the probability that human patients will move during the procedure.
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