Comparison of two techniques for total intravenous anesthesia in horses

Objective - To characterize responses associated with two 1-hour total intravenous anesthesia techniques in horses. Animals - 6 mature, healthy mares. Procedure - Each horse was anesthetized 3 times. Treatment order was determined by a series of Latin squares. After baseline measurements and instrumentation, horses were given xylazine (XYL) IV; anesthesia was induced 5 minutes later with 10% guaifenesin given IV, then either ketamine (KET) or propofol (PRO) was given IV. After anesthesia induction, each horse received an infusion of XYL and either KET or a low or high dose of PRO. Cardiopulmonary variables were measured at 20, 40, and 60 minutes after the start of the infusion; arterial blood samples were collected prior to each set of measurements, and blood gas tensions and plasma drug concentration were determined. A noxious stimulus was applied after each of the 3 sets of measurements. Results - Differences in measured cardiopulmonary variables were significant among all treatments at different times. Most notable differences were between KET and high PRO. Times to regaining sternal and standing posture were shortest for KET, and differed significantly from values for low and high PRO. Purposeful responses were not observed for high PRO in horses after noxious stimulation. In contrast, 4 horses given KET responded at all time points and 1 horse given low PRO responded. Conclusion - None of the infusion techniques were flawless, but results support, continued efforts at technique refinement and selected clinical use.