EVALUATION OF PROPOFOL FOR GENERAL-ANESTHESIA IN PREMEDICATED HORSES

Objective-To evaluate selected hemodynamic, respiratory, and behaviora l responses to propofol in horses premedicated with xylazine or detomi dine. Design-Xylazine (0.5 and 1.0 mg/kg of body weight) was administe red IV on different days to each of 6 horses prior to IV administratio n of propofol (2 mg/kg). In a second group of 6 horses, detomidine (15 and 30 mu g/kg) was similarly studied. Animals-2 groups of 6 mature h ealthy horses. Procedure-Rectal temperature, heart and respiratory rat es, arterial blood gas tensions, and direct arterial blood pressures w ere recorded before and at fixed intervals after drug administration. Induction and recovery events were quantitatively and qualitatively as sessed. Cardiopulmonary and behavioral data to follow were statistical ly analyzed (P less than or equal to 0.05). Results-Heart rate decreas ed in dose-dependent manner from a mean (+/- SD) of 39.5 +/- 5.1 beats /min after xylazine and detomidine. Second-degree atrioventricular dis sociation was commonly seen at the higher drug doses. After propofol a dministration, heart rate either transiently increased or was less dep ressed early in recumbency, compared with predrug values. Direct arter ial blood pressures varied inconsistently from predrug values. Mean ar terial carbon dioxide tension tended to increase after drug administra tion (significance variable) from predrug values of 42 to 46 mm of Hg in both drug groups. After xylazine or detomidine administration, arte rial oxygen tension decreased significantly from predrug values of 97 to 103 mm of Hg. The magnitude and duration of decrease was dose-depen dent and greatest during recumbency. Behavioral responses to anestheti c induction were variable, but horses were uniformly calm and coordina ted during recovery. Recumbency time increased in reponse to the highe r dose of either premedicant drug. Mean (+/- SD) times to standing wer e 25.02 +/- 4.42 and 35.57 +/- 6.83 minutes for the low and high doses of xylazine, respectively and 41.04 +/- 11.21 and 52.64 +/- 14.67 min utes for the low and high doses of detomidine, respectively. Conclusio n-Neither xylazine nor detomidine prevented excitation associated with propofol injection in horses. Clinical Relevance-Xylazine- or detomid ine-propofol combinations likely will not replace common anesthetic in duction techniques for horses. However, recovery characteristics assoc iated with propofol encourage further study in horses.