EFFECTS OF A COMBINATION OF DETOMIDINE AND BUTORPHANOL ON RESPIRATORY-FUNCTION IN HORSES WITH OR WITHOUT CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Objective-To evaluate the effects of detomidine and butorphanol in com bination on respiratory function in horses and to determine whether th ese effects are more severe in horses with pre-existing respiratory dy sfunction. Design-Pulmonary function testing and arterial blood gas an alyses were performed before and after administration of a combination of detomidine(10 mu g/kg of body weight, IV) and butorphanol (20 mu g /kg, IV). Animals-5 horses with chronic obstructive pulmonary disease and 5 horses free of respiratory disease (controls). Procedures-Flow r ates were obtained from a pneumotachograph attached to a face mask, an d esophageal pressure was measured with a catheter placed in the dista l third of the esophagus. Respiratory rate, tidal volume (VT), minute ventilation (VE), maximal change in transpulmonary pressure, pulmonary resistance, and dynamic compliance were calculated by use of a pulmon ary function computer. Arterial blood was collected from the transvers e facial artery, and blood gas partial pressures were measured with an automated blood gas analyzer. Results-The combination of detomidine a nd butorphanol caused significant changes with time in respiratory rat e, VT, VE, Pa-o2, and Pa-co2. Changes with time in VT, VE, and maximal change in transpulmonary pressure were significantly different betwee n groups. Conclusion-The combination of detomidine and butorphanol aff ects respiratory function in horses, and the observed changes are affe cted by the presence of preexisting respiratory dysfunction. Clinical Relevance-Changes in respiratory function after administration of a co mbination of detomidine and butorphanol are not necessarily more sever e in horses with pre-existing respiratory dysfunction.