Objective: To evaluate the effects of detomidine and butorphanol in combination on respiratory function in horses and to determine whether these effects are more severe in horses with pre-existing respiratory dysfunction,
Design: Pulmonary function testing and arterial blood gas analyses were performed before and after administration of a combination of detomidine (10 micrograms/kg of body weight, i.v.) and butorphanol (20 micrograms/kg, i.v.).
Animals: 5 horses with chronic obstructive pulmonary disease and 5 horses free of respiratory disease (controls).
Procedures: Flow rates were obtained from a pneumotachograph attached to a face mask, and esophageal pressure was measured with a catheter placed in the distal 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 pulmonary function computer. Arterial blood was collected from the transverse facial artery, and blood gas partial pressures were measured with an automated blood gas analyzer.
Results: The combination of detomidine and butorphanol caused significant changes with time in respiratory rate, VT, VE, PaO2, and PaCO2. Changes with time in VT, VE, and maximal change in transpulmonary pressure were significantly different between groups.
Conclusion: The combination of detomidine and butorphanol affects respiratory function in horses, and the observed changes are affected by the presence of pre-existing respiratory dysfunction.
Clinical relevance: Changes in respiratory function after administration of a combination of detomidine and butorphanol are not necessarily more severe in horses with pre-existing respiratory dysfunction.