Cardiorespiratory effects of a combination of medetomidine, midazolam, andbutorphanol in dogs

Objective-To characterize cardiorespiratory effects for a combination of me detomidine, butorphanol, and midazolam and to compare magnitude of cardiore spiratory depression with that induced by a commonly used inhalation anesth etic regimen (acepromazine-butorphanol-thiopenral-halothane). Animals-10 clinically normal dogs(2 groups of 5). Procedure-In treated dogs, medetomidine was administered (time, 0 minutes); midazolam and butorphanol were administered when effects of medetomidine w ere maximal (time, 20), and atipamezole was administered subsequently (time 60). In control dogs, drugs were administered after allowing effects of ea ch agent to be achieved: acepromazine was given at time 0, butorphanol and thiopental were administered at time 35, and halothane was administered fro m time 45 until 110. Various cardiorespiratory and hematologic variables we re measured or calculated. Results-Respiratory rate, arterial and venous pH, venous oxygen content, ox ygen consumption, and oxygen delivery decreased significantly below baselin e values for treated dogs; end-tidal CO2, afterial and venous Pco(2),, and O-2,extraction increased significantly above; baseline values. Compared wit h data obtained after anesthesia, arterial HCO3- concentration, venous Po-2 and So(2), cardiac output, oxygen extraction, and oxygen delivery appeared more modified in treated dogs. Oxygen consumption and physiologic shunt fr action were less modified in treated dogs than control dogs. Conclusions and Clinical Relevance-Medetomidine-butorphanol-midazolam combi nation induced respiratory depression, comparable in magnitude to that indu ced by a widely used inhalation anesthetic regimen. Respiratory variables r emained within acceptable limits during anesthesia; however, those associat ed with cardiovascular function were more severely affected.