Nalbuphine and butorphanol reverse opioid-induced respiratory depression but increase arousal in etorphine-immobilized goats (Capra hircus)

ObjectivesTo evaluate and compare the efficacy of two opioid agonist-antagonists, nalbuphine and butorphanol, in reversing etorphine-induced respiratory depression in immobilized goats. Study designProspective, crossover, experimental trial conducted at 1753m.a.s.l. AnimalsEight adult female Boer goats (Capra hircus). MethodsEight minutes following immobilization with an intramuscular injection of 0.1mgkg(-1) etorphine, goats were given one of nalbuphine (0.8mgkg(-1)), butorphanol (0.1mgkg(-1)) or sterile water intravenously, in random order in three trials. Respiratory rate (f(R)), ventilation, tidal volume, oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured continuously. Arterial blood samples to determine PaO2 and PaCO2 were taken 2minutes before and at 5minute intervals after etorphine administration for 25minutes. ResultsBoth nalbuphine and butorphanol increased mean PaO2 from 44mmHg (5.9kPa) to 63mmHg (8.4kPa) after etorphine administration. Butorphanol, but not nalbuphine, also corrected hypopnea and hypoventilation such that f(R) increasedfrom 134 to 217breathsminute(-1) (compared with 16 +/- 6breathsminute(-1) following nalbuphine) and ventilation increased from 4.69 +/- 3.04 to 6.91 +/- 4.42Lminute(-1) following butorphanol administration. Despite decreases in PaCO2 following nalbuphine and butorphanol, PaCO2 remained elevated compared with pre-immobilization values [nalbuphine: 34 +/- 3mmHg (4.5 +/- 0.3kPa); butorphanol: 34 +/- 2mmHg (4.5 +/- 0.3kPa)] throughout the immobilization. Both agents also decreased the level of immobilization, and increased O-2 and CO2. ConclusionsNalbuphine and butorphanol significantly improved respiratory function in immobilized goats, with butorphanol eliciting a greater positive response than nalbuphine. However, both opioid agonist-antagonists partly reversed etorphine-induced immobilization. Clinical relevanceButorphanol and nalbuphine can be used to improve respiratory parameters in etorphine-immobilized wildlife, with butorphanol being more effective, but unwanted arousal can occur.