Comparative cardiopulmonary effects of intramuscularly administered etorphine and carfentanil in goats

OBJECTIVE: To determine comparative cardiopulmonary effects of IM administered etorphine and carfentanil in goats. ANIMALS: Seven clinically normal adult female goats. DESIGN: Each goat received at least 9 drug treatments (etorphine HCl, 5 [twice], 10, 20, and 40 and carfentanil citrate, 5, 10, 20 and 40 micrograms/kg of body weight), with a minimal 2-day interval between trials. Although drug dosages were randomized, etorphine and carfentanil treatments were alternated. To assess for drug tolerance, the first and last treatments always were etorphine (5 micrograms/kg). PROCEDURE: All goats were instrumented for long-term cardiopulmonary variable data collection. RESULTS: Both drugs induced rapid catatonic immobilization, characterized by limb and neck hyperextension, with occasional vocalization and bruxation. Etorphine elicited transient violent struggling and vocalization immediately. Time to immobilization appeared dose-dependent, and was more rapid with carfentanil ( 2 hours) at all dosages. Both drugs at all dosages significantly (P < or = 0.05) increased systemic and left ventricular (LV) end-diastolic pressures, LV peak negative dP/dt, total peripheral resistance (TPR), hemoglobin concentration, and left atrial (LA) and pulmonary O2 contents. They also significantly decreased heart and respiration rates, and TPR. A significant increase was observed at some dosages for LV stroke volume and index, LV peak positive dP/dt, mean pulmonary artery pressure, PaO2, pulmonary artery oxygen partial pressure, PaCO2, pulmonary mixed venous carbon dioxide partial pressure, LA hemoglobin saturation, LA transport index, and body temperature. Pulmonary and systemic mixed venous carbon dioxide and oxygen contents were significantly decreased at some dosages. CONCLUSIONS: Intramuscularly administered etorphine and carfentanil induce hypertension, bradycardia, and bradypnea in goats. The hypertension appears attributable to an increase in TPR. CLINICAL RELEVANCE: Although the cardiopulmonary effects of carfentanil occurred more rapidly, these effects were similar in magnitude for etorphine and carfentanil over the evaluated dosage range.