There is a growing necessity to perform long-term
anesthesia in wildlife, especially antelope. The costs and logistics of transporting wildlife to veterinary practices make surgical intervention a high-stakes operation. Thus there is a need for a field-ready total
intravenous anesthesia (TIVA) infusion to maintain
anesthesia in antelope. This study explored the feasibility of an
etorphine-
ketamine-
medetomidine TIVA for field
anesthesia. Ten wild-caught, adult impala ( Aepyceros melampus ) were enrolled in the study. Impala were immobilized with a standardized combination of
etorphine (2 mg) and
medetomidine (2.2 mg), which equated to a median (interquartile range [IQR])
etorphine and
medetomidine dose of 50.1 (46.2-50.3) and 55.1 (50.8-55.4) μg/kg, respectively. Recumbency was attained in a median (IQR) time of 13.9 (12.0-16.5) min. Respiratory gas tensions, spirometry, and arterial blood gas were analyzed over a 120-min infusion. Once instrumented, the TIVA was infused as follows:
etorphine at a variable rate initiated at 40 μg/kg per hour (adjusted according to intermittent deep-
pain testing);
ketamine and
medetomidine at a fixed rate of 1.5 mg/kg per hour and 5 μg/kg per hour, respectively. The
etorphine had an erratic titration to clinical effect in four impala. Arterial blood pressure and respiratory and heart rates were all within normal physiological ranges. However, arterial blood gas analysis revealed severe
hypoxemia,
hypercapnia, and
acidosis. Oxygenation and ventilation indices were calculated and highlighted possible co-etiologies to the suspected
etorphine-induced
respiratory depression as the cause of the blood gas derangements. Impala recovered in the boma post
atipamezole (13 mg) and
naltrexone (42 mg) antagonism of
medetomidine and
etorphine, respectively. The
etorphine-
ketamine-
medetomidine TIVA protocol for impala may be sufficient for field procedures of up to 120-min duration. However,
hypoxemia and
hypercapnia are of paramount concern and thus
oxygen supplementation should be considered mandatory. Other TIVA combinations may be superior and warrant further investigation.