The Nile hippopotamus has historically been difficult to chemically restraint in both the wild and in captivity. Current anesthetic protocols using a combination including concentrated opioids have been risky and have resulted in apnea, cyanosis, bradycardia and fatalities in up to 1/3 of the cases.1
In this study, 13 hippopotamus, 3 captive and 10 wild hippopotamus, ranging in weight from 350 kg to 1800 kg were chemically restrained with a protocol using a combination of medetomidine, butorphanol and azaperone. The hippopotamus were anesthetized via remote injection utilizing a 10 cc Dan-inject dart with a 2.2x60 mm needle. Adult hippos were darted with a combination of medetomidine 0.04–0.05 mg/kg, butorphanol 0.10–0.12 mg/kg, and azaperone 0.08–0.10 mg/kg. Once anesthetized, vital signs were monitored via capnography, blood gas analysis, heart rate, respiratory rate, pulse oximetry and blood pressure every 5 min for 30 min. The hippopotamus were then reversed with an intramuscular injection of atipamezole (2 times the medetomidine dose) and naltrexone (2 times the butorphanol dose) with a 3.5 inch 18 gauge spinal needle in the neck or tongue. Induction time were was 8±5 min and recovery time (until standing) was 10±5 min. Total working time (from the time the hippo was darted handled until it was reversed) was 60±6 min. Capnography and blood gas analysis were the most reliable monitoring tools. Overall, this appears to be a successful anesthetic protocol but additional anesthetic events will allow for a more refined technique.
1. Miller, M. 2007. Hippopotami. In: West, G, D.G. Heard, and N. Caulkett (eds.). Zoo Animal and Wildlife Immobilization and Anesthesia. Blackwell Publishing, Oxford, UK. 579–584.