Use of a medetomidine-ketamine combination for anesthesia in captive common hippopotami (Hippopotamus amphibius).

Objective: To establish an anesthetic protocol suitable for surgical interventions in hippopotami (Hippopotamus amphibius).

Design: Prospective case series.

Animals: 10 adult male hippopotami undergoing castration.

Procedures: A combination of medetomidine (60 to 80 mg/kg [27.3 to 36.4 mg/lb]) and ketamine (1 mg/kg [0.45 mg/lb]) was administered IM on the basis of mean estimated weights of 1,330 ± 333 kg (2,926 ± 733 lb; median, 1,350 kg [2,790 lb]; range, 900 to 2,000 kg [1,980 to 4,400 lb]). Monitoring included sequential blood gas analyses, pulse oximetry, and capnography. Reversal of anesthesia with atipamezole (0.34 ± 0.06 mg/kg [0.15 ± 0.027 mg/lb]; median, 0.33 mg/kg [0.15 mg/lb]; range, 300 to 500 mg total dose]) was uneventful and rapid in all cases.

Results: Complete immobilization and a surgical anesthetic plane were achieved 27 ± 11.8 minutes (median, 24.5 minutes [range, 14 to 44 minutes]) after initial injection. Anesthesia (97.3 ± 35.3 minutes; median, 95 minutes [range, 57 to 188 minutes]) was maintained with 3.4 ± 2.2 (median, 3) additional doses of ketamine (0.1 to 0.4 mg/kg [0.045 to 0.18 mg/lb]). Transitory apnea of 4.71 ± 2.87 minutes (median, 4 minutes [range, 1 to 9 minutes]) was documented in 5 animals. Apnea during anesthesia was viewed as a physiologic condition in this semiaquatic mammal because related vital parameters (heart rate, pH, peripheral hemoglobin oxygen saturation as measured by pulse oximetry, venous partial pressure of CO(2), and lactate and HCO(3) concentrations) remained unchanged and did not differ significantly than those parameters for the 5 animals with continuous respiration.

Conclusions And Clinical Relevance: Both in captivity and in the wild, common hippopotami are difficult to anesthetize. The combination of medetomidine and ketamine provided an excellent surgical plane of anesthesia and a self-limiting dive response.