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

Gabrielle L. Stalder Dr med vet1, Thierry Petit Dr med vet2, Igal Horowitz DVM3, Robert Hermes Dr med vet4, Joseph Saragusty DVM, PhD5, Felix Knauer Dr rer silv6, and Chris Walzer Dr med vet7
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  • 1 Institute of Wildlife Ecology, University of Veterinary Medicine, A-1160 Vienna, Austria.
  • | 2 Zoo de La Palmyre, 6 Rue de Royan, 17570 Les Mathes, France.
  • | 3 Zoological Center Tel Aviv–Ramat Gan, POB 984, Ramat Gan 52109, Israel.
  • | 4 Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke St 17, D-10315 Berlin, Germany.
  • | 5 Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke St 17, D-10315 Berlin, Germany.
  • | 6 Institute of Wildlife Ecology, University of Veterinary Medicine, A-1160 Vienna, Austria.
  • | 7 Institute of Wildlife Ecology, University of Veterinary Medicine, A-1160 Vienna, Austria.

Abstract

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 µg/kg [27.3 to 36.4 µg/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 CO2, and lactate and HCO3 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.

Abstract

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 µg/kg [27.3 to 36.4 µg/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 CO2, and lactate and HCO3 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.

Contributor Notes

The authors thank Dr. Viktor Molnar and Andreas Hiebl for technical support.

Address correspondence to Dr. Stalder (gabrielle.stalder@fiwi.at.