Compare and Contrast Two Successful Anesthetic Protocols in the Nile Hippopotamus (Hippopotamus amphibius spp.)
American Association of Zoo Veterinarians Conference 2012

Gregory J. Fleming1, DVM, DACZM; Christian Walzer2, Dr. med. vet., DECZM

1Department of Animal Health, Disney’s Animal Programs and Environmental Initiatives, Bay Lake, FL, USA; 2Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna, Austria


Historical immobilization of the Nile hippopotamus has resulted in apnea, cyanosis, bradycardia and fatalities in up to 1/3 of the cases1 and only 2 of 16 successful anesthesia’s (16%) resulted in surgical anesthesia.2 Recently two successful anesthetic protocols have been developed for the Nile hippopotamus using medetomidine (60–80 mcg/kg) and ketamine (1 mg kg) i.m. (MK) in captive settings, while a second combination utilizing butorphanol (0.12 mg/kg), azaparone (0.05–0.1 mg/kg), and medetomidine 0.04 i.m. (BAM) has been used in both captive and free-ranging settings (Table 1).3

Table 1. Anesthetic protocols for Nile hippopotamus


Dose mg/kg

Induction time

Working time

Recovery time


0.01–0.12 i.m.

8±5 min

60±6 min



0.08–0.12 i.m.





0.04–0.05 i.m.





2 x med i.m.





2 x but i.m.





0.06–0.08 i.m.


97 min



0.34 i.v./i.m.





Over 30 anesthetic events were recovered between the two protocols. Induction times varied with BAM having faster induction of 8±5 min vrs 27±11.8 min in MK protocol. Working times of 60–97 min with the MK group receiving additional ketamine in boluses equaling 0.007±0.002 mg kg min. While recovery was faster with the MK protocol (4.8±2.86 min) with atipamezole (65% i.v./35% i.m.) compared to the BAM protocol with (10±5 min) with i.m. administration of naltrexone (0.2 mg/kg i.m.) and atipamezole (0.1 mg/kg i.m.).

Transient apnea was seen in both combinations resulting in self-limiting breath holding for 4–7 min, which resolved over time and SpO2 levels re-bounded once respirations resumed. Heart rates remained constant in both protocols (35–55 bpm) while metabolic acidosis was evident in blood gas analysis.

In conclusion, both protocols provide effective immobilization of the Nile hippopotamus; however, the collection of additional physiologic data may assist with developing safer and more effective anesthetic techniques.

Literature Cited

1.  Miller M. 2007. Hippopotami. In: West G, Heard DG, Caulkett N (eds.). Zoo Animal and Wildlife Immobilization and Anesthesia. Blackwell Publishing, Oxford, UK. 579–584.

2.  Ramsay EC, Loomis MR, Mehren KG. Chemical restraint of the Nile hippopotamus (Hippopotamus amphibius) in captivity. J Zoo Wildl Med. 1998;29:45–49.

3.  Stalder GL, Petit T, Horrowitz I, Hermes R, Saragusty J, Knauer F, Walzer C. 2012. Use of a medetomidine-ketamine combination for anesthesia in captive common hippopotami (Hippopotamus amphibius). J Am Vet Med Assoc. 241:110–116.


Speaker Information
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Gregory J. Fleming, DVM, DACZM
Department of Animal Health
Disney’s Animal Programs and Environmental Initiatives
Bay Lake, FL, USA

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