Effective, safe, efficient induction of anesthesia is a common goal for clinicians handling free-ranging or captive gorillas (Gorilla gorilla). For many years, prior to development of other agents, the drug phencyclidine was the standard. This was followed by ketamine, then tiletamine-zolazepam, and then the combination medetomidine-ketamine.1-3 There is a paucity of literature detailing anesthetic regimens in gorillas and the few studies that have been published are recent. No published compilation of data regarding the use of ketamine in gorillas is available.
In February 1999, 19 gorillas were moved to the new Congo Gorilla Forest exhibit at the Bronx Zoo. All animals, except for three animals less than 2 years old, were chemically immobilized for relocation. Although tiletamine-zolazapam had previously been used frequently for gorilla immobilizations at the Bronx Zoo, ketamine HCl was selected as the primary immobilizing agent to accomplish the moves. The data presented includes all immobilizations in which ketamine was used for induction or as the sole anesthetic agent for gorillas at the Bronx Zoo for these relocations and for other procedures over a period of 9 years.
Materials and Methods
Bronx Zoo gorilla immobilization records from 1991 to present were reviewed. Five male gorillas (age: 2–41 y) were anesthetized a total of 12 times and 12 female gorillas (age: 2–37 y) were anesthetized a total of 23 times, for an overall total of 35 immobilizations in which ketamine HCl (Ketaset, Fort Dodge Animal Health, Fort Dodge, IA 50501 USA) was used as the anesthetic induction agent. The animals were usually darted using CO2-powered projectiles containing ketamine. Atropine (Amvet Scientific, Yaphank, NY 11980 USA) was often included (n=22) in the initial dart at a dosage rate of 0.04±0.02 mg/kg. Five 4-year-old animals received 5 mg diazepam orally, 2 hours prior to ketamine being administered via hand injection. All animals subsequently received oxygen via nasal tube, facemask, or endotracheal tube. Isoflurane (Aerrane, Baxter Caribe Inc, Deerfield, IL 60015 USA) was administered via the same route, if needed, to complete procedures. Propofol (Gensia Sicor Pharmaceuticals, Irvine, CA 92618 USA) was used to maintain anesthesia in one animal. Supplemental IV ketamine was used for maintenance of anesthesia and to facilitate intubation as needed.
During the translocations, 13 animals underwent cardiac evaluation via transesophageal ultrasound, reproductive evaluation including transabdominal and transvaginal ultrasound, and dental examination and treatment. Several animals underwent field radiography. Procedures performed during other anesthesias included CAT scan, sinus surgery, arthroscopic surgery, laceration repairs, and medical evaluations of ill animals.
Monitoring included a combination of thoracic auscultation, pulse oximetry, peripheral non-invasive indirect blood pressure measurement, rectal temperatures, and/or end tidal capnography.
Mean dosage for immobilization of all animals was 10.9±3.0 mg/kg. For females (n=23) the mean dosage was 11.1±3.8 mg/kg; for males (n=12) it was 10.6±1.7 mg/kg. For animals 2–9 years (n=18) the dosage was 10.0±3.4 mg/kg, for 10–19 years (n=5) it was 14.3±3.5, and for 20–41 years (n=12) it was 10.9±2.0 mg/kg.
Time from the initial dose of ketamine to the first effect was 2.3±2.0 min. Time from initial dose to light anesthesia was 9.9±7.0 min. Mean heart rate, respiratory rate and mean arterial blood pressure with ketamine alone were 118±21 beats per minute, 25±12 respirations per minute, and 125±20 mm Hg, respectively.
Ketamine was chosen as the immobilizing agent for these gorillas due to its history of safety in many species. In particular, the number of gorillas aged 20 years and above, with unknown or uncertain cardiovascular function, was an impetus to try to avoid agents known to cause cardiac depression or prolonged hypertension. The use of an agent that preserves laryngeal reflexes afforded an extra measure of safety until animals could be intubated. Additionally, the availability of ketamine in a concentration of 200 mg/ml made injection of appropriate doses to large individuals via dart more feasible than in the past. The anesthesias in this survey were all rated excellent for induction and recovery. All animals were calm during recovery, displaying minimal anxiety and only short duration ataxia.
1. Cohen, B.J., and M.M. Bree. 1978 Chemical and physical restraint of nonhuman primates. J. Med. Primatol. 7(4):193–201.
2. Horne, W.A., T.M. Norton, and M.R. Loomis. 1997. Cardiopulmonary effects of medetomidine-ketamine-isoflurane anesthesia in the gorilla (Gorilla gorilla) and chimpanzee (Pan troglodytes) Proc. Am. Assoc. Zoo. Vet., Pp. 140–142.
3. Vercruysse, J. and J. Mortelmans. 1978. The chemical restraint of apes and monkeys by means of phencyclidine or ketamine. Acta Zool. Pathol. Antwerp. (70):211–20.