Evaluation of Induction, Intubation, and Recovery Times with Fentanyl or Sufentanil with Ketamine and Midazolam in Gorillas (Gorilla gorilla gorilla)
American Association of Zoo Veterinarians Conference 2019
Ryan S. Bailey1,2, DVM, DACVAA; Julie Balko1,3, VMD DACVAA; Sathya K. Chinnadurai1, DVM, MS, DACZM, DACVAA, DACAW
1Chicago Zoological Society, Brookfield Zoo, Brookfield, IL, USA; 2Premier Veterinary Group, Chicago, IL, USA; 3North Carolina State University, Raleigh, NC, USA


Due to prevalence of cardiovascular disease in adult gorillas (Gorilla gorilla gorilla), recommended anesthetic protocols avoid drugs that can cause significant alterations in cardiovascular dynamics (e.g., alpha-2 agonists) and instead, rely heavily on dissociative anesthetics (e.g., tiletamine).1-6 While dissociatives like tiletamine are effective anesthetics, the lack of reversibility and long duration of action usually produce prolonged, turbulent anesthetic recoveries.1,2,6 Fentanyl and sufentanil are both short-acting full mu opioid agonists that result in minimal cardiovascular depression in other species, allowing for rapid recovery and cardiovascular stability.7 This study evaluated coinduction combinations of ketamine and midazolam with fentanyl (FKM) or sufentanil (SKM).

Five male and five female adult gorillas were anesthetized with FKM (fentanyl 1–1.5 µg/kg, ketamine 4–5 mg/kg, and midazolam 0.2–0.3 mg/kg) followed by maintenance with isoflurane or sevoflurane (Table 1). For females, this combination resulted in smooth, calm induction, and calm, rapid recoveries. In male gorillas, multiple supplemental injections of ketamine were required before animals reached a working depth of anesthesia. Based on these results, an additional group of males (n=7) was anesthetized with SKM (midazolam 0.2–0.3 mg/kg, ketamine 4–5 mg/kg, and sufentanil 0.25–0.3 µg/kg) and maintenance with sevoflurane. SKM resulted in smooth inductions and rapid recoveries after reversal with 10 mg naltrexone IM per animal. With both FKM and SKM, rare cases of bradycardia were successfully treated with atropine. In FKM females and SKM males, time course from initial injection to intubation was approximately 40 min. Time from reversal to standing in SKM males ranged from 15–54 min (Table 2).

Table 1. Demographic data and drug dosage amounts, presented as mean±standard deviation, for adult gorillas (Gorilla gorilla gorilla) anesthetized with either fentanyl, ketamine and midazolam (FKM) or sufentanil, ketamine and midazolam (SKM)

Treatment group


Age (yr)

Weight (kg)

Fentanyl (µg/kg)

Sufentanil (µg/kg)

Ketamine (mg/kg)

Midazolam (mg/kg)

FKM female








FKM male








SKM male








Table 2. Times of anesthetic milestones in minutes from injection, presented as median and range, for adult gorillas (Gorilla gorilla gorilla) anesthetized with either fentanyl, ketamine and midazolam (FKM) or sufentanil, ketamine and midazolam (SKM)

Treatment group

First effect


Safe working depth

Time to LMA/ETT placement

Total anesthesia time (time to reversal)

Reversal to sternal

Reversal to standing

FKM female

5.5 (4–8)

12.5 (4–38)

27 (7–40)

42 (20–74)

87 (56–120)

9 (6–13)

10 (8–15)

FKM male

5 (3–11)

23 (6–43)

40 (28–65)

61 (32–76)

158 (72–279)

19 (13–20)

44 (28–81)

 SKM male

4.5 (3–15)

22.5 (9–27)

29 (14–43)

39 (17–49)

91 (63–334)

12.5 (3–18)

23 (15–54)

LMA signifies laryngeal mask airway and ETT signifies endotracheal tubes.


The authors thank the veterinary and animal care staff at Brookfield Zoo, Toledo Zoo and Omaha’s Henry Doorly Zoo for participating in this study and for their care of these animals.

Literature Cited

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Speaker Information
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Sathya K. Chinnadurai, DVM, MS, DACZM, DACVAA, DACAW
Chicago Zoological Society
Brookfield, IL, USA

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