Lack of Isoflurane-Sparing Effect of Butorphanol in Field Anesthesia of Harlequin Ducks (Histrionicus histrionicus)
We investigated the effect of administration of butorphanol at several dosages on the use of isoflurane as an anesthetic for the implantation of abdominal radio transmitters into harlequin ducks (Histrionicus histrionicus) under field surgery conditions. Transmitters were implanted using a standard technique.2
This study was conducted at Prince William Sound, Alaska as part of a project following the 1989 M/V Exxon Valdez oil spill comparing over-winter survival of mature female harlequin ducks from the western, oil-exposed side to the eastern, unoiled side of Prince William Sound. We sampled free-ranging female harlequin ducks greater than 3 years of age based upon cloacal examination of bursal involution.3 The birds were captured using shore net traps during early fall molt of the primary feathers in 1997. The body weights averaged 620 g. Birds were captured and placed on board ship within 90 minutes of initiation of chase in ambient temperatures between 14.5 and 16.2°C.
Intramuscular injections of 0.5, 1.0, 1.5, or 2.0 mg/kg butorphanol tartrate were given to the ducks 15 minutes prior to induction. We induced all birds by mask with isoflurane (Forane, Ohio Medical Products, Madison, WI, USA) at 5% in oxygen (1.0 L/m) delivered from an out-of-circuit, agent specific, flow, and temperature compensated vaporizer using a mask attached to a modified Jackson-Rees non-rebreathing circuit. Early efforts to use a toe pinch with a forceps to elicit a response to pain, similar to that described in studies in other birds, were unsuccessful as even unanesthetized birds failed to demonstrate withdrawal. Because the toe pinch convention was ineffective, the bird’s response to plucking of the surgical site, skin incision, and suturing during the transmitter implantation was used to evaluate the effectiveness of the anesthetic gas concentration after a minimum of 2 minutes equilibration at a given concentration.
Intramuscular injections of ducks with 0.5, 1.0, 1.5, or 2.0 mg/kg butorphanol tartrate 15 minutes prior to surgery did not reduce levels of isoflurane required to maintain a surgical plane of anesthesia compared to control harlequin ducks which did not receive butorphanol premedication. Our findings differed from a study involving psittacine birds in which doses ≤2.0 mg/kg effectively reduced the required level of inhalant anesthesia.1 Higher dosages of butorphanol may have been more effective in harlequin ducks, but we were reluctant to test such dosages because of the risk of residual depression that could have affected post-release survival in the wild.
1. Curro TG, Brunson DB, Paul-Murphy J. Determination of the ED50 of isoflurane and evaluation of the isoflurane-sparing effect of butorphanol in cockatoos (Cacatua spp.). Vet Surg. 1994;23:429–433.
2. Korschgen CE, Kenow KP, Gendron-Fitzpatrick A, Green WL, Dein FJ. Implanting intra-abdominal radiotransmitters with external whip antennas in ducks. J Wildl Manage. 1996;60:132–137.
3. Mather DM, Esler D. Evaluation of bursal depth as an indicator of age class of harlequin ducks. J Field Ornithol. 1999;70:200–205.