Determination of Minimum Anesthetic Concentration of Isoflurane in Thick-Billed Parrots (Rhinchopsitta plachyrhyncha)
American Association of Zoo Veterinarians Conference 2006
Julio A. Mercado1,2, MVZ, MPVM; R. Scott Larsen3, DVM, MS, DACZM; 3Raymund F. Wack, DVM, MS, DACZM; Bruno Pypendop4, DrMedVet, DrVetSci, DACVA
1Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA, USA; 2Zoological Society of San Diego, San Diego, CA, USA; 3Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA; 4Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA, USA


The thick-billed parrot (Rhinchopsitta plachyrhyncha) is an endangered species native to the southwestern U.S. and northern Mexico.5 Clinically, anesthesia in this species has been maintained with relatively low concentrations of isoflurane and unexplained mortalities related to anesthesia have been observed (Lamberski, personal communication). This study was conducted to determine if the minimum anesthetic concentration (MAC) of isoflurane is lower in thick-billed parrots (TBP) than values reported for other species of birds. Fifteen healthy thick-billed parrots were induced and maintained with isoflurane. Birds were intubated, artificially ventilated, and monitored. The first bird was maintained at 1.00% isoflurane; after 15 minutes at the target vaporizer setting an end-tidal isoflurane sample was measured via a modified endotracheal tube. The toe was then pinched to evaluate whether the bird had a conscious response to a painful stimulus. This bird was recovered, and the isoflurane equilibration concentration was then increased or decreased by 10% for the next bird, depending on whether the previous bird did or did not respond to the painful stimulus. This “up and down” approach was used for all birds, and quantal analysis was used to make an estimate of MAC.2 Using these methods, the MAC for isoflurane in thick-billed parrots was estimated to be 1.07%, which is lower than the MAC estimated for cockatoos (1.44%), sandhill cranes (1.34%), and Peking ducks (1.30%).1,3,4 This may help explain clinical problems observed in these birds under anesthesia. By defining the species-specific requirements of thick-billed parrots, isoflurane anesthesia can be performed more safely in this endangered species.


This research was supported by funding from the Center for Companion Animal Health and the Veterinary Medicine Teaching Hospital at the University of California, Davis. The authors thank the animal care staff at the Sacramento Zoo and the Anesthesia Service at the UC Davis School of Veterinary Medicine for their assistance with this investigation.

Literature Cited

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.   Dixon WJ. The up-and-down method for small samples. Am Stat Assoc J. 1965;60:976–978.

3.  Ludders JW. Isoflurane anesthesia in sandhill cranes (Grus canadensis): minimal anesthetic concentration and cardiopulmonary dose-response during spontaneous and controlled breathing. Anesth Analg. 1989;68:511–516.

4.  Ludders JW, Mitchell GS, Rode J. Minimal anesthetic concentration and cardiopulmonary dose response of isoflurane in ducks. Vet Surg. 1990;19:304–307.

5.  Stattersfield AJ, Capper DR. Threatened Birds of the World. Cambridge, England: Lynx Editions and Birdlife International; 2000.


Speaker Information
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Julio A. Mercado, MVZ, MPVM
Zoological Society of San Diego
San Diego Zoo
San Diego, CA, USA

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