Minimum Alveolar Concentration: Its Meaning and Application Across the Amniota
American Association of Zoo Veterinarians Conference 2006
Jennifer C. Hess1, DVM, MS; Elizabeth A. Martinez1, DVM, DACVA; Jean A. Paré2, DMV, DVSc, DACZM
1Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Texas A&M University, College Station, TX, USA; 2Toronto Zoo, Scarborough, ON, Canada


The term “minimum anesthetic response” (MAR) was coined by Merkel and Eger with the intent of providing a means of comparing two anesthetic agents.6 The concept of MAR was developed in reference to the gas anesthetic concentration required to prevent gross purposeful movement in dogs following a noxious stimulus. It became known as the “minimum alveolar concentration” (MAC). The MAC 1.0 is defined as the “minimal anesthetic concentration in the alveolus required to prevent gross purposeful movement in response to a painful stimulus.”2 However, the term “minimum alveolar concentration” is mammal oriented. Mammals have alveoli while birds and reptiles do not. The term “minimum anesthetic dose” was proposed by Ludders et al. to try to be inclusive of mammals, birds, and reptiles.4 Minimum anesthetic concentration (MAC) also has been suggested and is used in the poultry literature.5,8 These terms all denote the same basic idea, but some are anatomically correct, some are anatomically indistinct, and some are anatomically incorrect. Another problem with MAC is that it denotes the plane of anesthesia which in turn impacts cardiopulmonary parameters. Some species, like dogs and horses, have MAC without a large deviation between individuals within a species. Some reptile species appear to have a similar MAC distribution across individuals while others have a range within members of a single species.3,6,7 For the collection of cardiopulmonary parameters, the ideal for reptiles would be to predetermine the MAC of a specific inhalant anesthetic for each animal at the temperature in which an experiment is to occur.9


I would like to thank Dr. John Benson, Dr. Peter Constable, and Ms. Ragenia Sarr for their support during the completion of my master’s thesis upon which this abstract is based.

Literature Cited

1.  Bertelsen, M.F., C.A. Mosley, G.J. Crawshaw, D. Dyson, and D.A. Smith. 2005. Minimum alveolar concentration of isoflurane in mechanically ventilated Dumeril monitors. J. Am. Vet. Med. Assoc. 226:1098–1101.

2.  Eger, E.I. II, L. Saidman, and B. Brandstater. 1965. Minimum alveolar anesthetic concentration: a standard of anesthetic potency. Anesthesiol. 26:756–763.

3.  Hess, J.H. 2005. Chapter IV: Determination of minimum faveolar concentration of isoflurane and cardiopulmonary values in Iguana iguana. In: The determination of minimum faveolar concentration of isoflurane and arterial blood gas and acid-base values in Iguana iguana. University of Illinois at Urbana-Champaign Graduate College 2005.

4.  Ludders, J.W. 1992. Minimal anesthetic concentration and cardiopulmonary dose-response of halothane in ducks. Vet. Surg. 21:319–324.

5.  Ludders, J.W., J. Rode and G. Mitchell. 1989. Isoflurane anesthesia in sandhill cranes (Grus canadensis): minimal anesthetic concentration and cardiopulmonary dose-response during spontaneous and controlled breathing. Anesth. Analg. 68:511–516.

6.  Merkel, G. and E.I. Eger, II. 1963. A comparative study of halothane and halopropane anesthesia including method for determining equipotency. Anesthesiol. 24:346–357.

7.  Mosley, C.A., D. Dyson, and D.A. Smith. 2003. Minimum alveolar concentration of isoflurane in green iguanas and the effect of butorphanol on minimum alveolar concentration. J. Am. Vet. Med. Assoc. 222:1559–1564.

8.  Naganobu, K., Y. Fujisawa, H. Ohde, Y. Matsuda, T. Sonoda, and H. Ogawa. 2000. Determination of the minimum anesthetic concentration and cardiovascular dose response for sevoflurane in chickens during controlled ventilation. Vet. Surg. 29:102–105.

9.  Quasha, A.L., E.I. Eger, and J.H. Tinker. 1980. Determination and applications of MAC. Anesthesiol. 53:315–334.


Speaker Information
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Jennifer C. Hess, DVM, MS
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
Texas A&M University
College Station, TX, USA

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