Minimum Alveolar Concentration: Its Meaning and Application Across the Amniota
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.
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9. Quasha, A.L., E.I. Eger, and J.H. Tinker. 1980. Determination and applications of MAC. Anesthesiol. 53:315–334.