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Minimum alveolar concentration
Other uses of MAC include MAC-BAR (1.7-2.0 MAC), which is the concentration required to block autonomic reflexes to nociceptive stimuli, and MAC-awake (0.3-0.5 MAC), the concentration required to block voluntary reflexes and control perceptive awareness.
Additional recommended knowledge
The MAC is the concentration of the vapour (measured as a percentage at 1 atmosphere, i.e the partial pressure) that prevents the reaction to a standard surgical stimulus (traditionally a set depth and width of skin incisions) in 50% of subjects. This measurement is done at steady state (assuming a constant alveolar concentration for 15 minutes), under the assumption that this allows for an equilibration between the gasses in the alveoli, the blood and the brain.
The MAC of a volatile substance is inversely proportional to its lipid solubility (oil:gas coefficient) , in most cases. This is the Meyer-Overton hypothesis. MAC is inversely related to potency i.e. high mac equals low potency.
The hypothesis correlates lipid solubility of an anaesthetic agent with potency (1/MAC) and suggests that onset of anaesthesia occurs when sufficient molecules of the anaesthetic agent have dissolved in the cell's lipid membranes, resulting in anaesthesia. Exceptions to the Meyer-Overton hypothesis can result from:
Eger, E.I. 2nd (1965), " ", Anesthesiology 26(6): 756-763
Daniel, M. (1998), " ", Anesthesiology 88(1): 43-49
Katoh, T. (1999), " ", Anesthesiology 90(2): 398-405
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Minimum_alveolar_concentration". A list of authors is available in Wikipedia.|