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14.02.12 MAC

Definition
  • Concentration of the vapour 
    • Measured as a percentage at 1 atmosphere, i.e. the partial pressure
    • At steady state (after 15 mins)
  • That prevents patient movement in response to a supramaximal stimulus 
    • Traditionally a set depth and width of skin incisions

MACs of common anaesthetics
  • Nitrous oxide - 104
  • Xenon - 72
  • Desflurane - 6
  • Ethyl Ether - 3.2
  • Sevoflurane - 2
  • Enflurane - 1.7
  • Isoflurane - 1.2
  • Halothane - 0.75
  • Chloroform - 0.5
  • Methoxyflurane - 0.16
 
Meyer-Overton hypothesis
  • The MAC of a volatile substance is inversely proportional to its lipid solubility (oil:gas coefficient), in most cases
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