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