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