Mechanism of Action

• Primarily augments GABA_A receptors with various other protein and ion channel interactions
  • Except nitrous oxide which is primarily an NMDA‐receptor antagonist

Minimum Alveolar Concentration (MAC)

• MAC is additive
• MAC is inversely proportional to potency (Figure 5.1)
• MAC is directly proportional to oil:gas coefficient (Figure 5.1)
• MAC can vary depending on a variety of factors (Figure 5.2)

Minimum Alveolar Concentration (Definitions)

• MAC
  • The concentration of volatile agent at one atmosphere which prevents movement in 50% of patients exposed to a surgical stimulus (Figure 5.1)
  • MAC ~1.0
• MAC Amnesia
  • The concentration of volatile agent at one atmosphere which prevents recall in 50% of patients
  • MAC ~0.2
• MAC Awake
  • The concentration of volatile agent at one atmosphere which prevents a wakeful response in 50% of patients
  • MAC ~0.3
• MAC₉₀
  • The concentration of volatile agent at one atmosphere which prevents movement in 90% of patients
  • MAC ~1.5
• MAC BAR
  • Prevents any adrenergic/autonomic response to surgical stimulus
  • MAC ~1.8

Factors Affecting MAC (Figure 5.2)