Which property is most closely associated with the minimum alveolar concentration (MAC) of inhaled anesthetics?

Which property is most closely associated with the minimum alveolar concentration (MAC) of inhaled anesthetics?

• A. Oil/gas partition coefficient
• B. Blood/gas partition coefficient
• C. Vapor pressure
• D. Molecular weight

Answer: (A)

The key idea is that how potent an inhaled anesthetic is depends mainly on its lipid solubility. MAC measures potency—the lower the MAC, the more potent the drug, because only a small alveolar concentration is needed to suppress movement in response to a stimulus. Lipid solubility, captured by the oil/gas partition coefficient, predicts this potency: the higher the oil/gas coefficient, the more the agent dissolves into lipid-rich brain tissue, so it achieves anesthesia at a lower alveolar concentration. The other properties influence different aspects. The blood/gas partition coefficient reflects how soluble the agent is in blood, which affects the speed of onset and recovery but not the intrinsic potency or MAC. Vapor pressure relates to how readily the agent can be delivered from the vaporizer and in the gas phase, not to how potent it is once it reaches the brain. Molecular weight doesn’t reliably determine MAC. Thus, the oil/gas partition coefficient best explains why some inhaled anesthetics are more potent and have lower MAC values.

The key idea is that how potent an inhaled anesthetic is depends mainly on its lipid solubility. MAC measures potency—the lower the MAC, the more potent the drug, because only a small alveolar concentration is needed to suppress movement in response to a stimulus. Lipid solubility, captured by the oil/gas partition coefficient, predicts this potency: the higher the oil/gas coefficient, the more the agent dissolves into lipid-rich brain tissue, so it achieves anesthesia at a lower alveolar concentration.

The other properties influence different aspects. The blood/gas partition coefficient reflects how soluble the agent is in blood, which affects the speed of onset and recovery but not the intrinsic potency or MAC. Vapor pressure relates to how readily the agent can be delivered from the vaporizer and in the gas phase, not to how potent it is once it reaches the brain. Molecular weight doesn’t reliably determine MAC. Thus, the oil/gas partition coefficient best explains why some inhaled anesthetics are more potent and have lower MAC values.