Which factor primarily determines the potency of a volatile inhalation anesthetic agent?

Which factor primarily determines the potency of a volatile inhalation anesthetic agent?

• A. Blood-gas partition coefficient
• B. Vapor pressure
• C. Minimum alveolar concentration
• D. Boiling point

Answer: (C)

Potency of a volatile inhalation anesthetic is determined by the minimum alveolar concentration (MAC). MAC is the alveolar concentration required to prevent movement in 50% of patients in response to a standard surgical stimulus; the lower the MAC, the more potent the agent because a smaller concentration is needed to achieve immobility. This reflects the drug’s strength in depressing CNS pathways that mediate movement in response to pain. Other properties influence how fast the drug acts and how long it lasts rather than its intrinsic potency: blood–gas partition coefficient affects solubility in blood and the rate of rise and fall in brain concentration (onset/offset), vapor pressure relates to how readily the liquid vaporizes and is delivered, and boiling point ties to volatility but not to the immobilizing strength.

Potency of a volatile inhalation anesthetic is determined by the minimum alveolar concentration (MAC). MAC is the alveolar concentration required to prevent movement in 50% of patients in response to a standard surgical stimulus; the lower the MAC, the more potent the agent because a smaller concentration is needed to achieve immobility. This reflects the drug’s strength in depressing CNS pathways that mediate movement in response to pain. Other properties influence how fast the drug acts and how long it lasts rather than its intrinsic potency: blood–gas partition coefficient affects solubility in blood and the rate of rise and fall in brain concentration (onset/offset), vapor pressure relates to how readily the liquid vaporizes and is delivered, and boiling point ties to volatility but not to the immobilizing strength.