For rapid onset of an inhaled anesthetic, which property is most favorable?

For rapid onset of an inhaled anesthetic, which property is most favorable?

• A. High MAC
• B. High oil/gas partition coefficient
• C. Low blood/gas partition coefficient
• D. High vapor pressure

Answer: (C)

Rapid onset hinges on how quickly the anesthetic moves from the lungs into the blood and then the brain. A low blood/gas partition coefficient means the agent is poorly soluble in blood, so it won’t be held up in the bloodstream. As alveolar gas partial pressure rises, the drug rapidly equilibrates into the blood and then to the brain, producing anesthesia quickly. If the agent is highly soluble in blood or tissue (high blood/gas or high oil/gas coefficients), it acts as a reservoir and slows the rise in brain concentration, delaying onset. Potency (MAC) and volatility (vapor pressure) affect other aspects like how much is needed and how readily it vaporizes, but they don’t predict onset as reliably as how soluble the agent is in blood. So the most favorable property for rapid onset is a low blood/gas partition coefficient.

Rapid onset hinges on how quickly the anesthetic moves from the lungs into the blood and then the brain. A low blood/gas partition coefficient means the agent is poorly soluble in blood, so it won’t be held up in the bloodstream. As alveolar gas partial pressure rises, the drug rapidly equilibrates into the blood and then to the brain, producing anesthesia quickly. If the agent is highly soluble in blood or tissue (high blood/gas or high oil/gas coefficients), it acts as a reservoir and slows the rise in brain concentration, delaying onset. Potency (MAC) and volatility (vapor pressure) affect other aspects like how much is needed and how readily it vaporizes, but they don’t predict onset as reliably as how soluble the agent is in blood. So the most favorable property for rapid onset is a low blood/gas partition coefficient.