Which property most closely determines the rate of onset of an inhaled anesthetic?

Which property most closely determines the rate of onset of an inhaled anesthetic?

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

Answer: (A)

The speed of onset for an inhaled anesthetic is governed mainly by how soluble it is in blood relative to gas in the alveoli. This is described by the blood/gas partition coefficient. A low blood/gas coefficient means the agent stays mostly in the alveolar gas and rapidly reaches equilibrium with the brain, producing a fast onset. A high blood/gas coefficient means more of the agent dissolves in blood, so the alveolar-to-blood and blood-to-brain equilibration takes longer, slowing onset. Oil/gas partition coefficient reflects lipid solubility and largely relates to potency and tissue distribution, not the speed of onset. Vapor pressure indicates how readily the liquid evaporates to form vapor and influences delivery, but the intrinsic rate-limiting step for onset is the blood/gas solubility. MAC measures potency, not onset time. So the property that most closely determines onset rate is the blood/gas partition coefficient.

The speed of onset for an inhaled anesthetic is governed mainly by how soluble it is in blood relative to gas in the alveoli. This is described by the blood/gas partition coefficient. A low blood/gas coefficient means the agent stays mostly in the alveolar gas and rapidly reaches equilibrium with the brain, producing a fast onset. A high blood/gas coefficient means more of the agent dissolves in blood, so the alveolar-to-blood and blood-to-brain equilibration takes longer, slowing onset.

Oil/gas partition coefficient reflects lipid solubility and largely relates to potency and tissue distribution, not the speed of onset. Vapor pressure indicates how readily the liquid evaporates to form vapor and influences delivery, but the intrinsic rate-limiting step for onset is the blood/gas solubility. MAC measures potency, not onset time.

So the property that most closely determines onset rate is the blood/gas partition coefficient.