How does the blood-gas partition coefficient of an inhaled anesthetic relate to its onset and offset?

• A. Higher coefficient = faster onset and offset; lower coefficient = slower onset/offset.
• B. Higher coefficient = slower rise to equilibrium and slower offset; lower coefficient = faster onset/offset.
• C. Coefficient does not affect onset or offset.
• D. Lower coefficient leads to longer duration of anesthesia.

Answer: (B)

Blood-gas partition coefficient reflects how soluble an inhaled anesthetic is in blood compared with alveolar gas. A higher coefficient means the drug dissolves more in blood, so during induction much of it is taken up by the blood rather than staying in the alveolar gas. That slows the rise of alveolar and arterial concentrations, leading to a slower onset. It also creates a blood reservoir that must be emptied before the drug can be cleared from the body, so recovery and offset are slower. Conversely, a low coefficient means the drug equilibrates quickly between air and blood, producing rapid onset, and it doesn’t linger in the blood, so offset is faster.