Which inhaled anesthetic has the lowest blood/gas partition coefficient, resulting in the fastest onset of anesthesia?

Which inhaled anesthetic has the lowest blood/gas partition coefficient, resulting in the fastest onset of anesthesia?

• A. A Halothane
• B. B Isoflurane
• C. C Sevoflurane
• D. D Desflurane

Answer: (D)

The key idea is that how fast an inhaled anesthetic works depends on how soluble it is in blood, measured by the blood/gas partition coefficient. Lower solubility means the gas in the lungs doesn’t dissolve much in blood, so the alveolar concentration rises quickly and the brain reaches the anesthetic level rapidly. Desflurane has the lowest blood/gas partition coefficient among common volatile anesthetics, so it equilibrates between the alveoli and blood fastest, yielding the quickest onset of anesthesia (and also rapid emergence when you stop administering it). In contrast, agents with higher blood solubility linger in the blood longer, delaying the rise in brain concentration and slowing onset.

The key idea is that how fast an inhaled anesthetic works depends on how soluble it is in blood, measured by the blood/gas partition coefficient. Lower solubility means the gas in the lungs doesn’t dissolve much in blood, so the alveolar concentration rises quickly and the brain reaches the anesthetic level rapidly. Desflurane has the lowest blood/gas partition coefficient among common volatile anesthetics, so it equilibrates between the alveoli and blood fastest, yielding the quickest onset of anesthesia (and also rapid emergence when you stop administering it). In contrast, agents with higher blood solubility linger in the blood longer, delaying the rise in brain concentration and slowing onset.