Increased fresh gas flow will accelerate the rate of rise of the FA/FI ratio the most for which agent?

Increased fresh gas flow will accelerate the rate of rise of the FA/FI ratio the most for which agent?

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

Answer: (D)

Fresh gas flow speeds the rise of alveolar concentration (FA) toward the inspired concentration (FI) by delivering more anesthetic and reducing the influence of uptake into blood. The amount FA can rise before reaching FI depends on how soluble the agent is in blood; highly soluble agents are taken up more, which slows FA rise. Increasing fresh gas flow minimizes that bottleneck, so the rise is faster for agents with high blood–gas solubility. Halothane has the highest solubility among these options, so it shows the greatest acceleration in the FA/FI ratio when fresh gas flow is increased. The other agents are less soluble, so their FA tracks FI more closely anyway, and boosting FG flow doesn’t change their FA/FI rise as dramatically.

Fresh gas flow speeds the rise of alveolar concentration (FA) toward the inspired concentration (FI) by delivering more anesthetic and reducing the influence of uptake into blood. The amount FA can rise before reaching FI depends on how soluble the agent is in blood; highly soluble agents are taken up more, which slows FA rise. Increasing fresh gas flow minimizes that bottleneck, so the rise is faster for agents with high blood–gas solubility. Halothane has the highest solubility among these options, so it shows the greatest acceleration in the FA/FI ratio when fresh gas flow is increased. The other agents are less soluble, so their FA tracks FI more closely anyway, and boosting FG flow doesn’t change their FA/FI rise as dramatically.