Second Gas Effect Mechanism — FRCA Primary MCQ
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Correct answer: E — The rapid uptake of a large volume of N2O concentrates the second agent in the alveolus and increases its rate of rise
When N2O (at high concentration e.g. 70%) is rapidly absorbed from alveoli into blood the remaining alveolar gas is concentrated (including the second volatile agent). Additionally the volume loss draws more fresh gas into the alveolus (augmented inflow). Both mechanisms accelerate the rise of FA/FI of the second agent.
Reference: Peck Hill Williams 2014 Pharmacology for Anaesthesia and Intensive Care