MAC Additivity Calculation — FRCA Final MCQ

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EasyGeneral AnaesthesiaMAC Additivity CalculationFRCA Final

During maintenance with sevoflurane, the inspired concentration is 2.0% in a 50:50 O2/N2O mixture. What is the approximate MAC?

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Correct answer: D — 1.6 MAC

Sevoflurane MAC ~2.0% in 100% O2. At 2.0% inspired: sevoflurane contributes 2.0/2.0 = 1.0 MAC. N2O MAC ~104%; at 50% it contributes 50/104 = 0.48 MAC. Total = 1.0 + 0.48 ≈ 1.5 MAC. MACs are additive.

Reference: RCOA – 2020 – Primary FRCA curriculum: Physics and clinical measurement