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Adrenaline Concentration Calculation — FRCA Final MCQ

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EasyAnaesthetic Equipment & SafetyAdrenaline Concentration CalculationFRCA Final

A 35-year-old man (ASA I) is having an inguinal hernia repair under local anaesthesia. The surgeon infiltrates lidocaine 1% with adrenaline (epinephrine) 1:200000. What concentration of adrenaline (in mcg/mL) does 1:200000 represent?

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Correct answer: B — 5 mcg/mL

1:200000 adrenaline = 1 g in 200000 mL = 1000000 mcg in 200000 mL = 5 mcg/mL. This is a common exam calculation. Other concentrations: 1:1000 = 1 mg/mL (IM adrenaline for anaphylaxis); 1:10000 = 100 mcg/mL (IV adrenaline for cardiac arrest); 1:100000 = 10 mcg/mL (surgical infiltration); 1:200000 = 5 mcg/mL (standard LA infiltration concentration). The adrenaline in LA solutions causes local vasoconstriction, prolonging block duration, reducing systemic absorption, and reducing surgical field bleeding.

Reference: RCOA – 2023 – Final FRCA curriculum: local anaesthetic pharmacology; BNF – 2025 – Adrenaline concentrations