Clark Electrode Method — FRCA Primary MCQ
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Correct answer: B — A polarographic method with platinum cathode and silver/silver chloride anode
The Clark electrode: platinum cathode + Ag/AgCl anode in KCl electrolyte separated from blood by an O2-permeable membrane. Applied voltage of 0.6V causes O2 reduction at cathode: O2 + 2H2O + 4e⁻ → 4OH⁻. Current is proportional to PaO2.
Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment