Max K+ Infusion Rate Peripheral — FRCA Primary MCQ

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HardPhysiology - Endocrine & MetabolicMax K+ Infusion Rate PeripheralFRCA Primary

A 70 kg patient has moderate asymptomatic potassium deficiency with serum potassium 3.0 mmol L−1. Using the SmPC estimate, mmol required = body weight × 0.2 × 2 × (4.5 − measured potassium), what is the calculated requirement before clinical adjustment?

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Correct answer: A — 42 mmol

The best answer is “42 mmol”. Substitution gives 70 × 0.2 × 2 × (4.5 − 3.0) = 14 × 2 × 1.5 = 42 mmol. This is an estimate rather than an instruction to give the entire amount rapidly: route, renal function, ongoing losses, acid-base state, infusion concentration, rate limits and repeat serum measurements determine the actual replacement plan.

Reference: Sterile potassium chloride concentrate 15% w/v, UK SmPC: https://www.medicines.org.uk/emc/product/15218/smpc; Royal College of Anaesthetists, Primary FRCA syllabus v2.2: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf