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CRRT Electrolyte Losses — FRCA Final MCQ

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ModerateIntensive Care MedicineCRRT Electrolyte LossesFRCA Final

A 55-year-old man (ASA III) in the ICU has been on CRRT for 5 days. He is being fed enterally at target rate. His phosphate is 0.35 mmol/L, potassium 3.0 mmol/L, and magnesium 0.6 mmol/L. In addition to refeeding risk, what is another important cause of electrolyte depletion in CRRT patients?

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Correct answer: A — Thyroid dysfunction

CRRT removes electrolytes (phosphate, magnesium, potassium, calcium) in proportion to their plasma concentrations and the sieving coefficient of the membrane. This is a significant and often underappreciated cause of electrolyte depletion in ICU patients. Phosphate losses are particularly significant and can cause respiratory muscle weakness, impaired oxygen delivery (reduced 2,3-DPG), and cardiac dysfunction. Electrolyte replacement protocols specific to CRRT should be in place, with supplementation in the replacement fluid or separate infusions. Daily monitoring is essential.

Reference: KDIGO – 2012 – AKI guidelines; ICS – 2023 – CRRT management standards