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Metabolic alkalosis delaying weaning — FRCA Final MCQ

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HardICUMetabolic alkalosis delaying weaningFRCA Final

A 70-year-old man is sedated and ventilated after oesophagectomy. On day three he is difficult to wake, pH is 7.53, PaCO2 6.8 kPa, bicarbonate 42 mmol/L, potassium 2.7 mmol/L, and nasogastric losses have been high. What is the most likely cause of the complication?

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Correct answer: A — Metabolic alkalosis from gastric losses and hypokalaemia

The high pH with raised bicarbonate and hypokalaemia after gastric losses indicates chloride-responsive metabolic alkalosis. PaCO2 is elevated as respiratory compensation rather than primary respiratory alkalosis. DKA and lactic acidosis would produce acidaemia with a low bicarbonate. Correction involves chloride and potassium repletion, reviewing diuretics and addressing ongoing losses.

Reference: Faculty of Intensive Care Medicine acid-base guidance; RCoA Final FRCA Syllabus 2026