A post-operative bowel resection patient is being started on total parenteral nutrition (TPN). On day 3, serum phosphate drops to 0.4 mmol/L; the patient develops weakness, cardiac arrhythmias, and altered sensorium. What is the most likely metabolic complication?

• A Wernicke's encephalopathy from thiamine deficiency
• B TPN-related septicemia
• C Hypomagnesemia from insulin-mediated uptake
• D Refeeding syndrome with hypophosphatemia ✓

Explanation

Refeeding syndrome occurs when carbohydrate is introduced in a malnourished patient — insulin release drives cellular uptake of phosphate, potassium, and magnesium (all shift from extra- to intracellular), causing precipitous drops in serum levels. Hypophosphatemia (<0.5 mmol/L) is the hallmark and causes cardiac dysrhythmias, respiratory failure, neuromuscular weakness, and hemolysis. NICE guidelines recommend identifying at-risk patients (BMI <16, minimal intake >10 days, significant weight loss), replacing electrolytes prophylactically before starting nutrition, and starting at 50% of target calories with slow titration. Thiamine deficiency causes Wernicke's but does not cause hypophosphatemia acutely.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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