A surgical patient is started on total parenteral nutrition (TPN). On day 3, serum phosphate drops to 0.4 mmol/L (normal 0.8-1.45) with onset of muscle weakness and confusion. The most likely diagnosis and its mechanism is:

• A Refeeding syndrome — insulin surge from glucose drives phosphate into cells, causing hypophosphatemia ✓
• B Hyperglycemia — glucose excess causing osmotic diuresis and phosphate loss
• C Zinc deficiency — TPN-related micronutrient deficiency
• D TPN-related cholestasis causing phosphate malabsorption

Explanation

Refeeding syndrome occurs when malnourished patients receive carbohydrate-rich nutrition (enteral or parenteral). The glucose load stimulates insulin secretion, which drives intracellular uptake of phosphate, potassium, and magnesium. Severe hypophosphatemia (<0.5 mmol/L) causes: respiratory failure (diaphragm weakness), cardiac dysfunction, hemolytic anemia, neurological symptoms (confusion, seizures), and rhabdomyolysis. Prevention involves identifying at-risk patients (weight loss >10%, minimal intake >5 days), starting TPN at 50% target rate with thiamine supplementation, and replacing electrolytes before and during feeding. NICE criteria identify refeeding risk and guide management.

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

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Written and medically reviewed by the StethoPrep medical team.