Clinical Scenario:
A 29-week infant weighing 1.1 kg has had minimal enteral nutrition for several days because of severe intestinal dysmotility. Parenteral nutrition is commenced and advanced rapidly to provide adequate energy and amino acids.
Forty-eight hours later, the infant develops increasing oxygen requirement and poor cardiac function. Investigations show:
- Phosphate: 0.45 mmol/L
- Potassium: 2.8 mmol/L
- Magnesium: 0.55 mmol/L
- Glucose: 9.8 mmol/L
- Serum calcium: normal
There is no evidence of sepsis, renal failure or significant fluid overload.
Which mechanism best explains this infant’s biochemical abnormalities after initiation of parenteral nutrition?
A. Renal phosphate wasting
B. Insulin-mediated intracellular shift
C. Reduced phosphate absorption
D. Increased urinary calcium loss
E. Suppressed insulin secretion
Correct Answer & Explanation:
Correct answer: B. Insulin-mediated intracellular shift
Explanation: Refeeding Syndrome in neonates
This infant has refeeding syndrome following rapid advancement of parenteral nutrition after a period of minimal nutritional intake.
When carbohydrate is introduced, insulin secretion increases, stimulating cellular uptake of glucose along with phosphate, potassium and magnesium. This produces the characteristic combination of hypophosphataemia, hypokalaemia and hypomagnesaemia.
Severe hypophosphataemia can reduce ATP production and impair cardiac and respiratory muscle function, explaining the poor cardiac function and increasing oxygen requirement.
Why the other options are wrong
- A. Renal phosphate wasting — Incorrect: the acute fall in phosphate after nutritional repletion is primarily due to intracellular redistribution, not renal phosphate loss.
- C. Reduced phosphate absorption — Incorrect: this does not explain the simultaneous hypokalaemia and hypomagnesaemia occurring shortly after PN initiation.
- D. Increased urinary calcium loss — Incorrect: calcium loss does not produce this characteristic electrolyte pattern.
- E. Suppressed insulin secretion — Incorrect: carbohydrate administration increases insulin secretion, which drives phosphate, potassium and magnesium into cells.
Exam pearl
Minimal nutrition → rapid nutritional repletion → hypophosphataemia + hypokalaemia + hypomagnesaemia ± cardiac/respiratory dysfunction = refeeding syndrome.
Find more High yield MCQs on TPN in neonates
External Resources
- ESPGHAN/ESPEN/ESPR/CSPEN — Pediatric Parenteral Nutrition: Fluid and Electrolytes Discusses refeeding-like electrolyte changes, including hypophosphataemia and hypokalaemia, in very-low-birth-weight infants. Read the guideline (PDF)
- ASPEN — Guidelines for Parenteral Nutrition in Preterm Infants (2023) Provides neonatal-specific guidance on parenteral nutrition and nutrient provision in preterm infants. It is useful background, although it is not a dedicated refeeding syndrome guideline. Read the full guideline
Reference
Robinson DT, Calkins KL, Chen Y, et al. Guidelines for parenteral nutrition in preterm infants: the American Society for Parenteral and Enteral Nutrition. JPEN J Parenter Enteral Nutr. 2023;47(7):830–858. doi: 10.1002/jpen.2550
