Neonatal fluid, electrolyte and nutritional management — formative SAQs

SAQ 1 (10)

A 1000-gram infant is born at 28 weeks' gestation. On day 2 of life the infant is on 80 mL/kg/day of parenteral fluid with a serum potassium of 7.0 mmol/L and peaked T waves on the ECG, despite a urine output of 3 mL/kg/h. ^{[4] [3]}

1. Outline your initial fluid prescription for this infant from day 1 through the first week, including the expected weight trend. (3) ^[3]
2. Explain the mechanism of the hyperkalaemia and your immediate management of the ECG changes. (4) ^[4]
3. Describe your nutritional strategy for the first two weeks, including the rationale for early parenteral nutrition. (3) ^{[2] [1]}

Model answer

1. Start at 60 mL/kg/day on day 1 and advance by about 20 mL/kg/day toward 130-150 mL/kg/day, titrated to weight, intake/output and serum sodium. The infant is expected to lose 5-15% of body weight in the first days as the extracellular fluid contracts (the physiological diuresis) — this weight loss is expected and is not treated with extra fluid, because liberal fluid increases the risk of PDA and NEC. Sodium is withheld until diuresis begins (day 2-3); potassium is added only once urine output is established. ^[3]
2. This is non-oliguric hyperkalaemia of prematurity — a developmental phenomenon caused by a shift of potassium out of cells due to immature Na+/K+-ATPase activity and rapid cell turnover, occurring with good urine output rather than renal failure. The peaked T waves and K+ above 7.0 demand immediate management: cardiac monitoring, calcium gluconate (0.5 mL/kg of 10% slowly with ECG monitoring) to stabilise the myocardium, then measures to shift potassium into cells (insulin-dextrose, a beta-agonist) and remove it. ^[4]
3. Start parenteral nutrition on day 0 with amino acids at 1.5-2 g/kg/day to prevent catabolism and negative nitrogen balance during the period of highest brain growth, advance lipid toward 3-3.5 g/kg/day, and provide the energy (110-135 kcal/kg/day), glucose at a glucose infusion rate of 4-6 (advancing toward 10-12) mg/kg/min, calcium, phosphate and micronutrients. Begin minimal enteral feeds of expressed breast milk (10-20 mL/kg/day) to prime the gut, advance cautiously toward full feeds with fortification, and wean parenteral nutrition as enteral feeds build — tracking growth on the Fenton chart as the judge. ^{[2] [1]}