Neonatal fluid, electrolyte and nutritional management — viva

Stem

The examiner hands you the chart of a 1000-gram, 28-week infant on day 2 of life: on 80 mL/kg/day of parenteral fluid with parenteral nutrition, a serum potassium of 7.0 mmol/L with peaked T waves on the ECG, urine output 3 mL/kg/h, and a weight 6% below birthweight. [4]

Examiner: Walk me through your assessment of this infant's fluid and electrolyte status. [4]

Strong answer: This infant is following the expected physiological trajectory — the 6% weight loss is the contracting extracellular fluid compartment (the diuresis), expected and not to be treated with extra fluid, and the fluid of 80 mL/kg/day on day 2 is appropriate. The concern is the potassium: at 7.0 mmol/L with peaked T waves, this is non-oliguric hyperkalaemia of prematurity — a developmental shift of potassium out of cells from immature Na+/K+-ATPase activity, not renal failure, given the good urine output. The ECG changes make this an emergency: I would institute cardiac monitoring, give calcium gluconate to stabilise the myocardium, and shift and remove potassium. [4]