Renal and Fluid-Electrolyte Management
Fluid management
Start day 1 with 60-80 mL/kg/day of 10% dextrose; increase by 10-20 mL/kg/day toward 150 mL/kg/day, higher in extremely preterm infants because of insensible losses. Add sodium (3-5 mEq/kg/day) and potassium (1-3 mEq/kg/day) after diuresis, usually day 2-3. Expected weight loss is 5-10% in term and up to 15% in preterm infants. Urine output should be 1-3 mL/kg/hour.
Electrolyte emergencies
Hyperkalemia: obtain ECG, give calcium gluconate for cardiac protection, insulin plus glucose, salbutamol, and a potassium binder; avoid indomethacin. Hyponatremia is usually dilutional; restrict fluid and use 3% saline only for seizures or severe symptoms. Acute kidney injury causes oliguria and rising creatinine; adjust drug doses and avoid nephrotoxins.
Renal development
Nephrogenesis continues to 34-36 weeks, so preterm infants have fewer nephrons and limited concentrating ability. They are prone to dehydration and sodium wasting, but also to fluid overload. Creatinine in the first days reflects maternal values.
Worked example
A 28-week infant on day 2 has gained 8% of birth weight, Na 128 mEq/L, and urine output 0.4 mL/kg/hour. Reasoning: fluid overload with immature renal function. Reduce fluid to insensible losses plus urine output, recheck electrolytes in 12 hours, and avoid a fluid bolus. Consider furosemide only after volume status is assessed, and watch the PDA.
Traps
- Treating oliguria with fluid boluses when the infant is edematous.
- Interpreting the initial creatinine as the infant's own.
- Forgetting to adjust gentamicin dosing in AKI.