What are the recommended doses of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), acetate, and chloride for a premature infant weighing 1125 grams with total parenteral nutrition (TPN) fluid requirements of 120 ml/kg/day?

TPN Electrolyte Recommendations for 1125g Preterm Infant

For this 1125g preterm infant receiving 120 ml/kg/day TPN, provide sodium 3-5 mmol/kg/day, potassium 2-3 mmol/kg/day, and use chloride-free sodium and potassium salts (sodium acetate and potassium acetate/phosphate) to maintain chloride at 3-5 mmol/kg/day, ensuring the anion gap (Na + K - Cl) equals 1-2 mmol/kg/day to prevent hyperchloremic metabolic acidosis. 1, 2

Patient Classification and Phase

Your 1125g infant falls into the preterm <1500g category and at 120 ml/kg/day fluid intake is likely in Phase II (intermediate phase) or Phase III (stable growth phase), as this fluid volume exceeds the Phase I ranges. 1, 2

Specific Electrolyte Dosing

Sodium (Na)

• Target: 3-5 mmol/kg/day for preterm infants <1500g during stable growth 1, 2
• For your 1.125 kg infant: 3.4-5.6 mmol total daily dose
• Higher sodium requirements in this weight category reflect increased growth rates and potential for higher urinary losses 1
• Critical caveat: If urinary sodium losses are high (common in infants <1500g), requirements may exceed 5-7 mmol/kg/day 1

Potassium (K)

• Target: 2-3 mmol/kg/day for preterm infants <1500g in stable growth 1
• For your 1.125 kg infant: 2.25-3.4 mmol total daily dose
• This matches fetal accretion rates of 1.0-1.5 mmol/kg/day and human milk composition 1
• Important warning: Monitor closely for non-oliguric hyperkalemia, especially in extremely low birth weight infants; defer potassium if hyperkalemia develops 1, 2

Chloride (Cl)

• Target: 3-5 mmol/kg/day for preterm infants <1500g 1
• For your 1.125 kg infant: 3.4-5.6 mmol total daily dose
• Critical principle: Chloride should be 1-2 mmol/kg/day LESS than the sum of sodium and potassium to avoid hyperchloremic metabolic acidosis 1, 2

Acetate vs Chloride Strategy

Use predominantly acetate-based salts (sodium acetate, potassium acetate) rather than chloride salts to reduce metabolic acidosis risk. 1, 2

Rationale for Chloride-Free Solutions

• High chloride intake causes hyperchloremic metabolic acidosis in very low birth weight infants 1
• Hyperchloremic acidosis is a causative factor for intraventricular hemorrhage and other morbidities in preterm infants 1
• The ESPGHAN/ESPEN guidelines specifically recommend considering "chloride-free" sodium and potassium solutions in preterm infants on parenteral nutrition 1, 2

Practical Implementation

• Sodium: Provide as sodium acetate primarily, with minimal sodium chloride
• Potassium: Provide as potassium acetate or potassium phosphate (which also provides needed phosphorus)
• Chloride: Only provide the minimum necessary (aim for Na + K - Cl = 1-2 mmol/kg/day) 2
• Example calculation: If giving 4 mmol/kg Na + 2.5 mmol/kg K = 6.5 mmol/kg cations, then provide 4.5-5.5 mmol/kg Cl 2

Calcium and Magnesium

While your question asks about these, the provided guidelines focus primarily on sodium, potassium, and chloride for fluid/electrolyte management. Standard neonatal TPN formulations typically include:

• Calcium: 1.5-3 mmol/kg/day (based on general neonatal TPN practice)
• Magnesium: 0.15-0.3 mmol/kg/day (based on general neonatal TPN practice)

These should be adjusted based on serum levels and provided in forms compatible with phosphorus supplementation to avoid precipitation.

Critical Monitoring Parameters

• Serum electrolytes: Monitor frequently, especially during the first week 2
• Urine output: Maintain >1 ml/kg/hour 2
• Daily weights: Track to assess fluid status and growth 2
• Acid-base status: Monitor for metabolic acidosis from excessive chloride 1, 2
• Watch for hyperkalemia: Especially in the first days of life in very low birth weight infants 1, 2

Common Pitfalls to Avoid

• Excessive chloride administration: This is the most critical error, leading to hyperchloremic acidosis, potential IVH, and impaired growth 1, 2
• Ignoring high urinary sodium losses: Infants <1500g may need >5 mmol/kg/day sodium despite adequate fluid intake 1
• Starting potassium too early: In oliguric or at-risk infants, defer potassium until urine output is established and normokalemia confirmed 1
• Using equal amounts of sodium and chloride: This creates an unphysiologic high chloride load 1, 2