Does an unstable infant require calcium (Ca) and phosphorus (Phosph) in Total Parenteral Nutrition (TPN) on the first day?

Calcium and Phosphorus in First-Day TPN for Unstable Infants

Yes, unstable infants require calcium and phosphorus in TPN on the first day, though at lower doses than stable growing infants. 1

Recommended First-Day Dosing

For preterm infants during the first days of life, provide:

• Calcium: 0.8-2.0 mmol/kg/day (32-80 mg/kg/day) 1
• Phosphorus: 1.0-2.0 mmol/kg/day (31-62 mg/kg/day) 1
• Magnesium: 0.1-0.2 mmol/kg/day (2.5-5.0 mg/kg/day) 1, 2

These doses are specifically lower than those recommended for stable growing premature infants (Ca 1.6-3.5 mmol/kg/day, P 1.6-3.5 mmol/kg/day), recognizing the unique metabolic state of unstable neonates in the first days of life. 1

Critical Phosphorus Considerations

Phosphorus supplementation within the first 24 hours is particularly important to prevent severe hypercalcemia and life-threatening hypophosphatemia. 1

• In extremely low birth weight infants, delayed phosphorus introduction (starting at 72 hours) resulted in 50% incidence of severe hypercalcemia (ionized calcium >1.60 mmol/L), which decreased to 21.4% when phosphorus was started within 24 hours. 3
• Preterm infants with intrauterine growth restriction are at highest risk and require careful plasma phosphate monitoring within the first days of life, as severe hypophosphatemia can result in muscle weakness, respiratory failure, cardiac dysfunction, and death. 1

Optimal Calcium-to-Phosphorus Ratio

Use a molar Ca:P ratio below 1.0 (specifically 0.8-1.0) during early PN when mineral intakes are at the lower range. 1

• This lower ratio reduces the incidence of early postnatal hypercalcemia and hypophosphatemia when protein and energy are being optimized. 1
• Once infants are stable and growing, the ratio should increase to approximately 1.3 (mass ratio 1.7), which matches fetal mineral accretion patterns. 1

Formulation and Safety Considerations

Use organic calcium and phosphorus salts to prevent precipitation in TPN solutions. 1

• Calcium gluconate packaged in polyethylene (not glass vials) is preferred to reduce aluminum contamination, which should not exceed 5 mg/kg/day. 1
• Organic phosphorus compounds (such as disodium glucose-1-phosphate or sodium glycerophosphate) circumvent precipitation issues with inorganic phosphates. 1
• The sodium content of some organic phosphorus compounds may limit early utilization in premature infants requiring fluid restriction. 1

Monitoring Requirements

Regular monitoring of serum calcium, phosphorus, magnesium, and alkaline phosphatase is required, along with urine calcium and phosphorus concentrations. 1

• Plasma phosphate concentration monitoring is critical in the first days of life, particularly for growth-restricted infants. 1
• Adequacy of intake can be assessed when both calcium and phosphorus are excreted simultaneously in urine with low concentrations (>1 mmol/L), indicating a slight surplus. 1

Special Circumstances

If the mother received magnesium sulfate therapy (for preeclampsia or tocolysis), reduce magnesium supplementation and adjust based on postnatal blood concentrations. 1, 2

• These infants have elevated magnesium levels and limited renal excretion capacity in the first week of life. 1, 2