Management of Hypocalcemia in Small for Gestational Age (SGA) Infants
SGA infants require immediate calcium supplementation when hypocalcemia is detected, with treatment initiated at ionized calcium <4.4 mg/dL (1.1 mmol/L) or total calcium <8 mg/dL (2 mmol/L), using oral calcium 40-80 mg/kg/day of elemental calcium for asymptomatic cases and intravenous calcium gluconate 10-20 mg/kg for symptomatic presentations. 1, 2
Initial Assessment and Monitoring
Screen SGA infants for hypocalcemia at 24 and 48 hours after birth, as they are at high risk for early-onset hypocalcemia due to interrupted placental calcium transfer and delayed parathyroid hormone surge. 3, 2
Measure ionized calcium rather than total calcium alone, as ionized calcium is the physiologically active fraction and provides the most accurate assessment. 3, 2
Check magnesium levels in all hypocalcemic SGA infants immediately, as hypomagnesemia impairs parathyroid hormone function and must be corrected before calcium levels will normalize. 1, 3
Monitor phosphate levels carefully in the first days of life, as SGA infants with intrauterine growth restriction are at particularly high risk for severe hypophosphatemia when protein and energy intakes are optimized, which can result in muscle weakness, respiratory failure, cardiac dysfunction, and death. 4
Treatment Algorithm for Asymptomatic Hypocalcemia
Administer oral elemental calcium 40-80 mg/kg/day for asymptomatic SGA infants with documented hypocalcemia. 1, 2
Continue treatment for at least 72 hours for early-onset hypocalcemia presenting within the first 72 hours of life. 5
Add vitamin D supplementation to optimize calcium absorption, particularly if late-onset hypocalcemia develops after 72 hours. 1, 3
Treatment Algorithm for Symptomatic Hypocalcemia
For infants with tetany, seizures, or cardiac dysfunction, administer calcium gluconate 10-20 mg/kg of elemental calcium (1-2 mL/kg/dose of 10% calcium gluconate) as a slow intravenous infusion. 1, 2
Administer through a central venous catheter when possible, as extravasation through peripheral IV can cause severe tissue injury including local necrosis and calcinosis cutis. 1, 6
Monitor heart rate continuously during administration and stop if symptomatic bradycardia occurs, as calcium administration can cause vasodilation, hypotension, bradycardia, and cardiac arrhythmias. 1, 6
Infuse slowly over 30-60 minutes for non-arrest situations to minimize cardiovascular complications. 1
Critical Adjunctive Management
Correct hypomagnesemia first if present, as magnesium deficiency creates PTH resistance and hypocalcemia will not resolve until magnesium is normalized. 1, 3
Investigate for late-onset hypocalcemia causes after 72 hours, including excessive phosphate intake, maternal vitamin D deficiency, hypoparathyroidism, or persistent hypomagnesemia. 3, 2
Consider genetic testing for 22q11.2 deletion syndrome if hypocalcemia is persistent or recurrent, as this carries an 80% lifetime prevalence of hypocalcemia. 7
Parenteral Nutrition Considerations for SGA Infants
During the first days of life, provide calcium 0.8-2.0 mmol/kg/day (32-80 mg/kg/day) and phosphorus 1.0-2.0 mmol/kg/day (31-62 mg/kg/day) via parenteral nutrition if enteral feeding is not established. 4
Use a molar Ca:P ratio below 1.0 (0.8-1.0) in early parenteral nutrition when protein and energy intakes are optimized from the first day of life, to reduce the incidence of early postnatal hypophosphatemia and consequent hypercalcemia. 4
Use organic calcium and phosphate salts (calcium gluconate in polyethylene packaging, not glass vials) to prevent precipitation and reduce aluminum contamination, which should not exceed 5 mg/kg/day. 4
After stabilization in growing SGA infants, increase to calcium 1.6-3.5 mmol/kg/day (64-140 mg/kg/day) and phosphorus 1.6-3.5 mmol/kg/day (50-108 mg/kg/day) with a molar Ca:P ratio around 1.3. 4
Common Pitfalls to Avoid
Do not delay treatment while investigating etiology - initiate calcium replacement immediately in infants with reduced calcium levels, then investigate the underlying cause. 2
Do not overtreat - calcium toxicity with elevated concentrations can cause cardiac arrhythmias and must be avoided through careful monitoring. 1, 6
Do not use calcium gluconate stored in glass vials due to aluminum contamination; use polyethylene packaging instead. 4
Do not assume normal total calcium excludes hypocalcemia - ionized calcium may be low even when total calcium appears normal, particularly in symptomatic infants. 3, 8
Do not administer calcium with ceftriaxone in neonates ≤28 days old due to fatal outcomes from ceftriaxone-calcium precipitates in lungs and kidneys. 6
Ongoing Monitoring Requirements
Monitor serum calcium levels every 4 hours initially during acute treatment, particularly in symptomatic infants or those receiving parenteral nutrition. 1, 7
Monitor alkaline phosphatase, calcium, phosphorus, and magnesium serum concentrations regularly, along with urinary calcium and phosphorus concentrations to assess adequacy of mineral intake. 4
Adjust calcium and phosphorus intakes until both start being excreted simultaneously in urine with low concentrations (>1 mmol/L), indicative of a slight surplus. 4