Initial Management of Non-Anion Gap Metabolic Acidosis (NAGMA) in a Neonate
The first priority is to reduce excessive chloride intake in parenteral nutrition and switch to chloride-free sodium and potassium solutions, as iatrogenic hyperchloremic acidosis from high cumulative chloride intake is the most common cause of NAGMA in neonates receiving PN. 1
Immediate Assessment and Intervention
Step 1: Identify and Address Iatrogenic Causes
Evaluate cumulative chloride intake from parenteral nutrition, as intake >10 mmol/kg during the first 3 days (>3.3 mmol/kg/day average) or >45 mmol/kg during the first 10 days (>4.5 mmol/kg/day average) induces severe metabolic acidosis (pH <7.2 with base deficit >10 mmol/L or bicarbonates <12 mmol/L). 1
Switch to chloride-free sodium and potassium solutions immediately in preterm infants on PN to reduce the risk of hyperchloremia and metabolic acidosis. 1
Adjust the chloride-to-cation ratio so that chloride intake is slightly lower than the sum of sodium and potassium intakes (Na + K - Cl = 1-2 mmol/kg/day) to prevent excessive chloride accumulation. 1
Step 2: Ensure Adequate Ventilation Before Any Bicarbonate Consideration
Establish effective ventilation first, as sodium bicarbonate produces CO2 that must be eliminated through adequate ventilation. 1
Do NOT give bicarbonate routinely for metabolic acidosis; it should only be considered in documented severe metabolic acidosis after effective ventilation has been established. 1
Step 3: Bicarbonate Administration (Only if Severe and Refractory)
Bicarbonate is indicated only for severe metabolic acidosis (pH <7.2 with base deficit >10 mmol/L or bicarbonates <12 mmol/L) that persists despite addressing the underlying cause and ensuring adequate ventilation. 1
Dosing for neonates: 1-2 mEq/kg IV/IO given slowly. 1
Use only 0.5 mEq/mL concentration for newborn infants; dilution of available stock solutions may be necessary. 1
Do NOT give by endotracheal route. 1
Do NOT mix sodium bicarbonate with vasoactive amines or calcium. 1
Step 4: Monitor for Associated Electrolyte Disturbances
Check serum potassium levels, as NAGMA is often associated with hyperkalemia, which may require concurrent management with calcium chloride (20 mg/kg IV/IO) if severe (K >7 mmol/L). 1
Monitor for hypocalcemia, as bicarbonate administration can worsen ionized calcium levels. 2
Critical Pitfalls to Avoid
Do NOT use bicarbonate as first-line therapy without addressing the underlying cause (excessive chloride intake in PN). 1
Do NOT administer bicarbonate without ensuring adequate ventilation, as the CO2 produced will worsen respiratory acidosis if ventilation is inadequate. 1
Do NOT use lactate-buffered solutions in neonates with liver dysfunction or metabolic compromise. 2
Avoid fluid overload when giving bicarbonate, particularly in extremely low birth weight (ELBW) infants with large patent ductus arteriosus (PDA), weight loss >15%, as they are at highest risk for complications. 1
Differential Diagnosis Considerations
While iatrogenic hyperchloremic acidosis from PN is most common, also consider:
Renal tubular acidosis (proximal or distal), which presents with normal anion gap acidosis and may require specific urine pH and electrolyte assessment. 3, 4
Gastrointestinal bicarbonate losses from diarrhea or ileostomy output. 5
Renal bicarbonate wasting in premature infants with immature tubular function. 1