What is a normal umbilical artery bicarbonate level?

Normal Umbilical Artery Bicarbonate Levels

The normal umbilical artery bicarbonate level is approximately 22.3 ± 2.5 mEq/L in term infants following uncomplicated vaginal deliveries. 1

Normal Reference Values for Umbilical Cord Blood Parameters

Umbilical cord blood gas analysis is an important tool for assessing fetal well-being at birth. Understanding normal reference ranges helps clinicians interpret these values correctly and identify potential neonatal complications.

Normal Umbilical Artery Values:

• pH: 7.28 ± 0.05
• PCO₂: 49.2 ± 8.4 mm Hg
• PO₂: 18.0 ± 6.2 mm Hg
• Bicarbonate: 22.3 ± 2.5 mEq/L 1

Normal Umbilical Venous Values:

• pH: 7.35 ± 0.05
• PCO₂: 38.2 ± 5.6 mm Hg
• PO₂: 29.2 ± 5.9 mm Hg
• Bicarbonate: 20.4 ± 4.1 mEq/L 1

Clinical Significance and Interpretation

Umbilical cord blood gas analysis is particularly valuable in cases where there's concern about fetal distress or potential hypoxic-ischemic events. When interpreting bicarbonate levels, it's important to consider them alongside other parameters:

• Bicarbonate levels should be interpreted in conjunction with pH and base deficit values
• Low bicarbonate levels often reflect metabolic acidosis, which may indicate fetal distress
• The metabolic component of fetal acidemia (base deficit and bicarbonate) is the most important variable in predicting subsequent neonatal morbidity 2

Pathologic Values and Clinical Outcomes

When umbilical artery pH falls below 7.0 (pathologic acidemia), the bicarbonate level becomes an important predictor of neonatal outcomes:

• Lower bicarbonate levels correlate with increased risk of:

  • Hypoxic-ischemic encephalopathy
  • Need for cardiopulmonary resuscitation
  • Seizures
  • Need for intubation 2

• After controlling for birth weight and gestational age, base deficit and bicarbonate are independently related to death or morbidity in neonates with pathologic acidemia 2

Clinical Pitfalls to Avoid

1. Don't assess bicarbonate in isolation: Always interpret bicarbonate in the context of other blood gas parameters (pH, PCO₂, base deficit)

2. Consider gestational age: Preterm infants may have slightly different normal ranges compared to term infants 3

3. Timing matters: Delayed cord clamping can affect blood gas values, so standardized collection techniques are important

4. Technical factors: Improper sample handling (air bubbles, delayed analysis) can affect bicarbonate measurements

5. Don't overinterpret small deviations: Minor variations from normal ranges may not have clinical significance if other parameters are normal

Understanding normal umbilical artery bicarbonate levels is essential for accurate interpretation of cord blood gases and appropriate clinical decision-making in the immediate postnatal period.