Umbilical cord blood acid-base state: what is normal?

Area of Science:

• Neonatology
• Perinatal Medicine
• Biochemistry

Background:

• Establishing normal reference ranges for umbilical cord blood gases is crucial for neonatal assessment.
• Vigorous newborns, typically defined by high Apgar scores, are expected to have specific physiological parameters.
• Understanding these parameters aids in differentiating normal physiological states from pathological conditions.

Purpose of the Study:

• To determine the normal values and ranges for umbilical cord blood gases and acid-base status in vigorous neonates.
• To provide a benchmark for assessing the acid-base balance in healthy newborns immediately after birth.

Main Methods:

• Utilized the University of California, San Francisco, Perinatal Data Base (1977-1993).
• Selected 15,073 newborns with 5-minute Apgar scores of 7 or higher, indicating vigorous status.
• Analyzed umbilical artery blood gas (pH, PCO2, PO2) and base excess data.

Main Results:

• Median umbilical artery pH was 7.26 (2.5th percentile 7.10), PCO2 52 mm Hg (74), base excess -4 mEq x L(-1) (-11), and PO2 177 mm Hg (6).
• Mean values +/- 2 standard deviations were comparable to median values, despite skewed distributions.
• Minor variations in blood gas parameters were observed across different delivery methods, gestational ages, presentations, and meconium presence, but differences were small.

Conclusions:

• A broad spectrum of acid-base values is normal in vigorous newborns with high Apgar scores.
• These findings define the "physiologic acidemia" characteristic of healthy, vigorous neonates.
• The study provides essential reference data for perinatal and neonatal care providers.