[Deeper understanding of fetal acid-base equilibrium]

Area of Science:

• Biochemistry and Neonatal Physiology
• Fetal Acid-Base Balance
• Clinical Chemistry

Context:

• Current pH measurements in obstetrics lack detail on metabolic and respiratory contributions to H(+)-ion synthesis.
• Accurate assessment of fetal acidosis is crucial for neonatal well-being and quality control during childbirth.
• Existing methods do not fully differentiate the pathways contributing to fetal acidosis.

Purpose:

• To develop and validate a novel method for quantifying de novo H(+)-ion synthesis from both metabolic and respiratory pathways.
• To correlate these quantified pathways with the clinical condition of newborns, specifically using Apgar scores.
• To provide a more comprehensive understanding of fetal acidosis beyond standard pH measurements.

Summary:

• A new method using umbilical cord blood pH, pCO2, and pO2 measurements was developed to compute metabolic (pHqu40) and non-metabolic (pHnm) pathways of H(+)-ion synthesis.
• Analysis of 8882 newborns revealed distinct patterns: respiratory acidosis dominates in mild depression (Apgar 7-10), both pathways are equal in moderate asphyxia (Apgar 4-6), and metabolic acidosis appears dominant in severe asphyxia (Apgar 0-3).
• The study established a reference point using Apgar 10 newborns to compute de novo H(+)-ion synthesis across different clinical neonatal conditions.

Impact:

• The findings highlight the limitations of Apgar scoring and standard pH measurements in differentiating asphyxia severity, particularly in newborns with pH values between 6.7 and 7.1.
• Actual pH measurements remain clinically vital for severely asphyxiated newborns and should not be abandoned.
• The study demonstrates the intercorrelation of acid-base variables and the diagnostic potential of umbilical venous blood parameters for assessing placental function.