Fetal Oxygenation and Acid-Base Balance Flashcards

Metabolic acidosis in the fetus is primarily caused by:

Answer: Accumulation of lactic acid from anaerobic metabolism

When oxygen delivery is insufficient, the fetus shifts to anaerobic metabolism, producing lactic acid that accumulates and causes metabolic acidosis.

Compared to umbilical artery blood, umbilical vein blood would normally show:

Answer: Higher pH and lower PCO2

Umbilical vein blood returns from the placenta with higher pH and lower PCO2 because CO2 has been exchanged at the placenta and O2 has been loaded.

An elevated fetal PCO2 in cord blood gas analysis most directly indicates:

Answer: Impaired CO2 clearance across the placenta

Elevated PCO2 indicates that CO2 produced by fetal metabolism is not being adequately cleared by the placenta, typically due to acute uteroplacental insufficiency or cord compression.

The normal lactate level in umbilical artery blood is approximately:

Answer: < 4.8 mmol/L

Normal umbilical artery lactate is less than 4.8 mmol/L; values above this suggest significant anaerobic metabolism and fetal metabolic acidosis.

The bicarbonate buffer system in fetal blood primarily serves to:

Answer: Neutralize excess hydrogen ions produced by anaerobic metabolism

Bicarbonate is the primary extracellular buffer and neutralizes excess H+ ions from anaerobic metabolism, maintaining pH during periods of hypoxia.

Base excess (BE) in fetal cord blood is negative (base deficit) when:

Answer: Bicarbonate stores have been consumed by buffering excess acid

A negative base excess (base deficit) indicates that bicarbonate stores have been depleted by buffering metabolic acids, reflecting prior metabolic stress.

Mixed acidosis in fetal cord blood gas analysis is characterized by:

Answer: Low pH, elevated PCO2, and elevated base deficit

Mixed acidosis has components of both respiratory (elevated PCO2) and metabolic (elevated base deficit) acidosis, indicating a more complex and often more serious acid-base disturbance.