EFM Fetal Oxygenation and Acid-Base Balance 2 — Questions and Answers
Question 1: Metabolic acidosis in the fetus is primarily caused by:
- Acute hyperventilation by the mother
- Accumulation of lactic acid from anaerobic metabolism (Correct answer)
- Elevated maternal PCO2 levels
- Decreased fetal respiratory rate
Correct 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.
Question 2: Compared to umbilical artery blood, umbilical vein blood would normally show:
- Lower pH and higher PCO2
- Higher pH and lower PCO2 (Correct answer)
- Same pH and lower PO2
- Lower pH and lower PO2
Correct 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.
Question 3: An elevated fetal PCO2 in cord blood gas analysis most directly indicates:
- Anaerobic metabolism
- Impaired CO2 clearance across the placenta (Correct answer)
- Bicarbonate depletion
- Fetal sepsis
Correct 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.
Question 4: The normal lactate level in umbilical artery blood is approximately:
- < 2 mmol/L
- < 4.8 mmol/L (Correct answer)
- < 8 mmol/L
- < 12 mmol/L
Correct 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.
Question 5: The bicarbonate buffer system in fetal blood primarily serves to:
- Transport oxygen to fetal tissues
- Neutralize excess hydrogen ions produced by anaerobic metabolism (Correct answer)
- Facilitate CO2 transport from fetus to placenta
- Regulate fetal blood glucose levels
Correct 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.
Question 6: Base excess (BE) in fetal cord blood is negative (base deficit) when:
- Respiratory alkalosis is present
- Metabolic alkalosis is present
- Bicarbonate stores have been consumed by buffering excess acid (Correct answer)
- PCO2 is elevated above normal
Correct 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.
Question 7: Mixed acidosis in fetal cord blood gas analysis is characterized by:
- Low pH, normal PCO2, and normal base deficit
- Low pH, elevated PCO2, and elevated base deficit (Correct answer)
- Normal pH with elevated PCO2 only
- Low pH with normal bicarbonate and normal PCO2
Correct 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.
EFM Fetal Oxygenation and Acid-Base Balance 2
Metabolic acidosis in the fetus is primarily caused by: