Human fetal oxygenation following paracervical block

Area of Science:

• Obstetrics
• Fetal Medicine
• Anesthesiology

Background:

• Paracervical blocks are commonly used for labor analgesia.
• Changes in fetal heart rate (FHR) following paracervical block are a concern.
• The underlying cause of these FHR changes, particularly fetal hypoxia, requires further investigation.

Purpose of the Study:

• To investigate the hypothesis that fetal heart rate alterations after paracervical block are secondary to fetal hypoxia.
• To continuously monitor human fetal oxygenation during paracervical block administration.

Main Methods:

• Continuous measurement of human fetal oxygenation using a transcutaneous electrode (tcPO2).
• Monitoring of fetal heart rate (FHR) and variability.
• Assessment of uterine activity.
• Correlation of tcPO2 changes with FHR patterns and uterine activity post-paracervical block.

Main Results:

• A decline in fetal oxygen tension (tcPO2) was observed in all fetuses within 5 minutes post-block, reaching lowest values around 11.5 minutes.
• Fetal heart rate variability initially increased, followed by a decrease starting around 11 minutes, lasting approximately 17 minutes.
• Decreased FHR variability was not consistently associated with low tcPO2.
• Fetal tcPO2 declined in some instances without increased uterine activity.
• The severity of tcPO2 decline correlated with the analgesic effectiveness of the block.

Conclusions:

• Paracervical block administration is associated with transient fetal hypoxia.
• Fetal heart rate changes, particularly decreased variability, may be partly explained by hypoxia, but other mechanisms could be involved.
• The degree of fetal oxygen desaturation appears related to the block's efficacy.