Fetal cardiac bypass: improved placental function with moderately high flow rates

Area of Science:

• Cardiovascular Surgery
• Fetal Medicine
• Perinatal Physiology

Background:

• Prenatal correction of congenital heart defects may offer advantages over postnatal repair.
• Developing safe and effective fetal circulation support is essential for in utero cardiac interventions.
• Previous fetal cardiac bypass studies indicated placental dysfunction due to hypoxemia and acidosis.

Purpose of the Study:

• To assess the impact of varying flow rates during fetal cardiac bypass on fetal oxygenation and metabolism.
• To evaluate the placenta's function as an in vivo oxygenator under different bypass flow conditions.

Main Methods:

• Fetal cardiac bypass was performed in 18 late-gestation fetal lambs for 30 minutes under normothermia.
• The fetal aorta was cross-clamped, and cold cardioplegia was administered to exclude cardiac output.
• Nine fetuses underwent low-flow bypass (109 ± 20 mL·kg⁻¹·min⁻¹), and nine underwent high-flow bypass (324 ± 93 mL·kg⁻¹·min⁻¹).

Main Results:

• Low-flow bypass resulted in decreased mean aortic pressure, arterial pH, and oxygen tension, with increased carbon dioxide tension and lactate levels.
• High-flow bypass maintained fetal aortic pressure, pH, oxygen tension, carbon dioxide tension, and lactate levels similar to pre-bypass values.
• Upon weaning from high-flow bypass, fetuses showed transient decreases in oxygen tension and pH, and increased carbon dioxide tension.

Conclusions:

• Higher flow rates during fetal cardiac bypass are critical for maintaining fetal oxygenation and metabolic stability.
• Adequate flow rates are necessary to prevent placental dysfunction and support the fetus during bypass.
• These findings are vital for advancing the development of safe fetal cardiac bypass techniques for prenatal interventions.