Fetal Circulation

What are the 3 structures that are different in fetal hearts vs adults?

1. Patent Ductus Arteriosus

2. Foramen ovale

3. Ductus Venous

What is the name of the structure that bypasses the fetal lungs and brings O2 and nutrients to the heart?

umbilical vein

Fetal circulation order before it goes into distinct pathways

Placenta —> Umbillical Vein —> Through liver (1/2 BF) & other ½ through ductus venous—> IVC

Fetal circulation path 1

1. IVC

2. RA

3. Foramen Ovale

4. LA

Fetal circulation path 2

IVC —> RA —> RV —> Pulmonary Trunk —> Ductus arteriosus —> Aorta

Fetal circulation path 3

IVC —> RA —> RV —> Pulmonary Trunk —> Lungs (10-15%)—> PV —> LA

What is the purpose of the 3rd pathway?

To grow the vessels at the lungs

Which pathway is the most similar to normal circulation?

3

Transition from fetal circulation steps

1. Labor starts

2. Hormones released = active lympathtics to remove fluids

3. Baby through canal

4. First Breath

5. lungs expand with air

6. push out fetal lung fluid into vasculature

7. Increase in O2 and CO2 drops

8. Majority of FLF removed

9. Ductus arteriosus starts to closed due to rise in O2 and falling of CO2

10. Cord clamped = FO closes

11. blood directed through lungs = Normal

What causes the Ductus arteriosus to close?

Rise in O2

Drop in CO2

What causes the foramen ovale & ductus venous to close

When SVR > PVR

Cyanotic CHD

Right to left shunting

Acyanotic CHD

Left to right shunting

BF through the FO and DA is dependent on the balance of

SVR and PVR

Right arm monitoring is called

Preductal

• upstream from mixing at the PDA

Left arm monitoring is called

Post Ductal

• downstream from mixing happening at the PDA

If the DA stays open it is called

Patent ductus arteriosus (PDA)