Fetal circulation & Congenital Heart Defects

VickyRN, MSN, DNP, RN · Dec 27, 2006

I'll refer to my lecture notes on the subject. Hope this helps! ?

Fetal circulation differs from neonatal circulation in three areas: the process of gas exchange, the pressures within the systemic and pulmonary circulations, and the existence of anatomic structures that assist in the delivery of oxygen-rich blood to vital organ systems.

In fetal circulation, gas exchange occurs in the placenta; the lungs are nonfunctional with very little blood flow. The placenta provides oxygen and nutrients for the fetus, and removes carbon dioxide and other waste products. The mother and fetus' blood vessels intertwine but do not join (no mixture of blood). The exchange of oxygen, nutrients, and waste materials between the mother and fetus occurs by diffusion.

The umbilical cord connects the fetus to the placenta, and contains two small arteries and one large vein, providing for the transport of blood to and from the fetus and placenta. Oxygenated blood from the placenta flows by way of the umbilical vein to the inferior vena cava.

Resistance in the pulmonary circulation is higher than resistance in the systemic circulation.

A shunt is a detour that directs blood flow in a different direction.

In utero, the fetus receives blood carrying oxygen and nutrients from the placenta through the umbilical vein.

The liver is bypassed along the way, by the first fetal shunt--the ductus venosus. Blood routed to the ductus venosus bypasses the liver and is routed to the inferior vena cava.

Only a small amount of blood circulates to hepatic tissue. Liver function is minimal in the fetus, so very little blood supply is required.

Oxygenated blood from the placenta flows into the right atrium. Two-thirds of the oxygenated blood flows directly to the head, heart, and upper extremities. The brain and coronary arteries receive the blood with the highest oxygen concentration.

In fetal circulation, the pressures on the right side of the heart are greater than pressures on the left side.

The foramen ovale is an opening between the atria (top chambers of the heart) that allows blood flow from the right atrium directly to the left atrium. This is the second fetal shunt. Most of the blood received from the inferior vena cava is shunted through the foramen ovale and into the left atrium. From the left atrium, the blood is pumped through the left ventricle into the aorta.

The direction of the blood flow as well as the high blood pressure in the right atrium propels this blood through the foramen ovale into the left atrium.

Most of the lungs are bypassed, supplying the heart and the brain with oxygenated blood. These are the two most oxygen-needy organ systems (remember, growth and development in the fetus/ infant always follows the cephalocaudal pattern).

The remainder of the less oxygenated blood now returns from the upper body, head, neck, and arms, and travels from the superior vena cava into the right atrium, where it mixes with some of the oxygen-rich blood coming up from the inferior vena cava. Because of the direction of the blood flow, the right ventricle pumps most of the blood returning from the superior vena cava. This blood travels through the tricuspid valve and the right ventricle into the pulmonary artery.

A very small portion of this blood flows from the right atrium into the right ventricle and out the pulmonary artery into the nonfunctioning lungs. The pressure in the pulmonary circulation is very high. The lungs are collapsed and filled with fluid. Because of the high pressure, most of the blood bypasses the lungs.

Most of the blood pumped out by the right ventricle bypasses the lungs by flowing through the third fetal shunt, the ductus ateriosus, into the descending aorta. This supplies blood to the lower portions of the body.

The ductus arteriosus is a conduit between the pulmonary artery and the aorta that shunts blood away from pulmonary circulation.

Blood then flows from the descending aorta to the other organ systems, then back to the placenta for gas exchange by way of the two umbilical arteries.

With the neonate's first breath, gas exchange is transferred from the placenta to the lungs. This means that the baby must use his/her lungs to take in oxygen and get rid of carbon dioxide. With the initiation of respirations, the pa02 levels are increased and pac02 levels are decreased.

Inspired oxygen dilates the pulmonary vessels, and pulmonary vascular resistance is decreased. Because resistance in the lungs has decreased, blood flow into the lungs increases.

After the first breath, resistance to pulmonary blood flow decreases and a marked increase in pulmonary blood flow follows. Decreased pulmonary resistance (after the first breath) allows for the increased pulmonary blood flow. Resistance in the systemic circulation increases.

Umbilical cord clamped = less blood flow to right side of the heart.

Pressures on the left side of the heart become greater than pressures on the right side.

Systemic vascular resistance becomes greater than pulmonary vascular resistance.

The right heart receives poorly oxygenated blood from the body, while the left heart receives highly oxygenated blood from the lungs. Deoxygenated blood flow starts flowing into the right heart and lungs.

Because of these favorable pressure changes, more blood flows to the lungs, where it is oxygenated.

Desaturated blood returning from the superior vena cava and inferior vena cava enters the right atrium and is pumped through the tricuspid valve to the right ventricle.

The right ventricle then pumps the blood through the pulmonic valve to the pulmonary artery to the lungs, where the blood is oxygenated.

The oxygenated blood returns from the lungs to the left atrium by the four pulmonary veins. The left atrium pumps the blood through the mitral valve to the left ventricle.

The left ventricle then pumps blood through the aortic valve and into the aorta. From the aorta, the oxygenated blood circulates throughout the body.

After the neonate's first breath, the fetal shunts close in response to pressure changes and increased pa02 levels in the pulmonary and systemic circulations.

Clamping of the umbilical cord causes blood to the ductus venosus to fall instantly. The absence of blood will cause the ductus venosus to close and it will eventually turn into a ligament.

There is dramatically less blood flowing to the right side of the heart after the umbilical cord is cut. This causes an immediate drop in blood pressures on the right side of the heart. At the same time, the pressure in the left side of the heart builds as the greatly increased blood flow from the lungs enters the left atrium. The systemic vascular resistance increases because of more blood flowing to the left side of the heart.

The foramen ovale opens only from right to left (a one-way valve or doorway). The decreased pressure on the right side of the heart, along with increased pressure on the left side of the heart stimulates the closure of the foramen ovale.

The change in circulation patterns causes the ductus arteriosus to close. The closure of this shunt causes blood to flow from the pulmonary artery into the lungs for oxygenation. The increased pulmonary blood flow enhances the left ventricular output. Resistance in the systemic circulation increases.

In some neonates, it may take several days for the fetal shunts to completely close.

*normal fetal circulation (lungs and liver bypassed)

*normal circulation after birth (systemic and pulmonary circulations; high systemic pressure)

Cardiovascular disorders - fetal circulation

The neonatal intensive care unit (nicu) - lucile packard children's hospital

Phillygryl, LPN · Dec 28, 2006

First of all Thanks a million!!! I am going to thoroughly study your response.

I still have to relate the correct fetal circulation (which you have spelled out)

to abnormal circulation., i.e., Atrial Septal Defect, Ventricular Septal Defect, etc. Now based on what I read in your post, correct circulation should be from the right atrium to the left atrium and I understand that the atrial defect comes from the foramen ovale not closing!!! The Atrial Septal Defect is one the acyanotic defects and can lead to CHF and it is also listed as one of the Left to Right Shunts along with the Ventricular Defect and the Patent Ductus Arteriosus. How does this relate to normal circulation?? How does it get to be a Left to Right Shunt? What is the significance. Believe me I read the textbook, and it sheds no light on why the Left to Right Shunt. I understand the resulting symptoms in the child, i.e., can lead to CHF, poor feeding, weak suck, but I think I need further clarification. Thanks for any help!!!

VickyRN, MSN, DNP, RN · Dec 28, 2006

ACYANOTIC (LEFT-to-right shunting) defects are the most common. The freshly-oxygenated blood is being backwashed from the left side of the heart to the right. The systemic pressure is greater than pulmonic. NO venous blood (deoxygenated blood) enters the systemic circulation. All of the blood returning to the right side of the heart passes through the lungs. The LUNGS are overloaded.

With mild acyanotic cases, the defect will often heal on its own with time. Medical management (Lanoxin, Lasix) may or may not be required. With severe cases, surgery is required.

Examples of acyanotic (left-to-right) heart defects:

Ventricular septal defect (VSD)

Atrial septal defect (ASD)

Patent ductus arteriosus (PDA)

Atrioventricular septal defect (AVSD) (endocardial cushion defect)

Manifestations of acyanotic defects:

NO cyanosis

Not always apparent at birth

INCREASED pulmonary blood flow (LEFT-to-right defect think LUNGS) - at risk for pulmonary HTN

Enlarged heart (right, sometimes left)

Congestive heart failure

Enlarged liver, dyspnea, tachypnea, intercostal retractions, poor growth, frequent respiratory infections

With CYANOTIC lesions, on the other hand, there is RIGHT-to-left shunting. The pulmonic pressure is greater than systemic pressure. Venous blood (deoxygenated blood) bypasses pulmonary circulation and goes directly to the left side of the heart to be pumped into the systemic circulation. Cyanotic heart defects are generally more complex than acyanotic defects and have a combination of defects. Surgery is needed to repair.

There is an obstruction on the right side of the heart. Pressures from obstructed blood in the right side of the heart exceed those in the left. The unoxygenated venous blood flows directly from the right sided chambers to the left-sided chambers (right to left shunt) while bypassing the lungs. Unoxygenated blood (venous blood) enters the systemic circulation and there is mixing of pure oxygen-rich blood with venous blood.

With CYANOTIC, remember CPR:

Cyanotic heart defect (can make a child turn blue)

Pulmonic pressure greater than systemic

Right-to-left shunt

Examples of cyanotic (right-to-left) heart defects:

Usually the ones starting with a "T" -

Tetralogy of Fallot (TOF)

Transposition of the Great Arteries (TGA)

Tricuspid Atresia

Truncus Arteriosus

Total Anomalous Pulmonary Venous Return

Hypoplastic Left Heart Syndrome (HLHS)

Manifestations of cyanotic heart (right-to-left shunt) defects:

Cyanotic at birth ("blue baby")

Symptomatic soon after birth

DECREASED pulmonary blood flow.

Hope this helps to clear up some of the confusion :)

VickyRN, MSN, DNP, RN · Dec 28, 2006

Without a doubt, these concepts are difficult to grasp. No one has an easy time understanding these congenital defects and the hemodynamics involved. It takes lots of study. Nice graphics always help (one picture is truly worth a thousand words). These sites are great:

New Page 0

Ventricular Septal Defect

Atrial Septal Defect

Cardiac defects

Patent Ductus Arteriosus

HeartPoint: Congenital Heart Disease

Other very helpful websites:

Congenital Heart Disease - Texas Heart Institute Heart Information Center - very thorough! Lots of pictures, also :)

Heart Defects: Birth Defects: Merck Manual Home Edition

Cardiovascular Disorders - Congenital Heart Disease

Pediatric Heart Conditions and Problems: Symptoms / Signs, Cincinnati Children's Hospital Medical Center

Acyanotic

Information about Cyanotic Congenital Defects

Philadelphia Adult Congenital Heart Center: Cyanotic Congenital Heart Defects

AllRefer Health - Congenital Heart Disease

Home Health Columnist / Guide · Dec 28, 2006

What a great review after reading this info as I work with adults and don't use this info......triggered brain cell response and 30yo knowledge came rushing back.

Good luck on our test....never know where you will land in the world of nursing. Stickied post.

Phillygryl, LPN · Dec 29, 2006

Thanks Vicki RN!!! Now I get the full picture. Thanks for taking the time.

Happy New Year

beth66335, BSN, RN · Aug 22, 2007

This post is so great! I have a son that was born with TGV, he had surgery at 3 days old ( this was in 1994). He is fine now except for a very loud murmur, which is good; loud= small. He is 13 and very healthy, he had surgery at Vanderbilt and they treated us very well! Those links gave me a better idea of what was going on inside of him and what they did to correct it. :lol2:

StudentNurseSteph, BSN, RN · Oct 24, 2007

http://www.indiana.edu/~anat550/cvanim/fetcirc/fetcirc.html

that site is amazing at showing you what goes.. I'm a BIG visual learner!!

4x4country · Jul 6, 2008

Okay i know this is a old thread but i am reviewing for a test and need some guideance and this thread has a lot so i felt no need to open a new thread. i am in peds/ob rotation and reviewing tetralogy of fallot (including tet spell, transposition of the great arteries and patent ductus arteriosis). ALL hard to understand!!, but i am really trying.

So my first question is Tetralogy of fallot is a right to left shunting right? The way i am understanding it is, rt. pressure is increased and let decreased dt obstructed pulmonary blood flow? But this confusing me:

Examples of acyanotic (left-to-right) heart defects:
Usually the ones starting with a "T" -
Tetralogy of Fallot (TOF)
Transposition of the Great Arteries (TGA)
Tricuspid Atresia
Truncus Arteriosus
Total Anomalous Pulmonary Venous Return
Hypoplastic Left Heart Syndrome (HLHS)

again i am trying to understand all this, so bare with me.

also i cant find any information relating tetralogy of fallot to patent ductus arteriosis? am i missing a big concept? i have been studying all day so brain is getting tired. all help is appreicated!

tiggerdagibit · Jul 6, 2008

Oh wow! I'm so glad I came across this post. We're starting to cover this tomorrow.

Wish I could help 4x4, but thank you for making this thread active! Good luck.

beth66335, BSN, RN · Jul 6, 2008

Try googling "Tetralogy of Fallot related to Patent Ductus Arteriosus" It gave me a whole page of sites. My son had TGV/A and they gave him meds to keep his Ductus Arteriosus open, but he did not have Tetralogy of Fallot so I don't know about the link. Hope this helps!