Trouble understanding PPHN...

Specialties NICU

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Hi all I'm a NICU rn (kinda new) and I am having such a hard time understanding the physiology of PPHN. I have read descriptions over and over and just have a mental block with this subject.

I understand that PPHN occurs when fetal circulation fails to covert to newborn. So, the blood is still bypassing the lungs because of the PDA and PFO, correct? Why does this fail? Why do the lungs have high pressure? Is this just because that's the way it was in the womb? And is the high pressure preventing blood from entering the lungs, therefore causing the poor O2 sats that those babies have?

What exactly is right to left shunting?

I know I have lots of questions but I need to understand this.

Also, how for you explain PPHN to parents?

Thank you!

- Lucy

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Specializes in NICU, ICU, PICU, Academia.

You've got it. 'Right-to-left' shunting is exactly that, blood is able to escape the high pressure in the right side of the heart (where it SHOULD go to the lungs) by shunting through the PFO and the PDA (by taking the path of least resistance), to the left side of the heart. This deoxygenated blood then gets pumped into the body by the left side of the heart.

TWO of my children had this, one resolved spontaneously, one needed a LONG time on the vent and finally indomethacin to close her PDA. (No sequelae, except they are both slobs! :) )

We do ECMO in our PICU for kids with intractable PPHN.

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Thanks for your response. So, then what is the difference between a kid with PPHN and one with just a PDA who frequently desats? Why don't they have PPHN?

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Specializes in NICU.

IF I'm not mistaken, PPHN is right to left (or bidirectional) shunting. A baby with a PDA is usually left to right shunting. The blood pressure in the lungs is not high and blood still goes there, just not as much because some goes through the PDA. The peripheral tissues are usually somewhat hypoxic, so some anaerobic metabolism goes on. That leads to low pO2 (paO2?), hypotension, desats, metabolic acidosis and a negative base. It's helpful to remember that the myocardium doesn't contract well when acidotic.

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Specializes in MSN, FNP-BC.

In PPHN the vascular resistance in the lungs is high so oxygen exchange is impaired. This also causes the pressure in the right side of the heart to increase because the heart has to pump harder to get blood into the lungs. The right ventricle pressures can double(I've seen them in the 120's).

Since there is less blood coming back from the lungs, the CO can also drop and start to cause changes systemically, especially in the kidneys.

Because of the decreases CO, this may be why you can see some of these kids needing pressors.

They use INO to dilate the lung vaculature to try to improve oxygenation.

Then when all else fails, there is ECMO.

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Specializes in Neonatal ICU (Cardiothoracic).

The above posters have done a good job explaining, but I just wanted to add a few things. I know I'm nitpicking, but when using the term "PPHN" which stands for "persistent pulmonary hypertension of the newborn" it implies that the baby is a newborn. In a 45 day old chronic, you would refer to it simply as "pulmonary hypertension" or "elevated pulmonary vascular resistance."

The term "persistent pulmonary hypertension" clues you in to the fetal component of the disease. In utero, the lung circuit naturally has "pulmonary hypertension" or elevated PVR, and since the fetal lungs don't really need all that blood flow until after birth, the oxygenated blood naturally shunts from the right side of the heart to the left/systemic side via the PFO and PDA. After the PVR drops after birth, the PDA and PFO close, and the systemic resistance rises, the blood flows now flows through the path of least resistance, ie..the pulmonary vascular bed. Think of the pulmonary bed as a little narrow pipe in utero with the systemic pipe being large, and then they switch after birth, with the pulmonary pipe getting big and allowing for more blood flow. You don't ever want to close a PDA in the setting of PPHN or pHTN, as the duct allows for a pop-off valve for that blood that can't get into the lungs. You need to fix the pressures first, then close the duct.

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Specializes in Med-Surg, Oncology, Neurology, Rehab.
The above posters have done a good job explaining, but I just wanted to add a few things. I know I'm nitpicking, but when using the term "PPHN" which stands for "persistent pulmonary hypertension of the newborn" it implies that the baby is a newborn. In a 45 day old chronic, you would refer to it simply as "pulmonary hypertension" or "elevated pulmonary vascular resistance."

The term "persistent pulmonary hypertension" clues you in to the fetal component of the disease. In utero, the lung circuit naturally has "pulmonary hypertension" or elevated PVR, and since the fetal lungs don't really need all that blood flow until after birth, the oxygenated blood naturally shunts from the right side of the heart to the left/systemic side via the PFO and PDA. After the PVR drops after birth, the PDA and PFO close, and the systemic resistance rises, the blood flows now flows through the path of least resistance, ie..the pulmonary vascular bed. Think of the pulmonary bed as a little narrow pipe in utero with the systemic pipe being large, and then they switch after birth, with the pulmonary pipe getting big and allowing for more blood flow. You don't ever want to close a PDA in the setting of PPHN or pHTN, as the duct allows for a pop-off valve for that blood that can't get into the lungs. You need to fix the pressures first, then close the duct.

Steve NNP thanks for clarifying, when using initials some may not be familar with it is good idea to state what ""PPHN is which is what you did. Thanks I was going to my books for the meaning.

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Specializes in L&D, CCU, ICU, PCU, RICU, PCICU, & LTC..
Steve NNP thanks for clarifying, when using initials some may not be familar with it is good idea to state what ""PPHN is which is what you did. Thanks I was going to my books for the meaning.

to Steve NNP's "The above posters have done a good job explaining, but I just wanted to add a few things. I know I'm nitpicking, but when using the term "PPHN" which stands for "persistent pulmonary hypertension of the newborn" it implies that the baby is a newborn."

This is a very good point for ALL posters, as many new nurses, as well as older ones, do not know what the abbreviations are for.

Some have multiple meanings depending on the area, such as PE for Pulmonary Edema or Pulmonary Embolism and MI for Mentally Ill or Myocardial infarction. Though some reads become quite funny with the wrong meaning, it is much better to have the correct understanding in the beginning.

Even PPHN could also be Persistent Pulmonary Hypertension Syndrome or Postoperative Pulmonary Hypertension.

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Specializes in NICU, PICU, PACU.

It was once called PFC=persistent fetal circulation...occasionally one of us old timers let that one slip. But in our world PPHN is persistent pulmonary hypertension, but older kids can develop it also, especially the ELBW kids that had a rough course, then it becomes just plain PH lol it depends on your facility as to what abbreviations are allowed :)

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Just curious about this...when an older kid develops pulmonary hypertension the PDA is typically closed, right? In that case we've kinda lost the safety net of pressure release. Do you find that these later developers of pulmonary hypertension have a more difficult course/worse prognosis as a result?

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Specializes in NICU, PICU, PACU.

We usually have a bad outcome with the late onset PPHN. Those kids are beyond sick sometimes. We have had a few survive but they have terrible chronic lung disease.

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Specializes in Neonatal ICU (Cardiothoracic).
Just curious about this...when an older kid develops pulmonary hypertension the PDA is typically closed, right? In that case we've kinda lost the safety net of pressure release. Do you find that these later developers of pulmonary hypertension have a more difficult course/worse prognosis as a result?

Typically which is why it's so difficult to treat, often requiring serious drugs like Flolan, Remodulin, Bosentan in additional to sildenafil or continuous Iloprost nebs. These kids are VERY tough to treat.

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