DISCLAIMER: this blog is written by a guest blogger and is not to be taken as medical advice or direction. It is solely their stance on PPHN which we’d like to share to our viewing audience and we welcome your feedback, insight or alternate views.
So you know the patho… right?
Understanding PPHN can be difficult and confusing. While it is obviously covered in NNP programs, having a thorough understanding and not just a memorized definition of what it is can help you make choices regarding care plans.
So what is sustained elevation of PVR with normal or low SVR?
Pulmonary vascular resistance is the resistance caused by the pulmonary arteries into the left atrium. This is minimized when lung volumes are at functional residual capacity, and therefore the PVR should decrease when ventilation occurs. This, in turn, forces closed both the PFO and the PDA.
SVR is the systemic vascular resistance, or left ventricle afterload.
If this transition to lower PVR (which in turn then increases pulmonary blood flow) does not happen and the PVR stays higher than the SVR, PPHN occurs secondary to the PDA and PFO not closing appropriately. With these two fetal circulatory mechanisms malfunctioning, right to left shunting across both PDA and PFO occurs complemented by extremely erratic hypoxemia.
Causes
Preterm infants were once thought to only get PPHN rarely, or after a diagnosis of BPD, but it is becoming clear that this is not always the case. IUGR babies are particularly at risk for developing BPD paired with PPHN.
Diagnosing
When diagnosing PPHN in either the preterm or term infant, RDS findings on XR, blood gas results, and preductal and postductal measured O2 saturations should be considered. When all other findings indicate potential PPHN, a difference in arterial PO2 of greater than 20 mmHg or sat differences >5-10% are indicative (but heart defects should be ruled out using an ECHO). Using echocardiography is still considered the gold standard for a true diagnosis of PPHN, and to understand the shunting and placement of blood flow.
Treatment
Finding which direction shunting and at what level it is occurring is important when deciding treatment for this disorder. All babies should be treated with minimal stimulation and other supportive therapies per NICU protocol, including TPN/PPN, sedation/analgesia, and appropriate lung expansion of 8-9 ribs on XR. There are now recommendations to focus on correcting electrolytes – particularly Calcium and Magnesium.
New studies are looking at the use of steroids for improvement of PPHN without the underlying presence of infection. Hydrocortisone is linked to improved oxygenation and reduced need for use of dopamine or boluses.
Paralysis is now no longer recommended as it is seen to be linked with increased mortality.
Left to right shunting should lead to more measures taken to recruit more alveoli, including increased PEEP, MAP, or surfactant administration. Normal PCO2 levels should be maintained, as opposed to hypercapnia (unless protecting against baro/volutrauma). Preductal sats are recommended in the low to mid-90’s with PaO2 55-80 mmHg.
Reducing V/Q mismatch is ideal – therefore the use of HFV and conventional ventilators are helpful. It is important to have “gentle” settings, and potentially allow hypercapnia in order to decrease the amount of barotrauma and volutrauma leading to potential BPD later in life. Gentle settings include optimal PEEP, relatively low PIP, and no hyper-oxygenation.
Right to left shunting indicates more success from vasodilation therapy (e.g. iNO, milrinone). Indications are pointing towards the potential use of inhaled PGE1 or PGI2, but RCT studies are not available as they have had low recruitment.
iNO is a highly recommended tool used to treat PPH, as it is selective to the vascular tissue and does not affect SVR. It is not recommended in preterm infants, with no correlation in decreased mortality or long term effects.
Sildenafil is recommended with or without the conjunction of iNO, but it does cause systemic effects. This is important to note in infants that may already have hypotensive issues, as it can cause severe hypotension. A loading dose is recommended in order to prevent this potential hypotensive crisis. This is a good option, especially for more rural or indigent communities, who may not have access to iNO due to cost or resources.
Milrinone is another course of treatment that can be used when cardiac dysfunction is occurring. Currently it is not licensed for use in the neonate population for PPHN, although it is used in the PICU and adult ICU. It improves both systolic and diastolic function. Again, this is not recommended for infants already struggling with hypotension. Loading dose and maintenance dosing is recommended.
Surfactant can be used to treat an underlying cause of PPHN related to deficiency or inactivation, as seen in RDS in preterm, MAS, or pneumonia/sepsis. It is not recommended for routine use without underlying reason.
For the very worst sick infants, ECMO can be the only other option if PPHN does not improve. Hemodynamic instability with no improvement in oxygenation are usually the triggers for this decision.
Regardless of your treatment plan…
for these sick infants, it is always good to know your options and the gold standard/recommendations of treatment. This is a quick look at PPHN with the current treatment plans. Hopefully, these children will have more options in the near future!
Please share with us your thoughts on the content of this blog and any alternate points of view or experiences you have had with PPHN. We can all benefit from other perspectives on this topic.
