Having been the neonatal SHO for a few weeks now, you feel in your element, grunting baby reviews? Done! Screened baby for infections? Also done, deliveries? You have lost track of how many you have attended. So, when you get the call to attend a forceps delivery due to prolonged labour and meconium-stained liquor, you walk into the labour ward with a smile, ready to go.
So what happens when the baby doesn’t do as told? They start working a bit hard to breathe and require some ventilatory support. You conduct a thorough head-to-toe examination, not forgetting to check the femoral pulses—a step one never overlooks. Besides increased breathing work and low oxygen saturations, everything else appears normal.
You take them to the neonatal unit, expecting a little bit of high flow will do the trick and sort out what you think is a case of transient tachypnoea of the newborn. But throughout the next hour, the baby required intubation and ventilation and was starting nitric oxide before you left.
What was that all about? Let’s talk about persistent pulmonary hypertension of the newborn.
Persistent Pulmonary Hypertension of the Newborn (PPHN) is a challenging condition characterised by the failure of normal circulatory transition after birth. This leads to sustained pulmonary hypertension that mirrors fetal circulation patterns, significantly impairing oxygenation.
PPHN is estimated to affect approximately two in every 1,000 births in the UK. It primarily occurs in babies born at full term, though it can also affect premature babies. Understanding the aetiological factors, pathophysiology, and implications of PPHN aids in prompt diagnosis and effective management.
The history of PPHN can be traced back to the late 1960s, when it was first recognised as a distinct clinical syndrome. Before this, cases of PPHN were likely misdiagnosed as other respiratory conditions. Two or three decades later, advancements in neonatal care, including the introduction of echocardiography and improvements in mechanical ventilation, helped in the diagnosis and management of PPHN.
The first successful case of PPHN treated with extracorporeal membrane oxygenation (ECMO) occurred in 1975. By the 1990s, treatments for PPHN began to include the use of inhaled nitric oxide (iNO), which has since reduced the need for more invasive treatments.
Pathophysiology of PPHN
To understand the pathophysiology of PPHN, we need to understand the physiological changes that occur at birth; however, to go into detail would be overwhelming for both you and me, so let’s make it brief and related to PPHN.
At birth, neonates undergo rapid physiological transitions to adapt from the intrauterine environment to independent life. The baby takes their first breath, replacing fluid in the lungs with air (usually without help or support). This decreases pulmonary vascular resistance, allowing for efficient pulmonary blood flow and gas exchange. Then, the closure of fetal circulatory shunts, such as the foramen ovale and ductus arteriosus, reconfigures the circulation to support oxygenation by the lungs rather than the placenta.
PPHN emerges due to the neonate’s pulmonary vessels’ inability to dilate sufficiently following birth. This failure impedes the anticipated shift from the high resistance circulation in the fetal lungs to the much lower resistance characterising healthy postnatal circulation. Consequently, this dysfunction leads to sustained high pulmonary vascular resistance (PVR).
Right-to-left shunts in the heart further exacerbate the condition. These further compromise the efficient exchange of oxygen and the overall blood flow throughout the body, significantly affecting the neonate’s oxygenation levels.
Aetiology and Risk Factors
The factors contributing to the high PVR are those that would give rise to PPHN. They include hypoxia, acidosis, and mechanical compression of pulmonary vessels due to lung over-distention or under-inflation (tricky, right? Imagine being a few hours old and dealing with this).
Hence, PPHN can be idiopathic or secondary to a variety of conditions such as meconium aspiration syndrome, respiratory distress syndrome, sepsis, asphyxia and congenital diaphragmatic hernia. Or it could be due to a delay in circulatory transition.
Some maternal factors can, in turn, increase the risk of the neonate presenting with PPHN. These include obesity, diabetes and certain medications.
How does PPHN present?
So now we know which are some of the babies at risk of developing PPHN, but how does PPHN generally present?Â
Neonates with PPHN typically present with severe respiratory distress, cyanosis, and hypoxaemia that is disproportionate to the lung disease’s severity.
It generally presents shortly after birth (or a few hours later)
On examination, there may be an audible murmur and a precordial impulse. There is often a difference in pre-ductal and post-ductal oxygen saturations, with the pre-ductal measurement being 5 to 10% higher. Occasionally, the baby will be hypotensive.
The diagnosis is primarily clinical, supported by echocardiography. This reveals right ventricular hypertrophy and pulmonary hypertension.
When examining a neonate with increased work of breathing, we tend to look for the cause at the time. So here, we must think about the risk factors for PPHN. Does the baby look septic? Are they covered in meconium? Were there any concerns during the pregnancy? Were there any abnormalities on ultrasounds? Identifying the cause (if at all possible) definitely helps treatment.
How do you manage PPHN?
The management of PPHN requires a multifaceted approach that includes optimising oxygenation, ensuring haemodynamic stability, and reducing pulmonary vascular resistance.
Think of it as a ladder: You have some steps before reaching the top treatment – ECMO.
Step 1: The basics
In all neonatal pathologies, we must never forget the basics. This means maintaining the baby as physiologically stable as possible by maintaining normothermia, preventing hypoglycaemia, treating infections by starting antibiotics as soon as possible, and, of course, the cornerstone of managing PPHN, ensuring correct oxygenation. Start with some non-invasive respiratory support.
Step 2: We go up a step in ventilation
Most of the time, you take two steps at a time when managing PPHN.
With babies who have markedly increased work of breathing and poor oxygen saturations despite non-invasive support, the next step is to prepare for intubation to support the infant’s breathing.
It’s also worth ensuring you have adequate access. A peripheral intravenous cannula won’t be enough. Once you finish intubating them while everything else is being set up, prepare for a central line. Most of the time, this will be an umbilical line.
Don’t forget to prescribe correct sedation, and remember maintaining comfort is crucial in neonates.
Step 3: We now get the happy gas and friends
Once we have intubated our baby, and if they still require high doses of oxygen, we know we are struggling to resolve the hypoxaemia with oxygen alone. This suggests elevated pulmonary arterial pressure with right-to-left shunting of blood. We need to selectively reduce pulmonary vascular resistance without decreasing systemic blood pressure.
We do that with inhaled nitric oxide (iNO), the vasodilator of choice in managing PPHN. Nitric oxide works by relaxing the smooth muscles in the walls of the pulmonary blood vessels, leading to vasodilation. This reduction in pulmonary vascular resistance allows blood to flow more easily through the lungs, where it can pick up oxygen.
Here, you also need to consider using inotropic support to maintain systemic blood pressure.
Step 4: We Google oxygenation index calculation.
The Oxygenation Index (OI) is calculated using the formula: OI = (Mean Airway Pressure (MAP) x FiO2 x 100) / PaO2, where MAP is measured in cm H2O, FiO2Â is expressed as a decimal, and PaO2 is measured in mmHg.
This helps assess the severity of pulmonary dysfunction and the effectiveness of ventilation in providing oxygen.
Generally, an OI of less than 15 suggests mild disease and can be managed with less intensive respiratory support. An OI between 15 and 25 indicates moderate disease, requiring closer monitoring and possibly more aggressive treatment. An OI greater than 25 signals severe lung disease, often necessitating advanced therapies such as inhaled nitric oxide or extracorporeal membrane oxygenation (ECMO) to improve oxygenation and reduce pulmonary vascular resistance.
Step 5: ECMO
Self-explanatory. You have done all you can medically. The next step to move on is ECMO.
You are not expected to crack out this management by yourself. The management of PPHN is done with a multidisciplinary team and, more often than not, with the involvement of more than one consultant. It is also worth mentioning that the PPHN ladder can sometimes be a slide. You keep moving from step to step – escalating and de-escalating care accordingly without forgetting about that vital first step – keeping the basics stable.
PPHN remains a complex clinical challenge requiring timely recognition, comprehensive evaluation, and a multidisciplinary management approach. Advances in understanding the pathophysiology and treatment have improved outcomes, yet PPHN is still associated with significant morbidity and mortality. Ongoing research and innovation are critical to develop strategies to reduce disease burden further. Early identification is key!
References
Keller, R. L., et al. (2010). Persistent pulmonary hypertension of the newborn. American Journal of Respiratory and Critical Care Medicine, 182(7), 157-164.
Lakshminrusimha, S., & Steinhorn, R. H. (2017). Pulmonary vasodilators in neonates with persistent pulmonary hypertension of the newborn. American Journal of Perinatology, 34(8), 770-778.
StatPearls Publishing. (2021). Physiology, Newborn. StatPearls [Internet]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499951/
Steinhorn, R. H. (2010). Neonatal pulmonary hypertension. Pediatric Critical Care Medicine, 11(2 Suppl), S79-S84.
Great Ormond Street Hospital. (n.d.). Persistent Pulmonary Hypertension of the Newborn (PPHN). Retrieved [20/03/23], from https://www.gosh.nhs.uk/conditions-and-treatments/conditions-we-treat/persistent-pulmonary-hypertension-newborn-pphn/
The Regents of the University of California. (2004). Persistent Pulmonary Hypertension of the Newborn (PPHN)
