Persistant Pulmonary Hypertension of Newborn

Definition And Perinatal Circulatory Transition

Persistent pulmonary hypertension of the newborn (PPHN) presents as severe unresponsive hypoxic respiratory failure.
It reflects the failure of the transition of fetal to neonatal circulation.
Normal perinatal transition requires a rapid fall in pulmonary vascular resistance (PVR).
It also requires a marked increase in systemic vascular resistance (SVR) after umbilical cord clamping.
If PVR remains high and does not fall below SVR, blood flows from right to left.
This abnormal shunting occurs across the patent foramen ovale (PFO) and patent ductus arteriosus (PDA).
This right-to-left shunting results in severe systemic hypoxia.

Epidemiology And Etiology

PPHN occurs at a rate of 1 to 2 per 1,000 live births.
It is most common among full-term and post-term infants.
Mortality associated with PPHN ranges from 5% to 30%.

Category	Pathophysiology	Associated Clinical Conditions
Primary (Idiopathic) PPHN	Remodeled or mal-developed pulmonary vasculature due to in-utero fetal stress or hypoxia.	Exposure to maternal nonsteroidal anti-inflammatory drugs (NSAIDs) or selective serotonin reuptake inhibitors (SSRIs). Characterized by "black lung" on chest X-ray.
Secondary PPHN	High PVR secondary to parenchymal lung diseases. This is the most common presentation.	Meconium aspiration syndrome (MAS), respiratory distress syndrome (RDS), congenital pneumonia, and neonatal sepsis.
Pulmonary Hypoplasia	Abnormalities of pulmonary development leading to structurally underdeveloped vascular tree.	Congenital diaphragmatic hernia (CDH), Potter's syndrome, prolonged oligohydramnios, and alveolar capillary dysplasia.
Myocardial Dysfunction	Increased PVR associated with cardiac dysfunction.	Perinatal asphyxia, congenital heart disease, or intrauterine constriction of the ductus arteriosus.

Pathophysiology

Pulmonary vascular remodeling is pathognomonic of idiopathic PPHN.
Abnormal muscularization of normally non-muscular intra-acinar arteries occurs.
This leads to increased medial thickness of the larger muscular arteries.
It results in a decreased cross-sectional area of the pulmonary vascular bed and elevated PVR.
Reversible pulmonary vasospasm is often the mechanism in non-fatal PPHN.
Hypoxia induces profound pulmonary vasoconstriction.
This vasoconstriction response is exaggerated by acidemia.
Right ventricular (RV) failure alters diastolic compliance.
This causes right-to-left atrial shunting, even in the absence of elevated PVR.
Left ventricular (LV) dysfunction causes pulmonary venous hypertension.
This contributes to secondary pulmonary arterial hypertension.

Clinical Presentation

History And Risk Factors

Severe or prolonged oligohydramnios indicates potential pulmonary hypoplasia.
Absent or decreased fetal movements suggest fetal hypoxia or acidosis.
Maternal intake of aspirin, NSAIDs, SSRIs, and lithium are known risk factors.
Meconium-stained amniotic fluid or perinatal asphyxia are strong indicators.

Physical Examination

Infants typically present with severe hypoxia and cyanosis.
They exhibit labile oxygen saturations that fluctuate with handling or agitation.
The oxygen requirement is often out of proportion to the parenchymal lung disease.
Differential cyanosis is a hallmark feature of PPHN.
The preductal oxygen saturation (right arm) is 5% to 10% higher than post-ductal limbs (lower limbs).
Tachypnea with cyanosis without retractions points to idiopathic PPHN or cyanotic heart disease.
The presence of retractions, grunting, or nasal flaring suggests secondary parenchymal disease.
Cardiovascular examination may reveal a single, loud S2.
A systolic murmur of tricuspid regurgitation may be heard.

Diagnostic Evaluation

Bedside Tests And Imaging

Test Modality	Key Findings And Clinical Utility
Pulse Oximetry	Pre-ductal SpO2 greater than post-ductal SpO2 by 10% or more indicates increased right-to-left shunting across the PDA. Absence of a pre-post ductal difference does not rule out PPHN, as shunting may occur at the PFO.
Arterial Blood Gas	Demonstrates severe hypoxia. Pre-post ductal PaO2 difference greater than 20 mm Hg can be noted.
Hyperoxia Test	A PaO2 less than 50 mm Hg in 100% oxygen is highly suggestive of cyanotic congenital heart disease. A PaO2 between 50 and 150 mm Hg with 100% oxygen necessitates further evaluation for PPHN.
Chest X-Ray	Findings depend on the underlying condition. Shows patchy infiltrates in pneumonia, localized hyperinflation in MAS, or a normal "black lung" in idiopathic PPHN.
Electrocardiogram	Most commonly shows RV predominance that is within the normal range for age.

Echocardiography

Echocardiography is the gold standard diagnostic tool for PPHN.
The first step is ruling out congenital heart disease by confirming situs and venous return.
It confirms PPHN by documenting increased pulmonary artery pressure.
Pulmonary pressures of 30 to 60 mm Hg are calculated from the tricuspid regurgitation (TR) jet.
It assesses the direction of the shunt through the PDA and PFO.
It helps evaluate right and left ventricular function.
Fractional shortening or ejection fraction are used for LV assessment.

Differential Diagnosis

Conditions associated with secondary pulmonary hypertension may be misdiagnosed as PPHN.
Obstructed total anomalous pulmonary venous connections (TAPVC) presents with refractory hypoxemia and white out of the lungs.
Left ventricular outflow obstruction, including aortic stenosis and coarctation of aorta, must be excluded.
Primary LV myocardial diseases like myocarditis and cardiomyopathies cause secondary PAH from venous hypertension.

Management Strategies

General And Supportive Care

PPHN is a medical emergency where immediate intervention is critical.
Maintain normothermia and avoid stress through minimal and gentle handling.
Nurse the neonate in quiet surroundings with low noise and direct lighting.
Sedation and analgesia may be used, as agitation can aggravate hypoxia.
Fentanyl or midazolam are useful adjuncts to minimize pain and agitation.
Correct metabolic abnormalities such as hypoglycemia, hypocalcemia, and acidosis.
Correct polycythemia, as hyperviscosity increases pulmonary vascular resistance.

Respiratory Management

Hypoxia is a powerful pulmonary vasoconstrictor, making oxygen a primary therapy.
Administer supplemental oxygen to maintain adequate PaO2 (50 to 80 mm Hg).
Maintain a preductal saturation target of 91% to 95%.
Hyperoxia must be avoided as it inactivates surfactant and increases PVR through free radicals.
Gentle ventilation strategies with optimal positive end-expiratory pressure (PEEP) are required.
Practice permissive hypercapnia with a target pCO2 of 40 to 50 mm Hg.
Hyperventilation and alkalosis are harmful and increase the risk of mortality.
High-frequency ventilation (HFV) achieves better lung recruitment in parenchymal lung disease.
Surfactant replacement improves oxygenation when PPHN is secondary to parenchymal lung disease like MAS.

Hemodynamic Support

Optimal cardiac output is necessary to maximize tissue perfusion and oxygenation.
Maintain adequate intravascular volume using fluid boluses of 10 mL/kg normal saline.
Avoid excessive volume expansion as myocardial activity may be compromised.
Maintain blood pressures in the normal range, as the right-to-left shunt size depends partly on systemic BP.
Dopamine is the primary inotrope used to augment cardiac output.
Norepinephrine or epinephrine may be utilized if systemic blood pressure remains low.
Milrinone is a phosphodiesterase-3 inhibitor used for ventricular dysfunction.
Milrinone functions as a pulmonary vasodilator and inotrope but can cause systemic hypotension.

Specific Pulmonary Vasodilator Therapy

Drug	Mechanism And Clinical Use	Dosage And Administration
Inhaled Nitric Oxide (iNO)	The first-line selective pulmonary vasodilator. It reduces the need for ECMO and mortality in term infants. It is initiated when the oxygenation index reaches 15 to 25.	Started at 20 parts per million (ppm). Weaned gradually in steps of 5 ppm to prevent rebound hypertension.
Sildenafil	Phosphodiesterase-5 inhibitor. Acts via cGMP to enhance NO-mediated vascular relaxation. Used as primary therapy in resource-limited settings where iNO is unavailable.	Loading dose of 0.4 mg/kg IV over 3 hours. Maintenance dose of 1.6 mg/kg/day as continuous IV infusion.
Prostacyclins	Activates adenylate cyclase to increase cAMP. Epoprostenol or iloprost can be used as an adjuvant when response to iNO is inadequate.	Administered via inhalation or continuous IV infusion.
Bosentan	Endothelin-1 antagonist. Relieves vasoconstriction by blocking endothelin pathways. Safe and effective oral option.	Oral dose of 2 mg/kg/dose, given twice a day.

iNO response is defined by the 20-20-20 rule: an increase in PaO2 by 20 mm Hg within 20 minutes of starting 20 ppm iNO.
Nearly 40% of infants may fail to sustain a response to iNO and require evaluation for LV dysfunction.

Advanced Therapies

Extracorporeal membrane oxygenation (ECMO) is a lifesaving rescue therapy.
It is indicated for refractory PPHN that fails conventional management and iNO treatment.
Glucocorticoids (hydrocortisone) may be beneficial in restoring normal pulmonary vasculature.
Hydrocortisone increases cGMP, attenuates oxidative stress, and improves systemic pressure.

Prognosis And Follow-Up

With improved therapy including iNO and ECMO, mortality has reduced to less than 10% in tertiary care centers.
Survivors of PPHN remain at a significant risk for medical and neurodevelopmental sequelae.
Approximately 24% to 26% of survivors have hearing and neurodevelopmental impairments at 18 to 24 months.
Infants who develop PPHN are at a higher risk of rehospitalization within 1 year of discharge.
Pulmonary hypertension may persist in some infants.
Echocardiography must be repeated at 3 to 6 months of age to look for unresolved pulmonary hypertension.