Persistent Pulmonary Hypertension of the Newborn (PPHN)
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PPHN is a syndrome of failed circulatory transition at birth. Normally, the first breath triggers a dramatic drop in pulmonary vascular resistance (PVR), allowing blood to flow to the lungs. In PPHN, the pulmonary arteries remain constricted. Pulmonary pressure exceeds systemic pressure, forcing blood to shunt Right-to-Left through the persistnt fetal channels (Foramen Ovale and Ductus Arteriosus), bypassing the lungs and causing severe systemic hypoxaemia.
Image: Fetal Circulation
Clinical Scenario: The Blue Term Baby
A term baby born through meconium-stained liquor is cyanosed and in respiratory distress. Saturations are 75% despite ventilation with 100% oxygen. The sats probe on the right hand reads 85%, while the foot reads 70%.
Key Teaching Points
- **Diagnosis**: **PPHN** (likely secondary to Meconium Aspiration).
- **Differential Cyanosis**: The Right Hand (Pre-ductal) receives oxygenated blood from the aorta before the ductus. The Foot (Post-ductal) receives deoxygenated blood shunted across the PDA.
- **Management**: Needs **Inhaled Nitric Oxide (iNO)** and high frequency ventilation.
Image Integration Plan
| Image Type | Source | Status |
|---|---|---|
| Management Algorithm | AI-generated | PENDING |
| Fetal Circulation Diagram | AI-generated | PENDING |
| CXR (Meconium Aspiration) | Web Source | PENDING |
| Diagram (Pre/Post Ductal Sats) | AI-generated | PENDING |
[!NOTE] Image Generation Status: Diagrams illustrating the Shunting mechanisms are queued.
Key Diagnostic Triad
- Severe Hypoxaemia: Disproportionate to X-ray findings.
- Labile Saturations: "Flip-flop" circulation. Tiny changes in handling cause massive desaturations (due to vasoconstriction spikes).
- Differential Cyanosis: Pre-ductal > Post-ductal.
- Incidence: 2 in 1,000 live births.
- Population: Typically Term or Post-Term infants. Rare in preterms (who lack muscle in pulmonary arterioles).
- Mortality: 10-20%.
- Maladaptation (Vasoconstriuction):
- Meconium Aspiration Syndrome (MAS): Plugging + Chemical inflammation.
- Sepsis / Pneumonia: Endotoxin causes vasoconstriction.
- Hypoxia / Acidosis: Potent vasoconstrictors.
- Maldevelopment (Structural):
- Congenital Diaphragmatic Hernia (CDH): Hypoplastic lungs have a reduced vascular bed (fewer vessels).
- Renal Agenesis: Oligohydramnios.
- Idiopathic: "Black PPHN" - healthy lungs but abnormal vascular reactivity. Linked to maternal SSRI/NSAID use.
- Saturations: Place probe on Right Hand (Pre-ductal) and Foot (Post-ductal). A difference of >10% suggests PPHN.
- Precordium: Prominent RV impulse (heave). Loud second heart sound (P2) due to high pulmonary pressure.
- Echocardiogram (Pre-ductal saturation): Gold Standard.
- Exclude Structural Heart Disease (e.g. TGA - Transposition).
- Confirm PPHN: Flattened/Bowed interventricular septum (RV pressure > LV pressure pushing septum to left). TR jet velocity used to estimate pressure. R->L shunt at PDA.
- Chest X-Ray:
- May show MAS (patchy opacities), Pneumonia, or CDH (bowel in chest).
- May be clear (Idiopathic PPHN).
Image: PPHN CXR
- Hyperoxia Test (The Nitrogen Washout):
- Protocol: Measure PaO2 on room air. Give 100% Oxygen via headbox for 10 mins. Remeasure PaO2.
- Interpretation:
- Lung Disease: PaO2 usually > 20 kPa (Oxygen overcomes V/Q mismatch).
- Cardiac / PPHN: PaO2 < 13 kPa (Shunt cannot be overcome). "Fixed Right-to-Left Shunt".
- Warning: Do not do this if baby is unstable on ventilator. Use Oxygen Index instead.
Oxygen Index (OI) Calculation
Formula: OI = (MAP × FiO2 × 100) / PaO2
- OI < 15: Mild.
- OI 15-25: Moderate (Consider iNO).
- OI > 40: Severe (Consider ECMO).
Goal: Lower Pulmonary resistance (PVR) and raise Systemic resistance (SVR) to reverse the shunt.
Image: Inhaled Nitric Oxide
A. General Measures ("Pink, Warm, Sweet, Still")
- Minimal Handling: Sedation (Morphine) and Paralysis (Rocuronium/Vecuronium) to prevent agitation-induced vasoconstriction. "Thumping the incubator kills the baby".
- Correction of Acidosis: Aim pH > 7.35. Acidosis is a potent pulmonary vasoconstrictor.
- Temperature: Avoid hypothermia.
B. Ventilation Strategy
- Oxygen: A potent vasodilator. Aim pre-ductal sats >90%.
- HFOV (High Frequency Oscillation):
- Used to recruit lung volume without high peak pressures (barotrauma).
- Ideal for MAS + PPHN.
- Surfactant: If underlying MAS or RDS.
C. Vasodilator Protocol
- Inhaled Nitric Oxide (iNO):
- Start Dose: 20 ppm.
- Response: rapid rise in oxygenation (within 30 mins).
- Weaning: Slow wean (1 ppm every few hours) once stable. Rapid weaning causes "Rebound Hypertension" (Crashing).
- IV Sildenafil:
- PDE5 inhibitor. Prevents breakdown of cGMP.
- Used if iNO fails or during weaning.
- Milrinone:
- PDE3 inhibitor. Inotrope + Vasodilator. Good if there is also LV dysfunction.
D. Cardiovascular Support (Inotropes)
- The Theory: PVR > SVR causes the shunt. We must raise SVR to satisfy: SVR > PVR.
- Drug Choice:
- Noradrenaline: Vasoconstrictor. Raises SVR.
- Dopamine: Raises SVR + Contractility.
- Adrenaline: Low infusion rates.
E. ECMO (Extracorporeal Membrane Oxygenation)
- Heart-Lung bypass.
- Criteria: OI > 40 on 2 gases + maximal therapy.
- Survival: 80% for PPHN (highest of all ECMO indications).
- Pulmonary:
- Air Leak: Pneumothorax / Pneumomediastinum (from high pressure ventilation).
- Chronic Lung Disease (CLD): Oxygen toxicity and barotrauma.
- Neurological:
- HIE: Hypoxic Ischaemic Encephalopathy. The #1 cause of long term morbidity.
- Cerebral Palsy: 15-20% risk in severe survivors.
- Hearing Loss:
- Sensorineural deafness is common (due to prolonged ventilation, alkalosis, and antibiotics). Audiology follow-up is mandatory.
- Feeding: Oral aversion is common after prolonged intubation.
- Survival: 80-90% overall (lower if CDH).
- Neurodevelopment: 25% have significant impairment at 2 years.
What is PPHN?
"When a baby is in the womb, they don't breathe air. Their blood bypasses the lungs through special 'shortcuts' (the ductus) because the mother does the breathing for them. At birth, these shortcuts normally snap shut, and blood floods into the lungs to pick up oxygen. In PPHN, the blood vessels in the lung stay tight and squeezed shut (high pressure). The blood hits this wall of pressure and can't get in. Instead, it is forced back through the old shortcuts, meaning the blood circulating to the body has no oxygen in it."
Why did it happen?
"It is often a reaction to stress during delivery. If the baby was deprived of oxygen or swallowed meconium (poo) during birth, their body went into 'defense mode' and clamped the vessels down. We need to help them relax again."
How do we fix it?
- Nitric Oxide: This is a magic gas. When the baby breathes it, it travels to the lungs and tells the blood vessels to relax and open up.
- Rest: We keep the baby sedated and still. Even a small noise can make the vessels clamp down again.
- Time: It can take 5-7 days for the circulation to reset.
- Nair J, Lakshminrusimha S. Update on PPHN: mechanisms and treatment. Semin Perinatol. 2014.
- Abman SH, et al. Pediatric Pulmonary Hypertension: Guidelines. Circulation. 2015.
- Konduri GG, et al. Inhaled nitric oxide... in term and near-term infants. Pediatrics. 2004.