Persistent Pulmonary Hypertension

Persistent Pulmonary Hypertension

Persistent Pulmonary Hypertension

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PPHN: Definition & Basics - Blue Baby Blues

  • Definition: Failure of postnatal circulatory transition; ↑ Pulmonary Vascular Resistance (PVR).
  • Pathophysiology: Persistent fetal circulation (Right→Left shunt via PDA/PFO) → severe hypoxemia.
  • Types:
    • Maladaptation (e.g., MAS, RDS)
    • Maldevelopment/Underdevelopment (e.g., CDH, pulmonary hypoplasia)
    • Idiopathic

⭐ PPHN is characterized by persistence of fetal circulatory pathways (right-to-left shunting via PDA/PFO) leading to severe hypoxemia. PPHN pathophysiology diagram showing persistent fetal shunts (PDA, PFO) and right-to-left blood flow)

PPHN: Pathophysiology - Vicious Vasoconstriction

  • Core Mechanisms:
    • Maladaptation: Failure of postnatal ↓ Pulmonary Vascular Resistance (PVR).
    • Maldevelopment: Abnormal pulmonary arteriolar muscularization.
    • Underdevelopment: Pulmonary hypoplasia (e.g., congenital diaphragmatic hernia).
  • Key Mediator Imbalance:
    • ↓ Nitric Oxide (NO) (vasodilator).
    • ↑ Endothelin-1 (ET-1) (vasoconstrictor).
    • Prostaglandins: ↓ $PGI_2$, $PGE_2$ (vasodilators); ↑ $TXA_2$ (vasoconstrictor).

Maladaptation (failure of normal postnatal drop in PVR), often due to lung parenchymal disease (e.g., MAS, RDS) or asphyxia, is the most common underlying mechanism.

PPHN pulmonary vasoconstriction and right-to-left shunting

PPHN: Etiology & Risks - Trouble Triggers

PPHN results from failed circulatory transition. Key triggers include:

  • Maternal Factors:
    • Diabetes Mellitus
    • NSAID use
    • SSRI use (late pregnancy)
  • Neonatal Factors:
    • Meconium Aspiration Syndrome (MAS)
    • Respiratory Distress Syndrome (RDS)
    • Sepsis
    • Perinatal Asphyxia
    • Congenital Diaphragmatic Hernia (CDH)

Maternal SSRI use in late pregnancy is a significant risk factor for PPHN.

PPHN: Clinical Features - Gasping & Grim

  • Respiratory Distress: Tachypnea, gasping, grunting.
  • Cyanosis: Severe, labile hypoxemia.
  • Differential Cyanosis:
    • Pre-ductal SpO2 > Post-ductal SpO2 by >10%.
    • Or PaO2 difference >20 mmHg.

    Pre-ductal vs. post-ductal SpO2 difference >10% (or PaO2 >20 mmHg) is a classic sign of PPHN indicating ductal shunting.

  • RV Failure Signs: Hepatomegaly.
  • Auscultation: Loud, single S2; harsh systolic murmur.

PPHN: Diagnosis - Echoing Evidence

  • Initial Clues:
    • CXR: Often normal or shows ↓ pulmonary vascularity.
    • ABG: Hypoxemia (PaO₂ ↓), often with hypercapnia.
    • Hyperoxia Test: PaO₂ fails to rise significantly (e.g., < 20 mmHg increase or remains < 100 mmHg) with 100% O₂.
  • Gold Standard:

    ⭐ Echocardiography is the gold standard for PPHN diagnosis, directly visualizing shunts and estimating pulmonary artery pressure.

    • Shows R→L shunt (PFO/PDA), ↑ PA pressure, RV dysfunction.
  • Severity:
    • Oxygenation Index (OI): $\frac{MAP \times FiO_2 \times 100}{PaO_2}$
    • OI > 25 indicates severe PPHN.

PPHN: Management - Breathing Better

  • Priorities: Supportive care, target O2 (pre-ductal SpO2 90-95%), gentle ventilation (HFOV if needed).
  • Key Interventions:

Inhaled Nitric Oxide (iNO) is a selective pulmonary vasodilator that improves oxygenation and reduces the need for ECMO.

High‑Yield Points - ⚡ Biggest Takeaways

  • PPHN involves failure of normal circulatory transition at birth, leading to persistently high pulmonary vascular resistance (PVR).
  • Results in right-to-left shunting of deoxygenated blood via the foramen ovale and ductus arteriosus.
  • Presents with marked cyanosis (often refractory to 100% oxygen), tachypnea, and respiratory distress.
  • A pre-ductal vs. post-ductal SpO2 difference >10% is a classic diagnostic indicator.
  • Echocardiography is the gold standard for diagnosis, confirming elevated pulmonary artery pressures and shunting.
  • Management includes supportive care (oxygen, ventilation), inhaled Nitric Oxide (iNO), and ECMO for severe, refractory cases.
  • Often associated with meconium aspiration syndrome (MAS), asphyxia, or sepsis.
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Practice Questions: Persistent Pulmonary Hypertension

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Drug not used in pulmonary hypertension is:

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The immediate next step in managing a apneic baby who's mother has been administered narcotics (meperidine) shortly before delivery is to do _____

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The immediate next step in managing a apneic baby who's mother has been administered narcotics (meperidine) shortly before delivery is to do _____

bag and mask ventilation

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