Neonatal Respiratory Distress - High-Yield Viva Questions
| Question | Answer / Practical Pearls |
|---|---|
| What is the physiological mechanism of expiratory grunting in a neonate? | • Expiratory grunting is a protective reflex where the infant exhales against a partially closed glottis. • Physiological Purpose: Generates auto-PEEP (Positive End-Expiratory Pressure), which prevents end-expiratory alveolar collapse, preserves functional residual capacity (FRC), improves alveolar ventilation-perfusion matching, and maintains oxygenation in non-compliant lungs. VIVA TRAP: Never administer sedatives or muscle relaxants to a grunting baby without securing the airway, as abolishing the grunt causes instant alveolar collapse! |
| Compare the Silverman-Anderson Score with the Downe Score. | • Silverman-Anderson Retraction Score (SARS): Designed specifically for preterm neonates with non-compliant lungs and soft, cartilaginous chest walls. Assesses: (1) Thoracoabdominal synchrony, (2) Intercostal retractions, (3) Xiphoid retractions, (4) Nares flaring, (5) Expiratory grunt. Scored 0-10 ($\ge 6$ indicates impending failure). • Downe Score: Used primarily for term / late-preterm neonates. Assesses: (1) Cyanosis, (2) Air entry, (3) Respiratory rate, (4) Retractions, (5) Grunt. Scored 0-10. |
| Why does maternal diabetes increase the risk of Respiratory Distress Syndrome (RDS) in the newborn? | • Fetal hyperglycemia stimulates fetal pancreatic beta-cell hyperplasia, producing fetal hyperinsulinemia. • Insulin is a potent antagonist to endogenous glucocorticoids in the fetal lung. • Hyperinsulinemia directly inhibits the transcription of surfactant protein genes (SP-A and SP-B) and suppresses the enzyme cholinephosphate cytidylyltransferase, impairing dipalmitoylphosphatidylcholine (DPPC) synthesis in type II alveolar pneumocytes. • Consequently, infants of diabetic mothers have delayed lung maturation and can develop severe RDS even at 36-38 weeks gestation! |
| What are the criteria for CPAP failure in preterm RDS, and what is the LISA / MIST technique? | • CPAP Failure Criteria: 1. Requirement of $\text{FiO}_2 >0.30$ in preterms $<28$ weeks or $>0.30-0.40$ in preterms $\ge 28$ weeks on PEEP $\ge 6\text{ cm }\text{H}_2\text{O}$ to maintain $\text{SpO}_2 >90\%$. 2. Severe retractions (Silverman score $>6$). 3. Respiratory acidosis with $\text{pH} < 7.20$ and $\text{PaCO}_2 > 60-65\text{ mmHg}$. • LISA / MIST Technique: Less Invasive Surfactant Administration. While the spontaneously breathing infant remains continuously on Bubble CPAP, a thin flexible catheter (16G vascular catheter or 4-5 Fr feeding tube) is placed through the vocal cords under direct laryngoscopy. Surfactant ($200\text{ mg/kg}$ of Poractant alfa) is instilled over 1-3 minutes. Avoids endotracheal intubation, reducing barotrauma, BPD, and death. |
| How do you diagnose and manage Persistent Pulmonary Hypertension of the Newborn (PPHN)? | • Bedside Screening: Check pre-ductal (Right Hand) and post-ductal (Foot) $\text{SpO}_2$ simultaneously. A gradient $>5-10\%$ (pre-ductal higher) confirms right-to-left shunting across a patent ductus arteriosus secondary to high pulmonary vascular resistance. • Echocardiography (Gold Standard): Right-to-left or bidirectional ductal/foramen ovale shunt, severe tricuspid regurgitation jet with estimated RV systolic pressure $>75\%$ of systemic pressure, and flattened or left-deviated interventricular septum. • Management: Oxygenation (target pre-ductal $\text{SpO}_2\text{ }92-97\%$, avoid hypoxia and hyperoxia), maintain systemic blood pressure with inotropes (Dopamine/Epinephrine), correct acidosis (target pH $7.35-7.45$), Inhaled Nitric Oxide (iNO at 20 ppm) as selective pulmonary vasodilator, IV Sildenafil or Milrinone. |