Define Respiratory Distress in Newborn & Hyaline Membrane Disease. Describe its causes, pathophysiology, clinical features and investigations.

Definition

• Respiratory distress in a newborn is the presence of at least two of the following three signs: respiratory rate > 60/min (tachypnoea), chest retractions, and grunting.
• Its severity is graded by the Silverman-Andersen score.

Silverman-andersen Scoring

Five parameters, each scored 0–2 (total 0–10). Higher score = worse distress (the opposite of Apgar).

Causes of Respiratory Distress

Pulmonary: hyaline membrane disease (RDS), transient tachypnoea of the newborn (TTN), meconium aspiration syndrome (MAS), pneumonia, pneumothorax, pulmonary haemorrhage, congenital malformations (CDH, TEF).

Non-pulmonary: congenital heart disease, sepsis, metabolic acidosis, hypoglycaemia, anaemia / polycythaemia, hypothermia, and CNS causes.

Hyaline Membrane Disease (RDS) — Definition

• HMD is respiratory distress in a preterm neonate due to deficiency of pulmonary surfactant, causing widespread alveolar collapse (atelectasis).
• It is the commonest cause of respiratory distress in preterm babies.

Pathophysiology

Surfactant deficiency → ↑ Alveolar surface tension → Progressive atelectasis → ↓ Lung compliance + V/Q mismatch → Hypoxia + hypercapnia + acidosis → Pulmonary vasoconstriction → ↓ pulmonary blood flow → Ischaemic injury → protein-rich exudate → hyaline membranes

Risk Factors

• Prematurity (the major factor — risk ↑ with decreasing gestation).
• Infant of a diabetic mother (insulin antagonises surfactant maturation).
• Male sex, second twin, elective caesarean without labour, perinatal asphyxia, hypothermia.
• Protective: antenatal steroids, chronic intrauterine stress, PROM, IUGR.

Clinical Features

• Onset within minutes to hours of birth, worsening over the first 48–72 hours (then improving as endogenous surfactant appears).
• Tachypnoea, grunting, retractions, nasal flaring, cyanosis.
• Reduced air entry; may progress to respiratory failure and apnoea.

Investigations

• Chest X-ray (classic): low lung volumes, a fine reticulogranular 'ground-glass' pattern with air bronchograms; severe disease → 'white-out' lungs.
• ABG — hypoxaemia, hypercapnia, respiratory + metabolic acidosis.
• Sepsis screen (to exclude pneumonia), blood glucose, and echocardiography if PDA/PPHN suspected.

Differential Diagnosis (high-yield Comparison)

Management — Supportive

• Neutral thermal environment; IV fluids; maintain glucose & perfusion; minimal handling.
• Monitor continuously — SpO2 (target 90–95%), heart rate, ABG, blood pressure.

Management — Respiratory Support

• Early CPAP (nasal CPAP 5–6 cmH2O) — first-line; maintains functional residual capacity and prevents collapse.
• Mechanical ventilation if CPAP fails / severe apnoea / respiratory failure.
• Surfactant replacement via ET tube — INSURE (Intubate-Surfactant-Extubate to CPAP) or LISA (less-invasive surfactant administration); give early ('rescue') for established RDS.

Others: antibiotics until sepsis is excluded; caffeine for apnoea of prematurity; treat a haemodynamically significant PDA.

Complications of RDS / its Therapy

• Air leaks — pneumothorax, pneumomediastinum, pulmonary interstitial emphysema.
• Bronchopulmonary dysplasia (BPD) — chronic lung disease (O2 dependence at 36 weeks corrected age).
• Patent ductus arteriosus; intraventricular haemorrhage; retinopathy of prematurity.
• Complications of mechanical ventilation and oxygen toxicity.

Prevention

• Antenatal corticosteroids — betamethasone / dexamethasone to the mother at 24–34 weeks when preterm delivery is anticipated (most effective if given > 24 h and < 7 days before delivery).
• Prevent prematurity; prevent birth asphyxia and hypothermia; optimise diabetic control in pregnancy.

WHY Surfactant Is Everything

• The whole of hyaline membrane disease turns on understanding why a lung without surfactant cannot stay open.
• Surfactant is a phospholipid produced by the type II pneumocytes from about 24 weeks, in adequate amounts only after 34–35 weeks.
• Its function is to reduce the surface tension at the air-liquid interface of the alveolus.
• Without it, Laplace's law takes over: the pressure needed to keep an alveolus open is inversely proportional to its radius — so small alveoli require more pressure than large ones, and therefore collapse, emptying into the larger ones.
• The result in the preterm lung is widespread alveolar collapse (atelectasis) at the end of every expiration — so the baby must generate enormous pressures to re-inflate the lung with every breath.
• Hence the clinical picture: tachypnoea, grunting (an attempt to generate auto-PEEP by expiring against a closed glottis — a highly efficient natural manoeuvre), intercostal and subcostal retractions, nasal flaring and cyanosis, worsening over the first hours, with the classic reticulogranular 'ground-glass' X-ray with air bronchograms.
• It also explains the treatment: replace the surfactant, and provide CPAP to hold the alveoli open.

WHY Antenatal Steroids Are the Greatest Intervention

• The most important fact about RDS is understanding why the single greatest advance was not a treatment given to the baby, but an injection given to the mother.
• Giving antenatal corticosteroids (betamethasone or dexamethasone) to a woman in threatened preterm labour, between 24 and 34 weeks, accelerates fetal lung maturation — inducing the type II pneumocytes to produce surfactant.
• The effect is dramatic and is one of the best-established interventions in all of medicine: it reduces respiratory distress syndrome, intraventricular haemorrhage, necrotising enterocolitis and — most importantly — neonatal mortality.
• And it is cheap, safe and available anywhere.
• The benefit begins within 24 hours and is maximal after 48.
• Understanding this explains why every woman in threatened preterm labour must receive steroids — and why this is a public-health intervention as much as an obstetric one.
• For the baby who is nevertheless born with RDS, the treatment is early CPAP (which splints the alveoli open and often avoids intubation altogether), exogenous surfactant given via the endotracheal tube, oxygen titrated carefully (to avoid retinopathy), warmth, nutrition and the treatment of sepsis.