Definition And Identification

• The National Neonatal Perinatal Database defines respiratory distress as the presence of any two specific clinical features.
• The first feature is a respiratory rate greater than 60 breaths per minute.
• The second feature includes subcostal or intercostal recessions.
• An expiratory grunt or groaning is the third feature.
• Additional indicators include nasal flaring, suprasternal retractions, and decreased air entry on auscultation.
• Signs such as gasping, choking, or stridor indicate life-threatening upper airway obstruction.
• Apnea, poor perfusion, and central cyanosis require prompt emergency intervention.

Common Causes By Gestation

Assessment And Evaluation

Clinical Evaluation

• A detailed antenatal and perinatal history is essential to identify the underlying cause.
• The evolution of respiratory distress gives critical diagnostic clues.
• Observe the overall color of the neonate to identify cyanosis or pallor.
• Ensure a pulse oximeter is placed on the right upper limb to measure preductal oxygen saturation.
• Auscultate to determine if breath sounds are symmetrical or if added sounds like rales are present.

Severity Scoring Systems

• The severity of respiratory distress can be objectively graded using standardized scores.
• Serial monitoring of these scores is more important than a one-time assessment.
• Higher scores correlate with impending respiratory failure and the need for mechanical ventilation.

Table: Silverman-Anderson Score for Preterm Neonates.

Table: Downe's Score for Term and Preterm Neonates.

Diagnostic Investigations

• The gastric aspirate shake test is a simple bedside procedure to predict the risk of RDS.
• The presence of a complete rim of bubbles in the shake test indicates adequate surfactant.
• Chest radiography is the primary diagnostic tool for evaluating neonatal respiratory distress.
• Point-of-care lung ultrasound is an increasingly popular mode of evaluation.
• Ultrasound provides faster decisions and involves lower radiation exposure.
• The hyperoxia test helps differentiate cyanotic congenital heart disease from pulmonary parenchymal disease.
• Arterial blood gas analysis is the gold standard for measuring carbon dioxide and oxygen levels.

Respiratory Distress Syndrome (RDS)

Pathophysiology

• RDS is a disease typical of preterm infants caused by generalized atelectasis.
• It results from absent or insufficient pulmonary surfactant production.
• Pulmonary surfactant is synthesized and secreted from alveolar type II cells.
• Preterm neonates have a small surfactant pool of only 10 mg/kg.
• Term infants typically possess a surfactant pool of 100 mg/kg.
• Surfactant insufficiency leads to an inappropriately high alveolar surface tension.
• High surface tension causes alveolar collapse and increases the work of breathing.
• Diffuse atelectasis ensues, leading to lung injury and hyaline membrane formation.

Clinical And Radiological Features

• The incidence of RDS is inversely proportional to gestational age.
• Neonates with RDS present with respiratory distress within the first 6 hours of life.
• Clinical signs include tachypnea, grunting, nasal flaring, and chest retractions.
• Hypoxia drives an increasing requirement for supplemental oxygen.
• Without surfactant replacement therapy, the severity peaks at 24 to 48 hours.
• The chest radiograph shows low lung volumes with a characteristic reticulogranular pattern.
• Moderate RDS reveals air bronchograms due to the collapse of distal airways.
• Severe RDS presents as a homogenous white-out lung due to diffuse alveolar atelectasis.
• Lung ultrasound reveals confluent B lines giving the appearance of a white lung.

Prevention

• Antenatal corticosteroids given to mothers at risk for preterm birth significantly decrease RDS incidence.
• Dexamethasone or betamethasone enhance lung fluid clearance and surfactant maturation.
• Tocolytic drugs may be used to allow completion of the antenatal steroid course.
• In-utero transfer to a tertiary center is recommended for extreme preterm deliveries.

Management Of RDS

Delivery Room Management

• The key principle is to establish and maintain functional residual capacity at the earliest.
• Delayed cord clamping for at least 30 seconds improves hemodynamic stability.
• Ensure meticulous thermoregulation using plastic wraps for neonates under 32 weeks.
• Use a T-piece resuscitator to deliver early continuous positive airway pressure (CPAP).
• CPAP pressure should be started at 5 to 6 cm H2O.
• Oxygen must be administered using a blender.
• Initial oxygen concentration is set at 21-30% for preterm neonates.

Continuous Positive Airway Pressure (CPAP)

• CPAP is the preferred primary respiratory support in preterm infants with RDS.
• It splints the airway, reduces airway resistance, and prevents atelectasis.
• Application of CPAP enables spontaneously breathing infants to recruit atelectatic airspaces.
• CPAP interfaces include short, snugly fitting binasal prongs or nasal masks.
• Alternate nasal prongs and masks to reduce the risk of nasal septum injury.
• Monitor for signs of CPAP failure, such as rising oxygen requirements or recurrent apnea.

Surfactant Replacement Therapy

• Exogenous surfactant acutely supplements insufficient endogenous stores.
• Natural animal-derived surfactants are preferred over synthetic preparations.
• Poractant alfa at a dose of 200 mg/kg is associated with better respiratory outcomes.
• Prophylactic surfactant is administered within 15-30 minutes of birth in selected extreme preterm infants.
• Early rescue surfactant is given within 2 hours of life to neonates exhibiting RDS signs.
• The InSurE method involves intubation, surfactant administration, and rapid extubation to CPAP.
• Less invasive surfactant administration (LISA) uses a thin catheter.
• LISA completely avoids the need for endotracheal intubation.

Mechanical Ventilation

• Invasive ventilation is reserved for CPAP failure or severe hypoxemic respiratory failure.
• Preterm lungs with RDS have low compliance and shorter time constants.
• Volume-targeted ventilation modes are strongly preferred.
• Volume limits minimize volutrauma and reduce the incidence of bronchopulmonary dysplasia.
• High-frequency oscillatory ventilation (HFOV) is used as a rescue mode for refractory hypoxia.
• HFOV improves gas exchange using supraphysiological rates and very small tidal volumes.

Pharmacological And Supportive Care

• Early caffeine therapy is the drug of choice for apnea of prematurity.
• Caffeine stimulates the medullary respiratory center and decreases bronchopulmonary dysplasia risk.
• Fluid management must be strictly monitored to prevent volume overload.
• Overhydration increases the risk of a hemodynamically significant patent ductus arteriosus.
• Maintain target oxygen saturations strictly between 90% and 95%.

Overview Of Other Common Causes

Transient Tachypnea Of The Newborn (TTNB)

• TTNB results from delayed clearance of fetal lung fluid after birth.
• It is common in late preterm and term infants delivered by elective cesarean section.
• It presents with mild respiratory distress that resolves rapidly over 48 to 72 hours.
• Chest radiographs show perihilar streaking, hyperaeration, and fluid in interlobar fissures.
• Lung ultrasound demonstrates a characteristic double lung point sign.
• Treatment is primarily supportive with supplemental oxygen or CPAP.

Meconium Aspiration Syndrome (MAS)

• Hypoxic stress leads to the in-utero passage of meconium.
• Aspiration of meconium causes peripheral airway obstruction and chemical pneumonitis.
• A ball-valve effect leads to significant air trapping and overinflated lungs.
• MAS is frequently complicated by persistent pulmonary hypertension of the newborn (PPHN).
• Radiographs show diffuse, asymmetric patchy infiltrates and hyperinflation.
• Severe cases require mechanical ventilation with lower PEEP to prevent air leak syndromes.
• Inhaled nitric oxide therapy is utilized for associated pulmonary hypertension.

Congenital Pneumonia

• It is a common manifestation of early-onset neonatal sepsis.
• In preterm babies, the clinical presentation is indistinguishable from RDS.
• Chest X-rays may reveal diffuse haziness, consolidation, or coarse granular infiltrates.
• Evaluation includes complete blood counts, C-reactive protein, and blood cultures.
• Empiric antibiotic therapy with ampicillin and gentamicin must be initiated promptly.

Air Leak Syndromes

• Pneumothorax and pulmonary interstitial emphysema (PIE) occur due to high transpulmonary pressures.
• Tension pneumothorax presents with sudden deterioration, severe hypoxia, and bradycardia.
• Bedside transillumination helps identify large air collections quickly.
• Emergency needle aspiration and intercostal tube placement are lifesaving interventions.
• PIE appears as linear or cystic radiolucencies radiating from the lung hilum.
• Management of PIE includes minimizing airway pressures and adopting high-frequency ventilation.