Respiratory Distress in the Newborn

Overview of Causes

1. Neonatal Respiratory Distress Syndrome (RDS) / Hyaline Membrane Disease

Epidemiology & Risk Factors

• ~60% of infants born before 28 weeks' gestation
• ~30% born at 28-34 weeks
• <5% born after 34 weeks

Pathogenesis

1. Increased alveolar surface tension -> progressive atelectasis
2. Infant must work as hard with every breath as the first
3. Hypoxemia and CO2 retention develop
4. Acidosis -> pulmonary vasoconstriction -> endothelial and epithelial damage
5. Plasma proteins leak into alveoli -> fibrin-rich hyaline membranes form
6. Hyaline membranes act as a barrier to gas exchange -> worsens hypoxemia -> further impairs surfactant synthesis (vicious cycle)

Pathophysiology of RDS (Robbins, Cotran & Kumar)

Morphology

• Lungs: normal size but heavy, airless, mottled purple
• Microscopically: collapsed (atelectatic) alveoli
• Early deaths: only necrotic debris in terminal bronchioles
• After several hours: eosinophilic hyaline membranes lining respiratory bronchioles, alveolar ducts, and alveoli - composed of necrotic type II pneumocytes + plasma proteins (mainly fibrin). Notably, minimal neutrophilic inflammation.
• With survival: reparative changes - type II pneumocyte proliferation and interstitial fibrosis

Clinical Features

• Grunting, tachypnea, nasal flaring, intercostal/subcostal retractions within minutes of birth
• Progressive worsening over the first 48-72 hours
• CXR: diffuse "ground glass" appearance, air bronchograms, low lung volumes

Management

• Antenatal corticosteroids (betamethasone/dexamethasone) given to mothers at 24-34 weeks if preterm delivery anticipated - accelerate lung maturation
• Exogenous surfactant therapy (intratracheal) - standard of care; dramatically reduces mortality
• Respiratory support: CPAP, mechanical ventilation as needed
• Oxygen supplementation (target SpO2 90-95% in preterm to minimize retinopathy risk)
• Blended oxygen (30%) or room air recommended for initial resuscitation of preterm infants

Long-term Complications

• Bronchopulmonary dysplasia (BPD): chronic lung disease resulting from oxygen toxicity, barotrauma/volutrauma from ventilation, and inflammation. Diagnosed by need for supplemental O2 at 36 weeks' corrected gestational age. "New BPD" seen in extremely preterm (<1000 g) infants with large simplified alveolar structures and impaired capillary configuration.
• Retinopathy of prematurity: from oxygen exposure
• Both complications have decreased in incidence with modern management

2. Transient Tachypnea of the Newborn (TTN)

• Symptoms within the first 6 hours, resolving within 72 hours (usually)
• Tachypnea >60 breaths/min, often 80-100 breaths/min
• Retractions, grunting, nasal flaring may be present; cyanosis/hypoxia are rare
• CXR: perihilar streaking, fluid in the interlobar fissure, congestion ("wet lung")
• Diagnosis of exclusion (rule out pneumonia, aspiration, congenital malformations, HIE, pneumothorax, acidosis, RDS)

• NPO with IV 10% dextrose for persistent tachypnea
• Supplemental oxygen and/or CPAP as indicated
• Diuretics and racemic epinephrine have no proven benefit
• Self-limiting; reassurance is key

3. Meconium Aspiration Syndrome (MAS)

• Mechanical obstruction - thick viscous material migrates to distal airways
• Ball-valve effect - partial obstruction causes alternating atelectasis and overinflation
• Chemical pneumonitis
• Alterations in pulmonary vasculature -> pulmonary arterial hypertension

CXR in a 42-week infant with meconium aspiration (Grainger & Allison's Diagnostic Radiology)

• ~30% of affected infants require mechanical ventilation
• Inhaled nitric oxide for severe pulmonary hypertension
• ECMO (extracorporeal membrane oxygenation) for cases failing conventional therapy, using either veno-arterial (VA) or veno-venous (VV) approach

4. Neonatal Pneumonia

• Transplacental (TORCH infections): toxoplasmosis, rubella, CMV, herpes - rare, seldom cause pulmonary abnormalities
• Perinatal: ascending vaginal infection, transvaginally during birth, or hospital-acquired (nosocomial)
• Most cases occur at birth via aspiration/swallowing of infected amniotic fluid or vaginal secretions
• Most common organism: Group B Streptococcus (GBS)
• Risk factor: prolonged rupture of membranes

5. Persistent Pulmonary Hypertension of the Newborn (PPHN)

1. Idiopathic (abnormally remodeled pulmonary vasculature)
2. Lung parenchymal disease (MAS, pneumonia/sepsis)
3. Abnormal transition at birth (TTN, RDS, perinatal asphyxia)
4. Congenital lung malformations (congenital diaphragmatic hernia, pulmonary hypoplasia)

• Treat underlying etiology
• Optimize oxygenation and ventilation (avoid overdistention; monitor preductal SpO2)
• Inhaled nitric oxide (iNO): best-studied agent; clear evidence in term and late preterm infants
• Adjuvant pulmonary vasodilators: sildenafil, bosentan, milrinone, prostacyclin (in selected cases)

6. Pneumothorax

• Occurs in 1-2% of normal newborns; higher with underlying RDS, MAS, or pneumonia
• Associated with use of high ventilatory pressures
• If tension pneumothorax suspected: needle thoracostomy and/or chest tube placement
• Monitor in NICU

7. Apnea of Prematurity

• Respiratory pause >20 seconds, or shorter pause with cyanosis, pallor, hypotonia, or bradycardia <100 bpm
• Types: central (no diaphragmatic activity), obstructive (upper airway), or mixed
• Occurs in most infants born at <28 weeks, ~20% at 34 weeks, <10% beyond 34 weeks
• Typically resolves by 34-36 weeks postmenstrual age
• Treatment: caffeine citrate (first line), CPAP, mechanical ventilation for severe cases

Summary of Key Points

• RDS (hyaline membrane disease) is the most common cause; fundamentally a surfactant deficiency disease of prematurity. Antenatal steroids and exogenous surfactant are the cornerstones of prevention/treatment.
• TTN is self-limiting (resolves within 72 hours) and is a diagnosis of exclusion.
• MAS carries risk of severe PPHN and may require iNO or ECMO.
• Neonatal pneumonia (most often GBS) radiographically mimics MAS and TTN.
• PPHN can complicate any of the above conditions and is treated with iNO.
• Long-term sequelae of prematurity and RDS management include BPD and retinopathy of prematurity, both reduced by modern ventilatory and oxygen management strategies.

Birth Asphyxia in the Newborn

Definition & Causes

• Cord prolapse or coiling of the umbilical cord around the neck
• Abruptio placentae or placenta previa
• Maternal hypotension or hemorrhage
• Prolonged or obstructed labor
• Uterine rupture
• Breech presentation, forceps delivery
• Maternal fever or infection

Pathophysiology

• Oxygen deprivation -> failure of Na+/K+-ATPase pumps -> cellular energy failure
• Glutamate release -> excitotoxicity -> neuronal depolarization
• Intracellular Ca²+ accumulation -> activation of destructive enzymes
• Immediate cell death (necrosis) in the most vulnerable regions

• Even after restoration of circulation, a second wave of neuronal death occurs
• Free radical generation, inflammatory cytokine release, mitochondrial dysfunction
• Apoptotic cell death ensues
• This latent phase is the therapeutic window for intervention (hypothermia acts here)

• Term infant: deep grey matter (basal ganglia, thalamus), parasagittal cortex, hippocampus
• Preterm infant: periventricular white matter (periventricular leukomalacia)

Clinical Assessment

The Apgar Score

• 7-10: Normal
• 4-6: Moderate depression
• 0-3: Severe depression

Hypoxic-Ischemic Encephalopathy (HIE) - Staging (Sarnat Classification)

Diagnosis Criteria for Therapeutic Hypothermia

1. Blood gas criteria: Cord gas or arterial blood gas in the first hour of life showing:
   • pH <7.0 OR base deficit >16 mEq/L
2. If pH 7.01-7.15 or base deficit 10-15.9, additional criteria required:
   • 10-minute Apgar score ≤5 OR
   • Need for assisted ventilation at birth for ≥10 minutes AND
   • Evidence of moderate to severe encephalopathy on clinical exam (Sarnat)

Neonatal Resuscitation (NRP Algorithm)

Neonatal Resuscitation Algorithm (Rosen's Emergency Medicine)

1. Warm, dry, stimulate (flick soles, rub back), position airway, clear secretions if needed
2. If term gestation + good tone + breathing/crying → routine care with mother
3. If apnea/gasping OR HR <100 bpm → PPV + SpO2 monitor + consider ECG
4. If HR still <100 bpm → check chest movement, corrective ventilation steps, ETT or laryngeal mask
5. If HR <60 bpm despite adequate ventilation → intubate, chest compressions (3:1 ratio), 100% O2, ECG monitor, emergency umbilical vein catheter (UVC)
6. If HR persistently <60 bpm → IV epinephrine 0.01-0.03 mg/kg; consider hypovolemia (volume 10-20 mL/kg NS or PRBCs), consider pneumothorax

• Preterm resuscitation: start with blended 30% O2 (or room air), not 100% O2
• Avoid rapid volume infusion in preterm infants (risk of intraventricular hemorrhage)
• Skin color is a poor indicator of oxygenation in the first minutes of life - use pulse oximetry

Therapeutic Hypothermia (Cooling Therapy)

• Target temperature: 33.5°C to 34.5°C (whole-body or selective head cooling)
• Must be initiated within 6 hours of birth (before secondary energy failure peaks)
• Duration: 72 hours, followed by slow rewarming over at least 4 hours
• Mechanism: reduces cerebral metabolic rate, limits excitotoxicity, free radical generation, and apoptosis during the latent phase
• Evidence: multiple RCTs (TOBY, CoolCap, NICHD, INFANT COOLING) confirm reduced mortality and improved neurologic outcome at 18 months

Multi-organ Effects of Perinatal Asphyxia

Long-term Sequelae

• Cerebral palsy (spastic diplegia, spastic quadriplegia, extrapyramidal/athetoid forms)
• Epilepsy
• Cognitive delay and intellectual disability
• Hearing and visual impairment
• Microcephaly

• Periventricular leukomalacia (most common, 42%) - associated with spastic diplegia
• Basal ganglionic/thalamic injury (13%) - associated with extrapyramidal CP
• Cortical-subcortical lesions - associated with spastic quadriplegia
• Focal infarcts (7%) - associated with hemiplegia

Recent Evidence