Respiratory Distress Syndrome in the Infant

1. Epidemiology
   1. Most common cause of premature Newborn Respiratory Distress
   2. Incidence: Affects 24,000 infants annually in the United States
   3. Prevalence varies by gestational age
      1. Gestational age <28 weeks: Affects a majority of newborns
      2. Gestational age 28-34 weeks: Affects <33% of newborns
      3. Gestational age >34 weeks: Affects <5% of newborns
2. Pathophysiology
   1. Inadequate pulmonary surfactant (normally lowers alveolar surface tension)
   2. Leads to Atelectasis (increased alveolar surface tension, decreased compliance)
   3. Pulmonary vasculature responds with Vasoconstriction
   4. Lung hypoperfusion results in lung tissue ischemia
   5. Hyaline membranes form from epithelial cell destruction and infiltration of fluid and protein
3. Risk factors
   1. Immature lung development at delivery
      1. Premature Infant (see Prevalence based on gestational age above)
      2. Maternal Diabetes Mellitus (confers 6 fold increased risk)
      3. White race
      4. Family History of RDS in siblings
      5. Male gender
   2. Inadequate surfactant
      1. Premature infant with perinatal asphyxia
         1. Antepartum Hemorrhage
            1. Abruptio Placentae
            2. Placenta Previa
         2. Second born Twin Gestation
      2. Cesarean birth without labor
4. Signs: Onset shortly after birth
   1. Tachypnea
   2. Nasal flaring
   3. Grunting
   4. Central cyanosis
   5. Intercostal muscle retractions
   6. Hypoxia
5. Labs
   1. Antepartum Assessment
      1. Fetal Lung Maturity Assessment
   2. Newborn Assessment
      1. Swallowed Amniotic fluid Shake Test
6. Imaging: Chest XRay
   1. Hypoinflated lungs
   2. Homogenous opaque infiltrates (Reticulogranular pattern, "ground glass" appearance)
   3. Air Bronchograms (contrast of air-filled Bronchi against airless lung tissue)
7. Management: General
   1. See Respiratory Distress in the Newborn
   2. See Newborn Resuscitation
   3. Artificial Surfactant Replacement (Exosurf)
   4. Oxygen Delivery
   5. Body temperature control
   6. Adequate hydration and nutrition
   7. Neonatal Sepsis Evaluation
      1. Administer antibiotics for 48 hours
8. Management: Continuous Positive Pressure Airway Pressure
   1. Indications
      1. FIO2 0.3 - 0.5 required to maintain PaO2 50-80 mmHg
   2. Delivery device
      1. No abdominal distention
         1. Nasal canula
         2. Face mask
      2. Abdominal distention from hyperinflation
         1. Nasopharyngeal tube
         2. Endotracheal Tube
   3. Technique
      1. Starting Pressure: 5-7 cm H2O
      2. Titrate pressure by 1-2 cm H2O to PaO2 and effort
      3. Maintain Adequate Flow: 5-10 L/min
   4. Weaning
      1. Reduce FIO2 by 0.05 steps until FIO2 <0.40
      2. Reduce CPAP by 1-2 cm H2O (follow Arterial Blood Gas)
      3. Discontinue CPAP when pressure 4-6 cm H2O
9. Management: Mechanical Ventilation
   1. Indications
      1. PaCO2 >55mmHg
      2. PaO2 <50 mmHg despite FIO2 >0.6
   2. Initial Respirator Settings
      1. Continuous-flow
      2. Pressure-limited
         1. Identify pressure settings with Anesthesia Bag
            1. Use manometer to measure pressures required
         2. Peak inspiratory pressure: 20-25 cm H2O
         3. Positive End-Expiratory Pressure (PEEP): 4-6 cm H2O
      3. Time-cycled
         1. Respiratory frequency: 20-30 breaths per minute
         2. Inspiratory duration: 0.4 to 0.6 second
      4. FIO2: 0.5 to 1.0
   3. Maintenance
      1. Maintain PaCO2: 45-60 mmHg
      2. Follow Arterial Blood Gas
         1. Every 4 to 6 hours
         2. Following every respirator setting change by 15 min
   4. Weaning
      1. Lower inspiratory pressure by 2 cm H2O steps to 30
      2. Lower FIO2 by steps of 0.05 to 0.5-0.6
      3. Lower inspiratory pressure by 1-2 cm H2O steps to 20
      4. Lower PEEP to 5 cm H2O
      5. Slowly decrease FIO2 to 0.40 in steps
      6. Lower respirator rate by 2-4 bpm steps to >8 bpm
10. Prevention
    1. Prenatal Corticosteroids
11. Complications: Short-term
    1. Air Leak
       1. Pneumothorax
       2. Pneumomediastinum
       3. Interstitial Emphysema
    2. Nosocomial infection
    3. Intracranial Hemorrhage
    4. Patent Ductus Arteriosus
       1. Associated with Pulmonary Hypertension
12. Complications: Long-term
    1. Bronchopulmonary Dysplasia (5-10%)
    2. Recurrent Wheezing through childhood and more complicated Asthma Exacerbations
    3. Retinopathy of Prematurity
    4. Neurologic Impairment
13. Reference
    1. Cloherty (1991) Neonatal Care, Little Brown, 188-95
    2. Hermansen (2007) Am Fam Physician 76(7):987-94