RDS

Definition

• • Syndrome in premature infants caused by developmental insufficiency of surfactant production and structural immaturity in the lungs

Risk Factors

• • Prematurity

  • Male

  • Hypothermia

  • Maternal diabetes

  • Cesarian

  • Perinatal asphyxia

  • Multiple pregnancy

  • FHx of RDS

Differential diagnosis

• Anemia, Acute

• Aspiration Syndromes

• Gastroesophageal Reflux

• Hypoglycemia

• Hypothermia, Circulatory Arrest and Cardiopulmonary Bypass

• Pneumomediastinum

• Pneumonia

• Pneumothorax

• Polycythemia

• Sudden Infant Death Syndrome

• Transient Tachypnea of the Newborn

Epidemiology

• • Affects about 1% of newborn infants and is the leading cause of death in preterm infants

  • Incidence decreases with advancing gestational age

    • About 50% in babies born at 26–28 weeks

    • About 25% at 30–31 weeks

    • > 90% at 28 weeks?

    • 50% at 32 weeks?

  • More frequent in infants of diabetic mothers and in the second born of premature twins

Aetiology

• • Surfactant deficiency

  • => full lung closure on expiration

Clinical features

• tachypnea

• tachycardia

  • chest wall retractions (recession)

  • expiratory grunting

  • breath against a partially closed glottis

  • flaring of the nostrils

  • cyanosis

  • Progression over 2-3 days

    • More O2 required

    • Either => death or recovery by 72 h

Pathophysiology

• • Deficit in surfactant

    • Complex system of lipids, proteins and glycoproteins

    • Produced in specialized lung cells called Type II cells or Type II pneumocytes

    • Packaged by the cell in structures called lamellar bodies, and extruded into the air-spaces

      • Unfold into a complex lining of the air-space

    • Reduces the surface tension of the fluid that lines the air-space

      • Surface tension is responsible for approximately 2/3 of the elastic recoil forces

    • Prevents the air-spaces from completely collapsing on exhalation

    • Allows re-opening of the air-space with a lower amount of force

  • Without adequate amounts of surfactant, the air-spaces collapse and are very difficult to expand

  • Lungs are characterized by collapsed air-spaces alternating with hyper-expanded areas, vascular congestion and, in time, hyaline membranes.

    • Hyaline membranes are composed of fibrin, cellular debris, red blood cells, rare neutrophils and macrophages

    • Appear as an eosinophilic, amorphous material, lining or filling the air spaces and blocking gas exchange

  • As a result, blood passing through the lungs is unable to pick up oxygen and unload carbon dioxide

  • Structural immaturity, as manifest by decreased number of gas-exchange units and thicker walls, also contributes to the disease process

  • Therapeutic oxygen and positive-pressure ventilation, while potentially life-saving, can also damage the lung

Investigations

• • Fetal lung maturity may be tested by sampling the amount of surfactant in the amniotic fluid, obtained by inserting a needle through the mother's abdomen and uterus

    • Several tests are available that correlate with the production of surfactant

      • Lecithin-sphingomyelin ratio ("L/S ratio")

        • less than 2:1 => fetal lungs may be surfactant deficient

      • Presence of phosphatidol glycerol (PG)

        • presence of PG usually indicates fetal lung maturity

    • Surfactant/albumin (S/A) ratio

      • • S/A ratio <35 indicates immature lungs, between 35-55 is indeterminate, and >55 indicates mature surfactant production

  • Blood gases

    • respiratory and metabolic acidosis along with hypoxia

  • CXR

  • Pulmonary mechanics testing (PMT)

    • Reduced complience

Management

http://eng.mapofmedicine.com/evidence/map/respiratory_distress_syndrome1.html

a) conservative

b) medical

• • Pre-term glucocorticoids speed the production of surfactant

  • Ventilation

    • High frequency oscillatory ventilation

    • Continuous positive airway pressure (CPAP)

    • High-speed mechanical ventilation (> 40 breaths per min)

  • Oxygen

  • Intravenous fluids to stabilize the blood sugar, blood salts, and blood pressure

  • Extracorporeal membrane oxygenation (ECMO)

    • Not appropriate for premature babies

  • Exogenous surfactant

    • Pig better than synthetic

c) surgical

Prognosis

• • Most common single cause of death in the first month of life of the developed world

  • Complications:

    • metabolic disorders (acidosis, low blood sugar)

    • secondary end-organ disorder due to hypoxia

    • secondary bacterial pneumonia

    • pneumonia

  • patent ductus arteriosus

    • low blood pressure

    • chronic lung changes

    • intracranial hemorrhage.