Newborn Respiratory Distress Syndrome Flashcards
Major factors in the pathophysiology of RDS
- Surfactant Deficiency
- Decreased alveolar surface area
- Increased small airways
- Presence of ductus arteriosus
- Decreased FRC and lung compliance
- Increased pulmonary vascular resistance
- V/Q mismatch
- Pulmonary edema that is rich in protein and dying epithelial cells
Respiratory Distress Syndrome
- Disorder of prematurity
- Prevalence: 20,000-30,000 newborns affected each year or about 1% of pregnancies(USA)
- Inversely related to gestational age and birth weight
- <28 weeks: 60-80% occurrence
- 32-36 weeks: 15-30% occurrence
Surfactant in RDS
Surfactant production depends on both the relative maturity of the lung and the adequacy of fetal perfusion.
In preterm infants, adequate amounts of surfactant are present in the lung; however, the surfactant is trapped inside type II cells. In infants with RDS, type II cells do not release adequate amounts of surfactant.
- The surfactant that is released is incompletely formed, so it does not make tubular myelin and does not decrease alveolar surface tension.
- Because the surfactant molecule in the alveolus is structurally abnormal, the type II cells and alveolar macrophages have more rapid uptake for recycling. Thus, there is a qualitative deficiency of alveolar surfactant.
Maternal Factors that Impair fetal blood flow
Abruptio placentae and maternal diabetes, which may lead to RDS.
The decrease in surfactant results in
- A qualitative decrease in surfactant increases alveolar surface tension forces, which causes alveoli to become unstable and collapse and leads to atelectasis and increased work of breathing. The increased surface tension draws fluid from the pulmonary capillaries into the alveoli.
- In combination, these factors impair oxygen (O2) exchange and cause severe hypoxemia. The severe hypoxemia and acidosis increase pulmonary vascular resistance (PVR). As pulmonary arterial pressure increases, extrapulmonary right-to-left shunting in- creases, and hypoxemia worsens. Hypoxemia and acidosis also impair further surfactant production.
Steroid Administration for ARDS
- Steroids given before birth (antenatally) have been shown to mature surfactant function in the fetus, decrease the severity of RDS, and improve outcomes
RDS Clinical Manifestations
1st signs of distress will appear right after birth
RDS Clinical Manifestation
- Tachypnea is normally the first sign and will be followed with worsening retractions, paradoxical breathing, nasal flaring, and grunting (to maintain FRC)
How do Retractions Appear
- Retractions have a See-Saw appearance: Abdomen protrudes as the chest is pulled in
Chest radiograph for ARDS
- A definitive diagnosis of RDS usually is made with chest radiography
- Diffuse, hazy, reticulogranular densities with the presence of air bronchograms with low lung volumes are typical of RDS.
- The reticulogranular pattern is caused by aeration of respiratory bronchioles and collapse of the alveoli.
- Air bronchograms appear as aerated, dark, major bronchi surrounded by the collapsed or consolidated lung tissue.
CXR “Stages” for RDS
Stage I RDS with fine, diffuse reticulogranular pattern over the lung fields
Stage II RDS reveals a denser lung, with the presence of air bronchograms within the heart border.
Stage III RDS shows increased density and the presence of air bronchograms beyond the heart border.
Stage IV RDS, termed “whiteout,” infant with severe disease complicated by pulmonary edema. The view of the heart border and edge of the diaphragm is obliterate
prevntion of RDS
- Delayed premature delivery with the use of tocolytics (weak evidence that they work
- Tocolytics will delay birth
- Promote the surfactant production with the use of steroids (bethamethasone)
Betamethasone
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Betamethasone: A corticosteroid used to stimulate lung maturation in fetal lungs
- Clinically proven to reduce perinatal mortality in RDS
- Treatment should consist of two 12mg doses of betamethason given IM 24 hours apart, or four 6mg doses given IM 12 hours apart.
- Due to insufficient data, repeated courses of corticosteroids should not be used routinely
- Pregnant women between 24 and 34 weeks’ gestation who are at risk of preterm delivery within 7 days
Strategies for Surfactant Therapy
- Prophylactic or preventative
- Surfactant is administered at the time of birth of shortly thereafter to neonates who are high risk for developing RDS
- <32 weeks gestational age
- Low birth weight(<1300g)
- L:S ratio < 2:1
- Surfactant is administered at the time of birth of shortly thereafter to neonates who are high risk for developing RDS
- Rescue or therapeutic
- Surfactant is administered after the initiation of mechanical ventilation in neonates with confirmed RDS
RDS CPAP THerapy
- Continuous positive airway pressure (CPAP) and positive end expiratory pressure (PEEP) are the traditional support modes used to manage RDS.
- Unless the infant’s condition is severe, a trial of nasal CPAP is indicated (4 to 6 cm H2O).
- For CPAP your 5 is normal but the 8 is high
Indication for Mechanical Ventilation with RDS
- Mechanical ventilation with PEEP should be initiated if oxygenation does not improve with CPAP or if the patient is apneic or acidotic.
- pH< 7.2 and PaCO >60 indication is the indication for mechanical ventilation
Aim of Mechanical Ventilation
The aim of mechanical ventilation for RDS is to prevent lung collapse and maintain alveolar inflation. In severe RDS, collapse of alveoli with every breath necessitates very high reinflation pressure. To prevent the need for this high reinflation pressure, use of end-tidal pressure is necessary.
relationship between arterial partial pressure of carbon dioxide (PaCO2) and functional residual capacity (FRC)
- Because of the relationship between arterial partial pressure of carbon dioxide (PaCO2) and functional residual capacity (FRC), PaCO2 is lowest when PEEP is used to optimize FRC. The time constant of the lungs in RDS is short, so the lung empties very quickly with each ventilator cycle.
- If alveolar ventilation is inadequate, either peak inspiratory pressure or rate should be increased. For minimizing the possibility of volutrauma, the peak inspiratory pressure should be kept less than 30 cm H2O for larger premature infants, and even lower peak inspiratory pressure is indicated for more immature infants.
What is RDS caused by?
Immaturity of the lungs.
What is the reason for immaturity of the lungs?
Lack of surfactant.
What causes low alveolar compliance?
A decrease in surfactant.
What is the biggest problem with RDS?
Surfactant deficiency.
What is known as lung tissue underdevelopment?
Lung hypoplasia.
