Respiratory Distress Syndrome ✅ Flashcards
What is the most common lung problem accompanying prematurity?
Respiratory distress syndrome
What can RDS lead to?
Severe respiratory failure and death
What causes RDS?
Surfactant deficiency
How does surfactant deficiency lead to RDS?
It leads to higher surface tension at the alveolar surface, difficulty in achieving adequate functional residual capacity, and interferes with the normal exchange of respiratory gases
What is the incidence and severity of RDS related to?
Inversely proportional to gestational age
Why is the incidence and severity of RDS inversely proportional to gestational age?
Because of the smaller number of functional alveoli with decreasing gestational age
Other than surfactant deficiency, what problems are there with premature infants lungs?
The airways are incompletely formed and lack sufficient cartilage to remain patent
What does the incomplete formation of airways and lack of cartilage in premature infants contribute to?
Collapse of lungs and increased airway resistance
What is the result of the higher surface tension in RDS?
Greater distending pressure is required to inflate the alveoli
What law describes the concept of higher surface tension requiring greater distending pressure to inflate the alveoli?
Laplace’s law
What is Laplace’s law?
P = 2T/r
P = pressure T = surface tension r = radius
How does the compliance of the lungs compare to that of the chest wall in a preterm infant?
The compliance of the chest wall is greater than that of the lungs
What is the result of the compliance of the chest wall being greater than that of the lungs in a newborn infant?
The lungs tend to collapse when the infant attempts to increase negative intrathoracic pressure
What functional abnormalities contribute to respiratory failure in preterm newborns?
- Decreased compliance
- Increased resistance
- Ventilation-perfusion imbalance
- Impaired gas exchange
- Increased work of breathing
What cells are involved with pulmonary surfactant?
Type 2 epithelial cells
What is the role of type 2 epithelial cells with regard to pulmonary surfactant?
They synthesise and secrete it into alevelar spaces
What is pulmonary surfactant made up of?
- Phospholipids (85%)
- Proteins (10%)
What do most of the phospholipids in pulmonary surfactant consist of?
Polyphatidylcholine (PC)
What molecule of PC is particularly important in pulmonary surfactant?
DPPC (dipalmitoyl phosphatidylcholine)
Why is DPPC important in pulmonary surfactant?
The structure of DPPC is suited to form a stable monolayer generating the lower surface tension required to prevent alveolar collapse at end-expiration
Do phospholipids alone exhibit all the biophysical properties of pulmonary surfactant?
No
What, alongside phospholipids, gives pulmonary surfactant its biophysical probelms?
The low-molecular weight surfactant specific SP-B and SP-C proteins
What is the role of SP-B and SP-C?
- Contribute to structural organisation and functional durability
- Promote rapid absorption of phospholipids at the air-liquid interface
- Account for sustained low surface tension activity after dynamic compression
What is the inheritance of SP-B deficiency?
Autosomal recessive
How severe is SP-B deficiency?
It is lethal and results in fulminant respiraotry failure
What effect does SP-C have on phospholipids?
It dramatically enhances the spread of phospholipids
How does SP-C gene mutation present?
Later in life as chronic interstitial lung disease
What other surfactant specific proteins are there
SP-A and SP-D
What is the role of SP-A and SP-D?
Play important role in defence barrier against pathogenic organisms and in recycling of surfactant
Only marginally involved in surface tension lowering ability of pulmonary surfactant
How does the total surfactant lipid pool in preterm babies compare to term infants?
10mg/kg in preterm babies, 100mg/kg in full term infants
How does the content of surfactant differ in preterm babies compared to term infants?
Lower percent of saturated phosphatidylcholine species, phosphatidylglycerol, and surfactant associated proteins
Where can exogenous surfactant preparations be derived from?
Either animal sources (bovine and porcine) or can be prepared synthetically
What do animal-derived surfactants consist of?
- More than 80% phospholipids
- Specific proteins SP-B and SP-C, but not SP-D
What are synthetic surfactants composed of?
Mainly DPPC
What are the advantages of administration of exogenous surfactant in a surfactant-deficient preterm newborn?
- Decreases minimum pressure required to open lungs
- Increases functional residual capacity and maximal lung volume
- Diminishes work of breathing
- Stabilises respiratory tract
- Improves mucociliary transport
- Prevents oedema
- Contributes to lung defence against pathogens
What is the result of increasing functional residual capacity and maximal lung volume with the administration of exogenous surfactant?
It prevents lung collapse at low pressures and end-inspiration
How is RDS diagnosed?
Using combination of clinical features, including;
- Gestational age
- Presence of respiratory distress with impaired gas exchange
- Characteristic radiographic abnormalities
What is involved in the management of RDS
- Prevention
- Exogenous surfactant replacement therapy
- Artificial respiratory support
- Adjunctive measures
- Avoidance of complications
How is RDS prevented?
Use of antenatal glucocorticoid to induce endogenous surfactant formation
In what forms can artificial respiratory support be given in RDS?
- Continuous distending pressure, such as CPAP
- Intermittent positive airway pressure ventilation through mechanical ventilator
What adjunctive measures may be used in RDS?
- Maintenance of adequate blood pressure
- Maintenance of adequate oxygen carrying capacity
- Maintenance of physiological pH
What complications should be avoided in RDS?
- Air leaks
- Bronchopulmonary dysplasia
Is exogenous surfactant replacement given prophylactically or as rescue therapy?
Can be either
What stages can the clinical response to surfactant therapy be divided into?
- Acute treatment response
- Sustained response to initial dose
- Continued response to initial dose
When does the acute treatment response to surfactant therapy occur?
Within 10 minutes
What does the acute treatment response to surfactant therapy result from?
The biophysical properties of surfactant to distal lung areas
What is usually the first clinical response to surfactant instillation?
An improvement in oxygenation
When does the second stage of response to surfactant therapy (sustained response to initial dose) occur?
Hours post administration
What does the sustained response to surfactant therapy result from?
- Improving lung mechanics
- Recycling of of surfactant components from air spaces into type 2 cells
How are surfactant components recycled in the sustained response to surfactant therapy?
Lipids are, in part, diverted into lamellar bodies for re-secretion
How does the recycling rates of surfactant therapy in pre-term infants compare to that of term?
They are higher in preterm lungs, as high as 80-90%
Does the recycling of surfactant components guarantee that only one dose of surfactant will be effective?
No
When will an infant receiving surfactant therapy require re-treatment?
If they are still receiving mechanical ventilation with FiO2 of more than 30-40% several hours after the first dose
What % of infants receiving surfactant therapy require re-treatment?
20-30%
What is the third stage of response to surfactant therapy?
Continued response to the initial surfactant dose
What is the continued response to the initial surfactant dose attributed to?
The long half life of surfactant components
What allows an infant with RDS to accumulate a large amount of surfactant over many daysu?
The net balance of slow synthesis, secretion, metabolism, and clearance of surfactant and its components
What are the advantages of surfactant therapy in preterm infants with RDS?
Reduces neonatal mortality and complications such as pneumothoraces
What is the limitation of surfactant therapy for preterm infants with RDS?
None of the trials or meta-analysis have shown any benefit in terms of reducing incidence of BPD
