Surfactant Flashcards
What is surfactant?
Surfactant alters the surface tension of the alveoli and the resulting pressures needed for alveolar inflation. It is a surface-active agent that reduces surface tension.
What else is surfactant known as
Detergent
Without surfactant reducing surface tension what will happen in the lungs
Every breath would take a considerable amount of pressure to expand the lung, comparable to the 80 to 90 cm H2O of pressure required for a newborn’s first breath
The lung would rapidly collapse during exhalation
What are surfactant agents?
They regulate the surface tension at gas-liquid interfaces.
What is Laplace’s Law?
Physical principle describing and quantifying the relationship between the internal pressure of a drop or bubble, the amount of surface tension and the radius of the drop or bubble.
Laplace’s Law is defined as?
The higher the surface tension, the more likely the alveolus will collapse.
What is LaPlace’s law relating to an alveolus?
Pressure = (2 x Surface tension)/Radius.
What are exogenous surfactants?
They are administered to replace missing pulmonary surfactant in RDS of the newborn. Artificial Surfactant/not native to the patient.
What type of surfactant is clinically indicated for the treatment or prevention of RDS in the premature newborn?
Exogenous surfactants.
What does the term Exogenous describe in regards to surfactant?
Surfactant that is produced outside of the patients’ body.
What is the typical method for administering exogenous surfactant to infants?
By direct instillation to the airway.
Exogenous Surfactants are indicated for the treatment/prevention of?
Respiratory Distress Syndrome in newborns.
What type of patients need Exogenous Surfactant to be given as a rescue treatment?
Rescue treatment for infants who have developed RDS.
What are the indications for the use of Exogenous Surfactant?
In premature infants at risk for RDS and as a rescue agent for infants with RDS.
What type of patients can exogenous surfactant as a prophylactic preventative be given?
immature lungs and infants at risk of developing RDS.
How is exogenous surfactant given to newborns?
Placed as a liquid down the ET tube (Intratracheal).
How many doses of Exogenous Surfactant are usually needed before improvement is seen?
1-2.
When and where will surfactant be produced
Type 2 alveolar cell will begin to produce surfactant around 24 weeks gestation and will be stored in the lamellar bodies in they cytoplasm of the alveolar type 2 cells
Surfactant Composition
The surfactant produced is composed of phospholipids, lipids, and proteins
Main lipid is dipalmitoylphosphatidylcholine (DPPC)
Surfactant Reabsorption
Surfactant will be reabsorbed into the alveolar type 2 cells
Up to 90% of DPPC will be recycled
This is the basis of success for surfactant replacement therapy as the surfactant given will be reprocessed and re-secreted
Function of Surfactant
Promotes the homogeneous gas distribution during inhalation and allows a residual volume of gas to be evenly distributed throughout the lung during exhalation and maintain FRC
Lessens the WOB (oxygen consumption)
Optimizes surface area for gas exchange and ventilation perfusion matching
Optimizes lung compliance
Protects the lung epithelium and facilitates clearance of foreign material
In the absence of surfactant what happens to ventilation
In the absence of surfactant, distribution of ventilation becomes uneven, the lungs become stiff, and atelectasis ensues during exhalation
Surface Tension
Surface tension is a force which is the result of the attraction between like molecules that occurs at a gas-liquid interface
Surface tension forces are present in the alveolus and must be overcome in order to inflate the alveolus
Surfactant and Surface Tension
Pulmonary surfactant lowers the surface tension at all lung volumes and a critical function as alveolar surface area decreases during expiration
As surface tension will decrease with a decreased lung volume, alveoli will require different distension pressures when at different sizes
Small alveoli would empty into large ones and there would be an overall tendency for the lung to coalesce into a smaller number of large alveoli as lung volume diminished.
This would significantly decrease the surface area for gas exchange as well.
• Surfactant not only decreases surface tension but also reduces it to a greater degree at low lung volume, counter- acting the effects of decreasing alveolar size.
Surfactant Mechanism of Action
- Lack of endogenous surfactant leads to high surface tension and alveolar collapse during expiration
- Exogenous surfactant can be distilled down the ETT
- Surfactant spreads across the inner layer of the alveoli reducing surface tension
- The established surfactant monolayer will facilitate oxygen diffusion
Corticosteroids for pregnant women
• A single course of corticosteroids is currently recommended for pregnant women between 24 weeks and 34 weeks of gestation who are at risk of preterm delivery within 7 days.
o This may consist of betamethasone (2 doses, 24 hours apart) or dexamethasone (4 doses, 12 hours apart).
o A single rescue course may be considered if the first course was given more than 2 weeks prior in women less than 32 6/7 weeks of gestation who are likely to deliver within the next week.
• The full effect on surfactant production is present by 48 hours after the first dose.
Bovine Lipid Extract Surfactant (BLES®)
Most common surfactant used in Calgary
Kept frozen or refrigerated and then rewarmed to room temperature and no greater than 37o C
BLES has lower viscosity and high protein concentration which allows for a rapid distribution
BLES Indications
• Rescue treatment for RDS that is confirmed by CXR, require mechanical ventilation with PaO2/PAO2 of < 0.22
o BLES is to be given ASAP once oxygenation criteria met
• Prophylaxis for infants < 27 weeks of age
• Moderate or severe meconium aspiration syndrome
• Contraindicated in patients with active pulmonary hemorrhage
• Not studied in infants < 380 grams or > 4460 grams
BLES dosing
The recommended dose is 5 ml/kg given via direct instillation
Can repeat dose up to 3 times within the first 5 days of life when needed
Hazards and Complications of Surfactant Therapy can be the result of
o Dosing procedure
Large volumes of the drug will be instilled which can result in blocked gas exchange
o Therapeutic effect of the drug itself
Hazards and Complications of Surfactant Therapy
• Obstruction during instillation (airway (with debris) and physically with the fluid) leading to desaturations and bradycardia
• Increased lung compliance and FRC resulting in high PaO2
o FiO2 must be lowered if PaO2 increase to prevent over oxygenation
• Over-ventilation and hypocarbia
o As compliance improves peak pressure, baseline pressure and ventilatory rate must be adjusted to avoid overventilation leading to hypocapnia and pneumothorax
• Apnea
• Pulmonary Hemorrhage – in 700 g at birth 10% incidence
o Pulmonary hemorrhage is the only consistent pulmonary complication seen with surfactant delivery
o Not seen in infants > 700 grams.
o PH more frequent in younger, smaller, males, PDA’s
What are exogenous surfactants?
They are administered to replace missing pulmonary surfactant in RDS of the newborn. Artificial Surfactant/not native to the patient.
