Surfactant Flashcards
Surfactant Agents
uSurface active agents (Surfactants) that are designed to alter the surface tension of pulmonary secretions
Surfactant agents (also referred to as detergents) purpose to reduce surface tension much like soap and other detergents.
Units – dyn/cm indicating the force required to cause a 1 cm rupture in the surface film
Surface Tension
Is a force caused by attraction between like molecules that occur at a gas-liquid interface
These forces are present and must be overcome to inflate the alveolus
The units of measurement are dynes/cm
La Places Law
Physical principal that describes the relationship between the internal pressure of a drop or bubble, the amount of surface tension and the radius of the drop or bubble
In the alveoli with a single air-liquid La Place’s Lae says:
Pressure= (2 x Surface Tension)/ Radius
The greater the surface tension the greater the compressing forces inside the alveolus, which can callapse or result in difficult inflation
Because an alveolus has a liquid lining, surface tension forces apply.
Increased surface tension = > compressing force = collapse or difficulty opening the alveolus.
Surfactant
Surfactant will begin to develop in Type 2 alveolar cells at 24-34 weeks gestation
Surfactnt is composed of phospholipids, lipids and proteins. With the main lipid being dipalmitoylphosphatidylcholine (DPPC)
Surfactant reduced the surface tension at the liquid gas interface in the alveoli
Surfactant is stored in the lamellar bodies in the cytoplasm of AT2 cells
100mg/kg in term infants
4-5 mg in preterm infants
½ life of 5-10 hours
Reabsorbed into the AT 2 cells (up to 90% of DPPC recycled)
Exogenous Surfactants
Exogenous (outside the patient’s own body) surfactants are used to replace the deficient pulmonary surfactant of the premature newborn with RDS
Composition of Pulmonary Surfactant
Mixture of lipids (90% with mostly DPPC:
Depalmitoylphosphatidylcholine (Lecithin) and sphingomyelinand others with 10% proteins - 20% of these proteins are surfactant specific proteins produced by alveolar type II cells
The first surfactant, EXOSURF, was created by Dr. Clements and released world wide while still experimental in 1989
How Does Surfactant Work
Surfactant lowers surface tension and decreases the amount of pressure and inspiratory effort to reexpandthe alveoli during inspiration
Exogenous Surfactant ► Decreased Surface Tension, Increased Compliance, Decreased WOB
A key feature of surfactant production that is the basis for the success of replacement therapy is the recycling in surfactant production
Most surfactant 90% to 95% is taken back into the alveolar type II cell reprocessed and re-secreted
Recycling of Surfactant
Recycling of the surfactant is what allows exogenous surfactant txto be successful with only 1 or 2 doses.
Exogenous Surfactant is taken back into the type II cells and becomes the surfactant pool to go through the same recycling process that endogenous surfactant goes through
Clinical Indications for Surfactant Use:
- Prevention of RDS in very low birth weight infants
- Prevention of RDS in other infants with evidence of immature lungs
- Retroactive or rescue treatment of infants with RDS
- Prophylactic use in extreme premature infants
- Basic problem in RDS is lack of pulmonary surfactant
- caused by lung immaturity
- The result is high ST forces and increased ventilating
- pressures to inflate alveoli
- The high pressures required to pop open alveoli to inflate them cause damage
Common Surfactants in Canada
Bovine Lipid Extract Surfactant (BLES®)
Beractant(Survanta®)
BLES
Natural animal derived surfactant
Made by lavagingnatural bovine lung extract mixed with DPPC, and agents to reproduce natural surfactant
Contains phospholipids and surfactant specific proteins SP-B, SP-C
Consists of 27 mg of phospholipid/mL
Most common in Calgary – is kept frozenor refrigerated
Rewarm to min of room temp no greater than 37C – read from monograph
Bles has lower viscosity and high protein concentration which allows for a rapid distribution
BLES Indication of Use
Rescue tx of NRDS/Hyaline Membrane disease
Infants with NRDS confirmed by CXR, who require mechanical ventilation, with PaO2/PAO2 of < 0.22 – BLES is to be given ASAP once oxygenation criteria met
Prophylaxis for infants < 27 weeks of age
Contraindicated in patients with active pulmonary hemorrhage
Not studied in infants < 380 grams or > 4460 grams
May be considered for the management of pulmonary hemorrhage – no RCT, some promising evidence
Some evidence for use in the second week of life of VLBW babies with clinical oxygenation deterioration – esp. if it is rapid and moderate to severe
Moderate or severe meconium aspiration syndrome
Dosing
Recommended dose is 5 ml/kg by direct tracheal instillation for 135 mg phospholipid/kg
Can repeat up to 3 times within the first 5 days of life if necessary
Beractant (Survanta)
Modified natural animal derived surfactant
Made with natural bovine lung extract mixed with DPPC,palmiticacid, and tripalmitin
Available in a 4 or 8 ml vial with a concentration of 25 mg/ml in normal saline
Contains surfactant specific proteins SP-B, SP-C
DPPC – colfoscerilpalmitate,pamiticacid and tripalmitinare used to standardize the composition of the drug preparation as well as to make it reduce surface tension more like natural surfactant
No SP-A in Survanta– the SP-A helps regulate surfactant reuptake and secretion by the alveolar type II cells.
When using weight – birth weight – dose = 4ml/kg of birth weight
Religious beliefs may preclude use of bovine or porcine products, and currently there is no synthetic surfactants available.
Beractant (Survanta)
Indication for Use
Rescue treatment of infants with RDS
Infants with RDS confirmed by CXR, who are mechanically ventilated – preferably before 8 hours of age
Useof survanta- < 600 grams and > 1750 grams (birth weight) not well studied in RCT
Beractant (Survanta)
Dosing
Recommended dose 100 mg/kg by direct tracheal instillation
Can be repeated once no sooner than 6 hours after initial dosing if evidence of respiratory distress present
Max of 4 doses
No evidence to support use of > 4 doses or giving it after 48 hours of age
Doses – not given more frequently than Q6H
Common Surfactants in the US
Infasurf (Calfactant): Modified natural bovine derived
Curosurf (Poractant): Modified natural porcine derived
Surfaxin/Aerosurf (Lucinactant): The only current synthetic surfactant being investigated at this time with an additive polypeptide to mimic natural surfactant specific proteins
Hazards and Complications of Surfactant Therapy
Should be an immediate and significant improvement in oxygenation and ventilation requirements of the infant within minutes to an hour
The infant has to be closely monitored to ensure that the pressures/volumes on the ventilator are brought down quickly as the FRC improves and pressure/volume requirements to inflate the lung decrease
Prevent barotrauma/volutrauma!
Specific Hazards:
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
Over-ventilation and hypocarbia
Apnea
Pulmonary Hemorrhage – in <700 g at birth 10% incidence
Administration
Via endotracheal tube
Direct instillation with catheter or via side-stream adapter
Surfactant Therapy Mechanism of Action
- Lack of endogenous surfactant leads to high surface tension and alveolar collapse during expiration
- Exogenous surfactat administration via ETT
- Surfactant spreads across inner walls of alveoli reducing surface tension
- Established surfant monolayer helps faciliate oxygen diffusion
