2. Basic Physics : Surface Tension
Attractive forces among liquid molecules are
responsible for phenomena of surface tension.
Each molecule is pulled equally in the
inside direction.
Thus, SPHERICAL SHAPE of water
molecule is seen.
3.
4. The lung alveoli are coated with surfactant molecules.
Thus, preventing collapse on expiration and reducing
pressure needed for next inspiration.
Hydrophobic
head
Hydrophillic
tail
5. Lipids form a monolayer at the air-water interface
Surface tension decreases as lipid monolayer is compressed
9. Stable alveolar volume depends
on a balance between:
1) Surface tension at the liquid-gas
interface.
2) Recoil of tissue elasticity.
10. Pulmonary Surfactant
Surface active lipoprotein
complex formed by Type
2 alveolar cells.
Contains both proteins
and lipids. Thus has both
hydrophilic and
hydrophobic regions.
13. How it works…???
Starts at the terminal sac stage of lung development
the Type 2 cells.
At 20wk gestation, the lamellar bodies appear in
cytoplasm.
Lamellar bodies are secreted by exocytosis into the
surface water layer lining the alveolar airspace.
Here, surfactant forms a meshwork of tubular
myelin.
15. Half life of alveolar
surfactant is 5-10 hrs
after secretion.
Broken down by
macrophages and/or
reabsorbed into the
lamellar bodies.
16. Functions of surfactant
Decreases the surface tension.
To promote lung expansion during inspiration.
To prevent alveolar collapse and loss of lung volume at
the end of expiration.
Facilitates recruitment of collapsed alveoli.
18. Why Preterms..????
TERM BABIES : have storage pool of
approximately 100 mg/kg of surfactant at birth.
PRETERM BABIES : have a storage pool of
approx. 4-5 mg/kg surfactant at birth.
19. Deficiency of surfactant
Progressive Atelectasis.
Loss of functional residual capacity.
Alterations in ventilation perfusion ratios.
Uneven distribution of ventilation.
20. Role of Antenatal Corticosteroids
Stimulation of developmentally regulated gene expression and physiologic
functions resulting in lung maturation.
Accelerate development of Type1 & Type2 pneumocytes, leading to structural
and biochemical changes that improve both lung mechanics (max lung volumes,
compliance) and gas exchange.
Induction of Type 2 pneumocytes increases surfactant production by inducing
enzyme responsible for surfactant proteins and phospholipid synthesis.
Enhances the neonatal response to postnatal surfactant administration.
21. Role of Antenatal Corticosteroids (cont…)
Other effects that help in lung fluid resorption :
1. Induction of pulmonary beta receptors which play a role in surfactant
release and absorption of alveolar fluid.
2. Induction of fetal lung antioxidant enzyme.
3. Upregulation of gene expression for the epithelial Na+ channel , which is
important for the absorbtion of lung fluid after birth.
22. Which steroid to use…???
The steroids used are generally Betamethasone or Dexamethasone.
They are identical biologically and readily cross the placenta.
They have little mineralocorticoid activity and are relatively weak in immune
suppression.
Dosage recommended :
2 doses of Betamethasone 12mg given 24 hrs apart
OR
4 doses of Dexamethasone 6mg given 12 hrs apart.
23. The lung alveoli are coated with surfactant molecules which act by reducing
the surface tension at the fluid-air interface.
Thus, preventing collapse on expiration and reducing pressure needed for
next inspiration.
The introduction of corticosteroids for fetal lung maturity in patients at risk of
preterm labor was a major milestone in reducing the neonatal morbidity and
mortality from RDS.
Studies have proved that antenatal steroids do not harm the health of the
mother.
Take Home messages……..!!!!!
24. Take Home messages……..!!!!!
Betamethasone and Dexamethasone are the steroids of choice.
Recommended dosages are :
2 doses of Betamethasone 12mg given 24 hrs apart
OR
4 doses of Dexamethasone 6mg given 12 hrs apart.
Efforts should be made to ensure that a single course is given at the most
beneficial time for the fetus rather than exposing the women and their fetuses
to multiple courses.
The possibility of ongoing long term harm need further evaluation.
