The Definitions Of Surfaction And Surface Tension

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Surfactant Agents

I. Definitions
a. Surfactant: A surface-active agent that lowers surface tension
i. Examples
1. soap
2. detergent
b. Surface Tension: Force caused by attraction between like molecules that occurs at liquid-gas interfaces and that holds the liquid surface intact
i. Units of Measure: dynes/centimeter (dyn/cm)
1. the force required to cause a 1 cm rupture in the surface film ii. a droplet forms because a liquid’s molecules are more attracted to each other than the surrounding gas
c. LaPlace’s Law: Physical principle that describes and quantifies the relationship between the internal pressure, amount of surface tension and the radius of a drop or bubble
i. In the alveoli where there is a single air-liquid interface, LaPlace’s
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r = radius of the alveoli

II. Application to the Lung
a. Increased surface tension can cause collapse or difficulty opening the alveoli
i. Surfactant lowers the surface tension to decrease the pressure needed to open the alveoli
b. In pulmonary edema, the surface tension of the liquid allows the formation of a bubbly froth
i. Lowering the surface tension will cause the foam bubbles to collapse and liquefy

III. Clinical Indications for Exogenous Surfactants
a. Prophylactic Treatment
i. Prevention of RDS in very-low-birth-weight infants and infants with higher birth weights who have evidence of immature lungs, at risk for developing RDS
b. Rescue Treatment
i. Retroactive or “rescue” treatment of infants who have developed RDS
1. the basic problem in RDS is lack of pulmonary surfactant as a result of lung immaturity
2. increased ventilating pressure is required to expand the alveoli during inspiration, which will lead to respiratory failure

IV. Previous Surfactant Agents in Respiratory Care
a. Ethyl alcohol
i. Application
1. used for treating pulmonary edema
2. was given by nebulizer
a. 3 - 5 ml. of 30 - 50% solution ii. Mode of Action
1. alcohol lowered the surface tension of the foamy exudate, reducing it to a liquid, clearable
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Specific Exogenous Surfactant Preparations
a. Colfosceril palmitate (Exosurf Neonatal)
i. Indications
1. Prophylactic therapy of infants weighing less than 1350g birth weight
2. Prophylactic therapy of infants with birth weights greater than 1350g with evidence of pulmonary immaturity and at risk for RDS
3. Rescue treatment of infants who have developed RDS ii. Dosage
1. 5 ml/kg of the reconstituted suspension q12° X 2 - 3 doses iii. Preparation
1. available as a dry powder that is reconstituted with 8 ml sterile water prior to use iv. Administration
1. instilled directly into the endotracheal tube through a side port adapter attached to ET tube, in 2 divided aliquots
a. 1st half of dose in midline position
i. infant rotated to the right and ventilated for 30 seconds
b. 2nd half of dose in midline position
i. Infant rotated to the left and ventilated for 30 seconds
2. a single vial can treat up to a 1600 g infant
a. 5 ml/kg x 1.6 kg = 8 ml

b. Beractant (Survanta)
i. Indications
1. Prophylactic therapy of premature infants less than 1250g birth weight or with evidence of surfactant deficiency and risk of RDS
2. Rescue treatment of infants with evidence of RDS ii. Dosage
1. 4 ml/kg (100 mg/kg) of the suspension

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