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Drug of the week- RT 101
Each week a drug will be introduced, during the pharmacology section all drugs and classifications will be discussed
Week 6- SURFACTANT
Surfactant is a complex substance containing phospholipids and a number of apoproteins. This essential
fluid is produced by the Type II alveolar cells, and lines the alveoli and smallest bronchioles. Surfactant
reduces surface tension throughout the lung, thereby contributing to its general compliance. It is also
important because it stabilizes the alveoli. Laplaces Law tells us that the pressure within a spherical
structure with surface tension, such as the alveolus, is inversely proportional to the radius of the sphere.
That is, at a constant surface tension, small alveoli will generate bigger pressures within them than will
large alveoli. Smaller alveoli would therefore be expected to empty into larger alveoli as lung volume
decreases. This does not occur, however, because surfactant reduces surface tension, more at lower
volumes and less at higher volumes, leading to alveolar stability and reducing the likelihood of alveolar
collapse. Surfactant is formed relatively late in fetal life; thus premature infants born without adequate
amounts experience respiratory problems associated with immature lungs. The baby presents with
retractions (inward movement of intercoastals on inspiration), grunting (an attempt to increase FRC with
back pressure), cyanosis, and tachypnea. Babies born with insufficient surfactant are determined to have a
disease called RDS (respiratory distress syndrome) or Hyaline Membrane Disease. Surfactant can be
distilled into the lungs following birth manually down an ETT.
Common Surfactants Used: Infasurf (synthetic), Survanta (modified natural bovine lung extract), Exosufr
neonatal, Curosurf (Pig extract)
Classification: Natural or synthetic surfactant used to treat prematurely of the lung as demonstrated by
RDS.
How it works: The active component colfosceril palmitate (dipalmitoylphosphatidylcholine) is the major
surface active component of natural lung surfactant and acts by forming a stable film that stabilizes the
terminal airways by lowering the surface tension of the pulmonary fluid lining them. The lowered surface
tension prevents alveolar collapse at end-inspiration; the hysteresis effect equalizes the distension of
adjacent alveoli and hence prevents over distension which might result in alveolar rupture and pulmonary
air leak.
Delivery Device: Through endotracheal tube, instilled with tracheal adapter, surfactant is drawn up in
syringe and instilled down ETT directly into lungs.
Doses: A dose of 5ml/kg birth weight of reconstituted Exosurf Neonatal, If the baby is still intubated, a
second equal dose should be given 12 hours later by the same route. Survanta- 4cc/Kg given initially,
second dose 2cc/Kg. Curosurf- 2.5 cc/Kg, second dose is the same; third dose is 1.25 cc/kg.
Administration of exogenous surfactants rapidly improves oxygenation and lung compliance. Following
administration, patients should be monitored so that oxygen and ventilatory support can be modified.
Administration
Administered to endotracheally intubated infants undergoing mechanical ventilation. Infants should not be
intubated solely for the administration of surfactant. The infant's airway should be cleared by suction prior
to the administration. Administered from a syringe into the endotracheal tube via the side-port on a special
endotracheal adaptor, without interrupting mechanical ventilation. The part of the endotracheal tube outside
the infant should be aligned vertically during administration. The total dose should be administered at a rate
slow enough to allow reconstituted surfactant suspension to pass into the lungs through the endotracheal
tube without accumulation. The minimum recommended time for administration of the full dose is 4
minutes. Dosing should be slowed or interrupted if the infant's skin color deteriorates, the heart rate slows,
arterial oxygen monitors indicate more than transitory depression of arterial oxygen concentration or
surfactant accumulates in the endotracheal tube.
After administration the RT should look for increased compliance and chest rise. The vent should be
adjusted appropriately so as not to cause a pneumothorax with too much pressure. Suction after 4 hours of
administration. A chest x-ray should be taken 2 hours after administration to look for improvement in RDS.