Page 582 - Clinical Application of Mechanical Ventilation

548 Chapter 17

to better visualize the vocal cords and advance the ETT through the vocal cords
The vocal cord marking under direct vision. If the cords are closed, wait for them to open before attempting
on the ETT should stop at
or slightly beyond the vocal to advance the ETT. Hold the tube against the baby’s palate while removing the
cords. laryngoscope blade and stylette (if used) and securing the ETT (AAP/NRP, 2005).
If the tube has a vocal cord marking, it should be at or slightly beyond the vocal
cords. If the tube does not have a vocal cord marking, a rule to estimate the depth of
intubation is to add 6 to the body weight in kilograms (kg). For example, the depth
A rule to estimate the of ETT for a 2-kg infant should be 8 cm (6 1 2) at the lips.
depth of intubation is to
add 6 to the body weight in Listen for breath sounds over both lung fields and place a CO detector on the ETT
2
kilograms.
and verify change in color. However, a CO detector should not be used when intu-
2
bating for meconium removal. After confirming endotracheal placement, the tube is
taped securely. A chest radiograph is done to confirm the depth of ETT placement.

SURFACTANT REPLACEMENT THERAPY

It has long been understood that the primary dysfunction in respiratory distress
The primary cause of RDS syndrome (RDS) is abnormally high alveolar surface tension resulting from a lack
is surfactant deficiency.
of pulmonary surfactant. Thus it became an item of major interest in the scientific
community to develop a surfactant that can be administered to an infant to replace
surfactant: A natural phospholipid that which is lacking (Robertson & Halliday, 1998).
that lowers the surface tension of Naturally occurring surfactant is composed of several phospholipids and lipids, and
the lungs. Deficiency of surfactant
causes high surface tension in the four or more specific apoproteins. Each component appears to have its own distinct
lungs and increases the work of characteristics with regard to production, secretion, and removal (Jobe & Ilkegami,
breathing.
1993). These factors have made it difficult to produce an ideal replacement surfactant.
Approximately 90% of surfactant is phospholipid, with phosphatidylcholine
(PC) comprising 85% of the total amount. Roughly 60% of the PC is dipalmitoyl
phosphatidylcholine (DPPC). It is the DPPC that allows surfactant to lower the
surface tension of alveoli (Holm & Waring, 1993). The remaining phospholipids
are phosphatidylglycerol (PG) and phosphatidylinositol (PI). Cholesterol is the pre-
dominant neutral lipid in surfactant. The four proteins found in surfactant, given
the names of surfactant proteins A, B, C, and D (SP-A, etc.), make up 5% to 10%
of the total. While small in quantity, their presence is essential for proper activity of
pulmonary surfactant (Holm & Waring, 1993).

History

Early studies were discouraging because researchers could not find the right com-
bination of components that formed an effective surfactant. Effective dosages and
ideal method of delivery were two other questions that hindered the development
of surfactant replacement therapy.
surfactant replacement: Direct
instil lation of synthetic surfactant Early surfactants were made with DPPC and were nebulized into the trachea.
(Surfaxin) or natural surfactant This type of surfactant alone and method of delivery did not produce the desired
(Survanta, Infasurf) into the trachea.
results. Continued research and later studies of surfactant and its biochemical and
biophysical properties illustrated the important role of the other proteins and lipids.

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