++
Respiratory failure is one of the most common problems requiring
admission to the neonatal intensive care unit. Respiratory failure
is often the final result of restrictive lung disease with regional
or global alveolar collapse or consolidation. In order to achieve
optimal alveolar gas exchange, the lung needs to be inflated at
end expiration (at functional residual capacity) and have sufficient
tidal and minute ventilation to eliminate carbon dioxide.1 Under
optimal conditions, several factors help prevent the collapse of alveoli
at the end of expiration and thereby maintain an adequate functional
residual capacity. Surfactant, which is produced in the type II
cells of the lung, dramatically reduces surface tension and opposes
the tendency of alveoli to collapse when lung volume is at its lowest.
In addition, the rigidity of the chest wall opposes lung collapse.
In comparison to the adult, several factors present disadvantages
for the neonate’s capacity to maintain optimal lung volumes.
The neonatal chest is highly compliant, which limits its ability to
oppose elastic recoil and collapse during expiration and increases
the potential for the development of collapse. This problem is greatly exacerbated
in the setting of surfactant deficiency or inactivation, in which
unopposed surface tension dramatically increases the chance of alveolar
collapse during expiration. Lastly, although the small diameter
of the neonatal tracheobronchial tree generally is sufficient to provide
unimpeded airflow, further small reductions in its diameter can
dramatically increase resistance and adversely affect gas entry
and egress.
++
A hallmark of treatment for most causes of neonatal respiratory
failure is the provision of positive airway pressure.2 (See
also Chapter 102.) Application of pressure to the proximal airway
may result in several beneficial effects. Most importantly, positive
pressure opposes the tendency of end-expiratory alveolar collapse caused
by elastic recoil and high surface tension. Moreover, positive proximal
airway pressure increases the pressure differential between the
upper airway and the distal airspace during spontaneous respiratory
effort, facilitating increased bulk flow of gas down the tracheobronchial
tree. In addition, positive pressure may help to maintain adequate
patency of the airway in disease states characterized by inflammation, plugging,
or anatomic (either fixed or dynamic) narrowing of the airway.
+++
Continuous Positive Airway
Pressure (CPAP)
++
The least invasive means for consistently delivering proximal
distending airway pressure is via CPAP.3 CPAP may
be delivered via prongs, which are placed in the nose, or by a mask
affixed over the mouth and nose. Generally, CPAP is provided at
a pressure range of 4 to 8 cm H2O, with the specific level
based on the type and severity of the underlying lung disease, the
degree of inflation achieved, and the baby’s tolerance
of the therapy. Common indications for use of CPAP in the neonatal
intensive care unit include mild hyaline membrane disease, disease
or narrowing of the airways, and as a bridge to extubation in preterm
infants recovering from hyaline membrane disease.4 CPAP
may also decrease the ...