with RDS from surfactant deficiency responds favorably
to this treatment. The need for high oxygen concentration,
and high ventilatory pressure during the early stages of
RDS have been identified as risk factors for an inadequate
response.
40,41
Whether the lack of response to surfactant is
secondary to the initial severity of the disease or to the
damage induced by short periods of aggressive ventilation
prior to or after surfactant replacement is not clear.
In contrast to the remarkable effects of surfactant ther-
apy on RDS, the incidence of other morbidities, including
intraventricular hemorrhage (IVH), sepsis, patent ductus
arteriosus, and BPD, has not been substantially altered by
surfactant therapy.
11,34
The lack of a more marked effect of surfactant replace-
ment on BPD is not too surprising, since the etiology of
BPD is multifactorial and cannot be attributed solely to
surfactant deficiency. BPD has been traditionally defined
as the need for supplemental oxygen at 28 days of life,
with chronic radiologic changes. More recently, the need
for supplemental oxygen at 36 weeks corrected postcon-
ceptional age has been used as a diagnostic criterion. Al-
though the deleterious effects of barotrauma/volutrauma
and oxygen toxicity on the surfactant-deficient lung are
paramount in the pathogenesis of BPD, a number of pre-
natal and postnatal factors have also been implicated (low
gestational age, low birthweight, male sex, white ethnicity,
patent ductus arteriosus, and prenatal and postnatal infec-
tion). Furthermore, many preterm infants develop BPD
without antecedent RDS.
7
The developmental immaturity
of the protective antioxidant systems, such as superoxide
dismutase, catalase, and vitamin E, may make the very-
low-birthweight infant particularly susceptible to oxygen
toxicity. Although individual studies have shown a de-
creased incidence of BPD, these results have not been
substantiated by meta-analysis of large, randomized tri-
als.
11,34
When different weight categories are analyzed, in
the larger infants (birthweight
Ͼ 1,250 g) in whom BPD
may be more directly associated with surfactant deficiency
and the effects of volutrauma/barotrauma, a trend toward
a lower incidence of BPD emerges.
42
With more immature
infants surviving, a significant increase in BPD might be
expected. However, the introduction of surfactant has sig-
nificantly decreased mortality from RDS, without a sub-
stantial increase in BPD rate. Data from clinical trials
suggest that more infants are surviving both with and with-
out BPD.
Ventilatory Management
The goals of ventilatory management during the early
stages of RDS are to maintain adequate oxygenation and
ventilation, while minimizing ventilator-induced lung in-
jury. The surfactant-deficient lung of the immature infant
characteristically has decreased lung compliance, increased
elastic recoil, and reduced functional residual capacity.
7
In
infants with RDS, surfactant administration rapidly im-
proves oxygenation by increasing functional residual ca-
pacity and reversing atelectasis.
43
The acute changes in
lung volume following surfactant administration increase
the surface area available for gas exchange. Though oxy-
genation improves quickly, changes in lung compliance
occur more gradually.
44 – 46
It is very important to recog-
nize this window of opportunity to appropriately wean
inspired oxygen concentration and ventilatory support, to
prevent lung injury.
Because of increased survival of more immature infants,
ventilator-induced lung injury in the form of BPD has
become a major concern for caregivers. Interestingly, a
substantial center-to-center variability in the incidence of
BPD has been reported. One could argue that, at least to
some extent, differences in ventilatory approach might be
responsible for the observed variation.
Conventional mechanical ventilation, primarily time-
cycled, pressure-limited ventilation, has traditionally been
used in neonatal intensive care units for the management
of RDS. Over the last 20 years, the technologic advance-
ment of ventilators has provided the practitioner with a
variety of new modalities, such as patient-triggered ven-
tilation, pressure-controlled ventilation, and volume-guar-
anteed ventilation. Several randomized, controlled trials
have shown encouraging short-term benefits, such as fewer
days on mechanical ventilation and less need for sedation.
However, these studies did not have the statistical power
to demonstrate a significant decrease in the incidence
of BPD.
47,48
The introduction of high-frequency ventilation (high-
frequency oscillatory ventilation [HFOV], high-frequency
jet ventilation, and flow interruption) was received with
great enthusiasm by neonatologists and therapists. These
techniques were loaded with great promise but, unfortu-
nately, several randomized trials have provided us with
mixed results in regard to pulmonary outcomes.
49 –51
Fur-
thermore, serious concerns have been raised regarding the
safety of these modalities for use in premature babies.
Wiswell et al reported more IVH and periventricular leu-
komalacia with high-frequency jet ventilation than with
conventional ventilation, and speculated that hypocarbia
might play a role.
52
A Cochrane systematic review on the
subject reinforced these concerns.
53
This was in contrast
with a meta-analysis by Clark et al of 9 studies that showed
no such an association.
54
Two recently published large,
randomized, controlled trials, one from the United King-
dom Oscillation Study Group (the UKOS trial)
55
and one
from Courtney et al in the United States,
56
showed no
difference in adverse neurological outcomes (IVH or
periventricular leukomalacia); however, results on the pri-
mary outcome, BPD, were discordant. The United States
trial
56
compared HFOV with synchronized intermittent
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