Discussion:
The respiratory course of premature infants in the NICU plays a
significant role in determining oral feeding success. Preterm infants
<30w GA are at increased risk for pulmonary complications,
especially BPD.7,8 BPD can lead to higher respiratory
support requirements, delaying the initiation of oral feeding
attempts.9 Gianni et al demonstrated that PMA
at the time of achieving full oral feeding was significantly earlier as
gestational age or birth weight increased. BPD was significantly
associated with an older PMA at full oral feeding.8Our data supports this conclusion as well. We showed that BPD is
associated with an older PMAff, the most important variable in our
original model describing risk for GT placement.4
Premature infants do not have mature suck-swallow-breathe coordination,
limiting their ability to orally feed. Preterm infants are prone to
initiate swallowing at unsafe phases of the respiratory cycle,
increasing the risk of desaturation and aspiration.10The earliest successful synchronization of sucking, swallowing,
respiration and esophageal function has been reported to occur in
premature infants sometime between 32-34w PMA.11 The
development of this coordination is further delayed in premature infants
with BPD, who often require higher levels of respiratory support for
longer periods of time.12,13 Positive pressure support
has been suspected to inhibit closure of the larynx and interfere with
the swallowing reflex.2,3 Infants on nasal CPAP have
been shown to have increased risk of aspiration during oral feeds,
likely due to interfering signals from the positive
pressure.11
In our original model development, although every respiratory variable
was associated with the GT/no GT outcome in univariate analysis, only
exposure to HFV remained in the final model.4 We
suspected that respiratory status is highly correlated to the most
significant variable in the model, PMAff, and now provide evidence
supporting that hypothesis. However, this conclusion may be confounded
because there is variability amongst NICUs regarding when infants may or
may not receive oral feeding attempts.14 For instance,
our NICU policy restricted oral feeding attempts to infants who were on
nasal cannula flow < 0.5 LPM. This fact provides an
interesting area for further study. Additionally, this suggests we
should be more thoughtful about when we introduce or withhold oral
feeding for infants requiring high respiratory support during their NICU
course. There are likely critical periods of neurodevelopment during
which we need to engage neural and muscular pathways for oral feeding;
if this window of time is missed, it may become much more difficult for
later development of this skill.15
We noted a significant gender difference in infants requiring a GT (63%
male) versus infants not requiring a GT (45% male) in the original test
cohort. This was significant in the test cohort on univariate analysis
but did not remain in the multivariate model. In the separate validation
cohort, this was no longer significant (57% vs. 49%). However, when
the two cohorts are combined, the p value is again significant: 47/78
(60%) males in the GT infants, vs. 148/313 (47%) in the non-GT cohort,
P = 0.040 by chi-square. Two recent studies reviewing GT trends by
collecting retrospective data across multiple hospitals reported no
gender differences in infants who received GTs (n = 333 and 360).
Studies have shown that males are more likely to develop BPD and more
likely to have more severe BPD and this may explain the sex difference
in GT outcome.16 Since this finding seems quite
variable, it should be examined in larger data sets to assess its
reproducibility.
In conclusion, our data show how NICU respiratory course affects
achieving full oral feeding. The documentation of respiratory
progression during the NICU course, showing improvement in the need for
respiratory support from day 30 of age to 32w PMA, and finally 36w PMA,
may guide us in finding an opportunity to allow more oral stimulation
and feeding during this time. One example, currently being employed at
UH Rainbow Babies & Children’s Hospital for older NICU infants with BPD
who are on HFNC, is decreasing flow to 2 LPM just for the 20-30 minutes
of an oral feeding, which has proven successful thus far (personal
communication, Dr. Monika Bhola). The unit policy is to allow oral
feeding if an infant is on ≤2 LPM. We are hoping to study this practice
as part of a quality improvement project. Are the differences among NICU
practices something that can teach us best practice? Our data offers the
impetus for those who are experts in oral feeding to help us do better.