Methods:
The two-year test cohort consisted of 204 infants born < 30w
GA admitted to the NICU at the Medical University of South Carolina in
2015 and 2016. The cut-off of 30w GA was derived from earlier work that
eliminated infants who received a GT for non-prematurity-related
reasons, such as congenital anomalies.4 Infants who
died before discharge or who were admitted after 7 days of age were
excluded. We collected retrospective data including demographics,
feeding, and other disease variables which are reported
elsewhere.4 Respiratory data were collected at three
time points in the original cohort: 30 days (d) of age, 32w PMA and 36w
PMA. Variables included FiO2 and mode of respiratory
support: none, low-flow nasal cannula (NC), heated humidified high-flow
NC (HFNC), continuous positive airway pressure (CPAP), nasal
intermittent positive pressure ventilation (NIPPV), conventional
ventilation (CV) or high frequency jet or oscillatory ventilation (HFV),
used as a rescue measure. We also collected total ventilator days, total
ventilator + CPAP days, PMA at last ventilator day, PMA at last CPAP
day, and PMAff. Some infants never had an oral feeding attempt due to
severity of illness or need for tracheostomy; for this data to
contribute to the model variable, these infants were arbitrarily
assigned a PMAff of 52w, which was one week beyond the highest PMAff
found for all GT infants (51w).
The validation cohort consisted of 187 infants born <30w GA
admitted to the NICU at the Medical University of South Carolina from
2017-2018. We recorded the same demographic data for each cohort. In the
original cohort, respiratory mode at 32w PMA was the most predictive
timepoint for respiratory parameters to predict GT outcome, so
respiratory variables were only recorded at 32w PMA in the validation
cohort. Any exposure to HFV was also again recorded. In the original
model development, we did not look specifically at bronchopulmonary
dysplasia (BPD). BPD diagnoses were retroactively assigned to infants in
the original cohort using the Shennan et al definition of “oxygen use
at 36 weeks PMA.”5 This data is not available in the
original model report.
These data were collected with approval of the MUSC Institutional Human
Subjects Review Board. Normally distributed continuous data are
presented as mean ± standard deviation and P-value derived by t-test;
non-normally distributed continuous data are presented as median,
interquartile range and compared with Wilcoxon rank sum test;
categorical data are presented as number (percent) and tested by
chi-squared test. A 2 (GT) by 3 (Fio2) repeated measures ANOVA was
utilized to examine Fi02 rates by GT status over the time periods of 30
days, 32 weeks, and 36 weeks. P-values of < 0.05 were
considered significant. Pearson’s coefficient was used to test for
correlation between respiratory variables and PMAff. Univariate analyses
were performed using STATA (State College, TX) and SPSS version 25
(Armonk, NY: IBM Corp). Some figures were created using SPSS version 25.