Statistical analysis
We compared illness differences between diuretic weaning groups, using
chi squared or Fisher’s exact tests for differences in proportions, and
Kruskal-Wallis tests for differences in medians. To compare our primary
outcome of duration of home oxygen therapy, we used Cox survival curves
to describe differences between diuretic weaning groups. Differences in
secondary outcomes were compared by chi-squared or Fisher’s exact tests
or Kruskal-Wallis tests. We similarly assessed whether other illness
covariates were associated with differences in duration of home oxygen
weaning. To evaluate the association between diuretics and duration of
home oxygen therapy adjusted for other illness covariates, we used a
series of Cox regression models of time to successful weaning from home
oxygen, with failure set as failure to wean by 1 year after discharge.
Model was run in steps with key covariate of diuretic management
retained at each step: first, an unadjusted comparison of diuretic
management; second, adjusted for potential NICU illness covariates that
were significantly associated in bivariable analysis with either
diuretic weaning plan or duration of home oxygen therapy; third,
adjusting for post-NICU significant covariates. Between the second and
third steps, variables associated at a p>0.2 were dropped
from the model. In the post-NICU-discharge model, emergency and
readmission encounters were retained a priori because it was
hypothesized that they significantly impacted clinical decision-making
about medication management. Variables that were not directly part of
the home oxygen weaning process, such as failed room air trials or
overnight pulse ox studies, were not included in modeling. A p value of
<0.05 was considered statistically significant for all
analyses. The institutional Review Board of Children’s Wisconsin
approved this study.