Statistical analysis
We compared the distribution of pre-discharge pCO2 between the NICU and
referral groups. We then compared differences between pre-discharge pCO2
by NICU variables; we repeated these comparisons using 36-week pCO2 for
the NICU group. Similarly, we compared differences between pCO2 and
outcomes. For all bivariable comparisons, we used sign-rank or
Kruskal-Wallis tests, as appropriate. For the primary outcome of
respiratory readmissions, we evaluated the association between pCO2 and
readmission before and after adjustment for other NICU illness
covariates. We chose illness covariates for inclusion in the model based
on both bivariable analysis and the clinical possibility that they could
impact the association between pCO2 and readmission; these included
gestational age, BPD severity, ductus arteriosus ligation, and diuretic
use 12,13. To further describe our secondary outcome
of duration of home oxygen use, we considered both corrected gestational
age at discontinuation of home oxygen in categorized groups, as well as
a survival curve of weeks post-NICU discharge on home oxygen. For all
analyses, p value of <0.05 was considered statistically
significant. This study was approved by the Institutional Review Board
of Children’s Wisconsin.