Results
Ninety-two infants were discharged from our NICU; 71 were discharged
with home oxygen. Our referral group included 54 patients discharged
from other NICUs that were seen in pulmonary clinic for home oxygen
management. Of the 125 infants evaluated in our home oxygen clinic, five
patients were lost to follow up between NICU discharge and 1 year,
leaving 120 patients as our final cohort for analysis. The median
gestational age of the cohort was 27 weeks (IQR 23-30); 56 were females
and 64 were males. The corrected median gestational age at discharge was
38 weeks (IQR 37-40) for infants with Grade 1 BPD; 43 weeks (IQR 40-46)
for infants with Grade 2-3 BPD, and 39 weeks (IQR 38-41) for infants
with BPD of unknown grade referred to our clinic from other NICUs.
The median pCO2 at NICU discharge was 55 mm Hg (IQR 51-58), with no
significant differences between the NICU group (median 55, IQR 52-59) or
the referral group (median 55, IQR 50-58; p=0.344). Only 18 infants from
either the NICU group (n= 11) or the referral group (n= 7) were
discharged home with pCO2 ≥ 60 mmHg. Table 1A displays associations
between pre-discharge pCO2 and NICU clinical illness characteristics.
Infants with higher discharge pCO2 were born at an earlier gestational
age and had more days of mechanical ventilation; at discharge they were
prescribed higher liter flow of oxygen and more bronchodilators.
Otherwise, there were no other significant associations between
discharge pCO2 and NICU variables, either in the total cohort, or in the
NICU and referral groups when examined separately.
The median pCO2 at 36 week corrected gestational age for the NICU group
was 59 (IQR 53-63). Table 1B displays associations between 36-week pCO2
and NICU illness characteristics. Higher 36-week pCO2 was associated
with earlier gestational age, lower birth weight, patent ductus
arteriosus ligation, severe BPD, more days of mechanical ventilation,
and more days of supplemental oxygen while in the NICU. At discharge, a
higher 36-week pCO2 was associated with later corrected gestational age
at discharge and discharge with diuretics.
For our primary outcome of readmissions, 23% of infants experienced at
least one respiratory readmission in the year after NICU discharge.
There was no significant association between either pre-discharge or
36-week pCO2 and respiratory readmission. Even after logistic regression
adjusting for other significant measures of illness severity including
gestational age, ductus arteriosus ligation, BPD severity, and diuretic
use, neither pre-discharge nor 36-week pCO2 were associated with
readmissions (Table 2).
Associations between pre-discharge
and 36-week pCO2 and secondary outcomes are shown in (Table 3). There
was no association between either pre-discharge or 36-week pCO2 and
secondary hospital encounter outcomes of emergency department visits,
number or duration of admissions, intensive care unit admissions or
intubation. For respiratory medical management, a higher pre-discharge
pCO2 was associated with receipt of systemic steroids and being
prescribed new or increased inhaled corticosteroids.
For home oxygen management, higher 36-week pCO2 was associated with
later corrected gestational age at which oxygen was discontinued (Figure
2), longer duration of home oxygen in weeks, failing more clinic room
air trials and home overnight oximetry studies (Table 3). Higher
pre-discharge pCO2 was only associated with failing clinic room air
trials. Infants with more clinic visits in the year after NICU discharge
had higher 36-week and pre-discharge pCO2, but there were no differences
in missed appointments or in unsupervised oxygen discontinuation.
The median time to discontinuing home oxygen for all infants was 21
weeks following NICU discharge; 85% of patients were off oxygen by 1
year following NICU discharge (Figure 3). For the 19 infants still
receiving oxygen at one year following NICU discharge, 12 had
experienced hospital admissions, ER visits and other significant
respiratory complications. Four of those infants also had pulmonary
hypertension that required medical management. The other 7 still
requiring supplemental oxygen at one year following NICU discharge had
poor outpatient follow up.