Discussion
This study describes respiratory healthcare utilization in the year
following NICU discharge for infants with BPD discharged with home
oxygen, in the setting of a standardized home oxygen weaning guideline.
We found that pre-discharge pCO2 was not associated with higher risk of
readmission or other hospital respiratory encounters but was associated
with prescription of systemic steroids and inhaled corticosteroids.
Higher pCO2 at 36 weeks correlated with longer duration of home oxygen
or later corrected gestational age
at which oxygen was discontinued.
Infants with BPD are at increased risk for hospital readmission and
other healthcare utilization. Kovesi et al. previously showed that an
elevated capillary pCO2 prior to discharge was associated with an
increased risk of readmission or a severe adverse event, defined as late
pulmonary hypertension, reintubation or death after discharge3. Since that publication, we have talked to
colleagues at many institutions who, like our institution, recommend
discharge after a pCO2 is less than 60; this is the first study of which
we are aware that evaluates outcomes in the setting of such a
recommendation. In our study, we did not find that capillary pCO2 at
discharge or at 36 weeks was associated with more readmissions or
reintubations; no infants in our cohort died after discharge and we had
few infants with late pulmonary hypertension. The lack of association
between pCO2 and readmission could be secondary to our recommendation to
discharge infants after the pCO2 is <60 mm Hg. We saw the same
non-association between pCO2 and readmission in the referral group, but
similar to our NICU group, few referral infants had high pCO2s prior to
discharge. Considering our readmission rate for infants discharged with
home oxygen therapy was not high, it is possible that close outpatient
follow up was successful in controlling symptoms that otherwise may have
led to readmissions 14,15. Infants were seen in
pulmonary clinic 4-6 weeks following discharge from the NICU, and then
every 4-6 weeks to 2-3 months until they were off supplemental oxygen.
It has been noted that outpatient management explains some variation in
readmission rates for premature infants15,16. For
infants with BPD discharged with home oxygen, one example of close
outpatient management may be the use of inhaled and systemic steroids,
which we noted to be more common in infants with a higher pre-discharge
pCO2. Ryan and colleagues similarly found in the Prematurity and
Respiratory Outcomes Program that inhaled steroids and bronchodilators
increased over the first year 8. It possible that
outpatient management such as early use of inhaled or systemic steroids
helps prevent our highest-risk patients from being admitted or
presenting to the emergency room. This raises the issue of whether to
continue the recommendation to delay discharge for infants with higher
pCO2. Our institution’s time to discharge for infants with BPD is still
similar or shorter than other children’s hospital institutions, so the
impact on NICU length of stay would likely be
modest14. But if close outpatient follow-up can
mitigate some potential risks, there may be benefits to individual
patients by facilitating earlier discharge. Future implementation and
quality improvement work will be needed to determine best practices
moving forward.
Clinical practice guidelines of the American Thoracic Society recommend
home oxygen therapy for infants with BPD who have chronic hypoxemia;
home oxygen therapy is used in at least half of infants with BPD
discharged from U.S. NICUs 17-20. After NICU
discharge, however, there are few published guidelines for the close
monitoring required to wean home oxygen therapy in the outpatient
setting 19,21,22. We developed an oxygen weaning
protocol in 2012 to standardize the care of infants being discharged
with home oxygen in our clinic. Using this guideline, we were able to
effectively wean home oxygen using home oximetry studies. Only 3
patients received sleep studies due to concerns for the quality of the
home oximetry study. Our use of this clinical guideline enabled us to
assess duration of home oxygen use as a secondary outcome in this study.
We found that a higher pCO2 at 36 weeks corrected age, but not
pre-discharge, was associated with a longer duration of home oxygen or
later corrected gestational age at
which oxygen was discontinued. We noted that pCO2 at 36 weeks was
correlated with other measures of NICU illness severity, such as
gestational age, days of mechanical ventilation, and BPD severity.
Kaempf and colleagues have previously shown that a 36-week capillary
blood gas pCO2 correlated with NICU illness severity; our findings
suggest that in the setting of a home oxygen weaning guideline, NICU
illness measures such as 36-week pCO2 may be used to predict duration of
outpatient home oxygen therapy 23. Rhein and
colleagues recently reported results of a randomized clinical trial of
two different strategies to wean home oxygen in the outpatient setting;
they noted that infants whose parents reported more home weaning
attempts were safely weaned from oxygen faster 24. In
this context, our findings present an opportunity to use NICU illness
measures to tailor outpatient management and counsel families in a more
individualized fashion. If parents have a better idea of the expected
duration of home oxygen therapy for their infant, it may influence them
to participate more actively in the home oxygen weaning process.
Strengths of this study include the level of clinical detail available
in a single center, the use of an outpatient clinical guideline and high
degree of follow-up. There are several limitations. The biggest
limitation was that this was a single-center study with a general
recommendation not to discharge infants until pCO2 < 60 mmHg;
we tried to examine associations between pre-discharge pCO2 and outcomes
from referral NICUs, but in a medium sized referral area those NICUs may
already follow a practice similar to our own. We cannot determine from
chart review what led to decisions regarding NICU discharge. Even in the
cohort from our own NICU, although outpatient oxygen weaning follows a
guideline, NICU weaning of respiratory support is not protocolized; we
were unable to determine how much of infants’ NICU length of stay was
attributable to our guidelines regarding pCO2. Although our clinic
follows a protocol for follow-up of infants with home oxygen, we were
not able to control the exact timing of when appointments were made for
each family that may affect the exact duration of home oxygen. We tried
to mitigate this somewhat by also evaluating proxy measures of ability
to wean home oxygen such as room air trials in clinic. For future
studies of oxygen discontinuation, we will delineate between the
providers approval to discontinue home oxygen and when the oxygen is
removed from the home.
In conclusion, we found that pCO2 prior to NICU discharge or at 36 weeks
corrected age was not associated with differences in one-year
respiratory readmissions. Higher pCO2 at 36 weeks was associated with
later corrected gestational age at which oxygen was discontinued, as
well as longer duration of home oxygen therapy. In the setting of an
outpatient oxygen weaning protocol, measures of neonatal illness
severity at 36 weeks such as pCO2 may be useful in communicating
expectations for home oxygen therapy to families. The association
between pre-discharge pCO2 and subsequent healthcare utilization,
including duration of home oxygen therapy requires further study,
especially as hospitals look toward earlier discharge of preterm
infants.