Guidelines for the management of acute asthma exacerbations recommend noninvasive ventilation as an “experimental approach for treatment of respiratory failure due to severe asthma exacerbation.”1(p398) Clinicians in our tertiary pediatric emergency department have the option to use bilevel positive airway pressure (BiPAP) as treatment for children with asthma exacerbations who have no signs of respiratory failure. We sought to examine whether these patients have improved clinical outcomes.
The study protocol was approved by the institutional review board of Vanderbilt University. Written informed consent was obtained from the parents and verbal assent from the participants. We performed a secondary analysis of data (which were not deidentified) from a prospective observational study of 933 children and adolescents aged 5 to 17 years who were admitted to our pediatric emergency department with acute asthma exacerbations. The objective of the parent study was to develop a clinical prediction rule for acute asthma exacerbations.2 For each participant, we performed a comprehensive pulmonary examination and calculated the Acute Asthma Intensity Research Score (AAIRS) before treatment.3 The clinical team was not provided with the results of the pulmonary examination or the AAIRS.
Our primary predictor variable was BiPAP treatment (yes or no) among participants who did not have signs of respiratory failure.1 Outcomes included hospital admission, admission to the pediatric intensive care unit (PICU), hospital length of stay, and time to spacing of albuterol inhalation to every 4 hours (hereinafter referred to as time to albuterol Q4h) (a metric of exacerbation resolution) based on severity scoring by respiratory therapists.
Individual clinicians may, for a given patient, have different preferences for use of BiPAP treatment and different likelihoods for hospital or PICU admission. These preferences may result in confounding by indication, in which BiPAP-treated patients have a risk for relevant outcomes dependent on nonindependent clinician characteristics. Estimating associations of BiPAP treatment with these outcomes in multivariable regression models may not adjust for this confounding.
To adjust for confounding by indication, we used propensity scoring that fitted a multiple regression model, with BiPAP treatment as the dependent variable.4- 6 Model predictors included the following covariates that might influence clinician decisions for BiPAP treatment: the individual pretreatment AAIRS components, age, sex, race, Hispanic ethnicity (per the National Institutes of Health Policy on Reporting Race and Ethnicity Data release NOT-OD-01-053, defined by the parent), symptom duration, prior PICU admission for asthma, prior respiratory failure due to asthma, insurance type, and clinician type deciding whether to use BiPAP treatment. The output of this model was a propensity score ranging from 0 to 1 that estimated the adjusted probability of being treated with BiPAP.
We then performed propensity score–matching analysis in which BiPAP-treated participants were matched 1:3 by the propensity score with participants not treated with BiPAP, without replacement. We also fitted multiple regression models adjusted for the propensity score and other covariates to examine adjusted associations of BiPAP treatment with each outcome of interest.
Characteristics and univariate associations for the 933 participants are displayed in Table 1. The median AAIRS in participants treated with BiPAP (n = 45) indicated episodes of moderate severity; the median AAIRS in those not treated with BiPAP (n = 888) indicated episodes of mild to moderate severity. No participant had signs of respiratory failure. The propensity score model yielded a C statistic of 0.895, and the matched groups were very well balanced on the covariates. Results of propensity score matching and propensity score–adjusted multivariable regression models are presented in Table 2. Those participants treated with BiPAP were more likely to be admitted to the hospital or to the PICU and did not differ in length of stay or time to albuterol Q4h.
Our results indicate that BiPAP treatment of children and adolescents with acute asthma exacerbations who have no signs of impending respiratory failure is associated with a greater likelihood of hospital and PICU admission and no apparent benefit in decreased length of stay or time to albuterol Q4h. Propensity score analyses have been proposed as a method to estimate the causal effect of an exposure.4,6 Nonetheless, this study is limited because it cannot resolve whether these findings are a consequence of clinical momentum after positive pressure ventilation or of increased air trapping and ventilation-perfusion mismatch, derangements that worsen an exacerbation. A randomized clinical trial should be performed before BiPAP is used in children with acute asthma exacerbations without respiratory failure.
Corresponding Author: Donald H. Arnold, MD, MPH, Division of Emergency Medicine, Vanderbilt Children’s Hospital, Room 1348, Nashville, TN 37232 (firstname.lastname@example.org).
Published Online: December 29, 2014. doi:10.1001/jamapediatrics.2014.2767.
Author Contributions: Dr Arnold had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Estrada, Arnold.
Acquisition, analysis, or interpretation of data: Golden, Xu, Arnold.
Drafting of the manuscript: Golden, Arnold.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Xu.
Obtained funding: Arnold.
Administrative, technical, or material support: Golden.
Study supervision: Estrada, Arnold.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was supported by grant K23 HL80005 from the National Institutes of Health (Dr Arnold) and Clinical and Translational Science Award UL1 RR024975 (Vanderbilt Institute for Clinical and Translational Research).
Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Golden C, Xu M, Estrada CM, Arnold DH. Clinical Outcomes After Bilevel Positive Airway Pressure Treatment for Acute Asthma Exacerbations. JAMA Pediatr. 2015;169(2):186-188. doi:10.1001/jamapediatrics.2014.2767