Observational Study of Intravenous versus Oral Corticosteroids for Acute Asthma: An Example of Confounding by Severity

Abstract

In this observational study, patients with worse asthma exacerbations were more likely to receive IV corticosteroids as compared with oral corticosteroids. Although we controlled for many markers of asthma severity, we were unable to completely control for baseline differences between the IV and oral corticosteroid groups. Observational research continues to serve as an important tool for describing problems and for understanding many exposure-disease associations. For examining the impact of treatments on adverse outcomes, randomized trials are often required to avoid intractable confounding by severity.

Clinical characteristics and outcomes in adult cystic fibrosis patients with severe lung disease in Porto Alegre, southern Brazil

“…Consequently, patients who receive inhaled tobramycin in our service are more likely to have worse disease severity. The association of tobramycin inhalation with time to death in the present study could interpreted as confounding by severity [24].…”

Multicenter Observational Study of the Use of Nebulized Hypertonic Saline to Treat Children Hospitalized for Bronchiolitis From 2008 to 2014

“…This can lead to confounding by severity in observational studies of medication effectiveness. 33 More recently, a systematic review reported on all available trials of HTS up to May 2015 and concluded that nebulized HTS is associated with reduced LOS among admitted infants and reduced hospital admissions when used in the outpatient setting. 34 However, a reanalysis of 2 large meta-analyses questions these results and shows that the improvement in LOS disappears when a single outlier study is removed and the results are controlled for day of illness at presentation.…”

“…In addition, this was an observational study, which complicates the evaluation of the treatment effectiveness of HTS. 33 Also, our sample included only children hospitalized for bronchiolitis in academic medical centers and not all eligible children were enrolled, which may limit the generalizability of the results. Finally, not all study sites enrolled participants in all years; some findings might be due to site variability and not necessarily usage variability.…”

How to prevent relapse after acute exacerbation of asthma?

“…In general, patients with worse asthma exacerbations are more likely to receive IV CSs as compared with oral CSs. This is the likely explanation of the fact that patients receiving IV CSs are more likely to be admitted or experience a relapse event within 48 hours [14].…”