Two previous meta-analyses of nebulized hypertonic saline (HS) on hospital length of stay (LOS) in acute viral bronchiolitis have suggested benefit. Neither study fully addressed the issue of excessive heterogeneity in the cohort of studies, indicating that it may be inappropriate to combine such dissimilar studies to estimate a common treatment effect.
To reanalyze the existing data set for sources of heterogeneity to delineate the population most likely to benefit from HS.
We used the previously analyzed cohort of randomized trials from 2 published meta-analyses comparing HS with normal saline (or, in 1 case, with standard of care) in infants hospitalized for bronchiolitis. We also repeated the search strategy used by the most recent Cochrane Review in the Medline database through September 2015.
Eighteen randomized clinical trials of HS in infants with bronchiolitis reporting LOS as an outcome measure were included.
Data Extraction and Synthesis
The guidelines used for abstracting data included LOS, study year, setting, sample size, type of control, admission/discharge criteria, adjunct medications, treatment frequency, mean day of illness at study enrollment, mean severity of illness scores, and mean age.
Main Outcomes and Measures
Weighted mean difference in LOS and study heterogeneity as measured by the I2 statistic.
There were 18 studies included of 2063 infants (63% male), with a mean age of 4.2 months. The mean LOS was 3.6 days. Two main sources of heterogeneity were identified. First, the effect of HS on LOS was entirely sensitive to the removal of one study population, noted to have a widely divergent definition of the primary outcome. Second, there was a baseline imbalance in mean day of illness at presentation between treatment groups. Controlling for either of these factors resolved the heterogeneity (I2 = reduced from 78% to 45% and 0%, respectively) and produced summary estimates in support of the null hypothesis (that HS does not affect LOS). There was a weighted mean difference in LOS of −0.21 days (95% CI, −0.43 to +0.02) for the sensitivity analysis and +0.02 days (95% CI, −0.14 to +0.17) for studies without unbalanced treatment groups on presentation.
Conclusions and Relevance
Prior analyses were driven by an outlier population and unbalanced treatment groups in positive trials. Once heterogeneity was accounted for, the data did not support the use of HS to decrease LOS in infants hospitalized with bronchiolitis.