Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Change in croup scores
Systematic review	135 children 3 RCTs in this analysis	Difference in change from baseline in croup score 20–60 minutes with humidified air with placebo Absolute results not reported	Weighted SMD –0.14 95% CI –0.75 to +0.47		Not significant
RCT 3-armed trial	140 children (3 months–10 years) evaluated in an emergency department with croup, modified Westley Croup Score 2 or greater (see table 1 )	Change in mean Westley Croup Score from baseline 30 mins with humidity delivered by blow-by technique (effectively the humidity of room air) with high humidity (100%) Absolute results not reported	Mean predicted change +0.19 95% CI –0.87 to +0.49		Not significant
RCT 3-armed trial	140 children (3 months–10 years) evaluated in an emergency department with croup, modified Westley Croup Score 2 or greater	Change in mean Westley Croup Score from baseline 60 mins with humidity delivered by blow-by technique (effectively the humidity of room air) with high humidity (100%) Absolute results not reported	Mean predicted change +0.14 95% CI –0.54 to +0.89		Not significant
RCT 3-armed trial	140 children (3 months–10 years) evaluated in an emergency department with croup, modified Westley Croup Score 2 or greater	Change in mean Westley Croup Score from baseline 30 mins with humidity delivered by blow-by technique (effectively the humidity of room air) with low humidity (40%) Absolute results not reported	Mean predicted change +0.03 95% CI –0.72 to +0.66		Not significant
RCT 3-armed trial	140 children (3 months–10 years) evaluated in an emergency department with croup, modified Westley Croup Score 2 or greater	Change in mean Westley Croup Score from baseline 60 mins with humidity delivered by blow-by technique (effectively the humidity of room air) with low humidity (40%) Absolute results not reported	Mean predicted change +0.05 95% CI –0.63 to +0.74		Not significant
RCT 3-armed trial	140 children (3 months–10 years) evaluated in an emergency department with croup, modified Westley Croup Score 2 or greater	Change in mean Westley Croup Score from baseline 30 mins with low humidity (40%) with high humidity (100%) Absolute results not reported	Mean predicted change +0.16 95% CI –0.86 to +0.53		Not significant
RCT 3-armed trial	140 children (3 months–10 years) evaluated in an emergency department with croup, modified Westley Croup Score 2 or greater	Change in mean Westley Croup Score from baseline 60 mins with low humidity (40%) with high humidity (100%) Absolute results not reported	Mean predicted change +0.09 95% CI –0.61 to +0.77		Not significant