Klassen 1994.

Methods	Randomised double‐blind controlled trial
Participants	Study period: October 1992 to October 1993 Setting: emergency department at the Children's Hospital of Eastern Ontario, Canada Inclusion criteria: children aged from 3 months to 5 years presenting to the emergency department between 9:00 a.m. and midnight (except holidays) with mild to moderate croup consisting of hoarseness, inspiratory stridor, and barking cough, and a Westley croup score ≥ 2 after breathing humidified oxygen for at least 15 minutes Exclusion criteria: diagnosis of epiglottitis or chronic upper or lower airway disease (not including asthma); corticosteroids administered within the past 2 weeks; severe croup (defined as a Westley croup score of 8 or higher or requiring treatment with racemic epinephrine immediately on arrival) Baseline demographics (N = 54): proportion males: treatment: 63%; control: 74% mean (SD) age in years: treatment: 1.8 (1.2); control: 2.2 (1.4) median (25th, 75th percentile) Westley croup score: treatment: 4 (3, 5); control: 4 (3, 5)
Interventions	Treatment (N = 27): single 2 mg (4 mL) dose of nebulised budesonide Control (N = 27): single 4 mL dose of nebulised placebo (0.9% saline solution) Both treatment and placebo administered by an updraft nebuliser with a continuous flow of oxygen at 5 to 6 L/min.
Outcomes	Change in Westley croup score from baseline to 4 hours; admissions to the hospital; 2‐point improvement in croup score at 4 hours; use of epinephrine, use of supplemental glucocorticoids
Notes	Funding source: Ontario Ministry of Health
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Randomization was performed in blocks of 10 by the pharmacy department, with a random number table"
Allocation concealment (selection bias)	Low risk	Quote: "The randomization list was kept concealed from the research assistants, parents and emergency physicians and from the child's regular physician until the end of the trial." "the pharmacy provided both budesonide and normal saline in opaque brown syringes"
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "the pharmacy provided both budesonide and normal saline in opaque brown syringes to ensure blinding. The research assistants then placed the study drug directly into an opaque nebulizer reservoir."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "the pharmacy provided both budesonide and normal saline in opaque brown syringes to ensure blinding. The research assistants then placed the study drug directly into an opaque nebulizer reservoir." Comment: research assistants blinded
Incomplete outcome data (attrition bias) All outcomes	High risk	Did not use intention‐to‐treat analysis. 7% (N = 4) lost, all from the placebo group (15%) due to worsening condition or lack of satisfaction with treatment. Unbalanced between groups
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol identified. All prespecified outcomes from methods appear in results.
Other bias	Unclear risk	Comment: 24 children were not enrolled because the emergency department failed to contact the study team; this could potentially have biased participant selection.
Overall risk of bias All outcomes	High risk	Comment: at least 1 domain judged as high risk.