Abstract: This review includes a total of 1897 children and 729 adults in 39 trials. Thirty-three trials were conducted in the emergency room and equivalent community settings, and six trials were on inpatients with acute asthma (207 children and 28 adults). The method of delivery of beta₂-agonist did not show a significant difference in hospital admission rates. In adults, the risk ratio (RR) of admission for spacer versus nebuliser was 0.94 (95% CI 0.61 to 1.43). The risk ratio for children was 0.71 (95% CI 0.47 to 1.08, moderate quality evidence). In children, length of stay in the emergency department was significantly shorter when the spacer was used. The mean duration in the emergency department for children given nebulised treatment was 103 minutes, and for children given treatment via spacers 33 minutes less (95% CI -43 to -24 minutes, moderate quality evidence). Length of stay in the emergency department for adults was similar for the two delivery methods. Peak flow and forced expiratory volume were also similar for the two delivery methods. Pulse rate was lower for spacer in children, mean difference -5% baseline (95% CI -8% to -2%, moderate quality evidence), as was the risk of developing tremor (RR 0.64; 95% CI 0.44 to 0.95, moderate quality evidence). Nebuliser delivery produced outcomes that were not significantly better than metered-dose inhalers delivered by spacer in adults or children, in trials where treatments were repeated and titrated to the response of the participant. Spacers may have some advantages compared to nebulisers for children with acute asthma. The studies excluded people with life-threatening asthma; therefore, the results of this meta-analysis should not be extrapolated to this patient population.

Plain-language summary: We found 39 clinical trials involving 1897 children and 729 adults. Thirty-three of the trials were conducted in an emergency room (or emergency department) and community settings (such as a GP's surgery), and six trials were on inpatients (people in hospital) with acute asthma (207 children and 28 adults). Overall we judged the quality of the evidence to be moderate. Taking beta-agonists through either a spacer or a nebuliser in the emergency department did not make a difference to the number of adults being admitted to hospital, whilst in children we can be fairly confident that nebulisers are not better than spacers at preventing admissions. In children, the length of stay in the emergency department was significantly shorter when the spacer was used instead of a nebuliser. The average stay in the emergency department for children given nebulised treatment was 103 minutes. Children given treatment via spacers spent an average of 33 minutes less. In adults, the length of stay in the emergency department was similar for the two delivery methods. However the adult studies were conducted slightly differently which may have made it more difficult to show a difference in the length of stay in the emergency department. Because all the adult studies used a so-called "double-dummy" design, the adults received a spacer AND a nebuliser (either beta-agonist in a spacer and a dummy nebuliser or vice versa) which meant both groups of people were in the emergency department for as long as it took to take both treatments. Lung function tests were also similar for the two delivery methods in both adults and children. Pulse rate was lower in children taking beta-agonists through a spacer (mean difference -5% baseline), and there was a lower risk of developing tremor. Metered-dose inhalers with a spacer can perform at least as well as wet nebulisation in delivering beta₂-agonists in children with acute asthma, but we are less certain about the results in adults. The review is current as of February 2013.