In a recent issue of CHEST (January 2005), Dolovich et al1reported on evidence-based guidelines for device selection and the outcomes of aerosol therapy. Overall, I agree with the authors in the equivalence of using nebulizers and metered-dose inhalers (MDIs) with holding chamber in the emergency department (ED) setting. Nevertheless, the recommendation that both methods are appropriate for the delivery of short-acting β-agonists in the ED is not entirely supported by the evidence. There are important potential limitations to this assertion. (1) Compared with nebulizers, MDIs with spacers provide a quicker and more cost-effective way to delivered β-agonists, with fewer adverse effects. (2) Nebulizers are more expensive (both in terms of equipment cost and personnel time), require a power source, need regular maintenance, and represent a potential cause of cross-infection. (3) The output can be highly variable. It is very dependent of the technique used by the operator, and small variations in the gas flow and filling alter the performance significantly. Not surprisingly, larger doses of the aerosol must be administered during acute episodes of severe asthma to achieve the maximal effect. (4) A systematic revision recently published2has demonstrated that the use of an MDI with a spacer is more effective in terms of decreasing the duration of hospitalization and improving clinical scores than the use of a nebulizer in the delivery of β-agonists to children < 5 years of age with moderate or severe acute exacerbations of wheezing or asthma. (5) Finally, all studies reviewed in these guidelines excluded patients with life-threatening acute asthma. Therefore, these recommendations were applied only to the subpopulation of patients without these characteristics. The fact that each treatment can take 15 to 20 min instead of 1 to 2 min is a very important aspect of the treatment of patients with life-threatening asthma. In our experience, the use of a pressurized pMDI plus spacer can be the only way to deliver high doses of bronchodilators quickly to patients with acute severe asthma with a reduced level of consciousness. In any case, the assertion that “in acute asthma with life threatening features the nebulized route (oxygen-driven) is recommended”3 does not have support from the evidence.