<qa>  What is the primary outcome measure?Metered dose inhalers with spacers are devices capable of providing higher rates of lung deposition of drugs such as beta agonists when compared to conventional nebulizers, but there is no consensus about the optimal dose when this is the device of choice and there is evidence that younger children need proportionally higher doses of albuterol in μgkg when compared to older children. Other factors that may interfere with response to albuterol treatment include the genetics of the beta adrenergic receptor ADRβ2 and infectious etiology of the wheezing attack. This study will assess the effectiveness of a dose regimen that prioritizes higher doses of albuterol, with doses in μgkg higher for younger children. Security of this new dosing regimen will be assessed by monitoring clinical side effects and serum levels of albuterol, but the investigators will also examine the presence of 12 different respiratory viruses in these patients and evaluate the influence of ADRβ2 receptor genetics in the response to albuterol. The primary outcome measure will be the need for hospitalization. Secondary outcomes will include a change in clinical score, respiratory rate and forced expiratory volume in the first second, the need for additional treatments and length of stay in the emergency room for those not hospitalized. 