Inclusion criteria are:  A prior physician diagnosis of asthma confirmed by a treating physician in the ED who has spoken with the patient and family and reviewed the medical record (ED attending or fellow physician) Severe acute asthma, defined as a PRAM score of 8 or greater as assessed by a treating physician at the time of screening using the study scoring instrument, which takes 60 seconds to complete Children 2-17 years of age  Exclusion criteria are:  Known pregnancy (by patient or parent report) or positive pregnancy test on females 12 years of age and older Age-adjusted hypotension at presentation using age-based Pediatric Advanced Life Support parameters (children >1 year to 10 years, SBP<(70 + 2 x age in years); >10 years, SBP < 90 mmHg)71 Known severe renal impairment (by parent or patient report) Application of assisted ventilation before enrollment assessment (intubated, bi-level positive airway pressure, continuous positive airway pressure) Received IVMg within 24 hours prior to screening (by parent or patient report or medical record review) Enrollment assessment is 60 minutes after the start of ED treatment (start of first albuterol treatment) Previous enrollment in the same trial (by research coordinator review of trial records)