Abstract Urgent visits to the clinic and emergency department for acute severe asthma exacerbations are all too frequent. Existing national guidelines do not present consistent or specific recommendations for the evaluation and treatment of individual asthma patients in respiratory distress. In this vein, we propose the term "critical asthma syndrome" (CAS) to describe any child or adult who is at high risk for fatal asthma. Acute severe asthma, refractory asthma, status asthmaticus, and near-fatal asthma all describe CAS where physical exhaustion from the overwhelming work of breathing leads to respiratory arrest and death from hypoxia or related complications. The authors of this supplement seek to emphasize the importance of early recognition, prompt and coordinated ...