The most appropriate management is to admit the patient to the ICU because of his high-risk asthma and arterial blood gas studies suggesting the possibility of impending respiratory failure. Patients with asthma who are at risk of poorer outcomes include those with limited access to health care or difficulty with medication adherence, poor perception of low lung function (and inability to gauge worsening of airways obstruction), an acute increase in use of short-acting β₂-agonist therapy, and lack of improvement with outpatient treatment. This patient has several of these factors, and he also had severe symptoms before seeking care. His initial blood gas studies showed an acute respiratory alkalosis, which is a typical finding in patients with an acute asthma exacerbation. However, his second blood gas determination after 1 hour of treatment showed a developing respiratory acidosis despite a continued high work of breathing, as reflected by his respiration rate. These changes suggest progressively ineffective ventilation and the possibility of impending respiratory collapse. Therefore, the most appropriate venue for treatment is an ICU setting, in which ventilatory failure could be managed if it occurs.

Admission to a general medical floor would not be appropriate because this patient's clinical indicators suggest the need for more intense monitoring that could not be provided in that setting.

Although ventilatory failure could be managed in an emergency department setting, continued therapy with reassessment in 2 hours would not be appropriate given this patient's changing clinical course.

Discharge with close follow-up would not be appropriate given this patient's current respiratory status and previous issues with poor asthma control.