Soru

An 18-month-old boy is brought to the pediatric pulmonology clinic due to persistent respiratory difficulties. Three months ago, he was hospitalized in the pediatric intensive care unit for a severe lower respiratory tract infection caused by *Adenovirus*, which required mechanical ventilation for seven days. Since discharge, he has exhibited continuous tachypnea, a daily wet cough, and audible wheezing. The patient has had no recent fever or rhinorrhea. Two separate five-day courses of oral prednisolone and regular administration of nebulized albuterol have provided no symptomatic relief. On physical examination, his temperature is $37.1^\circ\text{C}$ ($98.8^\circ\text{F}$), heart rate is $130/\text{min}$, respiratory rate is $52/\text{min}$, and oxygen saturation is $91\%$ on room air. Pulmonary auscultation reveals diffuse, bilateral expiratory wheezes and coarse crackles. A chest radiograph demonstrates bilateral hyperinflation without focal consolidation. Which of the following is the most appropriate next step in the evaluation or management of this patient?