A previously well 1-year-old infant has had a runny nose and has been sneezing and coughing for 2 days. Two other members of the family had similar symptoms. Four hours ago, his cough became much worse. On physical examination in the ED, he is in moderate respiratory distress with tachypnea and nasal flaring. Upon auscultation, he has easily audible wheezing with scattered crackles bilaterally. His arterial blood gas on room air revealed a pH of 7.46, a PaCO2 of 34 mm Hg, and a PaO2 of 75 mm Hg. His chest radiographs are shown. Which of the following is the appropriate next course of action?