An 18-year-old mother with her 3-month-old son arrives at urgent care clinic with a chief complaint of "my baby stopped breathing! " she and her baby are rushed into a triage room, where her son is noted to be very lethargic with increased work of breathing. as vital signs are being obtained, the mother reports "my baby stopped breathing in the car coming here, and didn't start again until i reached over and jostled his car seat! " mom then shared that "my boyfriend said he rolled off the couch last night. could it be related? " mom also stated that her son hasn't been as active as usual, and has been vomiting occasionally. physical exam is notable for a respiratory rate of 70 bpm with intercostal retractions and crackles in the right lower lung fields posteriorly. you admit this patient with the diagnosis of pneumonia for empiric antibiotics and support, pending additional evaluation. cxr subsequently demonstrates a rll infiltrate and faint, vertical lines on several posterior ribs bilaterally. what is the best next step in management?