Case Seven - Diagnosis

Patient Chart

History

KP is an 18-month-old female is brought into the ED by her mother because of shortness of breath of recent onset and that has gotten progressively worse over the past couple of hours. Her mother states that KP had been well up until two days, but since has had symptoms of a URI. Physical examination reveals a normal-appearing toddler who is moderate respiratory distress with intercostal and substernal retractions. Pulse is 122, respiratory rate 40, temperature 99o F, SpO2 (on room air) 95%. She has an occasional loose nonproductive cough.

Which of the following is the most appropriate diagnostic test to perform at this time?