DiagnosisTA is a 66-year-old female who had a right knee replacement two days ago. Currently, she is complaining of sharp pain in her right chest of sudden onset. Respiratory rate 30, temperature 98.9o F, SpO2 (on room air) 93%. She appears to be in mild to moderate respiratory distress with an occasional dry, nonproductive cough.
Which of the following is the most appropriate test to perform at this time?