A post-operative patient shows signs of a pulmonary embolism but has a nondiagnostic CT scan. What is the most appropriate next step?

In the context of a post-operative patient exhibiting signs of a pulmonary embolism (PE) with a nondiagnostic CT scan, the most appropriate next step is to perform an ultrasound of the legs. This is because a significant number of pulmonary embolisms originate from deep vein thrombosis (DVT) in the lower extremities. By conducting a leg ultrasound, the clinician can identify any existing DVT, which provides a direct source for the suspected PE. This approach is particularly beneficial in post-operative patients, who are at an increased risk for thromboembolic events.

If the ultrasound indicates the presence of DVT, it would support the diagnosis of PE and guide further treatment. This move prioritizes the assessment of a common and preventable cause of PE, linking the findings directly to the patient's clinical presentation. Therefore, performing an ultrasound of the legs is a logical step in establishing a diagnosis or ruling out DVT as the source of the pulmonary embolic event.