What initial step is indicated when a patient presents with respiratory distress and known risk factors for pulmonary embolism?

In the scenario where a patient presents with respiratory distress and has known risk factors for pulmonary embolism (PE), the initial step typically involves assessing for deep vein thrombosis (DVT) that may have contributed to the PE. This is where an ultrasound of the legs becomes vital.

An ultrasound is a non-invasive and effective method for visualizing the veins in the legs, allowing for the detection of thrombosis. If a DVT is found, it's a strong indicator of the likelihood of pulmonary embolism, given that clots from the legs are a common source of PE. Identifying a DVT may prompt further imaging of the chest to confirm the presence of an embolism and guide appropriate management.

While D-dimer testing can be useful for ruling out PE, it is often unreliable in patients with known risk factors or active respiratory distress due to potential false positives. CT scans are indeed definitive for diagnosing PE but are not the first step; they typically follow the suspicion of PE based on clinical assessment and initial tests such as D-dimer or ultrasound findings. A ventilation-perfusion scan is an alternative imaging option but is less commonly used as the first test in acute settings compared to other modalities.

Thus, starting with an ultrasound of the legs in