The chest x-ray shows-

hyperlucent lung fields especially in the upper zones (Westermark sign). This finding in the context of an unwell patient (ecg dots & oxygen tubing visible) with dyspnoea should raise suspicion for a pulmonary embolism.

Main role of chest x-ray in a patient with suspected PE is to rule out other etiology like pneumothorax, pneumonia.

The above patient had a saddle PE on CTPA.

Westermark sign is due to pulmonary oligaemia.