20 liters is a mighty high O2 setting, unless they are speaking about a ventilator setting? 

Achooo-bullshit-oooo!!!! Excuse me! What a huge sneeze! 

A cxr does Not demonstrate blood clots in the lung, it can rule out other suspicions but that’s the extent for a cxr and pe’s

In the past you think someone may have died from a clot this large? I’m pretty certain anyone in this day and age would be dead if they had a PE (pulmonary embolism) this size.