Air Versus Oxygen for Intermediate-Risk Pulmonary Embolism (AIRE)

Inclusion Criteria: * Confirmed PE by multidetector computed tomographic pulmonary angiography (MDCT). * Disfunction of right ventricle (RV to left ventricle \[LV\] diameter ratio \>1.0 in the apical 4-chamber view) in the echocardiogram performed in the first 12 hours after PE diagnosis. * Signed and dated informed consent of the subject. Exclusion Criteria: * \<18 years old. * Allergy to iodinated contrast. * Renal failure defined as a creatinine clearance less than 30 mL/min, according to the Cockcroft-Gault formula. * Use of chronic oxygen therapy. * Hypercapnia (pCO2 \>50 mmHg at the time of diagnosis). * Technically inadequate basal echocardiography. * Contraindication to anticoagulant therapy. * Symptoms duration \>10 days. * Haemodynamic instability. * Participation in other clinical trial for PE treatment during the present clinical trial. * Inability to use mask or nasal prongs. * Life expectancy less than 90 days.