We speak of pulmonary embolism when a clot, also called a thrombus, circulating in the blood will obstruct the pulmonary artery. It is one of the two manifestations, along with deep vein thrombosis, or thromboembolic disease.
The PESI (Pulmonary Embolism Severity Index) score is a prognostic severity score for patients with pulmonary embolism. Class I and II patients are considered at low risk of complications. The S-PESI score (simplified PESI), less reliable, is given as an indication. The given class and severity are calculated on the PESI score.