Within a few hours ofpulmonary infarction fever is the rule.Arterial blood gas analysis
usually demonstrates hypoxaemia.However, not all patients are hypoxaemic andhypoxaemia is in itself a very non-specific abnormality. Asa consequence of hyperventilation, there is hypocapnia.Patients with pulmonary embolic disease are frequentlyanxious as well as breathless, and their hypocapnia is notuncommonly taken to reflect anxiety. However, anxietyhyperventilation syndromes produce hyperoxaemia.Immediately following embolization there is often bronchoconstriction,there may even be wheeze, and later, areduction in surfactant in the affected lung is a contributoryfactor to atelectasis.Symptomatic pulmonary embolism occurs in about30% of patients with deep vein thrombosis in the leg orpelvis; if asymptomatic events are added to this figureabout 50-60% of patients with deep venous thrombosiswill have a pulmonary embolism at some stage. However,in patients with suspected deep venous thrombosis only25% will actually prove to have the condition when fullyinvestigated.