Diagnostic criteria for pulmonary embolism

The most important and consistent symptom of acute PE is the sudden onset of dyspnoea unexplained by pneumonia, heart failure, pneumothorax, or exacerbation of airway obstruction. The features commonly remembered such as haemoptysis and pleural rub may be absent in up to two thirds of patients. With previous cardiorespiratory disease the signs and symptoms become nonspecific and a relatively minor PE can produce clinical features more suggestive of a large embolus. Hypoxia and a raised respiratory rate are also suggestive but cannot be relied upon if there is pre-existing cardiorespiratory disease or in the elderly. Although the radiological appearance of an infarct shadow may be recognized, the chest X-ray is frequently nonspecific or normal. A negative perfusion scan excludes any significant emboli and an abnormal perfusion scan is suggestive of PE but not diagnostic; its specificity can be increased considerably if facilities are available for a concurrent ventilation scan. A deep venous thrombosis when present is also indicative of PE, although its absence does not preclude the diagnosis. Factors predisposing to deep venous thrombosis are usually present in the patient with PE. No single diagnostic aid can be relied upon in the diagnosis of PE. As with many illnesses much of the evidence begins with a careful consideration of the presenting history and physical signs. Further help can be obtained from various investigations, but results must be interpreted with consideration of the patient's age and pre-existing health. The final diagnosis may need to be established by pulmonary angiography.