Diagnostic studies

Screening

Patients with unrecognized pulmonary emboli frequently suffer additional embolizations which may be fatal. Therefore efficient use of diagnostic modalities is warranted once pulmonary embolism is clinically suspected. Several easily obtainable tests should be performed early in the diagnostic work-up.

ECG findings in patients with pulmonary embolism include T-wave changes, T-wave inversion, right bundle branch block, arrhythmia, and P pulmonale. Although these findings are non-specific, they may help to alert to other conditions in the differential diagnosis, such as myocardial infarction.

Arterial blood gas analysis can suggest pulmonary embolism in the face of the above signs and symptoms. The characteristic findings of hypoxemia with a respiratory alkalosis is frequently seen, with a direct correlation between the size of the embolus and decreased oxygenation. Arterial oxygen ( PaO2) is generally less than 80 mmHg (10.7 kPa) on room air; however, up to 12 per cent of patients with angiographically detected pulmonary embolism will have higher values. The alveolar-arterial (A-a) oxygen gradient is commonly elevated, suggesting a ventilation-perfusion discrepancy, and can easily be evaluated at the bedside using the following equation to determine expected normal values:

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