Use of a clinical model for safe management of patients with suspected pulmonary embolism

Background: The low specificity of ventilation-perfusion lung scanning complicates the management of patients with suspected pulmonary embolism. Objective: To determine the safety of a clinical model for patients with suspected pulmonary embolism. Design: Prospective cohort study. Setting: Five tertiary care hospitals. Patients: 1239 inpatients and outpatients with suspected pulmonary embolism. Interventions: A clinical model categorized pretest probability of pulmonary embolism as low, moderate, or high, and ventilation-perfusion scanning and bilateral deep venous ultrasonography were done. Testing by serial ultrasonography, venography, or angiography depended on pretest probability and lung scans. Measurements: Patients were considered positive for pulmonary embolism if they had an abnormal pulmonary angiogram, abnormal ultrasonogram or venogram, high-probability ventilation-perfusion scan plus moderate or high pretest probability, or venous thromboembolic event during the 3-month follow-up. All other patients were considered negative for pulmonary embolism. Rates of pulmonary embolism during follow- up in patients who had a normal lung scan and those with a non-high- probability scan and normal serial ultrasonogram were compared. Results: Pretest probability was low in 734 patients (3.4% with pulmonary embolism), moderate in 403 (27.8% with pulmonary embolism), and high in 102 (78.4% with pulmonary embolism). Three of the 665 patients (0.5% [95% CI, 0.1% to 1.3%]) with low or moderate pretest probability and a non-high-probability scan who were considered negative for pulmonary embolism had pulmonary embolism or deep venous thrombosis during 90-day follow-up; this rate did not differ from that in patients with a normal scan (0.6% [CI, 0.1% to 1.8%]; P> 0.2). Conclusion: Management of patients with suspected pulmonary embolism on the basis of pretest probability and results of ventilation-perfusion scanning is safe.