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

Background: The low specificity of ventilation-perfusion lung scanning comp licates the management of patients with suspected pulmonary embolism. Objective: To determine the safety of a clinical model for patients with su spected 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 pulmonar y embolism as low, moderate, or high, and ventilation-perfusion scanning an d bilateral deep venous ultrasonography were done. Testing by serial ultras onography, venography, or angiography depended on pretest probability and l ung scans. Measurements: Patients were considered positive for pulmonary embolism if t hey 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 o f pulmonary embolism during follow-up in patients who had a normal lung sca n and those with a non-high-probability scan and normal serial ultrasonogra m were compared. Results: Pretest probability was low in 734 patients (3.4% with pulmonary e mbolism), 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-pr obability scan who were considered negative for pulmonary embolism had pulm onary 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.