Patients Excluded from Analysis
Patients with conditions known to alter FPA levels (those who had undergone surgery within four days and those receiving anticoagulation therapy) were excluded from the final analyses. Patients who had an abnormal perfusion scan but did not undergo PA were excluded, except for those who fulfilled diagnostic criterion 2. buy birth control online
V/Q Lung Scan and Pulmonary Angiography
A detailed description of the technique and interpretation of V/Q lung scan at our institution has been published previously. Briefly, ventilation studies were performed with 20 mCi of Xe-133 gas, and single-breath, equilibrium, and wash-out images were obtained in the posterior projection immediately before the perfusion study. If a perfusion defect was not seen adequately in the posterior view, a ventilation study was repeated in the view that allowed the best visualization of the perfusion defect. Three millicuries of Tc-99m labeled macroaggregated albumin was used to obtain multiple perfusion images. The scans were interpreted according to the following criteria:
“No evidence of PE”: (1) A normal perfusion study.
“Low probability of PE”: (1) Normal chest roentgenogram, normal ventilation study, and a single or multiple nonsegmental or single subsegmental (size less than one anatomic segment) perfusion defect. (2) Normal chest roentgenogram, normal ventilation study, and several small subsegmental defects, the combined size of which is equivalent to less than one anatomic segment. (3) Normal chest roentgenogram and single or multiple segmental or nonsegmental perfusion defects with matched ventilation abnormalities; that is, the ventilation defect occurs with the same anatomic pattern as the perfusion defect.