Our initial concern when this phenomenon was first seen was that in situ thrombosis or embolic recurrence might have occurred perioperatively. Our analysis and other considerations make these possibilities unlikely. First, these patients are routinely protected by preoperative or intraoperative placement of a caval Greenfield filter, and lower extremity pneumatic compression plus heparin prophylaxis are begun in the immediate postoperative period. These measures should render perioperative embolism or rethrombosis low in probability—less than 4 percent overall for the caval filter alone. flovent inhaler
Second, if a perfusion scan is obtained within 18 hours after surgery, a policy we have recently adopted, the steal phenomenon is already present. Indeed, the immediate postoperative scan is often a mirror image of the preoperative scan (Fig 3).
Thirdly, if thrombosis in situ had occurred, we would expect it to occur in dissected segments in light of the thrombogenic potential of vessels whose endothelium has been perturbed. In fact, we found that steal occurred far more frequently in segments untouched at surgery.
Finally, the postoperative pulmonary arteriograms in this series have not demonstrated new occlusion of vessels that were patent on the preoperative angiogram. Absolute assurrance of vascular patency postoperatively in lung zones with steal would require an early postoperative pulmonary arteriogram. We have chosen not to carry out this procedure for ethical reasons.
Figure 3. Top panel: Preoperative portable perfusion scan, anterior view. Excellent perfusion to right upper lobe; by angiogram, no thrombi were present. Middle panel: Surgical specimen. Chronic thrombus was removed from the right middle and lower lobes, as well as all segments on the left. No thrombus was present in the right upper lobe. Bottom panel: Anterior view, portable perfusion scan, performed 12 hours after surgery (view is slightly tilted). There is striking steal of the previously well-perfused right upper lobe that persisted to the time of hospital discharge.
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