Preoperative duplex venous mapping: a comparison of positional techniques in patients with and without atherosclerosis.

PURPOSE: Preoperative duplex venous mapping is the preferred modality to measure the diameter of the greater saphenous vein and its suitability as an arterial conduit for infrainguinal bypass. We wanted to determine the optimal mapping technique and maximal venous diameter in patients with and without atherosclerosis. METHODS: Three groups of patients were prospectively studied: younger control subjects (n = 20), preoperative atherosclerotic patients (n = 10), and older control subjects (n = 10). All patients underwent greater saphenous vein duplex mapping in a standardized manner. Maximal internal vein diameters were measured with the subjects in the supine position in bed, in the 20 degree reversed Trendelenburg position, sitting on the edge of the bed, standing, and in the supine position with a high-thigh, low-pressure tourniquet. Measurements were taken just beyond the saphenofemoral junction, in the distal thigh, below the knee, at midcalf, and superior to the medial malleolus. RESULTS: In younger control subjects an increasingly more erect position resulted in progressively larger measured vein diameters at all levels along the length of the leg. Both patients with atherosclerosis and older control subjects had no such increase in venous diameter with any positional change from the supine position to standing. Patients with atherosclerosis also had significantly smaller measured veins than either younger or older control subjects. A high-thigh tourniquet significantly increased vein diameters in the atherosclerotic group to the size of vein diameters in the older control group, although the absolute size differences were not large. CONCLUSIONS: The optimal position for venous mapping is with the patient in a supine position. If the internal vein diameter is below an acceptable minimum size, a high-thigh tourniquet will maximally distend the vein in patients with atherosclerosis. Vein diameter decreases with age and is less distended in patients with atherosclerosis compared with older patients without atherosclerosis.

The limitations of impedance plethysmography in the diagnosis of acute deep venous thrombosis.

We reviewed our experience with impedance plethysmography (IPG) and duplex scanning in the diagnosis of acute deep venous thrombosis (DVT) to determine their respective accuracy and current role in our noninvasive vascular laboratory. During a recent 22-month period 1776 patients were evaluated in our laboratory for DVT. Sixty patients (64 limbs) underwent ascending venography within 48 hours of testing (49 limbs were evaluated by all three modalities). With the venograms used as the reference standard, B-mode scanning correctly identified the presence of acute thrombus in 24 of 27 limbs (88.8%) and the absence of thrombus in 31 of 34 limbs (91.2%), for an overall accuracy of 90.6%. IPG alone was less sensitive (75%) and less specific (44.8%), with an overall accuracy of only 57.1%. Twenty-eight IPGs were performed on patients with negative venous scans. Two positive IPGs were the result of chronic venous occlusion and two others detected clinically significant isolated iliac vein thrombi, but 13 patients had false positive IPGs. One false negative IPG occurred. The difference in the sensitivity of scan alone vs scan plus IPG was not significant (chi 2 = 0.045; difference not significant), but the decrease in specificity was chi 2 = 17.3; p less than 0.001). The rarity of isolated iliac vein thrombosis and the high false positive rate for IPG do not justify its continued use if B-mode venous scanning is available. Although positive scan results may be used confidently to institute therapy without the need for venography, in high-risk patients with a strong clinical suspicion of proximal DVT despite a negative scan venography should be obtained before withholding anticoagulation.