Upper extremity impedance plethysmography in patients with venous access devices.

Central venous access devices (VADs) are often associated with thrombotic obstruction of the axillary-subclavian venous system. To explore the accuracy of impedance plethysmography (IPG) in identifying this complication we performed IPG on 35 adult cancer patients before their VADs were placed and approximately 6 weeks later. At the time of the second IPG the patients also underwent contrast venography of the axillary-subclavian system. The venograms revealed partial venous obstruction in 12 patients (34%) and complete obstruction in two (5.7%). Although the IPG results from venographically normal and abnormal patients overlapped extensively, mean measurements of venous outflow were significantly lower in the patient population with abnormal venograms (P = 0.052 for Vo; P = 0.0036 for Vo/Vc). In our hands, therefore, upper extremity IPG cannot be used to make clinical decisions about individual patients with VADs, but it can distinguish venographically normal and abnormal populations.