A CRITICAL-APPRAISAL OF IMPEDANCE PLETHYSMOGRAPHY IN THE DIAGNOSIS OF ACUTE DEEP VENOUS THROMBOSIS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 161  (1) , 25-29
Abstract
Compulsive performance of impedance plethysmography [IPG] is paramount to obtaining good results. Sequential multiple tests with prolongation of the filling time to maximize venous filling and ultimately reaching a plateau is essential. Increase in venous filling by increasing the cuff pressure in the proximal lower thigh occluding cuff to 60 instead of 45 cm of water is helpful in obtaining optimum venous filling. Unrecognized patient apprehension or muscle contraction may be a reason for false-positive IPG. Patient relaxation, local heat application or even electromyography attachment may be helpful. The IPG can be repeated after a few hours if a false-positive test result is suspected. If a test falls above the stop line, the NPV is so high that no repetition of the test is necessary and the limb is read out as showing no proximal venous thrombosis. If a test is normal or borderline, the test may be repeated with sequential testing until divergence of either normal or abnormal is achieved. If the contralateral limb is clearly normal and an abnormal test result is obtained in the suspected limb, the test is likely to be reliable. Bilateral abnormal IPG, especially in the presence of congestive heart failure or severe edema, may indicate a false-positive test finding. Increased edema in the extremity decreases electrical resistivity and balancing the machine may become a technical problem. Elimination of the borderline zone or the standard scoring graph did not appear to affect overall accuracy, suggesting the possibility of eliminating this from the graph.