100 post-operative subjects were observed following total hip replacement using 125I-fibrinogen (125I-Fg) and impedance plethysmography (IPG) with thigh cuff. Phlebo-grams were obtained if these tests indicated venous thrombosis. Also, lung scan was obtained if clinical evidence of pulmonary embolism developed. Sustained significant isotope localization occurred in 40. 32 of these had abnormal IPG. Four patients had minor pulmonary embolism, which was associated with abnormality of either 125I-Fg or IPG. All major obstructive venous thrombosis and all moderately extensive thrombosis was associated with abnormal IPG. Only minute thrombi were not correctly classified by IPG. The following conclusions are supported by this experience. 1) If prospectively applied in patients at risk, the combination of both techniques (125I-Fg, IPG) is capable of detecting all silent venous thrombosis even minute thrombi of negligible significance. 2) IPG is capable of detecting all major obstructive and all moderately extensive thrombi, that is, all thrombosis of clinical significance arising in the leg. 3) Minute thrombi will not be detected by IPG alone and small emboli resulting from detachment of such minute thrombi would be unheralded unless monitoring includes 125I-Fg.
