Duplex scanning in post-operative surgical patients.

The technique of duplex scanning for the diagnosis of deep venous thrombosis (DVT) has been developed in 3 stages. Initially B-mode imaging with compression was used. Subsequently interrogation of the venous lumen using the Doppler facility was introduced and finally the latter became simple and efficient with the introduction of colour flow imaging. Sensitivities and specificities in excess of 90% have been produced for thrombosis proximal to the calf by all methods in symptomatic patients. Colour flow imaging has given the best results for calf DVT in symptomatic patients with 86% sensitivity and 91% specificity. Before the introduction of colour flow imaging the accuracy for the detection of old thrombi in asymptomatic patients was poor. With the introduction of colour, sensitivities and specificities in excess of 90% have been obtained for proximal DVT; for calf DVT, sensitivity of 79% and specificity of 97% have been reported by 2 studies. If further studies substantiate these recent results duplex scanning will become the non-invasive method to be used in screening asymptomatic patients.