The FAST D protocol: a simple method to rule out traumatic vascular injuries of the lower extremities.

Background: The aim of this study is to assess the accuracy of a Fast Doppler protocol for the examination of an injured lower limb, namely 2-Point Fast Doppler (2PFD), in order to rapidly triage arterial lesions after penetrating trauma.

Methods: The presence of flow and the aspects of the Doppler waveform of the dorsalis pedis artery (DPA) and posterior tibial artery (PTA) of the injured lower limb (2PFD) were evaluated immediately before the execution of a standardized Color Duplex Doppler (SD) evaluation in 149 limbs of 140 patients with gunshot penetrating injuries. We considered 2PFD normal exams as the ones with triphasic patterns in both the DPA and PTA, and 2PFD pathologic exams as the ones with absent, biphasic, or monophasic flow patterns in the DPA and/or PTA. 2PFD data were then analyzed to assess accuracy variables, using SD results as matching test reference. According to the trauma center standard protocols, SD positive cases underwent also angiography and surgical exploration, whose findings were used to further match the 2PFD specificity.

Results: The 2PFD protocol showed a sensitivity of 100%, and a specificity of 100% compared with the SD, in the diagnostic workup of arterial injuries of the lower limbs after penetrating trauma. Furthermore, all the pathologic cases that resulted in all true positives (TP), compared with SD, were confirmed as TP also when matched with the angiography evaluation results.

Conclusions: The 2PFD protocol can rapidly identify arterial flow and differentiate between normal and pathologic spectral Doppler analyses in distal arteries. The presence of the normal triphasic flows in DPA and PTA is as sensitive as the standardized Color Doppler Duplex assessment of the entire limb in ruling out arterial lesions in lower-limb penetrating trauma. The absence of flow or the presence of a biphasic or monophasic pathologic flow in DPA and PTA is pathologic and should be always followed by further investigation. 2PFD is faster and easier to perform compared with the SD approach. It could become a new first-line screening technique, both in pre-hospital and hospital critical scenarios, particularly in contexts where advanced diagnostic performance is limited by time concerns or scarce resources.