Literature Summaries - The FAST D protocol: A simple method to rule out traumatic vascular injuries of the lower extremities
Date: 25 October 2017
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Montorfano MA, Montorfano LM, Perez Quirante F, Rodriguez F, Vera L, Neri L. Crit Ultrasound J. 2017 Dec;9(1):8
This study investigates the accuracy of a FAST Doppler protocol for triage evaluation of arterial injury to the lower limbs following a penetrating trauma.
This prospective study was conducted in a level 1 trauma center in Rosario, Santa Fe, Argentina, between February 2011 and December 2015. It was carried out by the ultrasound department, which has a 4-year ultrasound residency program. All stable patients with gunshot injuries to the lower limbs were considered for this study. The method investigated is called 2-Point FAST Doppler (2PFD), which was used to evaluate the flow and Doppler waveform of the dorsalis pedis artery (DPA) and posterior tibial artery (PTA) of the injured lower limb (2PFD) before executing the Standard Color Duplex Doppler (SD) method. The triphasic patterns had a narrow spectral width throughout the pulse cycle in both areas of both arteries and were normal. Abnormal flow was defined by absent, biphasic, or monophasic flow patterns in at least one of the arteries considered. The 2PFD data were then analyzed for accuracy by comparing the SD obtained during evaluation of the entire arterial system of the injured lower limb, including the DPA and PTA as well as the fibular, anterior tibial, popliteal, femoral, superficial femoral, deep femoral, and iliac arteries.
All imaging was performed by two board-certified medical doctors and specialists in ultrasound and Doppler. The second evaluations were always performed by another blind attending physician. Ultrasound was done using a 5–12 MHz broadband linear array transducer (Toshiba Xario; Tokyo, Japan). Transverse and longitudinal scans of the vessels were obtained in a supine position. The DPA and TPA were scanned using a depth of 2–3 cm, while the proximal thigh was scanned using 5–6 cm (femoral artery, superficial femoral artery, and deep femoral artery).
Two types of Doppler ultrasound modalities were used. The first was color flow Doppler (CFD) imaging, which shows the mean flow velocity distribution as a color-encoded map superimposed on a gray-scale B-mode tissue image to identify the arteries in two planes. The second was pulsed wave Doppler (PWD), which was used to obtain a spectral Doppler image that shows the time-varying flow velocity distribution within a selected sample volume in a longitudinal section. To obtain reproducible information from PWD, the velocity scale was set between 10 and 60 cm per second, and the Doppler angle of insonation was less than or equal to 60°.
The 2PFD results were compared with the SD of the outcome data. All pathologic cases (SD+) underwent confirmatory computed tomography angiography or arteriography and went on to further surgical treatment.
Triphasic flow pattern PMID:28324353
Biphasic flow pattern PMID:28324353
Monophasic flow pattern PMID:28324353
A total of 149 limbs from 140 patients with penetrating gunshot injuries were included. The mean age was 27.15 ±10.64 years, and none of the patients had DM. Group A (n = 134 limbs) had non-pathological results (2PFD−), while group B (n = 15 limbs) showed pathological findings (2PFD+). In ruling out and ruling in vascular injuries of the lower limbs, the 2PFD protocol showed 100% sensitivity, specificity, and positive predicted value compared with the reference results of the SD technique. Furthermore, all pathological cases showed all true positives (TP) compared with SD, which was confirmed with the angiography results.
The 2PFD protocol can rapidly identify arterial flow and differentiate between normal and abnormal flow spectral Doppler analyses in distal arteries. Any lesion can impact distal flow, including arteriovenous fistulas, traumatic thrombotic arterial obstructions, pseudo-aneurisms, and external hematomas that compress the arteries. The result is abnormal patterns, such as monophasic, biphasic, or absent flow. SD has limitations. For example, it can be time consuming, and a properly trained radiologist is not always present in an emergency setting to perform the procedure. The presence of the normal triphasic flows detected with 2PFD is as sensitive as the standardized Color Doppler Duplex assessment.
The FAST D protocol
+ Doppler Measurements are made parallel to the blood flow.
++ While the current path is fully longitudinally visible, be careful to measure it by making the flow in the heart and large vascular completely parallel, in distals as parallel as possible.
+++ Trace; immediately prior to the Doppler analysis, the line that the applicant standing on the ultrasound screen should touch or twist on the ultrasonic keyboard to make it parallel to the flow on the screen.
++++ If the flow in artery is near parallel to the ultrasonic wave, this angle is "0" degrees and the cosine is close to "1". The increase of the angle causes the decrease of frequency and Doppler signals.
* Instant and variable wave Doppler (Pulsed Wave = PW) is called Duplex Doppler when synchronous on gray scale imaging is used.
** Spectral Doppler
*** Triphasic (3-Stage model)
**** Insonation angle is the angle between Doppler ultrasonogram and blood flow direction. It is ideal in 0-30 ° of this angle in distal arteries, not exceeding 60 °.
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