Gunshot injuries are a substantial cause of vascular damage in the civilian population worldwide. Furthermore, they are associated with high morbidity and mortality [3–7]. Arterial limb injuries can result in extremity amputation or become a life-threatening scenario which demands immediate attention.
Angiography and surgical exploration have been defined in the literature as the gold standard approaches when the clinical suspicion for vascular injury is high [18]. Angiography is sometimes limited in critical scenarios or remote locations. Surgical exploration carries severe limitations as it is very resource dependent, and it is not always widely available for all patients. In catastrophe sites, for example, the physician has to carry out a triage assessment and decide who is in the most-urgent need of transportation to the operating room.
Less-invasive methods such as arterial pressure indexes and standardized Color Doppler Duplex ultrasound can be considered as valuable alternatives for the triage assessment. Burg et al. [19] reported an ankle-brachial index (ABI) of 0.9 or less as a sensitive test for the identification of vascular injury of the lower extremities. However, the palpation of the peripheral pulses can be difficult in some patients due to vasoconstriction, hypovolemia, and pain. SD exam of the extremities allows for diagnosis of vascular lesions with a high sensitivity. Knudson et al. [20] stated that SD exam was equal in sensitivity compared with angiography in detecting vascular injury with the advantage of being noninvasive. The pulsed Doppler spectral analysis recorded from a peripheral lower extremity artery has the feature of a triphasic waveform with a narrow spectral width throughout the pulse cycle, indicating red blood cells moving at a similar speed and direction in a nondisturbed or laminar flow pattern [21]. Any lesion, including arteriovenous fistulas, traumatic thrombotic arterial obstructions, pseudo-aneurisms, or external hematomas compressing the arteries, will impact distal flow, presenting abnormal patterns, such as monophasic, biphasic, or absent flow. Nevertheless, SD has also limitations, as it can be time consuming, and a properly trained radiologist is not always present in the emergency setting to perform the study (e.g.,, peripheral and/or resource-scarce hospitals, extra-hospital, or disaster scenarios).
Point-of-care ultrasound is a novel tool being increasingly used not only by the emergency physician but also by clinicians in several other specialties [15–17]. In the trauma setting, it allows physicians to make faster diagnostic and therapeutic decisions. A large volume of the literature describes how point-of-care ultrasound can be used to diagnose and manage a broad spectrum of conditions in critically ill patients [22–24]. In trauma patients, the evaluation of the extremities using focused ultrasound is limited nowadays to the diagnosis of fractures, soft tissues injuries, and the presence of foreign bodies [25, 26]. Yet, to our knowledge, this is the first report in the literature that describes how to rapidly rule out/in vascular injuries in patients who suffered from penetrating trauma of the lower extremities, by means of a 2-point Doppler technique.
The 2PFD protocol allows physicians to rapidly asses the presence or the absence of flow in two distal arteries of the lower limb, PDA, and PTA. Once this first assessment is done and flow is detected, the physician evaluates the waveform pattern (triphasic or biphasic/monophasic flow). In the absence of vascular injury, the spectral Doppler analysis normally shows a triphasic waveform over each cardiac cycle, representing the blood acceleration during systole: an early diastolic flow reversal caused by the closure of the aortic valve; and a late anterograde diastolic flow related with the elasticity of the arterial wall, peripheral resistance, and transmural gradient. In the presence of any kind of vascular damage or external compression (i.e., large hematoma), the physician could find no flow or the presence of either a monophasic or biphasic waveform pattern.
The 2PFD protocol has the advantage of being noninvasive and a rapid test, requiring no more than 2 min and probably easier to learn by nonimaging specialist, although learning curve analysis of this technique is a subject matter of further investigation.
The 2P Fast Doppler imaging technique can present yet some limitations. The absence of flow or a monophasic/biphasic Doppler Duplex pattern in distal arteries can be detected not only in acutely injured arteries, but also as result of chronic conditions, such as proximal diabetic angiopathy, severe atherosclerosis, or aging. This can cause misinterpretation of the results. As the 2PFD cannot differentiate if the pathologic flow is caused by an acute or a chronic lesion in positive cases, further investigation is always required. In our series, there were no diabetic patients, and the average age was 27 years (24.8 among the pathologic cases). Probably for this reason, there were no false positives related to these comorbidities in this study. As such comorbidities are generally related to older patients, the latter ones may represent a targeted population for more thorough examination.
In targeted patient populations, such as the “injured nondiabetic young patients” of our study, due to the low prevalence, or even the absence of concurrent chronic lesions (i.e., low or no false positives for vascular injuries), 2PFD could be used also as a triage tool to “rule in” acute cases with high specificity equal to SD (Sp 100%).
On another note, if the injured artery has no distal extension (i.e., profunda femoris artery = PFA), and there are no hematomas compressing other arteries, there will be no distal repercussion [27]. In this particular case, the FAST Doppler protocol would not show any abnormal distal pattern, leading to potentially false negative results. We did not have any PFA injuries in our study so this limitation did not affect the sensitivity of our findings. To overcome this limitation, when a penetrating injury of the supero-internal part of the thigh is present, further workup may still be warranted, and physicians would have to explore the thigh with point-of-care ultrasound and SD to identify if large hematomas, pseudo-aneurysms, or arteriovenous fistulas are present in each particular case [28]. In our hospital, we always explore the region injured by gunshot wounds in order to search not only for vascular lesions but also for bone fractures and soft tissue lesions.
In our study population, the 2PFD protocol has proven to be a triage technique as sensitive as SD (Sn 100%). In fact, our data show that the detection of triphasic waveforms can be a highly sensitive method in ruling out vascular injuries of the lower extremities after penetrating trauma.
The absence of flow or the presence of a biphasic or monophasic pathologic flows in PDA and/or PTA must be considered pathologic and should be always followed by further investigation, such as SD, angiography, or surgical exploration, to confirm the proximal lesion, and define its type, extension, and distribution (Fig. 7).