Journal of Surgery

Introduction

Before FAST was formally standardized and disseminated - especially from the USA - focused trauma sonography had already been practiced in Europe since the 1970s [1]. Early cohort studies from the 1980s examined patients systematically [2,3]. The term FAST first appeared in 1996 [4], referring to focused abdominal sonography for trauma patients. The method involves searching for free fluid in the Right Upper Quadrant (RUQ) between the liver and kidney (Morrison’s pouch), in the Left Upper Quadrant (LUQ) around and between spleen and kidney, and in the suprapubic region-recto-uterine pouch in women, recto-vesical pouch in men. Inclusion of pericardial and pleural assessments led the FAST Consensus Conference Committee in 1997 to rename the exam Focused Assessment with Sonography in Trauma [5]. In 2004, pneumothorax assessment was added, producing the extended FAST (eFAST) [6]. The further development of FAST/eFAST has since stalled. However, that same year, FAST appeared in the 7th edition of the ATLS Student Course Manual of the American College of Surgeons, and in the 9th edition (2012) eFAST was adopted internationally as part of the standard initial assessment of severely injured patients in the primary survey. In the 10th edition [7], its role was further expanded. Today, eFAST is a central ATLS primary survey adjunct for rapidly identifying major peritoneal and pericardial hemorrhage, as well as pneumothorax and hemothorax. Current Status of Abdominal FAST (aFAST)

Within ATLS protocols, aFAST remains standard for acute trauma care [7,8], despite a 2015 Cochrane review concluding otherwise [9]. Two pathways are currently recognized:

• Unstable patients: Priority is rapid identification of significant free intraperitoneal fluid to expedite urgent laparotomy. This can be achieved within 1–2 minutes, in parallel with initial stabilization. If findings are negative or minimal, the  search for other  causesof shock  continues immediately.
• Stable patients: The key decision is whether an abdominal CT scan is necessary or can be avoided. Additional diagnostic support alongside aFAST may include clinical monitoring, repeat aFAST (abdominal Focused Assessment with Sonography for Trauma), or Contrast-Enhanced Ultrasound (CEUS) [7,8].

Are the current Approaches for unstable and stable patients still up to date?

It is high time to critically re-evaluate the two approaches that have remained essentially unchanged for about three decades. Rapid triage of hemodynamically unstable patients, using ultrasound to confirm significant free intraperitoneal fluid as an indication for immediate laparotomy, is evidence-based [10,11] and continues to be a valid strategy. However, with modern ultrasound technology and newly established diagnostic options in trauma sonography, we believe that even in unstable patients with a negative aFAST, it is worth taking a brief additional look for other causes of shock - performed in parallel with ongoing resuscitation. Although originally designed solely for unstable patients to detect lifethreatening bleeding into the peritoneal cavity, in daily practice the 1- to 2-minute aFAST is often promoted and performed in all stable trauma patients suspected of having intra-abdominal injury. Given that aFAST has only poor to moderate sensitivity for detecting direct intra-abdominal injuries - particularly in hemodynamically stable patients [9,12] - a negative result cannot reliably exclude injury to solid organs, the gastrointestinal tract, peritoneum, or retroperitoneum.

Because aFAST is insufficient for ruling out such injuries (low sensitivity but high specificity), several authors argue that a follow-up CT scan should be performed in every case [9,12,13]. Even when aFAST is positive and reveals blood in the peritoneal cavity, it cannot tell us the type, location, or severity of the underlying injuries-information only CT can provide. For this reason, some authors consider aFAST in stable patients to be an unnecessary, time-consuming, and costly intermediate step [13]. This view is widespread [14] and often leads to friction in clinical practice - a reality largely overlooked in literature. Yet, there are also well-documented opposing opinions supported by studies [15-17]. In stable patients, there is no strict time limit. Advances in technology and expanding indications make it possible to extend the examination beyond the sole search for free intraperitoneal fluid. This can markedly improve sensitivity for detecting intraabdominal injuries - a potential we should be exploiting.

Technological developments such as high-resolution imaging, more powerful color Doppler techniques [18], CEUS [19], and the many studies on abdominal ultrasound published over the last 30 years [20] enable new and broader ultrasound applications in both stable and unstable patients. These changes have had surprisingly little impact on aFAST itself or on the accepted indications for where and how focused ultrasound can be applied in suspected abdominal trauma. Finally, ultrasound - and aFAST in particular - depend heavily on the operator’s training and experience [21,22]. With the rapid, uncontrolled spread of point-of-care ultrasound and the availability of inexpensive portable and handheld devices, we can expect uncontrolled growth and inappropriate use [22]. This increases the risk of errors, partly because the huge demand for training has not kept pace with the expansion of use, some practitioners overestimate their skills, and inappropriate indications are made [22-24]. Considering the current situation, both a strong educational foundation and clear, evidence-based indications are essential. Against this backdrop, we present a new two-stage concept that reflects the advances of the past 30 years in ultrasound diagnostics and follows an established two-step framework: focused ultrasound and complete ultrasound.

Two-Stage Concept

Stage 1 – Unstable Patient

The focus is on three key questions:

• Is there an intra-abdominl hemorrhage requiring immediate surgical control?

This approach reflects the original aFAST concept. The detection of a large amount of free fluid in the peritoneal cavity via the three standard ultrasound windows (RUQ, LUQ, and suprapubic) is considered, in the appropriate clinical context, an indicator of bleeding and constitutes an indication for immediate laparotomy.

• Is there a large retroperitoneal hematoma, for example in the setting of vascular, renal, or pelvic injury? Currently, there are no prospective studies confirming the diagnostic value of aFAST in this context-except for the rapid diagnosis of an unstable pelvic ring fracture, which can lead to substantial hemorrhage [25].
• Is there a major hemorrhage outside the abdomen - such as in the pleural space, a pericardial tamponade, a tension pneumothorax, or a large hematoma in the extremities? These questions can be addressed with eFAST [5]. In addition, simple extremity ultrasound can be used to detect a large fractureassociated hematoma, although no studies to date have specifically examined this application within the eFAST framework.

Stage 2 - Stable Patient

The focus is on avoiding unnecessary  or insufficient diagnostics.

The key question is:

AbdominalCT - yes or no?

The aFAST is not designed to directly detect intra-abdominal injuries. Although CT is considered the gold standard in the diagnosis of such injuries, its diagnostic yield in hemodynamically stable patients with blunt abdominal trauma is low  [26]. This is primarily due to vague indications that are often based solely on clinical judgment and fear of missing an injury. Clinical experience shows that only a small proportion of these patients present with significant intra-abdominal injuries on CT, while many undergo unnecessary imaging. This low yield is problematic, as CT scans are not only costly and time-consuming, but also carry potential risks such as contrast-related allergic reactions and increased radiation exposure. To date, validated clinical decision rules that could help reduce unnecessary CT imaging are lacking  [26]. In this challenging context, the potential role of extended bedside ultrasound beyond the aFAST is increasingly coming into focus.

– CT yes

A CT scan is indicated whenever the not yet widely practiced Complete Abdominal Sonography in Trauma - abbreviated CAST - reveals direct or indirect evidence of injury.

CAST comprises eight structured examination components:

• The three FAST standard regions for detecting intraperitoneal fluid - RUQ, LUQ, and suprapubic.
• Extension with four additional acoustic windows: anterior inferior margin of the right hepatic lobe [27], subdiaphragmatic [28], paracolic gutter [29], and between the bowel loops [30], aimed at the detection of small amounts of intraperitoneal fluid.
• Assessment of the retroperitoneum [31] - in our opinion, a targeted evaluation is feasible, although sufficient prospective studies in trauma are lacking.
• Direct signs of injury in solid organs in B-mode - this approach has shown low sensitivity but high specificity in a few older studies [5] and in one more recent study [32]. However, there are no studies using equipment capable of substantially higher resolution than previously standard.
• Additionally, advanced color Doppler techniques (microvascular flow, B-flow) should improve detection of lacerations, ruptures, and hematomas-though these also lack prospective validation.
• CEUS-has been proven to markedly improve the detection of parenchymal organ injuries [20,33].
• Search for free intraperitoneal air [34].
• Repeat CAST examination [30].
• Thus, abdominal CT may be warranted in hemodynamically stable patients if at least one of the eight CAST criteria is fulfilled:
• A-FAST with fluid in the RUQ, LUQ, or suprapubic region
• Four additional, more sensitive ultrasound windows with fluid:
• at the anterior inferior margin of the right liver lobe
• subdiaphragmatic
• in the paracolic gutter o between the bowel loops
  • Fluid/hematoma in the retroperitoneum
  • Direct signs of injury in B-mode in the liver, spleen, kidneys, and adrenal glands (pancreas is difficult)
  • Direct signs of injury with high-sensitivity color Dopplerdefects in the liver, spleen, kidneys, and adrenal glands (pancreas is difficult)
  • Direct signs of injury using CEUS with defects or evidence of active bleeding with flow phenomena
  • Indirect sign of hollow-organ perforation with free air in the peritoneal cavity
  • Repeated exam positive

There is also good evidence that false-negative a FAST results occur more frequently in certain concomitant injuries, especially: concomitant traumatic brain injury [35], fractures of the lumbar spine and pelvis [36-38], microhematuria, and rib fractures overlying the abdominal area [38]. Such clinical constellations may indicate a higher risk of abdominal injuries missed by aFAST. In these situations, targeted CT imaging should be considered early to identify potentially relevant findings. Since no validated scoring system systematically accounts for risk factors associated with false-negative aFAST results, we propose the use of currently available indication criteria for abdominal CT in hemodynamically stable patients, which include known predictors of false-negative a FAST findings:

• Concomitant traumatic brain injury
• Fractures of the lumbar spine and pelvis
• Microhematuria
• Rib fractures over the abdomen

– CT no

A CT scan is not necessary if CEUS is positive and the identified organ injuries fully explain the clinical situation.

A repeatedly negative CAST, combined with an unremarkable clinical observation over 12 to 24 hours, is likely a reliable predictor for the absence of significant abdominal injury [39,40]. In cases of low clinical suspicion, a shorter observation period may be sufficient, provided the initial assessment and vital parameters remain stable.

This is supported by a large retrospective study showing that ultrasound screening of seven abdominal regions-the three FAST regions plus retroperitoneum, liver, spleen, and kidneys - is equivalent to CT in terms of mortality and false-negative rates [41].

In stable patients, criteria recommending against abdominal CT are based on predictors that suggest a high probability of a scan without additional or negative findings, meaning:

• Positive CEUS of isolated intra-parenchymal injury and injury fully explains the clinical presentation.
• Negative CAST on serial exams and unremarkable clinical follow-up (6 - 12 hours).

Conclusions

Stage 1: In hemodynamically unstable patients initiate aFAST, extending the examination to eFAST, retroperitoneal, and extremity ultrasound as needed, to support urgent surgical decisions.

Stage 2: In stable patients, apply CAST to broaden the diagnostic scope by integrating advanced modalities such as novel Doppler technologies and Contrast-Enhanced Ultrasound (CEUS). Decisions regarding the need for CT imaging should be guided by these tools, as well as by available predictors of a negative aFAST. This approach maximizes injury detection while minimizing unnecessary radiation exposure and imaging resource use.

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