Focused assessment with sonography in trauma: a review of concepts and considerations for anesthesiology
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The use of point-of-care ultrasound in trauma provides diagnostic clarity and routinely influences management. A scanning protocol known as the Focused Assessment with Sonography in Trauma (FAST) has been widely adopted by trauma providers of all specialties. The FAST exam addresses a broad array of pathologic conditions capable of causing instability, including hemoperitoneum, hemopericardium, hemothorax, and pneumothorax. The exam is an integral component to the primary assessment of injured patients and an iconic application of point-of-care ultrasound.
This review article aims to summarize the application of the FAST exam with special consideration, where relevant, to anesthesiologists. The scope of the FAST exam, technical considerations, and clinical decision-making in trauma are explored.
Évaluation ciblée avec l’échographie en cas de traumatisme : révision des considérations et concepts pertinents à l’anesthésiologie
Dans les cas de traumatisme, l’utilisation de l’échographie au chevet procure une facilité diagnostique et a souvent un impact sur la prise en charge. Un protocole d’examen, connu sous l’acronyme FAST (pour Focused Assessment with Sonography in Trauma, soit Évaluation ciblée du traumatisme grâce à l’échographie), a été largement adopté par les spécialistes de traumatologie dans toutes les spécialités. L’examen FAST porte sur un vaste éventail de conditions pathologiques pouvant provoquer une instabilité, y compris l’hémopéritoine, l’hémopéricarde, l’hémothorax et le pneumothorax. L’examen est une composante intégrale de l’évaluation initiale des patients blessés et une application phare de l’échographie au chevet.
Ce compte rendu vise à résumer l’application de l’examen FAST et porte une attention particulière, le cas échéant, aux anesthésiologistes. L’objectif de l’examen FAST, des considérations techniques et la prise de décision clinique en trauma sont expliquées.
Over the last 30 years, the incorporation of point-of-care ultrasound within the initial assessment of the injured patient has become an essential skill for trauma providers.1 The Focused Assessment with Sonography in Trauma (FAST) exam is a goal-directed ultrasound protocol fashioned to address common life-threatening injuries in traumatized patients.
Originally derived to assess for hemoperitoneum and hemopericardium, the FAST examination has evolved since its original introduction to North American trauma centres in the 1990s.2,3 The scanning protocol now routinely includes the assessment for hemothorax and pneumothorax. This expanded format may be referred to as the extended FAST or “eFAST” exam, but as this scope has become routine, special distinctions are no longer necessary.
The FAST exam is rapidly performed and can be completed in concert with the trauma primary survey. The exam has good diagnostic performance and, in the presence of altered physiology, can lead to life-saving interventions at the bedside or expedite transfer to definitive care.4-7
Statement of purpose
This review article aims to introduce the basic components of the FAST examination, with attention to methods of image acquisition and interpretation. We also aim to outline the role of the FAST examination in patient care from an anesthesiologist’s perspective.
FAST exam and the anesthesiologist
Beyond its traditional role in the trauma suite, the components of the FAST exam may be of additional value to the anesthesiologist caring for patients who deteriorate after abdominal procedures, allowing rapid assessment for evolving intra-abdominal hemorrhage, whether in the operating room, postanesthesia care unit, or intensive care unit.9 Furthermore, intraoperative assessment with ultrasound has been shown to facilitate the identification of pneumothorax, a condition that can go unrecognized in the trauma bay and may worsen as the patient is exposed to positive pressure ventilation.10-12
Components of the FAST exam
Components of the FAST examination
Presence of Hemoperitoneum?
Right upper quadrant
Hepatorenal interface, subphrenic space
Presence of anechoic fluid located in any of the potential spaces (hepatorenal, perisplenic, rectovesicular/pouch of Douglas) should be recognized as hemoperitoneum
Dependent on stability. If unstable, the patient should be transferred directly to the operating room to undergo a trauma laparotomy. Stable patients may undergo further radiographic testing (CT abdomen)
Left upper quadrant
Splenorenal interface, subphrenic space
Rectovesicular space, pouch of Douglas (female patients)
Presence of Hemopericardium?
Anechoic fluid located in the pericardium
Presence of instability should prompt emergent transfer to the operating room for cardiovascular procedure
Presence of Hemothorax?
Costophrenic recess (bilateral)
Dependent pleural space
Anechoic fluid located in the dependent thoracic space
Drainage with tube thoracostomy
Presence of Pneumothorax?
Anterior chest wall (bilateral)
Non-dependent pleural space
Lack of lung sliding indicating loss of visceral and parietal pleural continuity
Decompression with tube or needle thoracostomy
Image acquisition and interpretation
Right upper quadrant (RUQ)
Right upper quadrant anatomy
The hepatorenal interface, known as Morison’s pouch, has been shown to be the most common region in which hemoperitoneum is detected during a FAST examination.13 Given this predilection for fluid to collect in the right upper quadrant (RUQ), it is the first view obtained when performing the FAST exam.
Right upper quadrant image acquisition
There are two important considerations when interrogating both upper quadrants. First, the entire length of the interface where the kidney meets the liver/spleen, including the inferior pole of the kidney, must be visualized. Second, Morison’s pouch and the perisplenic interface are three-dimensional spaces, and the clinician must “sweep” the ultrasound beam through this space to image them completely (Video 1; available from Electronic Supplemental Material [ESM]).
Right upper quadrant image interpretation
If adequate views are not obtained due to operator, patient, or equipment factors, the exam must be interpreted as indeterminate and no clinical decisions should be made based on the exam. If the clinician interprets a positive exam in the RUQ, no further abdominal images need to be obtained, the presence of hemoperitoneum has been diagnosed and patient stability will dictate the next step in care (Fig. 1). If a negative or indeterminate RUQ study is interpreted, the clinician must continue with the remaining abdominal views.
Left upper quadrant (LUQ)
Left upper quadrant anatomy
There are important anatomic distinctions between the LUQ and the RUQ. The presence of the phrenicocolic ligament tends to direct free fluid to the subphrenic space, rather than to the renal interface. Compared with the RUQ, the kidney sits higher on the left side, structures are more cephalad, and some adjustments to technique are required.
Left upper quadrant image acquisition
Left upper quadrant image interpretation
The pelvic anatomy relevant to the FAST exam is more straightforward. In males, the region lies in the rectovesicular pouch. In females, fluid can be found collecting in the potential space between the posterior wall of the uterus and the rectum in the rectouterine space (pouch of Douglas).
Pelvic image acquisition
To maximize sensitivity, acquisition of the pelvic image is performed in two planes (Fig. 3). Image quality relies heavily on the presence of an adequately filled urinary bladder. For patients with Foley catheters, the creation of an acoustic window has been described by instilling fluid into the bladder retrograde through the catheter.
The urinary bladder should be visualized in the near field, and the uterus and/or the rectum will be seen deep to the bladder. Moving the probe subtly will allow imaging of the entire potential space in the search for free fluid.
Pelvic image interpretation
Pearls and pitfalls of the abdominal exam
Repeating the abdominal ultrasound exam sequentially is encouraged in a patient who is highly suspicious for intraperitoneal fluid or has a sudden change in hemodynamics, as repeat FAST exams have been shown to increase sensitivity.14
Trendelenburg positioning has also been shown to increase the sensitivity of the RUQ FAST exam by using gravity to drive fluid up the pericolic gutters into the RUQ and, to a lesser extent, the LUQ.15
The FAST examinations completed early in the patient’s course of illness may be falsely negative as it takes time for intraperitoneal fluid to collect.
- Once blood has begun to coagulate, it creates an iso- or hyperechoic appearance that may not be interpreted accurately (false negative) (Fig. 9).
With cardiac injury, rapid accumulation of hemopericardium can lead to significant hemodynamic compromise through cardiac tamponade.
Pericardium image acquisition
The near-field image is of the superficial liver, which acts as an acoustic window to the heart. Beyond the liver, a bright echogenic structure represents the pericardium which encases the heart (Fig. 10).
There could be many reasons why the subcostal four-chamber view may not be visualized, including body habitus, abdominal dressings, and subcutaneous emphysema. In these situations, additional echocardiographic views, such as the parasternal long- or short-axis view, can be employed to assess the pericardium with high sensitivity.
Pericardium image interpretation
Pearls and pitfalls of the pericardial exam
Epicardial fat is a common source of a false-positive subcostal pericardial exam (Fig. 12).
As hemopericardium begins to coagulate, it becomes more iso- or hyperechoic.
- Small pericardial effusions may lead to important hemodynamic consequences as the physiology of a rapidly accumulating hemopericardium is vastly different from slowly acquired medical effusion.
Chest radiograph (CXR) has evolved as the most rapid and reliable method of detecting the hemo- and pneumothoraces. Nevertheless, ultrasound is superior to a CXR for detection of pneumothorax in the supine patient.16 The ease of image generation, interpretation, portability, and immediate availability has led to the incorporation of thoracic ultrasound in the FAST examination.
Anatomic considerations in assessing for pneumothorax
With traumatic injuries, air can become entrained within the pleural space. In the supine trauma patient, image acquisition is directed at the most dependent location for air, the anterior thoracic wall.
Pneumothorax image acquisition
Pneumothorax image interpretation
In a normal lung, the pleural line can be seen sliding as ventilation creates movement between the visceral and parietal pleura. In the presence of pneumothorax, the two pleural layers are no longer apposed and sliding is absent as only the parietal pleura is seen (Video 2; available as ESM). The presence of lung sliding rules out pneumothorax at the site of the transducer with 100% accuracy. This power to rule out pneumothorax offers significant diagnostic advantage in an unstable patient and underlies the rapid uptake of this modality for trauma and for any context of cardiorespiratory failure.
The anterior chest wall offers the most sensitive location for detection of large life-threatening pneumothoraces. Marginal improvement in diagnostic accuracy for clinically significant pneumothoraces is gained with the addition of multiple scanning regions, but additional sites of insonation may be beneficial in some clinical scenarios (e.g., prior to air transport, long delays in radiography).17
Pearls and pitfalls of the assessment for pneumothorax
Imaging of the pleural space assesses for the presence or absence of pneumothorax only at the location of the transducer.
Absence of sliding is not specific to pneumothorax and may be caused by conditions that diminish or abolish normal pleural anatomy and function.
The assessment of hemothorax is now routinely incorporated into the FAST examination. Ultrasonographic assessment provides similar sensitivity to CT for detection of hemothorax.17
Anatomic considerations in assessing for hemothorax
Thoracic trauma can result in bleeding within the thoracic cavity and lead to accumulation of blood in the pleural space. As with pneumothorax, the assessment for hemothorax interrogates the most dependent location for the intrapleural process. For the pooling blood of hemothorax, this is the mid-posterior costodiaphragmatic recess.
Hemothorax image acquisition
In the trauma scenario, an assessment of the pleural space for blood is closely related to the abdominal upper quadrant views. The clinician needs only to move the probe 1-2 rib spaces cephalad in the same coronal plane and to ensure the probe is in the mid-posterior axillary plane.
Hemothorax image interpretation
In the absence of fluid in the pleural space, the ultrasound image should show a well-aerated lung above the diaphragm that, during tidal breathing, will largely obliterate the view of the diaphragm or any solid organs with the characteristic “curtain sign”.
Pearls and pitfalls of the assessment for hemothorax
Thoracic ultrasound is quite sensitive, thus identification of pathology does not always necessitate intervention. While unstable patients with positive findings may need tube thoracostomy, stable patients will typically benefit from further radiographic studies to assess and trend the size and anatomic burden of the disease process.
Similar to the assessment of hemoperitoneum, blood appears iso- or hyperechoic as it begins to coagulate.
The utilization of point-of-care ultrasound is rapidly growing in all disciplines of medicine.18-22 Within the care of trauma patients, a particular area of development that will be of interest to anesthesia providers is the use of ultrasound in traumatic brain injuries and its ability to detect intracranial hypertension through insonation of the optic nerve.23 Early work applying transcranial Doppler and transesophageal echocardiography in the trauma bay has also been described and appears promising.24-27
The number of scans required to achieve competency in performing and interpreting the FAST examination varies amongst practitioners.28,29 Emergency physicians practicing in Canada must perform 50 directly supervised scans before they are deemed to have achieved competency and receive credentialing to perform the FAST exam.30 That said, the authors discourage this kind of numeric, boilerplate approaches to credentialing and certification and instead favour incorporating point-of-care ultrasonography skills into the core competencies of residency training.31 This approach would ensure that all medical trainees responsible for the care of critically ill patients have baseline familiarity and skill with bedside sonography from which they can adopt advanced applications.
The FAST exam is one of the most widely used and iconic applications of point-of-care ultrasound. It rapidly surveys the torso for life-threatening events in the context of traumatic illness. The technical and cognitive elements outlined in this paper are transferable to multiple environments other than trauma, including the operating room or the postoperative setting where anesthesiologists are most likely to see its impact first hand.
Conflicts of interest
Dr. Arntfield has served as an educational consultant for Fujifilm Sonosite Inc.
This submission was handled by Dr. Gregory L. Bryson, Deputy Editor-in-Chief, Canadian Journal of Anesthesia.
Supplementary material 1 (MP4 47535 kb) Video 1 A complete Focused Assessment with Sonography in Trauma (FAST) examination in a healthy individual.
Supplementary material 2 (MP4 228 kb) Video 2 A right anterior chest wall view demonstrating the lack of lung sliding indicative of a pneumothorax at the site of insonation. Note that the image is acquired with a vascular probe, as evidenced by the transducer’s linear footprint.
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