Up your imaging game: The power of AFAST

Many veterinarians are familiar with the term “FAST scan,” which stands for focused assessment with sonography for trauma. This diagnostic tool was first used in human medicine by trauma surgeons in the 1990s, with some considering the approach an extension of the physical examination.¹ It came to veterinary medicine in the early 2000s as a tool to detect free fluid in the abdomen and thorax, usually in emergency cases.^2-5 Since then, it has evolved as a tool to assess trauma patients, triage critical and unstable patients presenting without a history of trauma, and track patient status over time.^5-9

Gregory R. Lisciandro, DVM, DABVP, DACVECC, of Hill Country Veterinary Specialists and CEO of Fastvet.com, played a key role in developing the abdominal FAST scan, now known as AFAST.³ This screening tool offers clinicians a systematic way to evaluate the abdomen and use a standardized, goal-directed template for recording findings. AFAST includes evaluation of target organs in its 5 defined acoustic windows and a fluid scoring system that better defines a positive result. Moreover, AFAST fluid scoring helps guide diagnostics and treatment, including blood transfusion and surgical intervention in bleeding patients.^3,5,8-10

During a session at the 2020 American Veterinary Medical Association Virtual Convention, Lisciandro discussed the essential components of the AFAST evaluation and why it should be used as an extension of the physical examination for all veterinary patients.

Patient preparation

One of the advantages of AFAST is that the patient does not need to be shaved. Images are obtained by parting the fur and placing the probe directly on the skin with a small amount of coupling gel. Another advantage is that AFAST can be performed with the patient standing, in sternal recumbency, or in lateral recumbency, all of which are much safer and less stressful than dorsal recumbency.

The fluid scoring system requires the patient to be in lateral recumbency; however, in standing or sternal AFAST-negative studies, lateral recumbency is likely unnecessary because the score will remain negative. Right lateral recumbency is preferred because it is standard for echocardiography and electrocardiography, facilitates visualization of the gallbladder and caudal vena cava, and has increased safety for abdominocentesis, when indicated, because the spleen is left-sided.

Basic principles of ultrasound for successful AFAST

Lisciandro stressed that a “repetitive, standardized approach is the best way to learn ultrasound.” In AFAST, standardized views are obtained in a set order and performed the same way in every study. Of note, AFAST is not a flash ultrasound, in which the probe is swept over the abdomen or thorax to search for free fluid, or point-of-care ultrasound (POCUS), in which only a specific organ or clinical question is addressed. Lisciandro cautioned that while flash and POCUS are sometimes referred to as AFAST examinations, they can be “detrimental to patient care and outcome” when performed in lieu of a complete AFAST exam because they lead to imaging errors such as satisfaction of search error (stopping the exam at the first abnormality found) and confirmation bias error through selective imaging.

According to Lisciandro, veterinarians do not need extensive ultrasound training to perform AFAST. “The only pressure is looking for anechoic [black] triangulations, which doesn’t take a lot of training, especially if you do your views the same way every time,” he said. “Everything else is a bonus, including obvious AFAST soft-tissue abnormalities.” In other words, as long as a clinician can recognize free fluid, they can perform AFAST and continue to develop their ultrasound skills with every subsequent study.

The ultrasound probe is kept in the longitudinal scanning plane throughout the AFAST exam with the marker oriented toward the patient’s head and the screen marker to the left of the screen. The presence of free fluid has been shown to be independent of probe orientation, and beginners generally recognize anatomy more easily in longitudinal planes. Transverse orientation is considered an add-on skill learned after mastering the fundamentals. At each location, the same probe maneuvers are used, following the mantra of “fan, rock cranially, and return” to the starting position.

Target organ evaluation in the 5 AFAST views

Every AFAST exam elicits 5 views, the first 4 of which are part of the abdominal fluid scoring system. These 4 views are as follows when the patient is in right lateral recumbency: diaphragmatico-hepatic (DH), spleno-renal (SR), cysto-colic (CC), and hepato-renal umbilical (HRU). These are followed by focused spleen and then the hepato-renal 5th bonus view, which is scored but not part of the total abdominal fluid score (Figures 1 and 2). Views are analogous in left lateral recumbency. See the Table for a summary of methodology, target-organs, and obvious soft-tissue abnormalities.

Table 1

(Courtesy of and with permission from Gregory Lisciandro, DVM, DABVP, DACVECC Hill Country Veterinary Specialists and FASTVet.com, Spicewood, Texas.)

AFAST evaluates its target organs for obvious soft-tissue abnormalities that are often missed or only suspected on physical examination, laboratory testing, and radiography. During AFAST, deviations from the expected at each respective AFAST view commonly indicate abnormalities. The use of this target organ approach is generally more specific than sensitive, meaning that a deviation from the expected is likely to be real. However, with detection being user dependent (and keeping in mind that AFAST is a screening test), observing no target organ abnormalities does not exclude their presence. Thus, AFAST does not replace other imaging modalities, including a complete abdominal ultrasound.

Figure 1. Four views of the AFAST fluid scoring system in a cat with the target organs shown. All views are negative for free fluid or any obvious soft-tissue abnormalities. The order is shown with arrows and numbering of 1 through 4. The hepato-renal 5th bonus view and the focused spleen view are not shown. The cat shown here was sedated and shaved for an ovariohysterectomy and photographed for didactic purposes; sedation and shaving are not performed in most patients. CC, cysto-colic; DH, diaphragmatico-hepatic; HRU, hepato-renal umbilical; SR, spleno-renal. (All images are provided courtesy of and with permission from Gregory Lisciandro, DVM, DABVP, DACVECC Hill Country Veterinary Specialists and FASTVet.com, Spicewood, Texas.)

When reporting AFAST soft-tissue abnormalities, Lisciandro suggests that practitioners record them as “suspect” abnormalities, so they are not assumed to be a diagnostic (eg, suspect renal pelvic dilation, suspect gallbladder mucocele, suspect cystic calculi). These suspect abnormalities can then be assessed further using other diagnostics, including a complete abdominal ultrasound and radiography.

Figure 2. Four views of the AFAST fluid scoring system in a dog. Each view is positive for free fluid evidenced by the anechoic (black) triangulations. The order is shown with arrows and numbering of 1 through 4 (center photograph). The hepato-renal 5th bonus view and the focused spleen view are not shown. CC, cysto-colic; DH, diaphragmatico-hepatic; HRU, hepato-renal umbilical; SR, spleno-renal.

The abdominal fluid scoring system

The AFAST abdominal fluid scoring system has been validated in lateral recumbency.^3,10 However, AFAST may be performed in the standing or sternal position in the same way as in lateral recumbency. If the standing or sternal AFAST is negative for free fluid, lateral positioning in unnecessary. If the AFAST is positive in sternal recumbency or standing, then place the patient in either right or left lateral recumbency and wait 3 minutes before scoring to allow the free fluid to redistribute for a more valid score.

To score, assign the DH, SR, CC, and HRU views each a score of 0 (no fluid present), ½ (weak positive), or 1 (strong positive), then add these numbers together for a final score with a maximum of 4. A maximum dimension of greater than 5 mm in cats and 1 cm in dogs is considered a strong positive score of 1, and less would be a ½.^9,10 Total scores of less than 3 are considered small-volume hemorrhage-effusion, and scores of 3 or higher are considered large-volume hemorrhage-effusion (Figure 3).^3,8,9

Figure 3. Illustrations showing AFAST-assigned abdominal fluid scoring in cats (A) and dogs (B). Smaller pockets of free fluid are considered weak positive, whereas larger pockets are considered strong positive using the over and under of maximum dimensions of 5 mm for cats and 1 cm for dogs. A visual of positives at the cysto-colic (CC) view with a weak positive is scored as ½ (C) and a strong positive is scored as 1 (D). (E-H) Illustrations demonstrating small-volume (<3) and large-volume (≥3) hemorrhage-effusion. DH, diaphragmatico-hepatic; HRU, hepato-renal umbilical; SR, spleno-renal.

A small-volume bleeder (fluid score <3) should not cause anemia directly, so perform a thorough physical exam and a Global FAST ultrasound by adding thoracic FAST (TFAST) and lung (Vet BLUE, veterinary brief lung ultrasound exam) to search for other sites of bleeding.^3,4,11,12 By contrast, a large-volume bleeder (fluid score ≥3) may indicate the need for a blood transfusion and possibly surgical intervention,³ depending on clinical profile, presence or absence of coagulopathy, and patient subset. Of note, by recording which AFAST views have fluid present, the clinician may also get a better idea as to the origin of the fluid based on the target organs in positive locations in lower-scoring patients (ie, source of bleeding and source of sepsis).^5,8

When free fluid is safely accessible, perform an abdominocentesis to collect a sample for analysis because ultrasound cannot characterize fluid reliably based on echogenicity. At a minimum, compare the packed cell volume measurement between the effusion and peripheral venous sample because blood contamination can appear grossly and falsely as hemorrhage, and perform cytology while saving a tube for culture and additional biochemical testing.

Finally, repeat scoring following patient resuscitation and rehydration, and track over time to monitor patients with any and all types of effusions for remaining static (no change in score), worsening (higher score), or resolving (lower score) (Figure 4).^3,5,8,9 Furthermore, AFAST and ultrasound are considered more reliable for the presence of fluid over abdominal radiographic serosal detail.³

Figure 4. AFAST and its abdominal fluid scoring system serve as a tracking tool when used in serial fashion moving in either direction from low scoring to high scoring for static, worsening, and resolving effusion whether hemorrhagic and nonhemorrhagic (eg, septic, transudate, modified transudate), showing clear advantages over physical examination, vital signs, and radiographic serosal detail by “seeing” the amount of ascites. CC, cysto-colic; DH, diaphragmatico-hepatic; HRU, hepato-renal umbilical; SR, spleno-renal.

Everyday ultrasound on nearly every patient

“AFAST is a screening tool that outperforms radiography for free fluid and soft-tissue abnormalities, and thus helps capture important problems that would otherwise be missed by physical exam, introductory blood and urine testing, and radiography,” Lisciandro said. “Moreover, by ‘seeing’ the problem list using the Global FAST approach, resuscitation, diagnostics, and treatment are better directed.”

Global FAST is 1 of only 3 standardized veterinary ultrasound formats and the only ultrasound examination that evaluates both body cavities by using a combination of AFAST, TFAST, and Vet BLUE.^8,9,13-15 Once trained in this technique, most clinicians can perform a Global FAST evaluation in under 6 minutes.

Lisciandro believes that Global FAST should be used as “everyday ultrasound on nearly every patient.” During his presentation, he encouraged veterinarians to use the Global FAST standardized approach not only in the emergency setting (ie, triage) but also as part of patient rounds, annual and semiannual wellness evaluations, and for preoperative testing. He showed preoperative case examples in which undetected uroliths, small splenic masses, and an unknown pregnancy were detected using AFAST, but could easily have gone undetected by physical examination, blood and urine testing, and radiography. Each of these conditions could have caused significant morbidity, and possibly mortality, if the patient had been anesthetized or left untreated, demonstrating the potential of Global FAST to improve patient outcomes, including diagnostics and treatment.

The upshot? According to Lisciandro, the use of AFAST and Global FAST should become a core skill for all veterinarians seeing clinical cases, as this ultrasound extension of the physical exam is fast becoming standardized in medical school curriculum and thus offers a rare opportunity for veterinarians to be ahead of our physician colleagues.

Kate Boatright, VMD, is an associate veterinarian and freelance speaker and author in western Pennsylvania. She is actively involved in organized veterinary medicine at the local, state, and national levels and is a former national officer of the Veterinary Business Management Association.

References

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