VETTEM, and Dr Jesús Paredes, CVM, Mexico City, Mexico.
Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Figure 6.31. Examples of typical negative studies at the HRU (SRU) view. The target organs are the small intestine and spleen. By imaging either or both, the sonographer knows they are within the abdominal cavity. (A) and (B) are the same image labeled and unlabeled, showing how the small intestine in cross‐section, transverse orientation, appears like “hamburgers” and in longitudinal or sagittal appears like “highways.” In (B) the circle highlights an area that may or may not have a small triangulation of free fluid, illustrating the difficulty in seeing small pockets of fluids (milliliters) in between intestinal loops because of the anechoic layers of intestine. A better strategy is shown in (C) by using the spleen as an acoustic window and looking for free fluid on its far side. In (D) is another region in which soft tissue is in proximity to small intestine as a better strategy to detect small‐volume effusions at this view than in (A) and (B).
Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
If the right (left in left lateral recumbency) kidney needs to be imaged because of concern for retroperitoneal injury, or when hematuria exists, then the HR5th (SR5th in left lateral recumbency) bonus view should be performed. Once the four AFAST views used for the AFS are mastered, the HR5th/SR5th bonus views should be considered as an add‐on skills and incorporated for all subsequent patients.
Typical HRU View Positives
The HRU (SRU) view is the most gravity‐dependent view in right lateral recumbency (the SRU when in left lateral recumbency) and completes the four AFAST views and the calculation of its applied fluid scoring system and assigning the AFS (see Chapter 7). The “rabbit ear sign” is typical in large‐volume effusions created by small intestine and omentum wafting in the free fluid and typical positives are shown in Figure 6.32. Furthermore, if positives were previously seen at the other less gravity‐dependent AFAST views, the sonographer is already anticipating the likelihood of performing abdominocentesis at the HRU view (SRU view in left lateral recumbency).
Pearl: Fluid must always be characterized if safely retrievable by abdominocentesis because ultrasound cannot characterize the type of fluid based on its echogenicity.
False Positives
Gastrointestinal (GI) Tract
Small intestine and stomach may be fluid‐filled or have their wall infiltrated (abnormal) in diseased states and may appear mistakenly as free fluid (see Figure 6.31).
Midabdominal Masses
Large centrally located necrotic fluid‐filled splenic, hepatic, or renal masses may be mistaken for free fluid (Figure 6.33).
Fluid‐filled Uterus
A large fluid‐filled uterus in an intact female may be mistaken for free fluid (see Figure 6.33). The female reproductive tract is further addressed in Chapter 14.
Pearl: Consider your patient’s signalment and don’t mistake an enlarged uterus for free fluid.
False Negatives
Serial AFAST Increase Sensitivity
Don’t sweat questionable small pockets of free fluid. Repeat the AFAST at least once four hours later (called a serial exam) as standard of care, and sooner in questionable or unstable patients (Lisciandro et al. 2009; Blackbourne et al. 2004; acep.org).
AFAST HR5th (SR5th) Bonus View
| Questions Asked at the HR5th (SR5th) Bonus Viewa | |
| Is there any free fluid in the abdominal (peritoneal) cavity? | Yes or no |
| How much free fluid is at the HR5th (SR5th) bonus view using the AFAST‐applied fluid scoring system?a | 0, 1/2, 1NOT part of the abdominal fluid scoring system |
| Is there any free fluid in the retroperitoneal space? | Yes or noTrivial, mild, moderate, severe (also can measure and record its greatest dimension) |
| What does the right (#left) kidney look like?b | Unremarkable or abnormal |
| What does the liver (#spleen) look like?b | Unremarkable or abnormal |
| Could I be misinterpreting an artifact or pitfall as pathology? | Know pitfalls and artifacts |
a Note that this view is the HR5th bonus view in right lateral recumbency and the SR5th bonus view in left lateral recumbency, often performed with the patient standing after AFAST (and TFAST and Vet BLUE) as the last view performed.
b It is important to know that the AFAST target organ approach for parenchymal abnormalities is binary as “unremarkable” or “abnormal” to capture the case for additional imaging and confirmatory testing. More interpretative skills may be gained through experience, and additional ultrasound study and training.
Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
The bonus 5th view of AFAST is a bonus in that it is not part of the AFS system; however, it does interrogate the right (or left) retroperitoneal space more thoroughly than the SR (HR) view alone, and assesses the right liver (left liver), and right (left) kidney for soft tissue abnormalities that may otherwise be missed (Figure 6.34).
The HR5th bonus view is imaged by placing the probe at the junction of the costal arch and hypaxial muscles, identical to the SR view but with the probe directed much further cranially because the right kidney is more cranially located and obliquely positioned. In dogs, the right kidney is cupped within the renal fossa of the liver, whereas in cats it is generally separated from the liver by interposing fat (see Figure 6.34). This anatomical feature is important for the sonographer because the canine right kidney is located by following and fanning the right liver caudally and dorsally. If you run out of liver caudally, then you must return to a more craniodorsal acoustic
