Читать книгу Point-of-Care Ultrasound Techniques for the Small Animal Practitioner - Группа авторов - Страница 148

Questions Asked at the DH View
Is there any free fluid in the abdominal (peritoneal) cavity?	Yes or no
How much free fluid is at the DH view using the AFAST AFS system?	0, 1/2, 1
Is there any pericardial effusion?Subjective amount?	Yes or noSmall (<1 cm), moderate (1–2 cm), large (>2 cm) (Candotti and Arntfield 2015)a Must be placed into clinical context
Is there any pleural effusion?Subjective amount?	Yes or noTrivial, mild, moderate, severe
What does the pulmonary‐diaphragmatic surface look like?Are there any lung lesions along the diaphragm?	Unremarkable (dry lung) or abnormalB‐lines and Vet BLUE B‐line scoring, shred sign, tissue sign, nodule sign, wedge sign
What does the gallbladder look like?	Unremarkable, halo sign (sonographic striation), abnormalities in its lumen or wall
What does the liver look like?	Unremarkable or abnormal
What do the caudal vena cava and its associated hepatic veins look like?	Unremarkable (bounce) or abnormal (FAT, flat): Tables 7.6 and 36.3 and Figures 36.8 and 36.9
Could I be mistaking an artifact or pitfall for pathology?	Know pitfalls and artifacts

^a The AFAST target organ approach for parenchymal abnormalities is binary using “unremarkable” or “abnormal” to capture the case for additional imaging and confirmatory testing. Over time, more interpretative skills may be gained through experience and accompanied by additional POCUS study and training.

Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, Texas.

The classic AFAST DH view is in fact part of AFAST, TFAST, and Vet BLUE because it provides a huge amount of clinical information, including structures within both the peritoneal and pleural cavities.

The DH view begins with longitudinal placement of the probe with the probe marker towards the patient's head immediately caudal to the xiphoid process.

Figure 6.8. The DH view in a dog. In (A) is shown where the probe is placed immediately caudal to the xiphoid (top image) and directed cranial (arrow) in middle and bottom images with overlay of heart, diaphragm (curved white line), gallbladder (black oval), CVC (black rectangle with white line as near wall and longer white line as far wall). In (B) inverted correlating lateral thoracic radiographs in the top image, unlabeled, the middle image having arrows for direction of the ultrasound beam (scanning plane), white circle for probe placement, and bottom image with overlay of structures including the gallbladder, diaphragm, CVC, including A‐lines beyond its far wall through the far‐field from aerated (dry) lung, and the heart with ventricles as triangles and atria as circles. In (C) is CT for another correlation of the anatomy of the DH View. (D) and (E) are unlabeled and labeled ultrasound images of the DH view's anatomical features. Note the consistency of where the diaphragm is located in each of the ultrasound images. CVC, caudal vena cava; DIA, diaphragm; GB, gallbladder; Hrt, heart; HVD, hepatic venous distension; LIV, liver. Computed tomography courtesy of Dr Daniel Rodriguez, 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.

The probe is then directed far more cranially than most sonographers expect (Figure 6.8). Depth should be adjusted so that the diaphragm courses through the distal two‐thirds of the image on the screen so that the near‐field is two‐thirds abdomen and the far‐field one‐third thorax. This allows for adequate screening of both the abdomen and thorax.

The gallbladder, if not in view, is found by fanning toward the table top (when in right lateral recumbency) because of its location right of the midline in dogs and cats (further right in cats). In normalcy, the canine gallbladder is easy to find because it is generally much closer to midline than the more laterally located feline gallbladder (see Chapter 39).

The mantra for the DH view is to have a general overview of three structures – the gallbladder, “cardiac bump”, and caudal vena cava – before starting the fanning, rocking, and returning. Start with a depth of 7–8 cm for cats and small dogs to 10–15 cm for medium to large dogs and then decrease depth as indicated.

Once the gallbladder is in view, then in a sequential way specifically interrogate the following.

 The abdominal cavity for free fluid by fanning through the gallbladder and adjacent liver in both directions, followed by…

 Rocking the probe toward the sternum to best image the “cardiac bump” where the muscular apex of the heart is very near or immediately against the diaphragm for pericardial effusion, and then…

 Imaging along the diaphragm for pleural effusion, and lung pathology along the pulmonary–diaphragmatic interface.

In this same plane or close by, and making sure that the probe is immediately against the xiphoid, look for the CVC as it traverses the diaphragm present in both canines and felines. The CVC is recognized by the two bright white (hyperechoic) bars that make up the near wall (short bar) and far wall (long bar) with reverberation artifact (A‐lines) extending through the far‐field dependent on depth and the presence of dry lung in that patient.

The steps taken during the AFAST DH view are as follows.

 The gallbladder wall and its shape should be noted and the gain adjusted based on the echogenicity of its luminal contents. In normalcy, the homogeneous anechoic (black) echogenicity of bile should approximate what would be expected for most types of free fluid.

 In dogs, the gallbladder reliably lies immediately against the diaphragm when positioned in right lateral recumbency; however, the gallbladder–diaphragm proximity is much less reliable in cats.

 When the canine gallbladder does not lie immediately against the diaphragm, liver enlargement should be suspected, and when the gallbladder is not located, the rule‐out list placed into clinical context should include its rupture, its displacement (diaphragmatic herniation), or the presence of gallbladder stones, mineralization, sludge, mucoceles, and emphysematous cholecystitis.

 Once the gallbladder is recognized, fanning takes place by directing the probe away from the tabletop to the patient's left, and then by fanning toward the tabletop toward the patient's right, interrogating the adjacent liver. The feline gallbladder and biliary tract differ from dogs (see Figures 8.4 and 39.4, and Chapters 8 and 39).

 By doing so, the liver and abdominal cavity are interrogated for obvious free fluid between liver lobes and between the liver and diaphragm, and the gallbladder and liver are screened for any obvious abnormalities or sonographic deviations from normal (Figures 6.9 and 6.10).

Pearl: To perform the DH view consistently and effectively, while fanning through the gallbladder and liver, maintain the diaphragm in the distal two‐thirds of the field of view.

Pearl: In low‐scoring benign and pathological small‐volume effusions, our research has shown the DH view as most commonly positive. These small‐volume effusions are detected between the liver and diaphragm as an anechoic stripe, and between liver lobes and within the “CC pouch” as anechoic triangulations (Lisciandro et al. 2009, 2015, 2019; Hnatusko et al. 2019).

After interrogating the abdominal cavity, return to the starting point of the DH view. The probe is then rocked toward the patient's sternum, remaining on a strict longitudinal plane searching for the “cardiac bump,” the reverberation of the beating heart against the diaphragm (Figure 6.11). The “cardiac bump” is used to diagnose pericardial effusion and rounded effusion, and as a single view, the “racetrack sign” (see Chapters 7, 18 and 21).

Then use the DH view as an acoustic window via the liver and gallbladder into the thorax to interrogate the pleural cavity for the presence or absence of pleural effusion, anechoic triangulated effusion, and lung along the pulmonary–diaphragmatic interface (see Chapters 7, 18, and 21).

Pearl and Pitfall: The “cardiac bump” is reliably imaged in dogs, but less reliable in cats because of more interposing feline lung in between the heart and diaphragm. However, most clinically relevant pericardial effusion is detected in both dogs and cats at the DH view (Lisciandro 2016a) (see Figure 6.11 and Chapter 39). Pneumothorax in either species is another reason for the inability to view the “cardiac bump.”

Always look cranially past the diaphragm into your patient's thorax for pericardial effusion, pleural effusion, and deep lung pathology along the diaphragmatic–pulmonary interface (see Chapters 18, 22, and 23) and use TFAST pericardial site views and Vet BLUE to confirm, refute and support findings at the FAST DH view.

Figure 6.9. Images showing various anatomic features at the DH view. None of these images are positive for free fluid and only (F) is labeled. Compare these images to those labeled in Figure 6.8. In (A) the gallbladder is expected to be in close proximity to the diaphragm. Note the mirror image of the gallbladder into the thorax. In (B) the caudal vena cava is seen in the far‐field as two hyperechoic bars, one as its near wall and the other as its far wall (see Figure 6.11 and Chapters 7, 26 and 36 for greater CVC detail). In (C) another image of the canine gallbladder is shown in close proximity to the diaphragm. (D) shows an anechoic triangulation formed by the CVC as it traverses the diaphragm that should not be mistaken for free fluid. A‐lines are seen past the CVC's far wall due to the dry lung against the CVC. In (E) the gallbladder appears bilobed in the cat and in the near‐field is robust falciform fat (see Chapter 39 for more detail). In (F) with the probe directed near parallel to the sternum, the heart (“Heart”) and its left ventricle are clearly in view and may be interrogated. The liver appears homogeneous as expected and is labeled “Liver” with it mirrored on the other side of the diaphragm due to mirror image artifact common at the DH View. Note how consistent the diaphragm is within the images as a landmark for proper DH view image acquisition.

Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

Figure 6.10. Variety of typical positive studies at the DH view. In (A) free fluid is apparent in the near‐field to the gallbladder. In (B) similarly free fluid is in the near‐field to the gallbladder. In (C) free fluid separates the liver from the diaphragm. In (D) there is a smaller abdominal effusion present separating the liver from the diaphragm. In (E) the same type of positive as in (D) is shown but with an even smaller volume. Note the probe is rocked cranial enough to get the diaphragm at the xiphoid, which is good practice for the DH view. In (F) the liver lobes are separated from one another due to the abdominal effusion. Note how consistent the diaphragm is within the images as a landmark for proper DH view image acquisition.

Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

Figure 6.11. The “cardiac bump” at the DH view. In (A) the apex of the heart is indenting the diaphragm and in real time can be seen clearly beating against the diaphragm. In (B) a heart is superimposed to give a better idea of orientation. The arrows point out the near and far wall of the caudal vena cava (CVC). In (C) the heart is unlabeled with the left ventricle and left atrium both in view as well as the mitral valves with the same image labeled in (D) and the heart is positioned similar to the pictorial of the heart in (F). This cardiac orientation is really important to learn because the heart is generally more sonographically accessible than transthoracic TFAST pericardial site views and its echo views in respiratory distressed patients. In (E) is the unlabeled heart against the diaphragm and labeled with the addition of an overlay of the cardiac orientation in (F). Note how consistent the placement of the diaphragm is within the images as a landmark for proper DH view image acquisition. CVC, caudal vena cava; DIA, diaphragm; LA, left atrium; LIV, liver; LV, left ventricle; RA, right atrium; RV, right ventricle.

Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

Following interrogation of the pleural cavity, pericardial sac, and lung along the diaphragmatic–pulmonary interface, along the same longitudinal plane of the “cardiac bump,” look for the CVC, making sure depth is adequate as the CVC is the deepest structure at the DH view (Figure 6.12).

If the CVC is not seen, look for it while you rock slowly back to your starting point, making sure you are on a longitudinal plane on midline and immediately caudal to the xiphoid.

The CVC is reliably imaged with experience and should be characterized where it traverses the diaphragm, searching for the small white line in the near‐field and the longer white line in the far‐field paralleling one another and representing the near and far walls of the CVC, respectively. The lines that extend beyond the CVC's far wall are in fact A‐lines created when aerated (dry) lung (most common) is immediately against the far wall or possibly in the presence of pneumothorax (far less common) (see Figure 6.12).

Pearl: Excessive probe pressure caused by pushing the probe into the patient's abdomen can distort the CVC, resulting in its flattening and false assessment (Darnis et al. 2018).