Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов
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opposition with the skin with an appropriate acoustic coupling medium.
Pearl: The alcohol‐based hand sanitizer is better than 70% isopropyl alcohol because it is not noxious to the patient, either directly on the patient's skin or indirectly via fumes in closed environments. Moreover, alcohol‐based hand sanitizer is not nearly as cooling as 70% alcohol, which can lead to hypothermia especially in smaller and critically ill patients.
Failure to Keep the Patient’s Head and Ultrasound Screen in the Same Sightline
The danger of not having the head of the patient and the ultrasound screen in the same sightline is twofold (Figure 5.3). First, if the patient decompensates or is critical, you have no idea if they are becoming distressed, cyanotic, having open‐mouth breathing, etc. when you and the technician are focused on the ultrasound screen in the opposite direction to your patient's head. Second, by not having the patient's head and ultrasound screen in the same sightline, you and your assistant are vulnerable, leaving your face, hands, and body open to bites and scratches without defense, while focusing on the screen. And finally, spatial orientation is better learned and established even by experienced sonographers by having the machine and head of the patient in the same sightline, and you will likely be more comfortable rather than craning your neck to look at a screen in an uncomfortable direction.
Understanding Your Hands
Your two hands will function differently while scanning. One is your “probe hand” (Figure 5.4). The probe hand always holds the probe and you may change which hand is your probe hand depending on where and from which side of your patient you are imaging. However, this hand's function is to work the probe. Your other hand is your “helper hand” which is used to palpate external landmarks and physically stabilize the patient or the probe on the patient, which is explained subsequently. Briefly, in standing patients, your helper hand is your “V trough” during TFAST and Vet BLUE, cupping the sternum to keep your patient from swaying (every time you lose contact, you prolong the study, which is not always in the patient's best interest) (see Figure 5.4). While performing AFAST, your helper hand is used to move less haired skin over your probe placement site for such views as the spleno‐renal (SR) and hepato‐renal (HR) in flank areas, and the cysto‐colic (CC). For TFAST recumbent views, the helper hand can lift the sternum off the table top for less weight on the probe head, which allows for finer movements and less pain because of less pressure on your patient's intercostal space. Finally, during Vet BLUE, the acoustic window you acquire may be moved together with skin, dependent on the mobility of your patient's skin, caudal and cranial over intercostal spaces at each Vet BLUE region.
Consistently Maintaining the Screen Orientation of Head to the Left and Tail to the Right
When imaging in longitudinal and sagittal planes, including short‐ and long‐axis views of the heart, maintain the head to the left and tail to the right on the screen. If the area of interest is to the left of the screen, you learn to slide or rock toward the patient's head to center the image and vice versa if to the right of the screen, slide or rock toward the patient's tail whether you are doing AFAST, TFAST or Vet BLUE (see Figure 1.6). In human medicine, physicians performing cardiac FAST and POCUS examinations will not necessarily reverse orientation, but stay consistent with all other imaging, with cranial to the left and caudal to the right of the screen (Walker and Mohabir 2014). I like to call this the “rogue way” in which to capture echocardiography views, but maintaining orientation whatever the region of interest is advantageous for localizing abnormal findings, and the noncardiologist doesn’t have to do any mental spatial adjustments because the cardiac ultrasound orientation is now the same as everywhere else (abdomen and lung).
Figure 5.3. Best practice is the head of the patient and machine in the same sightline. In (A), the assistant, the scanner, and the patient are all facing the ultrasound screen (arrows). This is safest because the patient can be observed for any stress and decompensation while imaging. In (B) the head of the patient is away from the ultrasound screen. Both the assistant and scanner are focused on the screen and thus cannot readily appreciate any stress or decompensation of the patient, and cannot quickly react if the dog turns to bite them. The large "X" denotes that this is risky practice.
Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Figure 5.4. The helper hand and probe hand make a difference. In (A) the helper hand moves less haired skin and can help spread the hair for optimal probe head to skin coupling. In (B) and (C) the helper hand in essence V troughs the standing patient, preventing swaying and better stabilizing the probe for maneuvering in small increments, especially important for cardiac imaging.
Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Fan, Rock Cranially, and Return for AFAST Views
As a result of work by Boysen et al. in the original FAST translational study from humans to dogs, we have simplified and standardized the probe maneuver for AFAST as “fan, rock cranially, and return to your starting point” because 397/400 views matched for detecting free intraabdominal fluid when comparing longitudinal to transverse orientation (Boysen et al. 2004). And most abdominal organ anatomy during AFAST is easier to recognize in longitudinal and sagittal planes. Consider transverse orientation as an add‐on skill (Figure 5.5).
Playing on the Short‐axis and Long‐axis TFAST Lines
In contrast to many echocardiography courses that begin with the long‐axis cardiac views, we begin TFAST with short‐axis views. Importantly, if the sonographer can grasp the “short‐axis line” and “long‐axis line” concept and fan the probe while staying on these lines, echocardiography views are learned more quickly and acquired more consistently by the noncardiologist sonographer (Figure 5.6). Without even looking at the screen, knowing you are on these TFAST cardiac lines will optimize success. We could literally teach you from across the room, without any screen knowledge, by just seeing whether or not you are maintaining the ultrasound beam on these lines while fanning from the apex to the base on short‐axis, and from side to side on long‐axis using our clockface approach (see Figures 17.25 and 17.26).
Figure 5.5. Anatomy generally better recognized in longitudinal (sagittal) orientation than transverse. In (A) the kidney is generally better recognized and then interrogated by fanning through longitudinal planes than in (B), showing the kidney in less recognizable transverse orientation.
Source: Courtesy of Dr Daniel Rodriguez, Mexico City, Mexico.