Pediatric emergency medicine trisk 1124
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (188.47 KB, 4 trang )
FIGURE 131.10 Probe position for the parasternal long cardiac view.
FIGURE 131.11 Normal parasternal long cardiac view: Right ventricle (RV), left ventricle
(LV), mitral valve (MV), aortic root (Ao), pericardium (P). Fluid will accumulate just above the
pericardium in a pericardial effusion.
The apical four-chamber view can be the most difficult cardiac view to obtain.
This window is obtained at the apex of the heart by placing the probe over the
patient’s point of maximal impulse, typically around the fifth intercostal space,
and aiming toward the patient’s right shoulder (probe marker pointing to the
patient’s right). In this view, all four chambers of the heart can be seen and it can
provide information about the relative dimensions of the right and left ventricles.
Pitfalls
There are several reasons why a sonographer may not see the heart during the
cardiac examination. In the subxiphoid view, the heart often lies deeper than the
depth set on the screen. To avoid this, the depth should be set to its maximum
level and once the heart is located, the depth should be changed accordingly to
optimize and center the image. In addition, the angle of the probe in the
subxiphoid view may be too steep. Remember that from the subxiphoid position,
the heart lies superiorly, and thus the head of the transducer must be pointed in
that direction, toward the left shoulder. In the subxiphoid view, air from the
stomach can scatter the ultrasound beams, rendering the image useless. Slide the
probe to the patient’s right, away from the stomach, thereby using the liver as an
acoustic window instead. In the parasternal views, rib shadows are often
encountered. The probe may be shifted to the patient’s left, be rotated, or be
angled obliquely to better fit the transducer footprint in between adjacent ribs.
The apical four-chamber view can be a challenging view to obtain. Having the
patient sit forward or lying in the left lateral decubitus position can bring the heart
forward and closer to the probe allowing better visualization.
Chest
Thoracic ultrasound can be used for the rapid identification of pulmonary
pathology, including pneumothorax and pleural effusion. Ultrasound has long
been the reference standard for the identification of pleural effusions and can also
be used to guide procedures such as thoracentesis. POCUS may be more sensitive
for the diagnosis of pneumothorax than a single supine chest x-ray.
Anatomy
The principles of lung ultrasound are different than those for ultrasound imaging
of other organs due to the fact that air scatters ultrasound waves, making direct
visualization of lung tissue difficult. Lung ultrasound thus relies mainly on the
interpretation of image artifacts in order to identify pathology.
In the normal lung, the visceral and parietal pleura merge to form a single
pleural line that appears as a hyperechoic (bright) line below the muscle of the
chest wall and immediately deep to the ribs. Normal lung sliding occurs as the
visceral pleura glides back and forth over the parietal pleura ( Video 131.11 ).
On dynamic ultrasound imaging this appears as a slight movement or “sparkling”
pattern of the hyperechoic pleural line that varies with the respiratory cycle. On
M-mode, normal lung sliding generates what is referred to as the “seashore sign”
where the top of the image (representing the nonmoving chest wall) appears as
horizontal lines, or the “waves,” and the bottom of the image (representing the
aerated, expanded lung) appears as the “grains of sand” (Fig. 131.12 A ).
Technique
Pediatric lung ultrasound is generally performed using a linear, high-frequency
probe because this provides adequate depth and higher-quality image resolution
than a convex, low-frequency probe.
Patient positioning will depend on the clinical scenario—patients who are
critically ill can be examined in the supine position, while those who are more
stable can be placed in the seated position. In addition, certain findings will be
more easily seen with different patient positioning. For example, pneumothorax
will be more easily detected in the anterior lung fields of a supine patient, while
pleural effusions will be better visualized in the lower lung fields of a seated
patient. Starting in the longitudinal view with the probe marker pointing toward
the patient’s head, the lung can be scanned sequentially in all areas of the thorax
or, alternatively, a more targeted assessment can be performed. Pneumothorax
will appear as the absence of lung sliding ( Videos 131.11 [normal] and 131.12
[pneumothorax]). On M-mode, this will appear as the “stratosphere” or “barcode”
sign, with the entire image showing no movement and thus appearing as
horizontal lines all the way down (Fig. 131.12 B ). Pleural effusions, which can
generally first be seen in the posterior costophrenic sulcus, appear as an anechoic
fluid layer overlying the pulmonary parenchyma. Transudate and hemothorax
may appear as simple, anechoic fluid ( Video 131.13 ) while an empyema can
have internal septations or organized fibers ( Video 131.14 ).
FIGURE 131.12 A: Normal motion-mode of lung. Commonly referred to as “seashore” sign
with “waves” and “sand.” B: Pneumothorax, known as the “barcode” sign.
Pitfalls
Lung sliding from the opposing pleura can be a subtle finding and has the
potential for misinterpretation by the novice sonographer. Additionally, cardiac
movement, especially when scanning on the left side of the chest, can sometimes
be confused for lung sliding. Newer ultrasound machines may have significant
postprocessing in order to minimize artifacts and create clearer images. This
postprocessing can interfere with traditionally described thoracic imaging
artifacts and make interpretation more difficult.
