Pediatric emergency medicine trisk 1130
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pneumothorax or pleural effusion from normal tissues and it identifies the level of
the diaphragm as it moves with respiration.
Technique
Any probe can be used to interrogate the lung. If identifying a pneumothorax, the
linear probe is appropriate because it provides the best visualization of the pleural
line. However, for the actual thoracentesis procedure a phased array or curvilinear
probe is preferred because it will provide a wider and deeper view of the chest
cavity (Fig. 131.24 ).
For identifying fluid in the chest, the probe should be placed in the midaxillary
line or posteriorly where the intended catheter will be placed. If the static
technique is used, the level of the diaphragm should be marked along with the
deepest pocket of intrathoracic fluid.
Pitfalls
If using the static technique, moving the patient after the area of fluid is marked
could lead to fluid shifts and inappropriate placement of the catheter or needle. It
is also important to identify the level of the diaphragm when diagnosing a pleural
effusion to ensure that the visualized fluid is not confused with intra-abdominal
free fluid.
FIGURE 131.24 Pleural effusion identification using phased array probe.
Bladder Catheterization
Bladder catheterization is commonly performed in the pediatric ED, especially in
infants. While the catheterization is not technically challenging, it may be
uncomfortable for the patient; hence, the importance of avoiding multiple
attempts. Using ultrasound to identify urine in the bladder may be helpful,
especially if the child has recently voided or had a dry bladder on prior
catheterization. For children who require suprapubic aspiration, it is important to
use ultrasound to not only identify that there is urine in the bladder, but also to
identify the epigastric vessels prior to the procedure.
Technique
A phased array or curvilinear probe is an appropriate transducer for identifying
urine in the bladder prior to urethral catheterizations (Fig. 131.25 ). For neonates
and smaller infants, a linear probe is also acceptable. For suprapubic aspiration,
the linear probe is also recommended as it is easier to visualize the needle
entering the bladder.
FIGURE 131.25 Bladder measurements.
FIGURE 131.26 Bladder and intra-abdominal free fluid.
Pitfalls
It is important that clinicians are comfortable identifying the bladder and are able
to differentiate it from free fluid or fluid within bowel (Fig. 131.26 and
Video
131.27 ).
Lumbar Puncture Guidance
POCUS is a useful adjunct when performing lumbar punctures. Ultrasound can
readily identify landmarks such as the spinous process and interspinous space.
These landmarks can be challenging to palpate in infants, in whom the anatomy is
smaller, and in obese children, in whom the landmarks may be obscured by body
habitus. In infants, the spine is mostly cartilage; therefore, ultrasound can identify
deeper anatomy, including the spinal canal, conus medullaris and cauda equina
fibers. In all age groups, the ability to visualize the necessary landmarks may
improve success rates and lead to fewer traumatic lumbar punctures.
Technique
A linear transducer is recommended for imaging the spine. In obese children,
however, a curvilinear or phased array probe may be required to provide adequate
depth. The transducer should be placed on the spine in both the longitudinal and
transverse planes. In the longitudinal axis, the transducer should be placed along
the spine with the interspinous space in the center and a spinous process on each
side. In older children, the spine will appear hyperechoic with clean, anechoic
shadows posteriorly, and the interspinous space will appear darker (Fig. 131.27 ).
In the transverse axis, clinicians should move the probe up and down to ensure
the spinous process is midline and then identify the interspinous space before the
next spinous process appears ( Video 131.28 ). Clinicians can then mark the
interspinous space with a marker or object such as a paperclip. After marking the
area, sterile technique should be used.
In infants, both the longitudinal and transverse images will display more
anatomical structures than in older children. The spinous processes will still
appear hyperechoic, but because the bones are not completely calcified, sound
waves are transmitted through the spine to the spinal canal (Fig. 131.28 and
Video 131.29 ). Clinicians can visualize the dura mater, which appears
hyperechoic, and surrounds the anechoic cerebrospinal fluid. Within the spinal
canal, the conus medullaris and cauda equina fibers are also often visualized (Fig.
131.29 ).
