Pediatric emergency medicine trisk 1127
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Pitfalls
The rib shadows often obstruct visualization of the kidney; slight probe rotation
can mitigate this effect. The left kidney often requires a more posterior and
superior approach than expected. If localization remains difficult, having the
patient breathe deeply often causes inspiration to push the kidney into view.
FIGURE 131.18 A, B, C: Longitudinal section of the left kidney reveals nephrolithiasis
(arrows ) in the superior and inferior poles in the same patient. (Images courtesy of Christi
Tumblin, Zanesville, OH. In: Kawamura D, Lunsford B, eds. Diagnostic Medical Sonography .
3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012. With permission.)
FIGURE 131.19 Full bladder measured in two different planes.
Bladder Ultrasound
Bladder ultrasound is performed for a variety of reasons. For the child who has
not voided for a prolonged period, assessing bladder size can inform the
practitioner if there is a problem with urinary retention. More commonly, bladder
ultrasound is done prior to bladder catheterization or suprapubic aspiration to
assess volume of urine and thereby improve success rates. It may be used
dynamically as well to guide needle placement and improve success rates of
suprapubic aspiration.
Technique
The same approach as the pelvic view of the FAST examination is used when
performing a bladder ultrasound. A high-frequency linear probe or low-frequency
abdominal probe may be used. A full bladder will appear as a well-circumscribed,
fluid-filled (anechoic) structure within the pelvis. Once the bladder is identified, it
should be measured in at least two planes (Fig. 131.19 ). Although studies differ
with respect to exact measurements, generally speaking if the wall-to-wall
distance measures greater than 2 cm in both planes, catheterization or suprapubic
aspiration will likely be successful.
Pediatric Abdomen
Pediatric patients often present to the ED for evaluation of vomiting and/or
abdominal pain. In infants less than 2 months of age, there is often concern for
hypertrophic pyloric stenosis (HPS), requiring ultrasound for definitive diagnosis.
In the toddler age group, colicky abdominal pain with associated emesis can be
signs of intussusception, a pathology that is also diagnosed with sonography. In
children of all ages, abdominal pain that is localized to lower right side of the
abdomen raises concern for appendicitis. Ultrasound has become the first-line
diagnostic modality for appendicitis but sensitivity depends on patient
characteristics and sonographer skill. Recent literature has demonstrated the
ability of pediatric emergency medicine providers to identify pyloric stenosis,
intussusception, and appendicitis on bedside sonography.
Hypertrophic Pyloric Stenosis
Anatomy
The gastric outlet in infants abuts the medial portion of the hepatic contour. The
pyloric channel connects the antrum of the stomach to the first portion of the
duodenum and is surrounded by muscle. The position of the pylorus is dependent
upon the fullness of the stomach, but is typically adjacent to the gall bladder and
anteromedial to the right kidney.
Technique
A high-frequency linear probe, preferably with a large footprint, positioned on the
upper abdomen to the right of midline, will allow visualization of the pylorus as it
extends from the stomach, deep to the liver. The probe is oriented longitudinally
with the marker angled slightly toward the right shoulder for the short-axis view
and then rotated 90 degrees in the transverse plane to obtain the long-axis view.
In the long axis, the inner channel appears as a narrow canal flanked by the linear
hyperechoic walls that are surrounded by the hypoechoic muscular pylorus (Fig.
131.20 ).
As the pylorus thickens, it often extends superiorly toward the gall bladder and
when the channel has become obstructed, absence of passage of liquids can be
seen as retrograde peristalsis into the stomach. Measurements of the pylorus
should be performed to assess for hypertrophy with an abnormal muscle thickness
measuring greater than 3 mm and an abnormal channel length measuring greater
than 17 mm.
Pitfalls
Infants with an air- and liquid-filled stomach often have a gastric outlet that is
pushed beyond midline to the right side of the abdomen, and often the pylorus
dives posteriorly. In this setting, rotating the infant to the right decubitus position
can improve visualization. Allowing the child to feed clear fluids during the
examination facilitates identification of the pylorus by providing an excellent
acoustic window. If available, warm gel will improve probe contact as infants are
particularly intolerant of cold gel.
FIGURE 131.20 Longitudinal view of pylorus. The “A” calipers measure the muscle thickness
and the “B” calipers measure the channel length.
Intussusception
Anatomy
Intussusception occurs when a loop of bowel, the intussusceptum, advances
distally and, through peristalsis, becomes trapped in the distal bowel lumen, the
intussuscipiens. The bowel wall becomes edematous and intestinal obstruction
ensues. The most common site of intussusception is the ileocolic region of the
bowel. Mesentery, vascular supply, and lymph tissue accompany the invaginated
loop and, as entrapment persists, ischemia develops and the bowel is at risk of
perforation. Small bowel intussusceptions can occur but are typically selfresolving.
