Technique
The high-frequency linear probe, preferably with a large footprint, should be
placed in the right lower quadrant in the transverse plane. The colon is then traced
from right to left, rotating the probe to the longitudinal plane at the level of the
transverse colon to maintain a short-axis view of the bowel. This focused
investigation identifies ileocolic intussusception, the most common type. The
appearance of the intussusception is noted to be alternating hyperechoic and
hypoechoic rings representing the telescoping bowel wall. In the center may be
noted hyperechoic mesenteric fat and/or hypoechoic lymph nodes which served
as lead point ( Video 131.18 ). Sometimes referred to as the target or donut
sign, the rings of bowel occupy up to 3 to 4 cm. In long axis, the invaginated
loops appear similar to the layers of a sandwich, with alternating hyperechoic and
hypoechoic layers ( Video 131.19 ).
Pitfalls
Overlying bowel gas can obscure visualization of the bowel and can prevent
identification of intussusception. Small bowel intussusception can also occur but
is typically self-resolving and often will decompress during observation on
ultrasound. This entity does not typically require reduction and should be
differentiated from ileocolic intussusception.

Appendicitis
Anatomy
The normal appendix arises from the cecum in the right lower quadrant. In
patients with abnormal anatomy this position can be variable. Normal intestine
appears as alternating hyperechoic and hypoechoic rings representing the
histologic layers of the intestinal wall, also known as gut signature. A
noninflammed appendix is compressible, measuring less than 6 mm.
Technique
With the patient in the supine position, the high-frequency linear or curvilinear
probe should be placed in the right lower quadrant to identify the appendiceal
body. In a patient with significant pain, narcotic analgesia is necessary to perform

graded compression to displace overlying bowel gas and facilitate visualization of
the underlying bowel. In the longitudinal plane, the cecum should be identified,
with its fluid-filled haustra and inferior termination into the ileum. The appendix
will extend from the cecum just proximal to the junction with the ileum. In the
transverse plane, identification of the psoas muscle laterally and the iliac vessels


medially will provide a focused area of investigation for the appendiceal body. A
noninflammed appendix will have intact gut wall signature with intact peristalsis.
An acute appendicitis will have notable increase in size measuring 6 mm or
greater, be noncompressible, and will often have surrounding periappendiceal fat
stranding (Fig. 131.21 and
Video 131.20 ).

FIGURE 131.21 Appendicitis. Note the enlarged appendix (arrow ) adjacent to the iliac vessels
(IV) and near the psoas muscle (PM) viewed in cross section.

Pitfalls
Obesity often prevents visualization of the appendiceal body on ultrasound. In a
patient with significant abdominal pain the ultrasound examination can cause pain
that limits the ability to perform graded compression. This can be mitigated with
narcotic analgesia but in a patient with peritonitis, there may still be difficulty in
obtaining adequate images. Retrocecal appendiceal bodies often require a lateral
approach and it may not be feasible to identify with the limited depth of a highfrequency linear probe. Finally, the sonographer should be aware of the variable
sensitivity of ultrasound in bedside assessment of appendicitis. Thus
nonvisualization of the appendix should be considered nondiagnostic rather than a
negative study.

PROCEDURAL APPLICATIONS



POCUS has the potential to make procedures safer and more efficient by reducing
the duration, the number of attempts, and complication rates. Ultrasound can be
used as an adjunct either before the procedure to identify landmarks and
important anatomic structures (static technique) or during the procedure (dynamic
technique), allowing for real-time guidance.

CENTRAL AND PERIPHERAL VENOUS CANNULATION
POCUS is an important aid in obtaining intravenous (IV) access for difficult
peripheral IV cannulation and for all cases of central venous (CV) access.
Ultrasound allows clinicians to identify the intended vein for cannulation and to
differentiate veins from nearby anatomic structures such as arteries and nerves.
Of note, most superficial peripheral veins are not paired with arteries.
However, deeper veins like the brachial veins and veins used for central access,
such as the femoral and internal jugular, do have arteries alongside them.

Central Venous Cannulation
Central vascular access is among the most commonly performed ultrasoundguided procedures. The Agency for Healthcare Research and Quality has stated
that ultrasound for CV access is a clear opportunity for safety improvement and
listed it as one of the “Top 11 Highly Proven” patient safety practices. It is
considered standard of care according to multiple subspecialty policy statements
and published international evidence-based consensus recommendations.
In adults, POCUS for central line placement increases success rates and
decreases procedural complications. Similar reports exist in the pediatric
population. In a recent meta-analysis, US-guided CV placement decreased the
number of attempts and improved success rates. The evidence in both the adult
and pediatric population, along with the generalizability of the procedure,
suggests that ultrasound is a necessary skill for the practitioner who places CV
lines in children.
Technique

The sonographic technique for identifying vessels is similar whether placing a
peripheral IV or a CV catheter. A high-frequency linear transducer is the probe of
choice. Relevant anatomy for the particular site chosen (femoral, internal jugular)
should be reviewed. Preprocedure steps are important to maximize success,
including adjusting the height of the bed, positioning the patient, positioning the
ultrasound machine, and having equipment and extra personnel ready for
assistance. For CV access, aseptic technique should be used with sterile probe
covers and sterile gel (if probe covers are unavailable, a sterile glove will suffice).


Prior to performing the procedure, the intended target vein should be identified
and confirmed first in the transverse plane and then in the longitudinal plane. On
ultrasound, veins are characterized by their easy compressibility, color flow, and
Doppler waveforms. Placing gentle pressure on the probe, the walls of vein
should collapse. In contrast, arteries will pulsate and the walls of the arteries will
resist collapsing when compressed ( Videos 131.21 and 131.22 ). Both veins
and arteries have characteristic patterns when assessed with color Doppler (
Video 131.23 ).
Once the vein is identified, the depth to the center of the vein should be
measured. When the needle is inserted into the skin, it is traveling along the
hypotenuse of a right triangle, and the distance it must traverse before hitting the
vein should be calculated.
In the static approach, once the vasculature and surrounding anatomy are
imaged, the position of the vein should be marked on the skin at two points along
the path of the vessel. The ultrasound probe is then set aside and the procedure
continues using the landmarks identified with ultrasound, but without active
ultrasound assistance. This method does improve success rates, although
complications are reduced further when using dynamic ultrasound.
The dynamic method uses ultrasound in real time to visualize the needle
puncturing the vein. It is important that the ultrasound machine be positioned in

front of the proceduralist, making direct visualization possible. The transducer
marker should face to the left, the same direction as the marker on the screen.
This is critical when redirecting the needle; as the needle is moved toward the left
of the probe, it moves toward the left side of the screen.