Diagnostic ultrasound ( PDFDrive )

996 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
FIG. 27.48 Chronic Clot in Brachial Vein. One of the paired brachial
veins is small and chronically occluded (arrow). A, Brachial artery; V,
other, normal brachial vein.
2. Distal occlusion of IJV: he distal aspect of the IJV must be
demonstrated lowing into the junction with the medial
subclavian vein in the area of the brachiocephalic vein. If the
vein being traced is located more than a few millimeters away
from the carotid artery, it probably represents a collateral
vessel, rather than the IJV. Well-developed collaterals may
demonstrate normal respiratory phasicity, an additional pitfall.
Collateral vessels tend to be multiple and serpiginous and to
follow the occluded vein.
HEMODIALYSIS
here were 661,648 patients being treated for ESRD by the end
of 2013 in the United States, with 117,162 new cases that year. 1
Approximately 64% of these patients were undergoing hemodialysis.
120 A major cause of morbidity among ESRD patients is
related to vascular access procedures and associated complications
that increase health care costs in patients undergoing hemodialysis.
121 here are two options for permanent access placement
for ESRD patients requiring hemodialysis—an arteriovenous
istula (AVF) or a synthetic arteriovenous grat. Mature AVFs
are the preferred access when appropriate, because of the lower
rates of infection and thrombosis than with grat or catheter
access. 122-124
Several studies have shown that preoperative ultrasound
evaluation of the upper extremity veins and arteries may increase
the number of successful AVF placements through optimization
of surgical planning 125-127 as well as before grat placement in the
thigh. 128 Although sonographic postoperative hemodialysis access
evaluation may be beneicial in assessing AVF maturation, 129-131
the role of postoperative ultrasound evaluation for the detection
of access pathology and early intervention to improve the longevity
of a particular access is still being studied. 132-139
Ultrasound is useful in evaluation of palpable masses adjacent
to the vascular access to diferentiate hematoma from pseudoaneurysm.
It is also used in the evaluation of the swollen upper
extremity in a patient with an AVF or grat, or a swollen lower
extremity in a patient with a thigh grat, assessing for outlow
vein stenosis and DVT. Ultrasound is also used in the evaluation
of patients with arm and hand pain ater access placement to
evaluate for symptomatic steal.
he surgical creation of an AVF is preferred over a grat when
surgically and clinically feasible. Placement of access in the
nondominant upper extremity is preferred to allow continuance
of daily activities of life while the access site heals; however, a
dominant arm AVF is preferred to a grat in most patients. Possible
sites of hemodialysis access in order of preference are as follows:
(1) forearm AVF (radiocephalic AVF or transposed forearm
basilic vein to radial artery AVF); (2) upper arm brachiocephalic
AVF; (3) transposed brachiobasilic AVF; (4) forearm loop grat;
(5) upper arm straight grat (brachial artery to upper basilic or
axillary vein); (6) upper arm axillary artery to axillary vein loop
grat; and (7) thigh grat (Fig. 27.49). he cephalic vein is preferred
over a basilic vein transposition for istula formation because
the cephalic vein procedure involves less dissection and venous
manipulation. Additional, less common access conigurations
may also be placed based on surgical experience. 140
Sonographic Examination Technique
Both gray-scale and color Doppler ultrasound techniques should
be optimized for venous and arterial imaging as previously
discussed in this chapter. A high-frequency linear array 12- to
15-MHz transducer provides optimal spatial resolution and
adequate depth penetration to successfully evaluate supericial
vascular structures. A lighter-weight transducer with a smaller
footprint, such as a hockey stick coniguration, can increase the
speed and ease of the examination. A lower-frequency linear
array 9- to 12-MHz transducer may be needed for adequate
penetration in larger patients. A small-footprint curved array
transducer may be useful for evaluation of the brachiocephalic
vein and distal SVC.
It is important to apply light pressure and use plenty of gel
so as not to deform the circular shape of the vessels during the
mapping examination for accurate vessel diameters. All diameter
measurements are of the inner lumen measured in the anteroposterior
dimension in the transverse plane. Color and spectral
Doppler evaluation are performed in the longitudinal plane with
angle correction of 60 degrees or less. Blood low rate measurements
are performed in the longitudinal plane in a straight area
that is not curvy. In blood low rate measurement, the Doppler
gate is increased in size to encompass the entire vessel diameter,
and is angle corrected to 60 degrees or less, parallel to the posterior
vessel wall. hree to ive spectral Doppler waveforms are analyzed,
using the automatic blood low rate calculation in most ultrasound
scanners, using the formula of time-averaged mean velocity
multiplied by the inner vessel diameter. hree measurements at
the same location are performed and averaged, to ensure measurement
reliability.
Vascular Mapping Before
Hemodialysis Access
Upper Extremity
Attention to technical detail is necessary for optimum ultrasound
evaluation for hemodialysis access planning. 126,130,141-143 In general,