Diagnostic ultrasound ( PDFDrive )

998 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
FIG. 27.51 Heavily Calciied Radial Artery at the Wrist. Longitudinal
image shows heavy arterial wall calciication (arrows).
FIG. 27.50 Sonographic Evaluation of the Forearm Veins With
Patient’s Arm Comfortably Resting on a Surgical Stand.
it is easier to map all the upper extremity arteries and veins on
the same side at one sitting so the surgeon has adequate information
if vessel character at surgery is suboptimal and another
access site needs to be chosen. If a suitable site for AVF creation
is not found on the arm evaluated, the other arm is evaluated.
he patient should be sitting upright for optimal evaluation of
the upper extremity arteries and veins, with the forearm resting
comfortably on a table or armrest. A tourniquet should be placed
ater arterial assessment, to assess vein caliber and distention 144
(Fig. 27.50). Central venous evaluation to include the IJV and
subclavian vein should then be performed with the patient supine,
for easier and potentially more accurate waveform assessment.
Sonographic assessment of the arterial wall should evaluate
the amount of calciication and degree of stenosis or occlusion,
if present. Vein walls should be described with as much detail
as possible to assess for wall thickening and thrombus, which
may limit future venous distention. he literature suggests that
preoperative criteria include a minimum intraluminal arterial
diameter of 2.0 mm and a minimal intraluminal venous diameter
of 2.5 mm to allow successful AVF creation, and a minimum
intraluminal venous diameter of 4.0 mm and a minimum arterial
diameter threshold of 2.0 mm for grats. 145,146
At least the caudal third of the brachial artery and the entire
radial artery are evaluated for intimal thickening, calciication,
stenosis, or occlusion, with more extensive evaluation of the
brachial and ulnar arteries as warranted, as well as the axillary
artery. he severity of arterial calciication may be categorized,
depending on surgeon preference, because it may be diicult to
suture into a heavily calciied artery, and the risk of emboli at
surgery may be higher 123 (Fig. 27.51). he arterial waveform is
evaluated for a normal triphasic or biphasic high-resistance low
pattern, and PSV is measured in these regions (Fig. 27.52). A
high brachial artery bifurcation is a common anatomic variant
and should be suspected when two arteries with accompanying
paired veins are seen in the upper arm 52 (Fig. 27.53). he two
arteries should be followed into the forearm to the wrist to conirm
the presence of a high brachial artery bifurcation and to exclude
a prominent arterial branch supplying the elbow, less commonly
seen.
For assessment of veins, the upright-seated position ensures
venous distention owing to hydrostatic pressure. For optimal
venous distention, the tourniquet should be placed on the arm
cranial to the area of interrogation so that the veins are distended.
Each vein should be inspected, with compression performed
along the entire venous length to exclude thrombus (Fig. 27.54).
he tourniquet is irst placed in the midforearm. he region of
the cephalic vein at the wrist is percussed for about 2 minutes
for maximal venous distention, and the cephalic vein inner
diameter is measured at multiple points in the forearm (Fig.
27.55, Video 27.25). hereater, the tourniquet is placed at the
antecubital fossa, and then the proximal upper arm, ater segmental
vein diameter measurement. Cephalic vein anterior wall
distance from the skin can be measured because if the cephalic
vein is too deep for easy cannulation, it may need to be supericialized
in a subsequent surgery (Fig. 27.56). It is not necessary to
measure the distance of the basilic vein from the skin; the vein
needs to be transposed for easier access. he median antecubital
vein typically connects the cephalic vein to the basilic vein and
is oten part of the AVF draining vein. he median antecubital
vein also can be used in creating an upper arm basilic or cephalic
vein AVF and so is commonly evaluated at the mapping ultrasound
procedure. he axillary vein, subclavian vein, and IJV
should be assessed for compressibility (when possible) and normal
waveforms (see Fig. 27.40).