Page 177 - Libro 2

10 — Upper Extremity Arterial Duplex Scanning
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the biceps muscle anteriorly and the triceps muscle posteriorly. The deep brachial artery is visualized in the upper arm passing posterior to the humerus. The deep brachial, radial, and ulnar recurrent arteries are important sources of collateral blood flow at the elbow. The most common anatomic variant at this level is a so-called high takeoff of the radial artery, where the radial artery originates in the mid to up- per arm instead of distal to the antecubital fossa. An accessory or duplicated brachial artery is seen with a prevalence as high as 19% of some angiographic se- ries. Less commonly, the ulnar artery may originate in the upper arm in 2% to 3% of the population.
At the elbow level, the brachial artery passes obliquely from medial to lateral, dividing into the ra- dial, ulnar, and interosseous arteries. The radial artery continues to the wrist deep to the flexor muscles of the forearm before taking a more superficial course at the wrist between the flexor carpi radialis tendon and the radius. This is where the radial artery is readily palpated by physical exam. At the wrist, the radial ar- tery divides into two branches. The superficial branch passes anterior to the thumb where it anastomoses with the superficial palmar arch. The main branch of the radial artery courses posterior to the thumb where it becomes the deep palmar arch.
The ulnar artery gives origin to the interosseous artery in the proximal forearm before passing deep to the forearm flexor muscles. The interosseous artery continues to the wrist as the median artery in 2% to 4% of patients.3 The ulnar artery courses toward the wrist adjacent to the flexor carpi ulnaris tendon before crossing the wrist where it then passes deep to the hook of the hamate bone. It terminates as the superficial palmar arch. The hamate is an im- portant landmark. Traumatic injury to the ulnar ar- tery in this region can lead to arterial degeneration, thrombus formation, and potential occlusion. This describes the hypothenar hammer syndrome.
Branches from the superficial palmar arch, and to a lesser extent the deep palmar arch, via communi- cating vessels, give origin to the metacarpal arteries. These continue to the digits, forming paired digital arteries.
SONOGRAPHIC EXAMINATION TECHNIQUES
The following techniques illustrate the standard du- plex ultrasound examination of the upper extrem- ity arteries. Later in the chapter, additional methods will be discussed when describing some common disorders affecting the upper extremities. It is im- portant to remember to keep the examination room at a comfortable temperature; too cold a room can
cause peripheral vasoconstriction, which will impact Doppler spectral waveforms, particularly in the digits.
PATIENT PREPARATION
An explanation of the procedure and obtaining a pertinent history are the initial steps in upper ex- tremity arterial duplex scanning. Clothing covering the areas to be examined should be removed and a patient gown should be provided. Any jewelry such as chains, necklaces, bracelets, and watches should be removed.
PATIENT POSITIONING
The patient is positioned supine with the head ele- vated to conduct the exam (Fig. 10-3). The evaluation of the axillary artery is conducted with the arm in the “pledge position,” with the arm externally rotated and positioned at a 45° angle from the body.
SCANNING TECHNIQUE
Blood pressure at the brachial artery is obtained and documented for each arm. Each extremity is exam- ined sequentially to include the subclavian, axillary, brachial, radial, and ulnar arteries. The peak systolic velocities (PSVs) are documented point to point in each major vessel using an optimal 45° to 60° trans- ducer angle in the longitudinal plane. When irregu- larities are noted, Doppler signals are obtained using a “stenosis profile” consisting of a prestenosis Doppler PSV, stenosis PSV, and documentation of poststenotic turbulence. When an aneurysm is encountered, mea- surements are obtained in the transverse view of the proximal, mid, and distal site in both the anterior– posterior (A/P) and lateral orientations. An attempt is made to visualize intraluminal thrombosis. It is im- portant to visualize the vessel in a true axial plane so as to not falsely overestimate the aneurysm diameter with an oblique view.
Examination of the subclavian artery can gener- ally be accomplished with a 5-MHz transducer. The windows for insonation of the origin of the subcla- vian artery include the sternal notch and supracla- vicular or infraclavicular approaches (Fig. 10-4A–C).
Obese patients may require a lower megahertz transducer. Using the sternal notch window, a recent study found 48 of 50 right subclavian artery origins and 25 of 50 left subclavian artery origins.4 To use the sternal notch approach, a small footprint, 3- to 5-MHz transducer is used. The artery may be iden- tified in the transverse view with the assistance of color Doppler. As the artery is identified, the trans- ducer is rotated 90° to obtain a longitudinal view (Fig. 10-5).