Page 422 - Libro 2

402 PART 6 — MISCELLANEOUS
PATHOLOGY BOX 26-1
AV Fistula Ultrasound Findings
B-mode Color Flow Doppler
Normal AV fistula
Stenotic AV fistula
Occluded AV fistula
AV, arteriovenous; PSV, peak systolic velocity; EDV, end-diastolic velocity; Vr, velocity ratio.
Compressible vessel
Intraluminal echoes, thickened walls
Phasic or nonphasic color flow pattern
Reduced flow lumen, disturbed color flow patterns
Turbulent flow pattern with unelevated velocities
PSV 150–300 cm/s EDV 60–200 cm/s Elevated velocities in
region of stenosis Vr 􏰀2
Absent Doppler signal
Intraluminal echogenicity, loss of flow lumen
No flow
SUMMARY
Ultrasound imaging when used in conjunction with clinical examination has proven to be an extremely powerful tool in the evaluation and management of hemodialysis access. It is a highly sensitive and noninvasive technique that complements the physi- cal examination. Preoperative imaging of both the arterial and venous systems should be performed to allow the surgeon to select the optimal hemodialysis access option. This technique has been shown to improve fistula maturation and has become the standard of care for preoperative vessel assessment. Ultrasonography has been shown to be extremely useful in access surveillance. Initial baseline examinations provide reference for follow-up studies. It has successfully been used to predict the matura- tion of fistulae. Criteria have been established to define threatened fistulae and grafts.
Critical Thinking Questions
1. B-mode imaging reveals a small (1.75 mm) calcified radial artery. What is the next step in the evaluation of this patient?
2. Dilated chest wall veins are seen during the examination of a patient with arm edema and a nonmaturing AV fistula. What noninvasive imaging study is recommended?
3. One week after the creation of a radiocephalic fistula, a patient presents with a cool, painful hand. What is the expected direction of flow in the distal native radial artery?
4. To assess fistula function, volumetric flow calculations are best measured in what part of the AV fistula?
REFERENCES
1. Sidawy AN. Arteriovenous hemodialysis access: the Society for Vascular Surgery practice guidelines. J Vasc Surg. 2008;48:1S–80S.
2. Macsata RA, Sidawy AN. Hemodialysis access: general considerations. In: Cronenwett JL, Johnston W, eds. Rutherford’s Vascular Surgery. 7th ed. Philadelphia, PA: Saunders Elsevier; 2010:1104–1114.