Hemodialysis is an important life-sustaining treatment for patients with advanced chronic renal insufficiency, and many patients prefer forearm arteriovenous fistulas, for which ultrasound is important for postoperative evaluation.
Ultrasound is frequently recommended by nephrologists for the following conditions.
1. the tremor or murmur of the endovascular fistula is diminished or absent.
2. postoperative difficulty in maturation of the fistula due to too many branches of the draining vein.
3. Difficulty with needling during dialysis.
4. Decreased blood flow, increased dynamic venous pressure, and increased access recirculation during dialysis.
5. edema and/or pain in the limb on the side of the fistula, prolonged bleeding time after puncture.
6, Unexplained Kt/v (an indicator of dialysis adequacy).
7. Suspected complications such as stenosis, thrombosis, blood theft, hematoma, aneurysm or venous aneurysm-like dilatation.
For the ultrasonographer, a careful and effective examination can provide more valuable information to the nephrologist, and the results can even be comparable to DSA, CT, and MRI. Because of the superficial nature of arteriovenous fistulae, we choose a 5-12 MHz linear array high frequency probe.
Before the examination, the ultrasonographer needs to understand a brief medical history, such as the number of dialysis, the location of the endovascular fistula, the anastomosis, the time of each use, and the blood flow. Observe the location of the surgical incision and the presence of body surface elevation; palpate for pulsations and tremors. Either lying or sitting position is acceptable, with upper limbs stretched.
The order of examination: inflow tract artery, arteriovenous fistula, outflow tract vein and geniculate branches, and check the distal artery after the fistula. During the examination, adequate amount of coupling agent should be used, the probe should touch the skin gently, and the technique should be gentle, so as not to put pressure on the vessels, especially the venous vessels, which may cause artificial stenosis; care should be taken to adjust the instrument conditions at any time. The color Doppler flow velocity scale should be adjusted at any time according to the flow velocity. Sometimes the flow velocity scale at the stenosis is adjusted to the maximum limit, but the flow is still mixed, and the diagnosis should be determined by combining gray-scale ultrasound and Doppler spectrum measurements. Tortuous veins may have a continuous irregular “S” shape or twist, lateral or deeper, making machine adjustment and tracking of the lumen particularly important.
Common complications of arteriovenous endovascular fistula
1. Stenosis: Most often occurs in the arteriovenous fistula and outflow tract veins. Ultrasound should measure the velocity of blood flow in the inflow tract artery (near the fistula), at the arteriovenous fistula, and in the outflow tract vein in segments. The diagnosis of arteriovenous fistula stenosis is generally based on the ratio of flow velocity at the fistula to flow velocity in the inflow artery; the diagnosis of outflow vein stenosis is generally based on the ratio of flow velocity at the suspected stenosis to flow velocity in the adjacent venous segment. There are no widely accepted ultrasound criteria for the diagnosis of stenosis. Recommended criteria: flow velocity ratio ≥ 2.5, stenosis ≥ 50%.
2, thrombosis and occlusion: thrombosis is closely related to stenosis, often occurring on the venous side, except for thrombosis due to deflation of the venous lumen. Color Doppler flow interruption and loss of spectral Doppler signal are seen at the occlusion. The inflow tract artery shows high resistance spectral changes.
Theft syndrome: For arteriovenous endovascular fistulas with end-to-side and lateral anastomoses, theft syndrome should be considered when the arterial flow at the distal end of the fistula is reversed and symptoms of hand ischemia are present. In some patients, there may be no ischemic symptoms in the hand when the arterial flow is reversed at the distal end of the fistula.
4, venous aneurysm-like dilatation: local internal diameter expansion can often appear on the outflow tract vein, measure its maximum internal diameter, range, and describe the relationship with the position of the internal fistula or elbow transverse.
5, pseudoaneurysm formation.
Report basic content and requirements
1. Ultrasound description: patency at the fistula, inflow tract artery and outflow tract vein flow, description of any complications such as stenosis, thrombosis, occlusion, venous aneurysmal dilatation, etc. If present, further description of the location, extent, and severity of the lesion is required.
2. Describe the spectral characteristics of the blood flow associated with the stenosis or occlusion and record the flow velocity. Describe the direction of arterial blood flow before and after the fistula.
3. Describe the location, internal diameter, and flow of the outflow tract veins if they have thick branches.
4, Other abnormalities are described accordingly.