Ultrasound Evaluation of Endo-AVF Using a Dialysis Access Clamp

Introduction

Percutaneous endovascular arteriovenous fistula (Endo-AVF) is a minimally invasive alternative to conventional surgical dialysis access. Hemodialysis is a process that requires a large volume of blood to be removed from the circulation and filtered through an external circuit to remove toxic by-products of oxidative metabolism such as potassium. Conventional dialysis access requires the surgeon to connect an artery and a vein either directly (arteriovenous fistula) or with the use of an intervening synthetic bridge graft (arteriovenous graft). These open surgical procedures involve 1 or more surgical incisions and often require general anesthesia with its associated risks.

In an Endo-AVF, a percutaneous technique is used to create a connection between an artery and vein without the need for a surgical incision or sutures. There are currently 2 commercially available devices that are designed to create Endo-AVF. Both devices share the common goal of connecting an adjacent artery and vein to provide a high flow superficial venous system sufficient to support the hemodialysis process.

One device uses 2 thin, flexible, magnetic catheters that are inserted percutaneously into an artery and vein in the arm (WavelinQ™—BD, Tempe, AZ). When placed in proximity, the magnets in each catheter attract each other, pulling the vessels together and aligning a radiofrequency electrode. The venous catheter, which contains the electrode, delivers a burst of radiofrequency energy to create a fenestration between the artery and vein. ¹ The anastomosis is either between the proximal radial artery and radial vein or ulnar artery and ulnar vein.

A competing technique (The Ellipsys® Vascular Access System—Avenu Medical, San Juan Capistrano, CA) ² uses thermal energy to fuse the walls of the artery and vein and create an arteriovenous communication between the deep communicating vein and the radial artery in the upper forearm. In both cases, it is essential to be able to monitor the flow in the superficial venous system with ultrasound to determine the suitability of the access for hemodialysis.

Methods

With the patient in the supine position, the superficial veins of the arm are evaluated with Color Doppler ultrasound. The diameter, peak systolic velocity, flow volume, and depth of the cephalic and basilic veins are recorded. To increase the flow through the cephalic vein, it may be useful to manually compress the basilic vein. This technique requires 2 operators and is cumbersome. Alternatively, one can use a standard spring-loaded dialysis fistula clamp which is designed to provide compression over a puncture site at the completion of dialysis. This clamp applies 1 to 1½ lbs. of pressure and provides effective hemostasis. The same device can be used to provide compression over the basilic vein during Color Doppler examination of the cephalic vein in the brachium (Figure 1).

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Figure 1.

Ultrasound guided placement of dialysis access clamp over the basilic vein.

The clamp is positioned over the medial aspect of the upper arm over the course of the basilic vein. The clamp does not impede arterial inflow but serves to obstruct venous outflow through the basilic vein. The diameter and flow volume in the cephalic vein are monitored (Table 1, Figure 4). Ultrasound images are obtained according to our exclusive 14-step protocol (Figure 5).

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Table 1.

Case Studies.

	Cephalic flow volume (without basilic compression) (mL/min)	Cephalic flow volume (with basilic compression) (mL/min)	Cephalic diameter (without basilic compression) (mm)	Cephalic diameter (with basilic compression) (mm)
Case 1	320	917	8.0	7.9
Case 2	407	1365	5.3	7.0
Case 3	47	236	3.3	3.5
Case 4	127	292	3.8	4.2
Case 5	516	776	6.2	6.0
Case 6 (Figure 4)	390	630	7.4	8.1
Average	301	703	5.7	6.1

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Figure 2.

B-Mode cephalic perforator vein.

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Figure 3.

Outflow vessel diagram post endo arteriovenous fistula creation.

Results

In addition, we do occasionally see the brachial veins diverting from the fistula outflow volume. One brachial vein is often coiled during the WavelinQ™ procedure where fluoroscopy is used to confirm placement and absence of flow. Coiling 1 brachial vein is an ancillary step taken to increase the outflow volume within the superficial system.

The cephalic perforator has 3 known connecting variations (Figure 3). The main connection identified is the cephalic perforator joining the ulnar system directly (Figure 2), the second is the cephalic perforator connecting to both the radial and ulnar systems (ie, “kissing perforator”), and third the cephalic perforator exclusively joining the radial system. When the cephalic perforator solely joins the ulnar system, usually the ideal location for endovascular anastomosis is thought to be a connection between the lateral ulnar vein and artery.

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Figure 4.

Case example: Color and pulsed wave Doppler comparison of with and without basilic vein compression.

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Figure 5.

Ultrasound protocol for post endo arteriovenous fistula creation.

With these specific fistulas, we tend to see lower peak systolic velocities in the outflow vessels. One reason slower flow is generated is secondary to the smaller anastomosis created in comparison with open surgical creation. It is also more reproducible. Another cause of lower flow is the wide-ranging outflow options attributable to the endovascular anastomosis. The outflow has the option to traverse through the superficial veins, the patent deep veins, as well as any branches that are anatomically unique to the patient.

Conclusion

We have successfully developed a simple non-invasive technique to predict the effect of basilic vein occlusion on cephalic vein flow that can be accomplished by a sole vascular technologist. The postoperative ultrasound exam is a crucial tool in assisting surgeons to determine whether further procedures or surgeries are necessary. Patent superficial branches are often noted by ultrasound and are evaluated for diameter and flow volume to determine whether they are usable for dialysis access. Our described above technique allows 1 operator to see how obstruction of the basilic vein would affect the flow in the cephalic vein and may guide further treatment.