AV access creation is appropriate for patients with end- stage chronic renal insufficiency or those with acute renal failure and little chance for recovery of renal function. Most patients will require dialysis when the GFR falls to 10-15 mls per minute. Absolute indications for dialysis include symptoms of uremia: vomiting, malaise or altered sensorium; fluid overload unresponsive to diuretics, and hyperkalemia. The latter associated with EKG changes of peaked T waves, prolonged QRS or PR intervals (below).
The ultimate test of a fistula is whether it can support repeated dialysis. It must be relatively large (>6mm diameter), superficial (<6mm from the skin), and have high flow (>600 cc/min). Less than ideal fistulas may work depending on the circumstances. For example, a smaller diameter fistula may work in a thin patient as long as the flow rate is high enough to give functional dialysis. High flows can be problematic. While high output cardiac failure is rare, the fistula may “steal” blood away from the hand creating ischemia.
In the image on the left the fistula is 4.7mm but quite superficial (distance from the vein to the top of the screen/skin) and the flow is good at 600cc. On the right the fistula is 8mm (not shown) and also superficial. There is considerable turbulence shown by the variation in color coded flow rates.
The most common options for upper extremity fistulas are radio-cephalic, brachio-cephalic and brachio-basilic (with transposition). The decision making is primarily driven by vein availability and a preoperative ultrasound to determine vein location, size and patency is mandatory. Generally, the desired preoperative size for a usable vein is >3mm, for a usable artery >2mm.
The classic venous fistula configuration is the radio-cephalic or, “Cimino” fistula. This is created in the distal forearm, classically at the wrist. The radio-cephalic fistula can result in dilation of the entire cephalic vein to the cephalo-subclavian venous junction at the shoulder. If the lower arm cephalic is not available but the upper arm cephalic is intact, the brachio-cephalic fistula is the second best option. The radio- cephalic and brachio-cephalic fistulaerequire mobilizing the cephalic vein and connecting it end to side of the respective artery. A second procedure is not planned except in obese patients whose veins are deep requiring transposition to a more superficial location.
The brachio-basilic fistula requires two procedures. First the basilic vein is connected to the brachial artery. These structures are often quite close to each other and little dissection is required. The basilic vein is deep and runs close to the brachial artery and vein making it difficult to safely and reliably cannulate. A second operation is needed after the basilic of vein has “matured" (approximately 6 weeks) to re-route the vein anteriorly and superficially to lay along the biceps muscle (see figure above).
The ulnar-basilic fistula is used less commonly. While this may result in a functional fistula, it is inconvenient to cannulate and the patient's arm may rest on the fistula during dialysis.
The axillary artery is occasionally used for fistula inflow. This requires reversal of flow in the vein and lysis of the vein valves. This is done to prevent arterial steal, a dreaded complication that creates ischemia of the hand. Patients with no palpable radial or ulnar pulse or with a history of arterial steal are at high risk to develop steal after any fistula creation. This proximal anastomosis utilizes the larger size of the more proximal artery to deliver and the flow for both the fistula and the arm.
Both the artery and the vein will dilate once a fistula is created. To have a 70-80% chance of reaching the desired rule of 6’s, the vein should be 3mm and the artery at least 2mm. Arteries with calcification and veins with thickened walls on ultrasound are usable but less likely to dilate.
This ultrasound shows a 3mm vein with thin walls that is <5mm from the skin. The ultrasound exams the entire length of the vein, its depth from the skin, wall thickness and compressability (to r/o thrombus).
A longitudinal incision that is closer to the radial artery than cephalic vein is used. The length of the incision varies with the amount of cephalic vein that will be needed to be mobilized to make the “swing” over to the artery. Rarely the vein is so distant a second incision is needed.