Alex Lionberg, Shantanu Warhadpande, and Rakesh Navuluri

A baseline knowledge of the indications for dialysis is a good starting point for understanding how IR is involved in the care of these patients. Short-term dialysis in the acute setting and permanent dialysis for kidney failure both achieve the same goal, which is either augmentation or complete replacement of inadequate kidney function.

Acutely, the main indications for dialysis include severe acidosis, electrolyte abnormalities, fluid overload, dialyzable toxemias (such as lithium or aspirin overdose), and uremia. Determining whether the problem is severe enough to initiate dialysis is typically determined by the consultant nephrologist. If the problem is believed to be reversible, a temporary hemodialysis (HD) line for access will often suffice. In most cases these are simply placed at the bedside by the clinical service taking care of the patient. IR does not put temporary lines in unless there have been multiple failed attempts (which may indicate complex/altered venous anatomy or central venous occlusion). When there is some indication at the outset that the patient will need access for longer than a week, IR may be asked to place a tunneled hemodialysis line.

Chronic kidney disease (CKD) is common and often asymptomatic in earlier stages, with hypertension and diabetes being the two biggest risk factors for disease progression. Prudent medical management of these comorbidities can prevent or at least slow a decline in kidney function. The glomerular filtration rate (GFR) is the best overall assessment for evaluating CKD, and is estimated using serum creatinine. A GFR less than 60 for at least 3 months defines CKD. In earlier stages, CKD can be managed by the primary care physician. Patients have their GFR and urine albumin checked at regular intervals to monitor for disease progression. Referral to nephrology is indicated when GFR is less than 30 or when there is rapid progression.

Kidney failure is defined by a GFR less than 15 with symptoms or other specific criteria that would necessitate initiation of chronic renal replacement therapy. Note that patients can be labeled as having kidney failure when they reach this threshold, but this does not necessarily indicate dialysis is imminent. The designation of end-stage renal disease (ESRD) refers to the requirements that are met in order to qualify for Medicare coverage of renal replacement therapy.

The timing of initiating dialysis has many factors that go into it, but generally speaking the process is started only when symptoms of uremia arise, and with a GFR typically below 12. Transplant is an option for selected kidney failure candidates, but for our purposes we’ll focus on the role of dialysis. Options include peritoneal dialysis (PD) and HD.

There are several types of peritoneal dialysis, but the concept is similar for each; dialysis solution is infused into the abdomen through a permanent catheter and allowed to dwell. Waste materials diffuse from the bloodstream across the peritoneum and equilibrate with the fluid before being removed. The exchanges are typically done multiple times a day, which can create inconvenience for the patient. Even so, outcomes for PD tend to be better than HD in the short term, and it’s also cheaper. Peritoneal catheters are usually surgically placed, though placement by IR is increasing in some practice settings. Aside from this, IR does not have a significant role in the care of these patients.

As described, dialysis access creation leads to desirable vascular and physiologic changes necessary for fistula or graft use. However, changes in flow dynamics can also have deleterious consequences. For example, turbulence within the vessel as blood flows in and out of the dialysis access site exposes the vessel walls to an inconsistent pattern of wall shear stress. Areas of low wall shear stress induces a proinflammatory state and results in neointimal hyperplasia. This is one of the underlying causes of stenoses.

Early dialysis access dysfunction occurs anytime between fistula or graft creation and the first 3 months of use, most commonly as a result of fistula nonmaturation. A nonmatured fistula cannot be cannulated due to a combination of inadequate flow rate, suboptimal dilation of the arterialized vein, and/or a fistula depth too far below the skin.

In order for a fistula to be accessed and achieve flow rates necessary for the machine, the vessel needs to dilate. If the artery or vein chosen for the fistula are poor quality, the total dilation may be limited. Similarly, poor surgical technique may lead to incomplete dilation or a fistula that is too deep. Any additional insults on top of this, including the development of inflow or outflow stenoses, can also limit the ability of the fistula to dilate and reach a sufficient flow rate.

Grafts do not go through the process of maturation as fistulas do and can be used for dialysis relatively quickly (sometimes immediately). However, downstream neointimal hyperplasia can also occur shortly after placement due to the same physiologic changes.

Arterial stenoses are more likely to be pre-existent rather than sequelae of access creation. The typical patient will have known peripheral arterial disease or risk factors for it (diabetes, smoking history, older age). Detection of arterial stenoses usually occurs with a nonmatured fistula and a low flow rate.

Venous stenoses are the most common reason for referral to IR. In addition to the instigating effect of turbulent flow, repetitive needle puncture of the access site causes endothelial cell damage and the release of proinflammatory cytokines, furthering the propensity for neointimal hyperplasia and stenosis in the downstream vein. Stenoses affecting the central veins can lead to venous hypertension as pooling increases hydrostatic pressure. This may result in extremity edema, prolonged bleeding time after venipuncture, and aneurysmal dilation of the access. Decreased flow rates will be noted during dialysis.