DIALYSIS ACCESS
The fistula, graft, or catheter through which blood is obtained for hemodialysis is often referred to as a dialysis access the anastomosis of an artery to a vein (e.g., the Brescia-Cimino fistula, in which the cephalic vein is anastomosed end results in arterialization of the vein. This facilitates its subsequent use in the placement of large needles (typically 15 ga circulation. Although fistulas have the highest long-term patency rate of all dialysis access options, fistulas are created i the United States. Many patients undergo placement of an arteriovenous graft (i.e., the interposition of prosthetic mate polytetrafluoroethylene, between an artery and a vein) or a tunneled dialysis catheter. In recent years, nephrologists, v health care policy makers in the United States have encouraged creation of arteriovenous fistulas in a larger fraction of initiative). Unfortunately, even when created, arteriovenous fistulas may not mature sufficiently to provide reliable acce they may thrombose early in their development. Novel surgical approaches (e.g., brachiobasilic fistula creation with tran fistula to the arm surface) have increased options for "native" vascular access.
Grafts and catheters tend to be used among persons with smaller-caliber veins or persons whose veins have been dama venipuncture, or after prolonged hospitalization. The most important complication of arteriovenous grafts is thrombosis failure, due principally to intimal hyperplasia at the anastomosis between the graft and recipient vein. When grafts (or f guided angioplasty can be used to dilate stenoses; monitoring of venous pressures on dialysis and of access flow, thoug may assist in the early recognition of impending vascular access failure. In addition to an increased rate of access failur catheters are associated with much higher rates of infection than fistulas.
Intravenous large-bore catheters are often used in patients with acute and chronic kidney disease. For persons on main tunneled catheters (either two separate catheters or a single catheter with two lumens) are often used when arterioven failed or are not feasible due to anatomical considerations. These catheters are tunneled under the skin; the tunnel redu from the skin, resulting in a lower infection rate than with nontunneled temporary catheters. Most tunneled catheters ar
jugular veins; the external jugular, femoral, and subclavian veins may also be used. Nephrologists, interventional radiol surgeons generally prefer to avoid placement of catheters into the subclavian veins; while flow rates are usually excelle frequent complication and, if present, will likely prohibit permanent vascular access (i.e., a fistula or graft) in the ipsilat rates may be higher with femoral catheters. For patients with multiple vascular access complications and no other optio access, tunneled catheters may be the last "lifeline" for hemodialysis. Translumbar or transhepatic approaches into the required if the superior vena cava or other central veins draining the upper extremities are stenosed or thrombosed.
Goals of Dialysis
The hemodialysis procedure is targeted at removing both low- and high-molecular-weight solutes. The procedure consis blood through the dialyzer at a flow rate of 300-500 mL/min, while dialysate flows in an opposite counter-current The efficiency of dialysis is determined by blood and dialysate flow through the dialyzer as well as dialyzer characteristic removing solute). The dose of dialysis, which is currently defined as a derivation of the fractional urea clearance during is further governed by patient size, residual kidney function, dietary protein intake, the degree of anabolism or catabolis comorbid conditions.
Since the landmark studies of Sargent and Gotch relating the measurement of the dose of dialysis using urea concentra National Cooperative Dialysis Study, the delivered dose of dialysis has been measured and considered as a quality assur tool. While the fractional removal of urea nitrogen and derivations thereof are considered to be the standard methods b dialysis" is measured, a large multicenter randomized clinical trial (the HEMO Study) failed to show a difference in morta difference in urea clearance. Still, multiple observational studies and widespread expert opinion have suggested that hig warranted; current targets include a urea reduction ratio (the fractional reduction in blood urea nitrogen per hemodialys and a body water-indexed clearance x time product (KT/V) above 1.3 or 1.05, depending on whether urea concentration For the majority of patients with ESRD, between 9 and 12 h of dialysis are required each week, usually divided into thre studies have suggested that longer hemodialysis session lengths may be beneficial, although these studies are confound characteristics, including body size and nutritional status. Hemodialysis "dose" should be individualized, and factors othe should be considered, including the adequacy of ultrafiltration or fluid removal. Several authors have highlighted improv associated with more frequent hemodialysis (i.e., more than three times a week), although these studies are also confo A randomized clinical trial is currently underway to test whether more frequent dialysis results in differences in a variety functional markers.