Renal Replacement Therapies

In end-stage kidney disease, kidney functions can be replaced only by dialysis or by kidney transplantation. The planning for dialysis and transplantation is usually started in Stage 4 of chronic kidney disease. Most patients are candidates for both hemodialysis and peritoneal dialysis (see below). There are few differences in outcomes between the two procedures. Your physician or an educator will discuss the appropriate options with you and help you make a decision that will match your personal and medical needs. It is best to choose your modality of dialysis after understanding both procedures and matching them to your lifestyle, daily activities, schedule, distance from the dialysis unit, support system, and personal preference.

Your doctor will consider multiple factors when recommending the appropriate point to start dialysis, including your laboratory work and your actual or estimated glomerular filtration rate, nutritional status, fluid volume status, the presence of symptoms compatible with advanced kidney failure, and risk of future complications. Dialysis is usually started before individuals are very symptomatic or at risk for life-threatening complications.

Dialysis

There are two types of dialysis 1) hemodialysis (in-center or home) and 2) peritoneal dialysis. Before dialysis can be initiated, a dialysis access has to be created.

Dialysis Access

A vascular access is required for hemodialysis so that blood can be moved though the dialysis filter at rapid speeds to allow clearing of the wastes, toxins, and excess fluid. There are three different types of vascular accesses: arteriovenous fistula (AVF), arteriovenous graft, and central venous catheters.

1. Arteriovenous fistula (AVF): The preferred access for hemodialysis is an AVF, wherein an artery is directly joined to a vein. The vein takes two to four months to enlarge and mature before it can be used for dialysis. Once matured, two needles are placed into the vein for dialysis. One needle is used to draw blood and run through the dialysis machine. The second needle is to return the cleansed blood. AVFs are less likely to get infected or develop clots than any other types of dialysis access.
   
   
2. Arteriovenous graft: An arteriovenous graft is placed in those who have small veins or in whom a fistula has failed to develop. The graft is made of artificial material and the dialysis needles are inserted into the graft directly.
   
   
3. Central venous catheter: A catheter may be either temporary or permanent. These catheters are either placed in the neck or the groin into a large blood vessel. While these catheters provide an immediate access for dialysis, they are prone to infection and may also cause blood vessels to clot or narrow.

Peritoneal access (for peritoneal dialysis): A catheter is implanted into the abdominal cavity (lined by the peritoneum) by a minor surgical procedure. This catheter is a thin tube made of a soft flexible material, usually silicone or polyurethane. The catheter usually has one or two cuffs that help hold it in place. The tip of the catheter may be straight or coiled and has multiple holes to allow egress and return of fluid. Though the catheter can be used immediately after implantation, it is usually recommended to delay peritoneal dialysis for at least 2 weeks so as to allow healing and decrease the risk of developing leaks.

Hemodialysis

Hemodialysis involves circulation of blood through a filter or dialyzer on a dialysis machine.

• The dialyzer has two fluid compartments and is configured with bundles of hollow fiber capillary tubes.
  
  
• Blood in the first compartment is pumped along one side of a semipermeable membrane, while dialysate (the fluid that is used to cleanse the blood) is pumped along the other side, in a separate compartment, in the opposite direction.
  
  
• Concentration gradients of substances between blood and dialysate lead to desired changes in the blood composition, such as a reduction in waste products (urea nitrogen and creatinine); a correction of acid levels; and equilibration of various mineral levels.
  
  
• Excess water is also removed.
  
  
• The blood is then returned to the body.

Hemodialysis may be done in a dialysis center or at home. In-center hemodialysis typically takes three to five hours and is performed three times a week. You will need to travel to a dialysis center for in-center hemodialysis.

Some centers may offer the option of nocturnal (night-time) hemodialysis wherein the therapy is delivered while you sleep. Long nocturnal dialysis offers patients a better survival and an improvement in their quality of life.

Home hemodialysis is possible in some situations. A care partner is needed to assist you with the dialysis treatments. A family member or close friend are the usual options, though occasionally people may hire a professional to assist with dialysis. Home hemodialysis may be performed as traditional three times a week treatments, long nocturnal (overnight) hemodialysis, or short daily hemodialysis. Daily hemodialysis and long nocturnal hemodialysis offer advantages in quality of life and better control of high blood pressure, anemia, and bone disease.

Peritoneal dialysis

Peritoneal dialysis utilizes the lining membrane (peritoneum) of the abdomen as a filter to clean blood and remove excess fluid. Peritoneal dialysis may be performed manually (continuous ambulatory peritoneal dialysis) or by using a machine to perform the dialysis at night (automated peritoneal dialysis).

• About 2 to 3 liters of dialysis fluid are infused into the abdominal cavity through the access catheter. This fluid contains substances that pull wastes and excess water out of neighboring tissues.
  
  
• The fluid is allowed to dwell for two to several hours before being drained, taking the unwanted wastes and water with it.
  
  
• The fluid typically needs to be exchanged four to five times a day.
  
  
• Peritoneal dialysis offers much more freedom compared to hemodialysis since patients do not need to come to a dialysis center for their treatment. You can carry out many of your usual activities while undergoing this treatment. This may be the preferable therapy for children.

Most patients are candidates for both hemodialysis and peritoneal dialysis. There are little differences in outcomes between the two procedures. Your physician may recommend one kind of dialysis over the other based on your medical and surgical history. It is best to choose your modality of dialysis after understanding both procedures and matching them to your lifestyle, daily activities, schedule, distance from the dialysis unit, support system, and personal preference.

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