Peritoneal Dialysis

Illustration of a patient receiving peritoneal dialysis. Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Peritoneal dialysis (PD), is a mechanical treatment that removes substances such as water, salts, and waste products which build up in patients with advanced and permanent kidney failure. Since the 1980s, when dialysis first became a practical and widespread treatment for kidney failure, much has been learned about how to make the procedure more effective and minimize side effects. Peritoneal dialysis, as opposed to hemodialysis, an alternative form of treatment, does not need to be performed in a hospital setting.

Why Peritoneal Dialysis is Done

Healthy kidneys clean the blood by removing excess fluid, minerals, and wastes. They also make hormones that keep bones strong and blood healthy. Kidney failure causes accumulation of harmful wastes in the body, high blood pressure, water retention, and prevents the formation of new red blood cells. When this happens, treatment is needed to replace the work of the failed kidneys. PD performs many of the functions of the kidney and can delay or prevent many complications of kidney failure.

Types

Two types of PD are available: continuous ambulatory PD (CAPD) and continuous Cycler-Assisted PD (CCPD). CCPD is also sometimes called automated peritoneal dialysis (APD). The types are interchangeable; users can switch types or use a combination.

Preparation

Two double-cuff Tenckhoff peritoneal catheters: standard (A), curled (B). Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Before starting PD, a soft catheter (or tube) must be placed in the abdomen. The catheter carries dialysis solution into and out of the abdomen. Catheters are placed in the peritoneal cavity either by open surgery or by insertion through a small cut beside the navel. The catheter can be used immediately, but often it is not used to its full capacity for 2–3 weeks. During this time, scar tissue forms that holds the catheter in place.

The standard catheter for PD is made of soft tubing for comfort. It has cuffs made of a polyester material, called Dacron, which merge with scar tissue. The end of the tubing that is inside the abdomen has many holes to allow the free flow of solution in and out.

How Peritoneal Dialysis is Done

First, the catheter is used to fill the abdomen with cleansing liquid, called dialysis solution. The walls of the abdominal cavity are lined with a membrane called the peritoneum, which allows waste products and extra fluid to pass from the blood into the dialysis solution. The dialysis solution contains a sugar called dextrose that pulls wastes and extra fluid into the abdominal cavity. These wastes and fluid are then removed from the body when the dialysis solution is drained. The used solution, containing wastes and extra fluid, is then thrown away. The process of draining and filling is called an exchange and takes about 30 to 40 minutes. The period the dialysis solution is in the abdomen is called the dwell time. A typical schedule calls for four exchanges a day, each with a dwell time of four to six hours. Different types of PD have different schedules of daily exchanges.

• CCPD uses a machine, called an automated cycler, to perform three to five exchanges during the night during sleep. In the morning, one exchange is performed with a dwell time that lasts the entire day. Sometimes CCPD creates a solution absorption problem with the daytime exchange, which has a long dwell time. Some users need an additional exchange in the mid-afternoon to increase the amount of waste removed and to prevent excessive absorption of solution.
• CAPD doesn’t require a machine. Instead, a fresh bag of dialysis solution is drained manually into the abdomen. The solution is removed and placed in a bag four or more hours later. The cycle is then repeated with a fresh bag of solution. Typically three or four exchanges are needed during the day and one in the evening with a long overnight dwell time during sleep. The long overnight dwell time of CAPD may pose a problem. It's normal for some of the dextrose in the solution to cross into the body and become glucose. The absorbed dextrose doesn't create a problem during short dwell times. But overnight, some people absorb so much dextrose that it starts to draw fluid from the peritoneal cavity back into the body, reducing the efficiency of the exchange. To avoid this problem, some people use a minicycler (a small version of the machine used in CCPD) to exchange the solution once or several times overnight during sleep.

Close-up drawing of patient holding his catheter and transfer set in his left hand and a Y-tube in his right. Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

The bag of dialysis solution is connected to the catheter by a tube called the transfer set. When the catheter is first placed, the exposed end of the tube is securely capped to prevent infection. Transfer set design varies with the manufacturer. Connecting the transfer set requires sterile technique: surgical masks are worn and the transfer set and end of the catheter are soaked in an antiseptic solution before use.

At the beginning of an exchange, the disposable cap is removed from the transfer set and connected to a Y-tube. The branches of the Y-tube connect to the drain bag and the bag of fresh dialysis solution.

The first step of an exchange is to drain the used dialysis solution from the peritoneal cavity into the drain bag. Near the end of the drain, a tugging sensation is sometimes felt that signals most of the fluid is drained.

After the used solution is removed from the abdomen, the transfer set is closed or clamped and some of the fresh solution is allowed to flow directly into the drain bag. This flushing step removes air from the tubes.

The final step of the exchange is to refill the peritoneal cavity with fresh dialysis solution from the hanging bag.

Benefits

PD offers more flexibility and freedom than hemodialysis, which requires being connected to a machine for three to five hours three times a week. Other benefits include:

• Personal control of the therapy
• No needles required. This decreases the risk of hepatitis (viral infection of the liver) and other blood-borne diseases
• Preservation of the remaining kidney function
• Lower doses of medication required
• Better results after kidney transplantation

Risks

Complications

Infection is the most common complication of PD. This infection, most commonly peritonitis (inflammation of the membrane lining part of the abdominal membrane and its organs), is caused by bacteria collecting on the catheter. Improved catheter designs have increased protection, but infection is still a problem. Sometimes the risk of infection is so great that PD must be discontinued. Below are some approaches to keeping the catheter bacteria-free:

• Storage of supplies in a cool, clean, dry place
• Ensure that each bag of dialysis is free of contamination
• Perform the exchanges in a clean, dry, well-lit space
• Wash hands before handling the catheter
• Keep the catheter exit site clean
• Wear a surgical mask when performing exchanges

Some signs of infection include the following:

• Fever
• Nausea or vomiting
• Redness or pain around the catheter
• Unusual color or cloudiness in used dialysis solution
• A catheter cuff that has been pushed out

Compliance

One of the big problems with PD is that patients sometimes don’t perform all of the exchanges prescribed by their medical team. They either skip exchanges or sometimes skip entire treatment days when using CCPD. Skipping PD treatments has been shown to increase the risk of hospitalization and death.

Effectiveness

Several tests are used to determine if the exchanges are removing enough waste products, such as urea. Several schedule changes can be made if the laboratory results show that the dialysis schedule is not removing enough urea and creatinine:

• Increasing the number of exchanges per day for patients treated with CAPD or per night for patients treated with CCPD
• Increasing the volume of each exchange (amount of solution in the bag) in CAPD
• Adding an extra, automated middle-of-the-night exchange to the CAPD schedule
• Adding an extra middle-of-the-day exchange to the CCPD schedule

Peritoneal equilibration test

The peritoneal equilibration test (often called the PET) measures how much sugar has been absorbed from a bag of infused dialysis solution and how much urea and creatinine have entered into the solution during a four-hour exchange. The peritoneal transport rate varies from person to person. A high rate of transport indicates that sugar is being absorbed from the dialysis solution quickly.

Clearance test

In the clearance test, samples of used solution drained over a 24-hour period are collected, and a blood sample is obtained during the day when the used solution is collected. The amount of urea in the used solution is compared with the amount in the blood to see how effective the PD schedule is in removing urea from the blood.

Remaining kidney function

Normally the PD prescription factors in the amount of residual, or remaining, kidney function. Residual kidney function typically falls, although slowly, over months or even years of PD. This means that more often than not, the number of exchanges prescribed, or the volume of exchanges, needs to increase as residual kidney function decreases.

Research

• A recently completed study looked at the hemodynamic effects (blood pressure) resulting from different amounts of intra-abdominal peritoneal fluid and different glucose concentrations in the fluid. ^[1]
• An experimental dialysis solution was recently evaluated. ^[2] The pain associated with the influx of this solution was also evaluated. ^[3]
• An evaluation of body fat changes in peritoneal dialysis patients. ^[4]
• Volume overload in dialysis patients is related to an increased risk of cardiovascular mortality. The mechanism by which the increased risk occurs was evaluated. ^[5]

Clinical Trials

A list of ongoing clinical trials is available at ClinicalTrials.gov: peritoneal dialysis trials.

References

1. ↑ ClinicalTrials.gov. Acute Haemodynamic Effects of Peritoneal Dialysis as Evaluated by Sphygmocor Technology
2. ↑ ClinicalTrials.gov A Study to Evaluate the Efficacy and Safety of an Experimental Solution for Peritoneal Dialysis
3. ↑ ClinicalTrials.gov. A Subjective Evaluation of Inflow Pain Associated With the Use of an Experimental Solution for Peritoneal Dialysis
4. ↑ Vasselai P, Kamimura MA, Bazanelli AP. Factors associated with body-fat changes in prevalent peritoneal dialysis patients. J Ren Nutr. 2008 Jul;18(4):363-9. Abstract
5. ↑ Cheng LT, Gao YL, Qin C, et al. Volume overhydration is related to endothelial dysfunction in continuous ambulatory peritoneal dialysis patients. Perit Dial Int. 2008 Jul-Aug;28(4):397-402. Abstract

External Links

American Association of Kidney Patients

American Kidney Fund

National Kidney Foundation, Inc.