What is peritoneal dialysis and how does it work?

PD is a process during which the peritoneal cavity acts as the reservoir for the dialysate and the peritoneum serves as the semipermeable membrane across which excess body fluid and solutes, including uremic toxins, are removed (ultrafiltrate). The peritoneal membrane surface area is approximately equal to the body surface area (1.73 m²). The peritoneum consists of the lining of the inner surface of the abdominal and pelvic walls, including the diaphragm (parietal peritoneum) as well as the covering of the abdominal organs (visceral peritoneum). In males the peritoneum is a closed cavity, but in females the fallopian tubes and ovaries open into the peritoneal cavity.

The peritoneal membrane is in contact with the rich blood supply to the abdominal organs. Dialysate is infused into the peritoneal cavity via a catheter, allowed to dwell for a predetermined amount of time, and then drained (effluent). This process is called an exchange. Dextrose is used in the dialysate to create an osmotic gradient that causes water to be moved into the peritoneal cavity. The excess fluid is removed when the effluent is drained. Electrolytes and uremic toxins are removed by diffusion from an area of higher concentration (bloodstream) to an area of lower concentration (peritoneal cavity). Solute removal is further enhanced by “solute drag,” created when hypertonic dialysate is used, which increases ultrafiltration (UF) and causes additional low molecular weight solutes to be “dragged” along with the ultrafiltrate by convective transport.

What solutions are used for peritoneal dialysis?

The solutions used for PD should be biocompatible and preserve peritoneal membrane structure and function as much as possible. Conventional solutions use glucose as the osmotic agent and lactate as the buffer base. Commercially available solutions approximate the composition of extracellular body water except for potassium because many patients tend to be hyperkalemic. Potassium may be added (2 to 4 mEq/L) if necessary to correct hypokalemia. Oral potassium supplementation may also be prescribed. Dextrose provides the osmotic gradient between the plasma and the dialysate that leads to fluid and solute removal. The more hypertonic the dialysate is (i.e., 2.5% and 4.25% dextrose), the greater the UF. After a 2-L exchange has been dwelling for 4 hours, an average of 200 mL of ultrafiltrate will be obtained with a 1.5% exchange and an average of 600 to 1000 mL will be obtained with a 4.25% exchange. Table 19-1 highlights some common compositions of peritoneal dialysis solutions.

Table 19-1 Typical Composition of Common Peritoneal Dialysis Solutions

What is icodextrin?

Newer PD solutions use different osmotic agents for UF and clearance. Icodextrin (Extraneal) is a newer PD solution that differs from standard dialysis solutions in that it does not contain dextrose. In standard PD dialysate, glucose is the osmotic agent. Icodextrin is a starch-derived osmotic agent made from a mixture of glucose polymers (polyglucose). This solution allows for increased fluid removal from the bloodstream during PD as well as reduced net negative UF and increased small solute clearance. Icodextrin is intended to be used for once daily, long dwell exchanges lasting 8 to 16 hours. The dialysate solution should be used for no more than one exchange in a 24-hour period. Icodextrin is contraindicated for those with glycogen storage diseases or an allergy to cornstarch. The most common adverse effect from the use of icodextrin is a skin rash. Sterile peritonitis, hypertension, cold, headache, flulike symptoms, and abdominal pain are other possible side effects.

Are there different ways to perform peritoneal dialysis?

PD can be done either manually or automatically with a cycler. The manual form of PD is called continuous ambulatory peritoneal dialysis (CAPD). In CAPD, four or more exchanges are performed each day, seven days a week. Each exchange takes approximately 30 minutes. The patient connects to a tubing system, drains the effluent, and infuses new dialysate to dwell for a prescribed amount of time, usually four to six hours. The last exchange of the day dwells overnight and is then drained in the morning. Most patients do “bagless” CAPD; they disconnect from the tubing system at the end of each exchange, leaving a short transfer set or the capped catheter. Most CAPD tubing systems involve a Y configuration that enables the patient to “flush” any contaminants that might have been introduced while connecting to the system. Spiking the bag has been eliminated from most systems thus reducing the potential for contamination by as much as 50%.

What is automated peritoneal dialysis?

Automated peritoneal dialysis (APD) is performed with a cycler, usually at night while the patient sleeps. Cyclers are programmed according to the physician’s prescription to perform the following functions automatically: (1) measure the volume of dialysate to be infused, (2) warm the dialysate to body temperature before infusion, (3) time the frequency of exchanges, (4) count the number of exchanges, and (5) measure UF. Cyclers can be programmed for volumes of 50 to 3000 mL per exchange, have a last bag option to accommodate a unique diurnal (day) dwell (volume, percentage, additives), and have the capability to program one or more exchanges during daytime hours. All machines can be programmed to perform tidal PD. APD enables the patient to mix dextrose concentrations to achieve the desired UF (e.g., 2.5% mixed with 4.25% to achieve 3.3%). Patients must be taught to set up and run the machine by a trained professional, such as a self-care home dialysis training registered nurse with at least 12 months of experience in providing care and an additional 3 months of experience in this modality.

What are the different forms of automated peritoneal dialysis?

What kinds of catheters are used for peritoneal dialysis?

Catheters for both acute and chronic PD must transport fluid into and out of the peritoneal cavity as rapidly as possible and be biocompatible (maintain normal structure and function of the tissues near the catheter tract). Catheters manufactured for both acute and chronic PD come in sizes to accommodate neonates to adults.

Catheters for acute PD are usually placed at the patient’s bedside and include rigid catheters or soft silicone catheters. The patient should have an empty bladder and the rectum should be free of stool at the time of insertion to minimize the risk of organ perforation. Placement may be by direct insertion with a trocar or guidewire or by use of a peritoneoscope. Dialysis may be initiated immediately after insertion. Risks with the rigid catheter include bowel or organ perforation, dialysate leaks, peritonitis, discomfort, and inadvertent catheter loss. Silicone catheters, used for acute dialysis, are more comfortable and may be used for chronic dialysis if necessary. When an acute PD catheter is used immediately, the patient should be kept supine whenever dialysate is in the peritoneal cavity to minimize the occurrence of leaking of dialysate around the catheter.

Catheters used for chronic PD are usually placed surgically during a laparotomy or laparoscopically. The exit site should be directed in a downward or lateral direction and be located in the right or left midquadrant area, avoiding the belt line, scars, and skinfolds. Catheters are made of silicone or polyurethane with a radiopaque stripe for x-ray visualization. Catheters may be straight or coiled and have one or two cuffs. Coiled catheters are believed to minimize catheter migration out of the pelvis and have fewer outflow problems than straight catheters. The coiled catheter is also thought to improve patient comfort by keeping the tip of the catheter away from direct contact with the peritoneal membrane.

Cuffs are made of Dacron polyester or velour and provide for tissue ingrowth to stabilize the catheter. Cuffs are also intended to prevent migration of bacteria along the subcutaneous tunnel into the peritoneum. When placing double-cuffed catheters, the internal cuff is placed in the rectus muscle and the external cuff is placed in the subcutaneous tissue proximal to the exit site. Implanted catheters (Fig. 19-1) consist of an intraperitoneal segment containing side holes and an open tip for fluid flow; a subcutaneous segment that passes through the peritoneal membrane, muscles, and subcutaneous tissues; and an external segment that extends from the external cuff to the exit site. There are several versions of chronic catheters, including the Tenckhoff, column disk, Toronto Western, Swan neck, Cruz, and Moncrieff-Popovich catheters (Fig. 19-2). All versions include features intended to improve dialysate flow and decrease catheter complications.

Figure 19-1 Placement of double-cuffed Tenckhoff catheter.

(From Ash SR, Carr DJ, Diaz-Buxo JA: Peritoneal access devices. In Nissenson AR, Fine RN, Gentile DE, editors: Clinical dialysis, ed 2, Norwalk, Conn, 1990, Appleton & Lange.)

Figure 19-2 Chronic catheters. A, Straight Tenckhoff catheter. B, Curled Tenckhoff catheter. C, Toronto Western catheter. D, Swan neck (Missouri) catheter.

(From Smith T, editor: Renal nursing, Philadelphia, 1998, Harcourt Brace & Co. Ltd. Bailliere Tindall.)

What is meant by catheter break-in?

Catheter break-in is the period after the chronic catheter is placed, during which there is healing and tissue ingrowth into the cuff(s). The goals are to promote healing and prevent complications such as dialysate leaks, infections, and catheter obstruction. Healing may take up to six weeks and includes scab formation, granulation of tissue at the exit site, and epithelialization of the sinus tract. Full-volume dialysis, especially CAPD, should be avoided for at least 10 to 14 days to allow healing to occur. This healing period may necessitate the placement of a temporary hemodialysis access if the patient is severely uremic or is fluid overloaded and in need of immediate dialysis. Postoperatively the patient should remain supine when possible and avoid activities that increase intraabdominal pressure, such as straining to defecate, excessive coughing, crying, and lifting. Treatment options during the postoperative period include the following:

How is exit site care performed?

The goals in the immediate postoperative period are to stabilize the catheter, promote healing, and prevent infection. The exit site dressing should not be changed for five to seven days postoperatively unless there is excessive drainage under the dressing (blood, exudate, dialysate). The first dressing change should be performed by trained dialysis personnel and then may be taught to the patient. It is recommended that masks be worn during dressing changes to avoid contamination with oral or nasal flora. The skin around the exit site may be pink, similar to a healing scar, or it may have a brownish or purplish discoloration. During dressing changes the exit site should be assessed for signs of infection (erythema, exudate, induration, tenderness), the subcutaneous tunnel should be palpated for tenderness, and the catheter and connections should be inspected for integrity. The exit site should be cleansed with an antibacterial soap and water and covered with a sterile nonocclusive dressing, such as gauze and tape, or an air-permeable adhesive sheet. Cytotoxic agents (such as 1% povidone-iodine, 3% hydrogen peroxide, and 0.5% sodium hypochlorite) may interfere with wound epithelialization during the postoperative period. The catheter should be secured to the patient’s skin with tape or an immobilization device to avoid tension on the catheter and trauma to the exit site.

The goal of chronic exit site care is the prevention of infection. Exit site care is usually performed in the shower and consists of daily cleansing with an antibacterial soap with careful rinsing and drying. An antibacterial solution (e.g., 1% povidone-iodine, 3% hydrogen peroxide, and 0.5% sodium hypochlorite) is then applied in a circular motion to the skin around the exit site. The exit site should not be submerged in bathwater or hot tubs. Many programs allow swimming in chlorinated pools and the ocean. After the healing period (four to six weeks) a dressing may or may not be worn, according to patient or unit preference. It is extremely important to secure the catheter to the skin with tape or an immobilizing device to avoid trauma and infection should the catheter be accidentally tugged.

How is the adequacy of peritoneal dialysis determined?

The clinical condition of the patient should be paramount when evaluating the adequacy of PD. An important element of the evaluation is careful attention to both overt signs of uremia (laboratory values, fluid overload) and covert signs (sleep and concentration disturbances, anorexia, nutritional indices). Because PD is primarily a home therapy, patient compliance with the prescribed regimen must also be assessed in the evaluation of dialysis adequacy.

The efficiency of PD depends on the ability of the peritoneal membrane to ultrafiltrate fluid and solutes. Peritoneal clearance of solutes is determined by diffusion, which is driven by the concentration gradient between dialysate and plasma and by the “solute drag” created by hypertonic dialysate. Solutes and fluid may move from the intravascular compartment to the peritoneal cavity or from the peritoneal cavity to the intravascular compartment. Other substances lost in the effluent include protein (8.8 to 12.9 g/day), amino acids, water-soluble vitamins, trace minerals, and certain hormones.

UF and solute clearance in PD are influenced by (1) permeability of the peritoneal membrane, (2) volume of the exchange, (3) dialysate glucose concentration, (4) dwell time, and (5) molecular size of the solute. Clearance of solutes is expressed as the dialysate/plasma (D/P) ratio at a given point in time during the exchange. Equilibration is achieved when the D/P ratio approaches 1. Small solutes, such as urea (molecular weight = 60 Da), are highly diffusible and approach equilibration at four hours. Creatinine (molecular weight = 113 Da) moves more slowly toward equilibration, never reaching it during the typical four-hour CAPD exchange. Table 19-2 demonstrates solute clearances that can be achieved with different types of peritoneal dialysis.

Table 19-2 Solute Clearances with Various Peritoneal Dialysis Modalities