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Peritoneal dialysis uses the peritoneum as a natural permeable membrane through which water and solutes can equilibrate. Peritoneal dialysis is less physiologically stressful than hemodialysis, does not require vascular access, can be done at home, and allows patients much greater flexibility. However, it requires much more patient involvement than in-center hemodialysis. Maintaining sterile technique is important. Of the total estimated resting splanchnic blood flow of 1200 mL/min, only about 70 mL/min comes into contact with the peritoneum, so solute equilibration occurs much more slowly than in hemodialysis. But because solute and water clearance is a function of contact time and peritoneal dialysis is done nearly continuously, efficacy in terms of solute removal is equivalent to that obtained with hemodialysis.
In general, dialysate is instilled through a catheter into the peritoneal space, is left to dwell, and then drained. In the double-bag technique, the patient drains the fluid instilled in the abdomen in one bag and then infuses fluid from the other bag into the peritoneal cavity.
Peritoneal dialysis can be done manually or using an automated device. Manual methods include the following:
Continuous ambulatory peritoneal dialysis (CAPD) does not require a machine to do the exchanges. A typical adult infuses 2 to 3 L (children, 30 to 40 mL/kg) of dialysate 4 to 5 times/day. Dialysate is allowed to remain for 4 h during the day and 8 to 12 h at night. The solution is manually drained. Flushing the infusion set before filling reduces peritonitis rates.
Intermittent peritoneal dialysis (IPD) is simple, achieves higher solute clearance than automated intermittent peritoneal dialysis, and is useful chiefly in the treatment of acute kidney injury. In adults, 2 to 3 L (in children, 30 to 40 mL/kg) of dialysate, warmed to 37° C, is infused over 10 to 15 min, allowed to dwell in the peritoneal cavity for 30 to 40 min, and drained in about 10 to 15 min. Multiple exchanges may be needed over 12 to 48 h.
Automated peritoneal dialysis (APD) is becoming the most popular form of peritoneal dialysis. It uses an automated device to do multiple nighttime exchanges, sometimes with a daytime dwell. There are 3 types:
Continuous cyclic peritoneal dialysis (CCPD) uses a long (12 to 15 h) daytime dwell and 3 to 6 nighttime exchanges done with an automated cycler.
Nocturnal intermittent peritoneal dialysis (NIPD) involves nighttime exchanges and leaves the patient's peritoneal cavity without dialysate during the day.
Tidal peritoneal dialysis (TPD) involves leaving some dialysate fluid (often more than half) in the peritoneum from one exchange to the next, resulting in greater patient comfort and avoiding the problems (eg, frequent repositioning) resulting from inability completely drain dialysate. TPD may be done with or without a daytime dwell.
Some patients require both CAPD and CCPD to achieve adequate clearances.
Peritoneal dialysis requires intraperitoneal access, usually via a soft silicone rubber or porous polyurethane catheter. The catheter may be implanted in the operating room under direct visualization or at the bedside by blind insertion of a trocar or under visualization through a peritoneoscope. Most catheters incorporate a polyester fabric cuff that allows tissue ingrowth from the skin or preperitoneal fascia, ideally resulting in a watertight, bacteria-impervious seal and preventing introduction of organisms along the catheter tract. Allowing 10 to 14 days between catheter implantation and use improves healing and reduces the frequency of early pericatheter leakage of dialysate. Double-cuff catheters are better than single-cuff catheters. Also, a caudally directed exit site (the opening of the tunnel through which the catheter enters the peritoneal cavity) lowers the incidence of exit site infections (eg, by collecting less water while showering).
Once access is established, the patient undergoes a peritoneal equilibration test, in which dialysate drained after a 4-h dwell time is analyzed and compared with serum to determine solute clearance rates. This procedure helps determine the patient’s peritoneal transport characteristics, the dose of dialysis required, and the most appropriate technique. In general, adequacy is defined as a weekly KT/V ≥ 1.7 (where K is the urea clearance in mL/min, T is dialysis time in minutes, and V is volume of distribution of urea [which is about equal to total body water] in mL).
Peritoneal dialysis can cause complications (see Table: Complications of Renal Replacement Therapy). The most important and common are peritonitis and catheter exit-site infection. Symptoms and signs of peritonitis include abdominal pain, cloudy peritoneal fluid, fever, nausea, and tenderness to palpation. Diagnosis is made by clinical criteria and testing. A sample of peritoneal fluid is obtained for Gram stain, culture, and WBC count with differential. Gram stain is often unrevealing, but cultures are positive in > 90%. About 90% also have > 100 WBCs/μL, usually neutrophils (lymphocytes with fungal peritonitis). Negative cultures and WBC counts <100/μL do not exclude peritonitis, so treatment is indicated if peritonitis is suspected based on clinical or laboratory criteria and should begin immediately, before culture results are available. Peritoneal fluid studies may be falsely negative due to prior antibiotic use, infection limited to the catheter exit site or tunnel, or sampling of too little fluid.
Empiric treatment should be adapted to microbial resistance patterns of a given facility, but typical recommendations are for initial treatment with drugs active against gram-positive organisms, eg, either vancomycin or a 1st-generation cephalosporin, plus drugs active against gram-negative organisms, such as a 3rd-generation cephalosporin (eg, ceftazidime) or an aminoglycoside (eg, gentamicin). Doses are adjusted for renal failure. Drugs are adjusted based on the result of peritoneal dialysis fluid culture. Antibiotic therapy is usually given IV or intraperitoneally (IP) for peritonitis and orally for exit-site infections. Patients with peritonitis are admitted to the hospital if IV treatment is necessary or if hemodynamic instability or other significant complications arise.
Catheter tunnel exit-site infection manifests as tenderness over the tunnel or at the exit site along with crusting, erythema, or drainage. Diagnosis is clinical. Treatment of infection without drainage is topical antiseptics (eg, povidone iodine, chlorhexidine); if ineffective, vancomycin is usually used empirically, with culture results guiding subsequent therapy.
Most cases of peritonitis respond to prompt antibiotic therapy. If peritonitis does not respond to antibiotics within 5 days or is caused by recurrence of the same organism or by fungi, the dialysis catheter is removed. Overall, 5-yr survival rate in peritoneal dialysis patients is similar to that in hemodialysis patients (about 36%).
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