Principles and Equipment
Peritoneal dialysis (PD) utilizes the patient's peritoneum as a semipermeable membrane. Dialysis solution is infused into the abdominal cavity, allowing the exchange of solutes between blood and the dialysis solution to remove metabolic waste, maintain electrolyte and acid-base balance, and eliminate excess fluid. Solute removal primarily occurs through diffusion, while water removal relies on ultrafiltration. The efficiency of solute removal is influenced by the concentration gradient between capillaries and the abdominal cavity, the volume of dialysis solution exchanged, the dwell time of the dialysis solution, the peritoneal surface area, the properties of the peritoneum, and the molecular size of the solutes. The efficiency of water removal depends on factors such as the water permeability of the peritoneum, the peritoneal surface area, and the osmotic gradient across the membrane.
Peritoneal dialysis equipment consists mainly of the peritoneal catheter, the connection system, and the dialysis solution. The peritoneal catheter serves as the pathway for the dialysis solution to enter and exit the abdominal cavity. It requires surgical placement, with the optimal location of the catheter tip being the pouch of Douglas in the rectouterine or rectovesical space. This area is the lowest position in the abdominal cavity, with minimal omental coverage, reducing the likelihood of catheter wrapping.
The external portion of the catheter connects to the dialysis solution via a connection system. The dialysis solution includes three main components: an osmotic agent, a buffer, and electrolytes. Glucose is the most commonly used osmotic agent, with concentrations of 1.5%, 2.5%, and 4.25%. Higher concentrations lead to greater ultrafiltration and increased water removal within a given time, with concentrations selected based on the patient's level of fluid retention. Newer dialysis solutions use agents such as icodextrin or amino acids as osmotic agents and often employ lactate instead of bicarbonate to provide buffer capacity.
Indications and Treatment
Indications
Peritoneal dialysis is indicated for both acute kidney injury and chronic kidney failure.
Given that peritoneal dialysis does not require specialized equipment, has minimal effects on hemodynamic stability, preserves residual renal function better, and does not require anticoagulation, it may be prioritized for certain chronic kidney failure patients, such as infants, children, those with unstable cardiovascular conditions, those with significant bleeding or a bleeding tendency, patients with poor vascular access or repeated failed arteriovenous fistulas, patients with good residual kidney function, and those with favorable household hygiene conditions. Additionally, peritoneal dialysis can be considered for certain toxic conditions or congestive heart failure in the absence of hemodialysis facilities.
However, peritoneal dialysis is not suitable for patients with extensive peritoneal adhesions, abdominal wall abnormalities preventing catheter insertion, or severe peritoneal defects.
Peritoneal Dialysis Modalities
Initial treatment modalities for peritoneal dialysis include continuous ambulatory peritoneal dialysis (CAPD), daytime ambulatory peritoneal dialysis, intermittent peritoneal dialysis, and automated peritoneal dialysis. CAPD is the most commonly used modality. The recommended dialysis volume is 6–10 liters per day, with 3–5 exchanges during the day (3–6 hours dwell time per exchange) and one exchange at night (10–12 hours dwell time). Dosage should be individualized to optimize solute clearance and fluid balance while preserving residual renal function as much as possible.
Assessment of Peritoneal Transport Function
Peritoneal transport function is assessed using the peritoneal equilibration test (PET). Transport function is classified into four categories: high transport, high-average transport, low-average transport, and low transport. High transporters tend to clear solutes effectively but may have difficulty with ultrafiltration, leading to excess fluid accumulation. Conversely, low transporters show the opposite pattern. For high transporters, dwell time can be shortened to improve ultrafiltration, whereas low transporters may require adjustments to dialysis volume to enhance solute clearance.
Assessment of Dialysis Adequacy
Dialysis is considered adequate if the weekly urea clearance index (Kt/V) is ≥1.7, the weekly creatinine clearance (Ccr) is ≥50 L/1.73 m2, and there are no signs of toxin accumulation, fluid overload, or poor nutritional status.
Complications
Peritoneal Catheter Dysfunction
Catheter dysfunction may include displacement or blockage of the catheter. Interventions such as urokinase thrombolysis, increased physical activity, or the use of mild laxatives to maintain bowel regularity may be employed. If these measures fail, surgical repositioning or catheter replacement may be required.
Infections
Infections related to peritoneal dialysis are common acute complications. These include peritoneal dialysis–associated peritonitis, exit-site infections, and tunnel infections. Infections are a major cause of technical failure and mortality.
Diagnostic criteria for peritoneal dialysis–associated peritonitis include:
- Abdominal pain and cloudy dialysis solution, with or without fever.
- Dialysis effluent white blood cell count >100/mm3, with neutrophils accounting for more than 50%.
- Positive culture for pathogenic microorganisms in dialysis effluent (meeting at least two of these three criteria).
If peritonitis is confirmed, immediate anti-infective treatment is required. Empirical antibiotic therapy should cover both gram-positive and gram-negative bacteria (e.g., a first-generation cephalosporin or vancomycin combined with an aminoglycoside or third-generation cephalosporin) and should be administered intraperitoneally. Antibiotics should be adjusted based on sensitivity test results, with treatment lasting at least two weeks. Severe or special infections may require three weeks or longer. If there is no improvement after five days of treatment with sensitive antibiotics, catheter removal should be considered. In cases of fungal infection, catheter removal is required promptly.
Exit-site and tunnel infections, collectively referred to as catheter-related infections, present as purulent or bloody discharge from the exit site, with surrounding skin erythema, tenderness, or induration. Tunnel infections can cause subcutaneous tenderness along the catheter's path. Common pathogens include Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. Treatment involves antibiotics guided by drug sensitivity testing, with a treatment duration of 2–3 weeks.
Hernias and Dialysate Leakage
The accumulation of large volumes of dialysate in the abdominal cavity increases intra-abdominal pressure, leading to the development of hernias in weakened areas of the abdominal wall. Incisional hernias are the most common, followed by inguinal and umbilical hernias. For patients with hernias, reducing the volume of dialysate dwell or switching to nighttime dialysis is necessary, with surgical repair often required.
Dialysate leakage is also associated with elevated intra-abdominal pressure. Leakage can occur through the catheter insertion site into loose abdominal tissues or into the scrotum and penis via the patent processus vaginalis, causing genital edema. Leakage may also occur into the pleural cavity through weak areas of the diaphragm, leading to pleuroperitoneal fistulas. Blood-based dialysis may be required, and surgical repair is necessary for persistent pleural effusion.