Peritoneal Dialysis

GENERAL PRINCIPLES

• There are two modalities in use: manual exchanges and automated cycler exchanges.

î The manual modality, also called continuous ambulatory peritoneal dialysis (CAPD), has the patient instill dialysis fluid into the peritoneum for a specified length of time, after which the dialysate is drained and replaced by another dwell.

î The automated modality, also called continuous cycling peritoneal dialysis (CCPD), typically operates overnight where a machine runs a preprogrammed set of exchanges while the patient sleeps. A final fill usually remains in the peritoneum and is carried during the daytime for continued solute exchange.

• Both PD modalities require strict adherence to sterile technique, and careful patient selection is necessary.

• Prescription and adequacy

î The choice between CAPD and CCPD usually depends on patient preference and on the transport characteristics of the peritoneal membrane. Manual exchanges (i.e., CAPD) can be used as a backup modality, particularly in the hospital where nurse staffing or machine availability may be limited.

î In writing PD orders, the following variables must be specified: dwell volume, dwell time, number of exchanges, and dextrose concentration of the dialysis solution. The dwell volume is typically between 2 and 3 L, and can vary based on patient characteristics. The dextrose concentration can be 1.5%, 2.5%, or 4.25%, providing the osmotic gradient for fluid removal. Higher dextrose concentrations allow for greater UF but also lead to more inward glucose diffusion and worsening hyperglycemia. Icodextrin is a glucose polymer preparation that can be used in longer dwell because it is minimally absorbed and thus maintains an effective osmotic gradient up to 18 hours. Commercially available PD solutions may have color-coded tabs with which patients may be more familiar rather than the actual concentrations (yellow for 1.5%, green for 2.5%, red for 4.25%).

î PD is less efficient than conventional hemodialysis. However, given its continuous nature, solute clearance and UF can approximate that of other modalities. Larger volumes and more frequent exchanges can assist with solute exchange. Increasing the concentration of dextrose can promote greater UF in volume-overloaded patients.

î Residual renal function is very important in the PD population, and avoidance of nephrotoxins should be practiced.⁵⁴

Complications

• Peritonitis is a common complication of PD and can be serious with up to 6% of peritonitis episodes resulting in death. It is diagnosed when at least two of the following are present: diffuse abdominal pain and/or cloudy dialysate effluent, a dialysate effluent WBC count of >100 cells∕μL (after a dwell time of at least 2 hours) with >50% neutrophils, and a positive dialysate effluent culture.

î Empiric intraperitoneal antibiotics should cover for both gram-positive and gram-negative organisms, with vancomycin or a first-generation cephalosporin PLUS a third-generation cephalosporin or an aminoglycoside.⁵⁵

î The intraperitoneal route is the preferred method of administration, unless the patient is overtly septic, in which case IV antibiotics should be used. Antibiotics can be tailored once culture results are known and should be continued for 2-3 weeks. Multiple organisms, particularly if gram negative, should prompt a search for intestinal perforation.

• Tunnel or exit site infections may present with local erythema, tenderness, or purulent drainage, although crusting at the exit site alone does not necessarily indicate infection. Treatment can be with oral cephalosporins (gram positive) or fluoroquinolones (gram negative). However, infections can be difficult to eradicate, and catheter removal may be required with a temporary transition to hemodialysis.

• Failure of PD fluid to drain is termed outflow failure. This may result from kinking of the catheter, constipation, or plugging of the catheter with fibrin strands.

• Small hernias are at particularly high risk for incarceration and should be corrected surgically while the patient is temporarily treated with hemodialysis. Fluid leaks can lead to abdominal wall and genital edema and typically result from anatomic defects. Hydrothorax usually occurs on the right side and can be diagnosed by a markedly elevated glucose concentration in the pleural fluid. Pleurodesis can eliminate the potential space and permit continuation of PD.

• Sclerosing encapsulating peritonitis is a complication of long-term PD. The peritoneal membrane becomes thickened and entraps loops of bowel, leading to symptoms of bowel obstruction. A bloody drainage may be present. Treatment is supportive with the focus on bowel rest and surgical lysis of adhesions. A trial of immunosuppression with prednisone 10-40 mg/d may have limited benefit.

• Hyperglycemia results from the systemic absorption of glucose from the dialysis fluid. Because peritoneal uptake of insulin is unpredictable, treatment with subcutaneous insulin is preferred.

• Unlike hemodialysis, patients on PD tend to experience hypokalemia, likely due to a continuous potassium exodus in the dialysate as well as from an intracellular shift from the increased endogenous insulin production. Oral replacement with low dose supplementation (10-20 mEq/d of potassium chloride) is usually sufficient. Potassium dietary restrictions may also be liberalized.

• Protein loss can be high, and the dietary protein intake should be 1.2-1.3 g/kg/d. Episodes of peritonitis can make the membrane even more susceptible to protein losses.