Peritoneal dialysis (PD) therapy has been used for decades to treat acute and chronic renal failure in children because it is technically easier to perform than hemodialysis, requires no vascular access or anticoagulation, and avoids rapid hemodynamic changes in the critically ill child. Technical advances have led to the development of the automated cycler, but PD is still done by manual exchanges in most parts of the world.

PD is possible because of the characteristics of the peritoneal membrane that lines the intra-abdominal wall and viscera. This membrane is a very thin mesothelial monolayer overlying a layer of loose connective tissue separated by an intervening basement membrane. The space between the parietal and visceral surfaces of the peritoneum normally contains only a small amount of fluid, but can hold a large volume of solution if needed. During PD, the peritoneal membrane functions as a semipermeable dialysis membrane, allowing water and permeable solutes to pass freely, through osmosis, diffusion, and convection, between the capillaries and venules comprising the vasculature of the peritoneal membrane and the dialysis solution instilled into the peritoneal cavity. In general, permeable solutes travel from areas of high concentration to lower concentration, but transfer also is affected by the permeability characteristics of the membrane itself. The surface area of the peritoneal membrane is roughly equal to the body surface area in older children and adults. Infants and small children have a greater peritoneal surface area–to–body weight ratio than adults, so PD is more efficient in these patients. On average, the peritoneal membrane is a little more permeable in infants and young children relative to adults, so equilibration occurs more rapidly and exchange times should be shorter (1 hour or less) in these patients.

During the PD procedure itself, a specific volume (dwell volume) of specialized dialysis solution is instilled into the peritoneal cavity via a peritoneal dialysis catheter (PD access) for a specified period of time (dwell time) during which equilibration occurs. After the desired period of equilibration, the
dialysis effluent containing waste products and excess fluid (ultrafiltrate) is drained out, and fresh dialysis solution is instilled again to continue the process. Small molecules like urea, creatinine, potassium, and phosphorus pass freely from their higher concentration in the blood into the peritoneal fluid, while larger particles like blood cells and large proteins remain in the vascular space. Albumin and smaller proteins are filtered and removed in the PD fluid and may exacerbate hypoalbuminemia in critically ill patients. Normal concentrations of the essential electrolytes and minerals are maintained by using dialysis solution with a desired concentration of these solutes.

Commercially available dialysis solutions contain physiologic concentrations of sodium, chloride, and magnesium; slightly higher than physiologic concentrations of calcium; and no potassium or phosphorus. Potassium can be added to the solution in low or physiologic concentration if clinically indicated at the time of dialysis. Phosphorus should not be added, because of the risk of precipitation with calcium and magnesium already present in the solution. Lactate, which can be converted rapidly by the liver to bicarbonate and is stable in stored solution with the other salts and minerals, is used to provide alkali to treat the acidosis of renal failure. Bicarbonate-based solutions, which are not commercially available currently in the United States, can be made up specially if needed, but should not contain calcium because of the risk of precipitation. When liver function is poor, or in critically ill children with persistent lactic acidosis, a bicarbonate-containing solution may be required. If so, serum ionized calcium levels should be monitored closely and supplemental doses of calcium administered as needed or provided as a continuous intravenous drip or part of total parenteral nutrition.

The removal of excess fluid by ultrafiltration during PD requires an osmotic gradient that favors the movement of water from vascular space into the peritoneal fluid. High concentrations of dextrose are used for this purpose in commercial dialysis solutions approved for use in the United States. Commercially available PD solutions contain 1.5, 2.5, or 4.25 g/dL of dextrose, which is 10 to 50 times higher than the usual range of blood glucose concentration (75 to 150 mg/dL). In infants and small children, because they have a larger surface area to body weight, the rapid absorption of dextrose from the dialysate solution may result in rapid equilibration and poor ultrafiltration with extended dwell times. For this reason, dwell times of 1 hour or less are usually preferred for acute peritoneal dialysis.

PD can be performed technically either manually or with an automated cycler. Each technique requires specialized supplies and equipment and should be performed by trained personnel to avoid complications. Manual PD is simple to perform utilizing a heating bag to warm the dialysis fluid and a two-bag, Y-tubing set for older children or the Gesco Dialy-Nate system (Utah Medical Products, Midvale, UT) with a buretrol contained in the tubing to allow for the accurate measurement of small-volume exchanges (less than 100 mL) for infants. Pediatric cyclers usually have the capability to deliver exchange volumes of 50 mL or more per exchange, using programmed increments as small as 10 mL. The newer cyclers are small, portable devices that are easy to accommodate in small bedside spaces.

In critically ill children, when continuous fluid removal is necessary, frequent small-volume exchange cycles performed hourly or more often, throughout the 24-hour period, are prescribed. In more stable acute conditions, the duration may be limited to 8 to12 hours/day. The recommended starting exchange volume is 10 mL/kg or 250 mL/m². If the patient has no respiratory or myocardial instability, the volume may be increased gradually to a maximum of 40 mL/kg or 1,100 mL/m². The time components of each exchange include a fill time, dwell time, and drain time. Fill time through a properly functioning PD catheter should take no more than 5 to 10 minutes, and drain time should take only 10 to 20 minutes. Drain time may be extended if outflow is sluggish. Dwell time for continuous manual or cycler exchanges is usually 30 to 120 minutes, with shorter dwell times used to attain higher ultrafiltration rates. Dwell times of less than 30 minutes are less efficient, both for the clearance of solutes and ultrafiltration, and these short dwell times are not recommended. The fill time, dwell time, and drain time together constitute one exchange cycle.