What are the contents of Peritoneal Dialysis solutions?
All PD solutions are sterile fluids containing physiologically balanced amounts of electrolytes and an osmotically active agent. The latter is needed to draw fluid across the peritoneal capillaries into the PD fluid (UF). There is a variety of commercial PD solutions available, with the main differences related to one of two things: the base buffer (and accompanying solution pH) and the osmotically active agent.
Contents of Peritoneal Dialysis Solutions
|Dianeal PD2||Dianeal PD4||Physioneal 35||Physioneal 40||Extraneal||Nutrineal||Plasma (Adult)|
|Osmotic Agent, Osmolarity (mOsm/L)|
|1.1% amino acids||—||—||—||—||—||—||365||—|
PD , Peritoneal dialysis.
The electrolyte composition of PD solutions is roughly
- • Sodium 132 mEq/L
- • Chloride 95 to 105 mEq/L
- • Calcium 2.5 to 3.5 mEq/L
- • Magnesium 0.5 mEq/L
Potassium is not in any PD fluid, but it can be manually added using sterile technique if necessary. Standard PD solutions contain lactate rather than bicarbonate as the base buffer to prevent precipitation of calcium and magnesium in the PD fluid. The usual concentration of lactate is approximately 40 mEq/L, and the resulting pH is 5.2 to 5.5. The pH rises rapidly to a physiologic level above 7.0 within about 15 minutes of infusion into the peritoneal cavity. Lactate absorbed from the PD fluid is converted to bicarbonate by a healthy liver. PD solutions containing exclusively lactate as the base buffer are contraindicated in patients with preexisting severe lactic acidosis.
Alternatively, bicarbonate can be used as the primary base buffer, enabling a final solution pH of 7.4. This can be done by separating bicarbonate from calcium and magnesium using a dual-chambered PD container, with the separation maintained until just before infusion into the peritoneum. This reduces or even eliminates the pain during infusion of PD fluid that is experienced by some patients. It also has other theoretical advantages based on the more physiologic or “biocompatible” nature of the solution (discussed later).
Both standard PD solutions and dual-chambered bicarbonate-buffered PD solutions utilize dextrose (D-glucose) as an osmotic agent. Dextrose-containing solutions are usually available in three concentrations: 1.5 g/dL, 2.5 g/dL, and 4.25 g/dL (concentrations based on dextrose in its monohydrous, rather than anhydrous, form*). Manufacturers of some brands of dual-chambered solutions contain 10% more dextrose, however. Increasing the glucose content of PD solutions increases their osmolality, thus augmenting their ability to remove fluid (UF). The osmolalities associated with the previous standard dextrose concentrations are 346, 396, and 478 mOsm/kg, respectively. The osmotic gradient generated by dextrose-containing PD solutions dissipates over time as the dextrose is absorbed by the peritoneal capillaries. This gradient will dissipate more rapidly when lower concentrations of dextrose are used (e.g., 1.5 g/dL or 1.36 g/dL dextrose-containing solution, monohydrous or anhydrous, respectively) and in patients who have a larger peritoneal capillary network (e.g., fast membrane transport). Long exchange dwell times (e.g., >6 hours) can result in poor fluid removal, or even net negative fluid balance, because lymphatic absorption of PD fluid occurs at a constant rate (typically 1 to 2 mL/min), and can exceed transcapillary UF, particularly toward the end of a long exchange.
Both icodextrin (Extraneal) and amino acids (Nutrineal) have been used as alternative osmotic agents to dextrose. Icodextrin is a polyglucose molecule having a very large molecular weight, a property that increases colloidal osmosis (oncotic pressure) of the containing PD solution (as opposed to crystalloid osmotic pressure generated by dextrose-containing solutions). Extraneal does not contain any dextrose, has an osmolality of 282 mOsm/kg, and has a pH of 5.2. The fluid-removing capacity of this novel solution is not attenuated over time, making it ideal for long daytime (APD) or nighttime (CAPD) exchanges. Nutrineal also has the benefit of being glucose-free, utilizing 1.1 g/dL of amino acids as an osmotic agent. It has a pH of 6.4 and an osmolality of 365 mOsm/L.