Maintaining Peritoneal Dialysis Adequacy: the Process of Incremental
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Advances in Peritoneal Dialysis, Vol. 34, 2018 Maintaining Peritoneal Dialysis Adequacy: The Process of Incremental Susie Q. Lew Prescription Urea kinetics (weekly Kt/V) greater than 1.7 generally Key words define adequate peritoneal dialysis (PD). Adequacy Adequacy, incremental dialysis, prescription, end- of PD depends on residual renal function and PD stage renal disease clearance. Preserving residual renal function and peritoneal membrane characteristics helps to main- Introduction tain PD adequacy. Weekly urea kinetics (Kt/V) greater than 1.7 from The dose of PD can be augmented by increas- peritoneal dialysis (PD) and residual kidney func- ing the total dialysate volume. Greater volume can tion defines adequate PD (1–4). Some authors will be achieved by increasing either the fill volume per note that PD adequacy is not determined solely by exchange or the number of exchanges. Increased time urea clearance or Kt/V urea (5,6). Other criteria for on dialysis can be achieved by keeping PD fluid in the PD adequacy include adequate creatinine clearance, peritoneal cavity at all times. Increasing the convec- normal blood pressure, euvolemic status, correction tive force enhances solute removal with ultrafiltration. of anemia, optimal nutrition status, low inflammation, Incremental PD is used during urgent starts and maintenance of electrolytes (sodium, bicarbonate, po- in patients who are newly starting or who have been tassium, phosphorus, magnesium) in the normal range, on PD. Urgent starts require use of frequent low- prevention of cardiovascular events, and prolongation volume exchanges to avoid leaks at surgical sites. of residual kidney function (5,6). The dialysate volume can be gradually increased The adequacy of PD changes with alterations in provided that no leakage occurs, up to approximately the peritoneal membrane or residual kidney function. 2 L per exchange on day 14 for an average-size adult. Preservation of the peritoneal membrane and residual New-start patients require only 1 – 2 exchanges daily kidney function retains patients on PD. Damage to if they still have residual renal function. Incremental the peritoneal membrane has been reported with PD retains patients on PD as residual renal function inflammation, peritonitis, exposure to high concentra- wanes and peritoneal membrane characteristics tions of dextrose or dextrose degradation products, change because of dextrose exposure, infection, and exposure to inflammatory factors in the renin– and inflammation. angiotensin–aldosterone or vascular endothelial Use of a cycler permits patients to achieve adequa- growth factor systems (7,8). cy by increasing the volume per cycle and the number Needless to say, peritonitis should be avoided by of cycles per treatment. Using a non-dextrose-based advocating proper PD connectology, preventing and solution, such as icodextrin, allows patients to achieve treating exit-site and tunnel infections, and maintain- adequate ultrafiltration with less dextrose exposure. ing good bowel hygiene to avoid both diarrhea and Adequate dialysis can be achieved by manipulat- constipation. Minimizing exposure to dextrose can ing the dialysate dwell volume and the frequency of be achieved with a low-sodium diet, fluid restriction, exchanges, and by optimizing ultrafiltration. and the use of non-dextrose-containing solutions such as icodextrin (9,10). Using PD solutions with a physiologic pH and blocking the renin–angiotensin– From: Department of Medicine, George Washington aldosterone and vascular endothelial growth fac- University, Washington, DC, U.S.A. tor systems also preserve the peritoneal membrane Lew 11 (10,11). Avoiding nephrotoxic agents such as nonste- ratio of 0.82 – 1.03 and 0.65 – 0.81 respectively. roidal anti-inflammatory drugs, radiocontrast materi- Low-average and low transporters reach a dialysate- als, and certain antibiotics (such as aminoglycosides) to-plasma creatinine ratio of 0.50 – 0.64 and 0.34 – helps to preserve residual kidney function. Urine 0.49 respectively. The high transporters have poor output can be maintained with oral loop diuretics. ultrafiltration and adequate solute clearance. High- Low and high blood pressure both tend to affect the average transporters have adequate ultrafiltration and glomerular filtration rate. Infections in the genitouri- solute clearance. Low-average transporters have high nary tract negatively affect renal function. Eating a ultrafiltration and adequate to inadequate solute clear- low-protein diet can work in chronic kidney disease ance. Low transporters have excellent ultrafiltration, stages 1 – 5, but its role is questionable in patients but inadequate solute clearance. receiving PD, in whom protein loss occurs with di- Ultrafiltration is affected by the dextrose concen- alysis. Individualizing the dialysis treatment to avoid tration of the PD solution (14). Crystalloid solutions over-dialysis provides solutes for osmotic diuresis. with higher osmolarity tend to filter more fluid. The In the evolution from a new-start to a vintage pa- ultrafiltration occurs rapidly during the first 1 – 2 tient, kidney function gradually wanes and peritoneal hours, after which glucose metabolism or dilution, or membrane characteristics change because of dextrose both, results in less ultrafiltration as the hypertonic exposure, infection, and inflammation. Compared with state is lost. If the osmolarity of blood exceeds that an anuric patient, the new patient requires less PD to of PD fluid, then fluid will be reabsorbed. A colloid- achieve adequacy. Hence, incremental dialysis is a containing solution having a macromolecule with a consideration for new-start and vintage patients alike. high reflective coefficient (icodextrin) induces ultrafil- tration with an isotonic solution (15). Water transports Discussion across small intercellular pores. Icodextrin is absorbed through the peritoneal lymphatics and is ultimately Factors affecting PD prescription metabolized into glucose. Icodextrin solution provides Many factors affect PD prescription. The three main slow, sustained ultrafiltration of approximately 200 – factors are solute transport characteristics, the results 300 mL during a period of up to 16 hours. of the peritoneal equilibration test (PET), and patient Patient size and position also affect clearance. On factors such as patient size and position. average, the peritoneal cavity can tolerate approximately Solutes and water cross the cells of the mesothe- 30 mL/kg without discomfort or effect on lymphatic lium and endothelium that line, respectively, the peri- drainage (16,17). An overfilled peritoneal cavity causes toneal cavity and the peritoneal capillaries. The 3-pore discomfort and risk for hernia and could impede lym- model explains solute and water movement (12). The phatic drainage. The lowest intra-abdominal pressure large pores (100 – 200 Å) transport macromolecules. is associated with the supine position, followed by the They are few in number and are located on the venular standing position. The sitting position is associated with end of capillaries. The small pores (40 – 60 Å) trans- the highest intra-abdominal pressure (18). port small solutes and water. The ultrapores (4 – 6 Å) are transcellular pores that transport water only. Adjusting the prescription Diffusion curves show that, during PD, solutes Manipulation of the factors discussed in the preceding move according to size: small molecules transport subsection can increase the dialysis dose. The dialy- faster than larger ones, such that blood urea nitrogen sate volume can be increased by increasing either the transports faster than creatinine, which transports fill volume per exchange or the number of exchanges. faster than middle molecules. Moreover, solutes Alternatively, if dialysate is not currently kept in the move more rapidly within the first few hours and then peritoneum throughout the day, the peritoneum could slowly toward equilibrium (4 – 6 hours for blood urea be used for the entire day, avoiding “dry” periods. Fi- nitrogen, for example). nally, ultrafiltration can be increased by using dialysate The second factor affecting solute transport is the with a high dextrose concentration, adding to solute individual’s membrane transport characteristics as removal during the convective process (19). determined by the PET (13). High and high-average To effectively increase the dialysis dose, auto- transporters reach a dialysate-to-plasma creatinine mated PD, with the patient in the supine position, 12 Incremental Prescription to Maintain PD Adequacy can be used to increase fill volume, to increase the when the number of exchanges is increased, taking number of cycles, and to administer a higher dextrose advantage of the steep curve for solute and volume concentration solution to increase ultrafiltration (20). removal during the early part of a dwell. In addition, a non-dextrose-containing solution can Knowledge of residual kidney function aids in be used during the long day dwell or a day exchange prescribing either incremental or full-dose PD. An could be added to the increase dialysis dose (21). end-stage renal disease–naïve individual tends to have some urine output. In these individuals, if the Effect of patient characteristics estimated glomerular filtration rate exceeds 2 mL/ The dialysis dose changes with alterations in residual min, PD could be initiated at a lower dose. As re- kidney function or peritoneal membrane characteristics. sidual kidney function wanes, the PD dose would A patient who