Choosing a modality for chronic peritoneal dialysis
- John M Burkart, MD
John M Burkart, MD
- Section Editor — Dialysis
- Professor of Medicine/Nephrology
- Wake Forest University Medical Center
Several different techniques are available for performing peritoneal dialysis. Before discussing these modalities, it is helpful to briefly review the determinants of solute clearance with peritoneal dialysis. The rates (in mL/min) of peritoneal blood flow and dialysate flow with peritoneal dialysis are well below those achieved with hemodialysis (where both are often above 400 mL/min). Thus, the clearance of urea and other small solutes per unit time is much less with peritoneal dialysis than with hemodialysis. However, peritoneal dialysis is often performed in a continuous fashion so that the weekly solute clearances approach those with hemodialysis.
When discussing removal of solutes from the body by dialysis, we generally talk about two processes: diffusion and convection. It is important to appreciate that rates of diffusion for various solutes vary by molecular weight. The molecular weight for urea is very small, so urea rapidly diffuses into the peritoneal dialysate (which initially contains no urea) so that the average dialysate-to-plasma urea ratio is 0.7 at two hours and 0.9 at four hours. Comparable values for creatinine (a slightly larger molecule) are 0.45 and 0.65, respectively (figure 1); other larger molecular weight solutes diffuse much more slowly. Thus, urea and other small solutes are rapidly removed in the first few hours of a dwell; after four hours, there is very little further removal of small solutes due to near equilibration in concentrations. There is, however, continued removal of larger solutes, which do not equilibrate as rapidly.
TYPES OF PERITONEAL DIALYSIS
Peritoneal dialysis can be performed in a continuous or intermittent fashion . Continuous ambulatory peritoneal dialysis (CAPD) involves multiple exchanges during the day (usually three), followed by an overnight dwell. A modification involves one nighttime exchange with an exchange device, resulting in two overnight exchanges and three exchanges during the day . There used to be a device designed specifically for this option (the nightly exchange device); however, this device is no longer available. As a result, this modification of CAPD is seldom used; when it is used, a standard cycler is required.
Automated peritoneal dialysis (APD) uses a cycler to perform multiple overnight exchanges. Modifications to this technique include continuous cycler peritoneal dialysis (CCPD), nightly intermittent peritoneal dialysis (NIPD), and tidal peritoneal dialysis (TPD) :
●CCPD has a long daytime dwell (typically called a "last bag fill" [LBF]) and several cycles overnight. A minority of patients undergoing CCPD do not have a daytime dwell ("dry day"), while some patients must also do a "midday exchange" (MDE) to meet adequacy or ultrafiltration targets .
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- TYPES OF PERITONEAL DIALYSIS
- CONTINUOUS AMBULATORY PERITONEAL DIALYSIS VERSUS AUTOMATED PERITONEAL DIALYSIS
- DIALYSIS PRESCRIPTION
- Peritoneal equilibration test
- - Rapid transporters
- - Slow transporters
- - Residual renal function
- CHOICE OF PERITONEAL DIALYSIS MODALITY
- Body surface area
- Intermittent peritoneal dialysis
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS