During peritoneal dialysis different molecules dialyze at different rates based on molecular weight. Creatinine, urea nitrogen and vitamin B12 have different molecular weights and different clearances based on the schedule of peritoneal dialysis employed.


Molecular weights:

(1) urea nitrogen: 60 Daltons

(2) creatinine: 113 Daltons

(3) vitamin B12: 1,352 Daltons


Different protocols for chronic peritoneal dialysis:

(1) continuous ambulatory peritoneal dialysis (CAPD)

(2) continuous cycler-assisted peritoneal dialysis (CCPD)

(3) nocturnal intermittent peritoneal dialysis (NIPD)


Factors affecting dialysis:

(1) volume of fluid in each exchange

(2) duration of dwell time for each exchange: the longer the dwell the time, the closer that the concentration of the compound in the dialysis fluid concentration gets to that seen in the plasma

(3) number of exchanges in a schedule


Different schedules may be employed

(1) daytime only

(2) nocturnal only

(3) daytime and nocturnal


Plasma levels of compound:

(1) for CAPD, the plasma urea or creatinine level should not change, so that the plasma level can be drawn anytime during the collection period

(2) for CCPD or NIPD, an "average" plasma urea or creatinine level should be used, based on a sample drawn midway through the dialysis period


clearance of compound in liters by schedule =

= (liters of fluid in drainage) * (drainage-to-plasma ratio for compound)



• liters of fluid in drainage = (collected volume of instilled fluid in liters) + (liters of ultrafiltrate)

• drainage-to-compound ratio for compound = (compound concentration in drainage) / (compound concentration in plasma)


clearance of compound in liters per day =

= (clearance in liters by schedule 1) + (clearance in liters by schedule 2) + .... + (clearance in liters by schedule n)


clearance of compound in liters per week =

= 7 * (clearance of compound in liters per day)


To read more or access our algorithms and calculators, please log in or register.