Peritoneal Dialysis

Principles of Peritoneal Dialysis

Peritoneal Dialysis

Diffusion

Transfer by diffusion is the passive transfer of solutes across the membrane, without the passage of solvent (water).

1

2

1 - Red blood cell2 - Bacteria

Sodium

Potassium

Chloride

Bicarbonate Urea

Creatinine

Uric acid

Beta 2-m (Solute PM>5000)

Blood

Dialysate

Membrane

Peritoneal Dialysis

Factors effecting diffusion

MembraneSurface area, type, thickness

Blood film thickness Dialysate flow configuration

Concentration gradient Size of solute

Ultrafiltration Temperature of dialysate Qb - Blood flow rate Qd - Dialysate flow rate Time

Peritoneal Dialysis

Factors relevant to PD

MembraneSurface area, type, thickness

Blood film thickness Dialysate flow configuration

Concentration gradient Size of solute

Ultrafiltration Temperature of dialysate Qb - Blood flow rate Qd - Dialysate flow rate Time

Peritoneal Dialysis

Substance CAPD CCPD NIPD HD Urea (mol wt 60)

57

57

58

126

Creatinine (mo wt 113

47

47

36

100

Vit B12 (mol wt 1352)

34

30

17

30+

Weekly plasma clearances L/week

Peritoneal Dialysis

Solute Clearance in PD

• Factors that deliver clearance• Total volume

Volume per exchange Number of exchanges

• Dwell time

• Factors driving clearance requirements• Urea generation(diet, weight, metabolic rate)• Residual renal clearance(kidney function)• U.F. rate (solution tonicity, fluid intake)• Peritoneal membrane (permeability)

Peritoneal Dialysis

Osmosis

Movement of water from an area of low solute concentration to an area of high solute concentration.

Blood280 - 295mOsm/L

Dialysis solution347- 486mOsm/L

Water

Solute

WaterSolute

Peritoneal Dialysis

1st

2d

3d

Daytime UF vol.ml.

Night Ex.

Night UF vol.

ml.

Total UF vol.

ml.

1.36% 1.36% 1.36% 200 x 3 = 600 3.86% 700 1300

1.36% 2.27% 1.36% 400 + (200 x 2) = 800 3.86% 700 1500

2.27% 2.27% 2.27% 400 X 3 = 1200 3.86% 700 1900

1.36% 3.86% 1.36% 800 + (200 x 2) = 1200 3.86% 700 1900

2.27% 3.86% 2.27% 800 + (400 x 2) = 1600 3.86% 700 2300

Ultrafiltration

CAPDCAPD

Peritoneal Dialysis

Ultrafiltration

Peritoneal Dialysis

Ultrafiltration

Peritoneal Dialysis

Clearance – Peritoneal Equilibration

Twardowski, University of Missouri

Peritoneal Dialysis

% Pts. Membrane type

4-Hr D/P Creatinine

Characteristics

10% High 0.82 -1.03 Very efficient membrane Transports solute quickly Increased glucose absorption May have difficulty achieving

ultrafiltration At risk for low serum albumin

53%

High

Average

0.65 - .81

Efficient membrane Transports solute well Ultrafilters well

31%

Low

Average

0.50 - .64

Less efficient membrane Transports solutes somewhat slowly Ultrafilters well

6%

Low

0.34 -.49

Inefficient membrane Transports solutes slowly Difficult to obtain Cr Cl when no

residual renal function Ultrafilters very well

Peritoneal Dialysis

Process of PD

• Exchange• Drain(<20 Minutes)• Fill(<10 minutes)• Dwell - (CAPD = 4 - 8 hours)

- (APD = 30mins – 2 hours)

• CAPD• Manual• Day Time Exchanges• Procedure Every 4-8 Hours

Peritoneal Dialysis

Medical

Good BP control Minimal cardiovascular stress

Sodium and water control No heparin Steady state chemistries No vascular access Better hematocrit Good middle molecule clearance

Psycho-social

Self care - control Fewer dietary restrictions Less travel to center Easier to vacation Easy to learn No need for electricity or running water

Outline benefits of PD

Peritoneal Dialysis

Disadvantages

Medical

Risk of infection Peritoneal access Less “effective” therapy Biocompatibility of solutions Long term impact on peritoneal

membrane Protein loss Glucose absorption

Psycho-social

Self Care - control “Constant” treatment Body image-catheter, girth Family commitment Storage requirements

Peritoneal Dialysis

CAPD

ContinuousTherapy

0

Vo

lum

e

Time

Benefits Limitations

Optimum dialysis for low permeability

No night time Tx Can perform anywhere

High transporters will have poor UF

4 x per day exchange IP pressure with large

volumes

Ambulatory

Anywhere

4 - 5 Exchanges

Long Dwells

24

Peritoneal Dialysis

APD

IntermittentTherapy

0

Vo

lum

e

Time

Benefits Limitations

Optimum dialysis for High permeability

No night time Tx Can perform

anywhere

Low transporter will have poor clearance

Exchange burden IP Pressure with large

volumes

Ambulatory

Anywhere

4 - 5 Exchanges

Shorter Dwells

Dry night

24