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
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