Principles of Peritoneal Dialysis

Diffusion Transfer by diffusion is the passive transfer of solutes across the membrane, without the passage of solvent (water). 1 2 Blood Membrane Dialysate 1 - Red blood cell 2 - Bacteria Sodium Potassium Chloride Bicarbonate Beta 2-m (Solute PM>5000) Urea Creatinine Uric acid

Factors effecting diffusion Membrane Surface 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

Factors relevant to PD Membrane Surface 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

Weekly plasma clearances L/week

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)

Osmosis Movement of water from an area of low solute concentration to an area of high solute concentration. Blood 280 - 295mOsm/L Dialysis solution 347- 486mOsm/L Water Solute

Ultrafiltration CAPD

Ultrafiltration

Ultrafiltration

Clearance – Peritoneal Equilibration Twardowski, University of Missouri

Process of PD Exchange CAPD 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

Outline benefits of PD Medical Psycho-social 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

Disadvantages Medical Risk of infection Psycho-social 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

CAPD Benefits Continuous Therapy Volume Limitations 24 Time 24 Time High transporters will have poor UF 4 x per day exchange IP pressure with large volumes Optimum dialysis for low permeability No night time Tx Can perform anywhere Ambulatory Anywhere 4 - 5 Exchanges Long Dwells

APD Benefits Optimum dialysis for High permeability No night time Tx Intermittent Therapy Volume Benefits Limitations 24 Time Optimum dialysis for High permeability No night time Tx Can perform anywhere Ambulatory Anywhere 4 - 5 Exchanges Shorter Dwells Dry night Low transporter will have poor clearance Exchange burden IP Pressure with large volumes