Principles and Techniques of Dialysis

Introduction 2 basic techniques – haemo or peritoneal Several refinements within these Haemo –Dialysis –Filtration –diafiltration Peritoneal –Ambulatory or automated

Introduction Brief introduction of each technique Pros and cons What we do

Haemodialysis Diffusion based, utilises a countercurrent mechanism – idealised solution run against blood, countercurrent preserves diffusion gradient Requires secure access Good for small molecules - eg drugs, potassium 4hrs 3x per week, hospital or satellite based, expanding home programme

Haemofiltration Blood filtered and then plasma replaced with idealised, isotonic solution Convection based, better for middle molecules – animal models of sepsis Slower, needs too be continuous to maintain clearances Slow shifts preferable when haemodynamics difficult Again now all veno-venous - needs secure access

Haemodiafiltration Dialysis plus an element of filtration Preserves diffusion base for fast transfer of small solutes Filtration and replacement solution slows down osmotic shifts so better haemodynamically Efficient enough to be 4hrs 3x per week Probably the future no outcome trials yet

Haemo summary Dialysis currently treatment of choice, speed and clearances Filtration ideal for ITU with haemodynamic instability Haemodiafiltration probably the treatment of the future, a lot of new satellite units use this only Access crucial >80% should start with AVF

Peritoneal dialysis Tenckhof tunneled PD catheter Previous surgery, hernias, severe COPD, obesity, large size relative CI Ambulatory and automated CAPD and APD Hypertonic glucose (some glucose polymers) three strengths Solutes diffusion water osmosis

Continuous ambulatory peritoneal dialysis -CAPD L exchange 4X a day Sterile technique vital - pt or relative ~40 min day Allows independence, compatible with travel, 3-4x hospital visits per year Supplies delivered to home or holiday destination

Automated peritoneal dialysis- APD 10-20L overnight exchanges Usually day bag too Machine A4 ring binder size opens and shuts valves Programmeable by staff and patients Again portable technique – pt or relative can set up

CAPD vs APD High and low transporters High transporters move solutes quickly and get high quality dialysis Osmotic gradient soon lost leads to problems with fluid and glucose load Low transporters get good fluid exchanges but slower solute transfer and need longer dwell times

CAPD vs APD CAPD Better in general for low transporters No disturbance of sleep pattern Glucose polymers can be used in high transporters to slow loss of osmotic gradient Cheaper APD Better in general for high transporters, machine set for short dwell times maintaining osmotic gradient Sleep and cost More convenient if a working relative is helping

HD vs PD Cost Independence Cardiovascular stability/fluid balance Infection Comorbidity, home support etc Efficiency Survival Same PD better (home HD) PD continuous HD if an AVF PD difficult in frailer older population HD > PD No measured difference

What do we do? Pt choice ~70:30 HD : PD Written info Videos Patient education programme including tour, and talks from staff and other patients Early planning of access (transplantation and conservative Rx)