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

• 1.5 -3L 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)