WHAT IS DIALYSIS?

The solute concentration of solution A (Blood) is altered by exposing it to solution B (Dialysate) through a semipermeable membrane

Small solutes and water can pass easily

Larger solutes can’t pass through

Solute Transport

Convection (UF) Diffusion

DIFFUSION

Movement of solutes across a semipermeable membrane down a concentration gradient

Clearance of a solute

Concentration

gradient

Membrane

Blood and

dialysate flow rate

Molecular weight

CONVECTION

Movement of solvent down a hydrostatic pressure gradient

Dialysis system

Dialysers

Extracorporeal circuit

Dialysis machine

Water and dialysis fluid

Haemodialysis techniques

Several thousand hollow fibres Blood in the fibre lumen separated

from the dialysate by the semi-permeable membrane

Surface are 0.5 to 2 m2

DIALYSERS

Dialyser Surface area (m2)

FX 50 1.0

FX 60 1.4

FX 80 1.8

FX 100 2.2

DIALYSER PERFORMANCE

Qb 300 mls / min FX 60 FX 80 FX 100

Ultrafiltration coefficient (ml/h *mm of Hg)

46 59 73

Urea (ml/min) 193 197 198

Phosphate 177 185 189

Vitamin B12 135 148 161

The Blood Circuit

A Needle

V Needle

Dialyser

Pv

Pa Heparin Infusion

Ultrasonic Level Detector

Blood Pump

Venous Clamp

DIALYSIS MACHINE

Supplies dialysis fluid at the prescribed rate,

temperature and chemical composition

Monitors the extra corporeal circuit

Removal of UF by volumetric methods

BTM, BVM, OCM and BCM

10/05

Te

mp

Urea Creatinine Sodium Potassium

Sodium 140 Potassium 1.5 Bicarbonate 37 Calcium 1.75

Bloo

d (3

00 to

500

mls

/min

) D

ialysate (500 to 800 mls /m

in)

WATER AND DIALYSIS FLUID HD patients – 300 litres of water per week HDF patients – 12 to 25 litres infused directly to blood stream

Contamination Aluminium toxicity

Chloramines – haemolytic anaemia Water purification

HAEMODIALYSIS TECHNIQUES

Conventional HD

Haemofiltration

High flux HD

Haemodiafiltration

HAEMODIALYSIS

Diffusive  solute  removal  

 

Poor  middle  molecule  clearance  

 

UF  pump  

 

High  flux  HD    -­‐  highly  permeable  

Sieving curves for low-flux and high-flux dialysis membranes and human glomerular basement membrane.

Ledebo I , Blankestijn P J NDT Plus 2010;3:8-16

© The Author 2009. Published by Oxford University Press [on behalf of ERA-EDTA].

HAEMOFILTRATION Purely  convective  treatment    Highly  permeable  membranes    

High  volume  substitution  fluid    Removal  of  dissolved  solutes    

Excellent  middle  molecule  clearance    Well  tolerated  haemodynamically

Addition of convection to high flux HD

Improved small and middle molecule clearance

Delayed dialysis related amyloidosis

?Better stability and improved survival

HDF

Pre dilution

Mixed dilution

Post dilution

Mid dilution

Schematic illustration of the Nephros OLpūr™ MD 190 mid-dilution haemodiafilter.

Krieter D H et al. Nephrol. Dial. Transplant. 2005;20:155-160

Nephrol Dial Transplant Vol. 20 No. 1 © ERA-EDTA 2004; all rights reserved

Ledebo I , Blankestijn P J NDT Plus 2010;3:8-16

© The Author 2009. Published by Oxford University Press [on behalf of ERA-EDTA].

Blood volume monitor (BVM)

RBV – ratio of current blood volume to the blood volume at the start of dialysis

Principle – blood cells, Hb, plasma protein remain confined to the vascular system whilst the plasma water can pass both capillary membrane and dialyser membrane

BV – concentration change of these blood constituents

Sound velocity in the blood – temperature, density and compressibility of the blood

Mass fraction of proteins – HB and plasma proteins

UF – mass of plasma water will change but intravascular protein mass remain constant

Measures the velocity of the sound across the blood

85

87

89

91

93

95

97

99

101

00:0

0 00

:05

00:1

0 00

:16

00:2

2 00

:28

00:3

5 00

:41

00:4

7 00

:53

00:5

8 01

:05

01:1

0 01

:16

01:2

1 01

:27

01:3

4 01

:39

01:4

4 01

:49

01:5

5 02

:00

02:0

6 02

:11

02:1

7 02

:23

02:2

9 02

:34

02:4

0 02

:46

02:5

3 02

:58

03:0

4 03

:09

03:1

6 03

:22

03:2

8

RB

V

Time

RBV

RBV

RBV with Food

88

90

92

94

96

98

100

0:00

:00

0:03

:00

0:06

:00

0:10

:00

0:13

:00

0:16

:00

0:19

:00

0:23

:00

0:26

:00

0:29

:00

0:32

:00

0:36

:00

0:39

:00

0:42

:00

0:45

:00

0:48

:00

0:52

:00

0:55

:00

0:58

:00

1:01

:00

1:05

:00

1:08

:00

1:11

:00

1:14

:00

1:17

:00

1:21

:00

1:24

:00

1:27

:00

1:30

:00

1:34

:00

1:37

:00

1:40

:00

1:43

:00

1:47

:00

1:50

:00

1:53

:00

1:56

:00

1:59

:00

2:03

:00

2:06

:00

2:09

:00

Time

RB

V %

UF profiles

SODIUM PROFILING

Sodium in the dialysate fluid is manipulated in order to influence fluid shifts between the ICF and ECF

Higher concentration of sodium in the dialysate fluid than in the plasma prevents reduction in ECF osmolality, preventing IC water absorption; it may also support plasma refilling

Sodium profiling consists of changing the dialysate sodium (or conductivity) level from high to low or low to high in stepwise, linear or exponential fashion

May be beneficial in headache

Online conductivity monitor (OCM)

Conductivity sensors to measure pre and post dialyser change in sodium concentration of dialysate

Ionic dialysance (net solute exchange) is

calculated from dialysis conductivity Correlates with urea clearance Adequacy of the treatment given

Body composition monitor (BCM)

Combines bioimpedance spectroscopy with physiologic tissue model

Volume model – TBW and ECF

BCM – calculates over-hydration, lean tissue and adipose tissue from ECW and TBW

Thank you