This document discusses the basics of hemodialysis, including the main principles of diffusion, osmosis, filtration, and convection that hemodialysis is based on. It also describes the technique of hemodialysis, varieties of hemodialysis methods like conventional hemodialysis and online hemodiafiltration, and provides details on assessing hemodialysis treatment adequacy using Kt/V.
1. Dr. Osama El-ShahatDr. Osama El-Shahat
Consultant Nephrologist
Head of Nephrology Department
New Mansoura General Hospital (international(
ISN Educational Ambassador
2. Basics of hemodialysis:Basics of hemodialysis:
◦ Definition.Definition.
◦ Technique of hemodialysis:Technique of hemodialysis:
◦ Main principles:Main principles:
Diffusion.Diffusion.
Osmosis.Osmosis.
Filtration.Filtration.
Convection.Convection.
◦ Varieties of hemodialysis.Varieties of hemodialysis.
3. When a semi permeable membrane is placed between different
solutions the solutes move across this membrane until they
reach equilibrium
This is the theory by which dialysis is based on
4. Difussion:
The process by which particles, atoms or molecule move from
area of higher concentration to lower concentration across
semipermeable membrane.
Factors affecting :Factors affecting :
Concentration gradient
MW of solutes.
8. Dialysate delivered at a rate of 500ml/min
◦ 120 liters of dialysate / 4-hour session!!
Concentrated solutions mixed with water
Usually 1:34 or 1:40
Conductivity is a measurement of electric conductivity of Na to check
if dilution is correct
With proper dilution conductivity = 13-15
Serious hyponatremia or hypernatremia occurs if dilution is incorrect
9. H+ neutralized by Na HCO3 in the body
Acetate
◦ Transformed in LIVER to HCO3 (10-15 min)
◦ BUT is a potent vasodilator
Hypotension especially with liver disease
Acetate intolerance in high flux dialyzers
Bicarbonate
◦ Immediately neutralizes H+
◦ BUT precipitates Calcium salts (CaCO3)
Should be delivered separately as NaHCO3
Short life span of machine
Needs a strong post dialysis acid rinse (citric acid)
10. Attempts are made to increase the surface area of
contact between dialysate and dialyzer
◦ The Hollow fiber
◦ The parallel plate dialyzer
11.
12. TypesTypes
◦ Surface area.
◦ Low flux vs high flux.
◦ Biocompatibility.
◦ Technique of manufacture including hemo- adsorption.
13. Cellulose membrane (Cuprophan)
◦ Is the first membrane to be used
◦ Contains free hydroxyl radicals
They are able to activate complement inflammatory reaction
chronic inflammation protein catabolism + anorexia + malnutrition
Cardiovascular accidents
Cause dialysis related Amyloidosis
Increased incidence of infection
Rapid loss of residual kidney function
14. Substituted Cellulose
◦ Chemically bonding the free hydroxyl group
Cellulose di acetate
Cellulose Triacetate
◦ Addition of a synthetic material to cellulose
Hemophane (semi synthetic)
Synthetic modified cellulose (SMC)
Synthetic material
◦ Contains no cellulose
Polysolphone
PMMA
PAN
15. There is no definite techniques for biocompatibility
measurement
There is no clear evidence for its superiority except in
AKI
16. Ability of the dialyzer to clear urea from blood
The more clearance the better the dialyzer
Clearance can be calculated in vivo=
Qb x [BUN ART – BUN VEN]
BUN ART
Clearance is closely related to the surface area of HF
17. HF with a high urea clearance
◦ They contain pores bigger in number and size
◦ Must be with bicarbonate dialysis
◦ They perform more adequate dialysis
◦ Clearance of bigger molecules toxins e.g. (B2 microglobulin)
◦ expensive
18. The more the patient’s weight the larger surface area (and clearance)
you need
Patients with increased weight gain (volume overload) need a dialyzer
with high KUF
Much debate is present with use of biocompatible membrane EXCEPT
in AKI
High Flux dialyzer gives a better adequacy but is expensive
19. ESRD patients are frequently oliguric
If excess water is ingested
accumulation of water in body
edema, hypertension, pulmonary edema
To remove water Ultrafiltration
Addition of hydrostatic force squeezing out water from dialysate!!!
may be –ve (machine UF)
Or +ve (partial venous clamping)
The net force is reflected by the transmembrane pressure (TMP)
22. Problems with conventional diffusive hemodialysis
Excessive cardiovascular mortality
Insufficient removal of middle molecules
Insufficient removal of phosphate
High risk of intradialytic hypotension
Suboptimal dialysate quality
Chronic inflammation and protein-energy wasting
23.
24.
25.
26.
27. FiltrationFiltration::
Is movement of fluid through a filter as a result of hydraulic
pressure.
In hemodialysis, ultrafiltration , is movement of water from
blood under pressure gradient effect.
28.
29. ConvectionConvection:
Transfer of heat and solute by
physical circulation or or movement
of parts of gas or liquid.
Countercurrent circulationCountercurrent circulation
30.
31. Hemoperfusion therapy (DHP) is a method of treatment to
eliminate causal substances of disease in the blood by adsorption
that takes place by passing the blood directly through an adsorbent.
DHP is characterized by a simple extracorporeal blood circuit and
easy operation. Activated charcoal, and either polymyxin B or
hexadecyl alkyl compound immobilized adsorbents, are clinically
available at present.
The DHP using activated charcoal is mainly applied in cases of
intoxication with either toxic substances or a drug overdose.
Hemodialysis or plasma exchange is also applied in these situations.
.
32. Application of either DHP, hemodialysis or plasma
exchange is done according to the characteristics of the
toxins or drugs.
DHP using PMX is applied in cases of septic shock, and
its efficiency is suggested to be due to the removal of
anandamide in addition to endotoxins in the blood.
DHP using BM-01 is applied to a specific disease, dialysis
related amyloidosis, for the purpose of elimination of β2-
microglobulin.
36. HDFHDF is a blood purification therapy combining
diffusive and convective solute transport using a high-flux
membrane characterized by an ultrafiltration coefficient greater
than 2020 mL/h/mm Hg/m2 and a sieving coefficient (S) for β2-
microglobulin of greater than 0.6.
Convective transport is achieved by an effective convection
volume of at least 20%20% of the total blood volume processed.
Appropriate fluid balance is maintained by external infusion of
a sterile, non-pyrogenic solution into the patient's blood.
37.
38.
39. Kt/VKt/V is a number used to quantify hemodialysis andis a number used to quantify hemodialysis and
peritoneal dialysis treatment adequacy.peritoneal dialysis treatment adequacy.
K - dialyzer clearance of urea
t - dialysis time
V - volume of distribution of urea, approximately equal to patient's
total body water
◦ Kt/V target is ≥ 1.3, so that one can be sure that the
delivered dose is at least 1.2. In peritoneal dialysis the target
is ≥ 1.7/week.
The patients blood contains a high concentration of unwanted solutes that can be effectively removed by diffusion. Diffusions key mechanism is to move a solute from a higher concentration gradient to a lower concentration gradient.
For example, let us assume the blood in the filter has a high concentration of potassium molecules and on the fluid/dialysate compartment has a low concentration of potassium. The potassium gradually diffuses through the membrane from the area of a higher potassium concentration to the area of a lower potassium concentration until it is evenly distributed.
Remember the transport of a molecule through a membrane is governed largely by its molecular weight. Generally, the more a molecule weighs, the larger it is in size and the more resistant it is to transport. The chart gives an indication of relative molecular weights for some of the common molecules that we are concerned with in CRRT. Molecular weights are measured in units called Daltons.
Small molecules <300 Daltons, e.g. urea, creatinine, Na+, electrolytes
Intermediate or middle molecules 500-5000 Daltons e.g. B12
Large molecules 5000-50000 Daltons e.g. LMW proteins, beta 2 micro globulins, cytokines, myoglobin
Here is a visual example of how ultrafiltration works. On the blood side of the hemofilter you have a positive pressure gradient. on the fluid side of the hemofilter you have a negative pressure gradient. The effluent pump applies pressure on the membrane causing the fluid to move from the positive pressure gradient to the lower pressure gradient.
This visual will provide you with a better understanding of how convection works. From the picture you can see a faucet which represents replacement solution. The top faucet is an example of pre-filter dilution, which means that the replacement solution mixes with the blood as it enters the filter. The bottom faucet is an example of post-filter dilution and is delivered as the blood is returning to the patient.
Now the effluent pump is removing ultrafiltration (just like SCUF), or patient plasma water and replacement solution.
This picture gives you a great visual picture of how adsorption occurs during CRRT. some molecules will attach to the membrane surface. While other molecules may permeate the membrane, but become stuck within the fibers. It is believed that inflammatory mediators are effectively removed via adsorption.