Hemodialysis is a treatment for renal failure that involves removing waste and excess fluid from a patient's blood. It works by having the patient's blood flow through a dialyzer, which is separated from a dialysate solution by a semi-permeable membrane. Unwanted substances diffuse out of the blood into the dialysate due to concentration gradients. Patients require multiple hemodialysis sessions per week to remove waste, with each session lasting several hours. Special equipment and vascular access points are needed to effectively perform hemodialysis and protect the patient.

1. Hemodialysis
By: Alaa ElDeen Mostafa
Minia university

2. What is hemodialysis:
• Blood of renal failure patients is full of unwanted substances
such as metabolic waste products as urea, excess of normal
electrolytes as sodium , potasium, phosphorus, and
exogenous toxins and drugs.
• we needed to figure a method to get rid of those unwated
substances without harming the normal homeostasis of the
body

3. Principles of dialysis
• By physics we know that any soluble substance tends to move
from medium with high concentration to medium with low
concentration by concentration gradient, this is called
diffusion.
• If we managed to get the patients blood to be in contact with
purified water separated by semipermeable membrane (which
allow small molecules to pass by concentration gradient but
not the large molecules and blood cells) so we can do purify
blood from unwanted substances.
• But, there is a problem…..

4. • Doing this caused the bad substances to diffuse out of blood .
But also good substances such as sodium, potassium diffused
out also causing fatal electrolyte disturbance
• So we needed to merge the water used for dialysis with near
physiologic concentration of these substances so that excess
amount of them can be removed.
• This fluid now is called dialysate.

6. Diffusion

8. • to remove excess amount of water we can expose the blood
to a negative pressure through this semipermiable membrane
to withdraw the excess amount of water.
• This is called ultrafiltration
• Removal of solute accompanying the filtrated water is called
Convection which is of low significance in hemodialysis due
to the small amount of ultrafilterate

11. • The substances removed by the dialysis process depends on
the size of pores of the semipermeable membranes and larger
molecules are removed more efficiently by hemofiltration
than by diffusion
• We may need to remove
Micro molecules through hemodialysis
Middle molecules through hemodiafiltration
Macromolecules through plasma-pherisis

12. Peritoneal dialysis
• In this proces we use the peritoneum as a large physiologic
semipermeable membrane
• We fix a catheter in the peritoneum and install the dialysis
fluid using it before sleep every night and evacuate it at the
morning
• It is easy, more physiologic, at home but the technical and
infection risk limit its use

14. Hemodialysis
• The patient needs three sessions every week four hour each, means
12 hours weekly
• Every session the patient needs to withdraw blood at an average
rate of 300 ml per minute to ensure effecacy of dialysis and to
prevent blood from clotting into the filter
• We also need to give the patient anticoagulants during the session
• Every session needs about 120 liters of dialysate.
• But also we need an accurate, sensetive machine which is able to
detect any mistake in the session which can endanger the patients
life

17. What we need for hemodialysis
• How to get sufficient blood
• Anticoagulants
• How to get dialysate
• Dialysis filters
• The machine

18. Vascular access
• As we need to get a huge amout of blood for every session, a normal
vein would collapse if you withdraw a few millimiters from it. So we
need to get blood from a central huge vein or even from the heart
itself!!.
• We use a wide pore central venous catheter called mahuker which
can be passed through the jugular, subclavian or even the femoral
vein and its tip is placed near or inside the right atrium.
• This maheuker is vulnerable to infection, thrombosis or even
bleeding if dislodged so it is considered a temporary method
• Another varient of these catheters is tunneled venouth catheter
(permacath) which uses a long subcutaneous tunnel before entering
the vein. This can be maintaied for months or even a year.

19. Mahurker

21. • Another more convenient option is withdrawing blood
through an arterialized vein though an operation called A-V
shunt or can be called A-V fistula
• This operation is usually done at then forearm or the arm
• The flow of blood from artery to vein is sufficient for dialysis
and that flow makes the vein gets more dilated and the wall
of the vein when exposed to this amount of pressure gets
arterialized means gets more thick. All of this make it tolerate
the big sized dialysis needles called fistula needles.

22. AV fistula

24. Fistula needles

25. Now , where can we get the
dialysate?
• Every patient needs about 120 liters every seesion.
• This needs to be highly purified and have accurate
concentration of solutes.
• Cost for producing and transporting this huge amount is way
too expensive……
• What is the solution !!!!

26. • The solution is to produce this dialysate locally at the dialysis
unit using the local water supply and a dialysate concentrate
which is mixed at the dialysis machine in a 34: 1 ratio to
produce the dialysate

27. • Water is purified through a huge set of filters called the water
treatment unit which have multiple sets of filters to remove
impurities and ultraviolet filter to kill microorganisms and a
reverse osmosis system to remove remaining electrolyte to
only leave pure water for dialysis
• There is also smaller units for home dialysis and most dialysis
machines have extra purifying filters to provide ultra pure
water

28. Water treatment system

29. There is also smaller units for home dialysis
and most dialysis machines have extra
purifying filters (Diasafe) to provide ultra pure
water

30. • The dialysate concentrates comes in small containers attached
to the dialysis machine itself
• Bicarbonate mainly is provided as salt packs which is dissolved
by the machine and mixed with the dialysate

33. Anticoagulation
• Blood tends to coagulate if left static or on if outside the
circulation
• So we need to avoid stasis by increasing blood flow through
the circuate and we need to give anticoagulant such as
heparin or LMWH pre and during the session
• Adding fluid before the filter as in predilution
hemodiafiltration reduces the risk of clotting even with lower
blood flow rates
• Dialysis machine have a heparin pump that can be used to
provide through the session anticoagulation

34. The dialysis machine

36. • Any dialysis machine can be considered mainly as two pumps,
each one runs a circulation one for blood flow and the other
for dialysate flow.
• Each circulation have multiple parameters to control it and
multiple sensors to detect if it is running normally

37. • The blood circulation
• It is an external circuit (blood never enters the machine) it
only run in a closed circuit which begin from the AV shunt
through the outward needle called artery!!
• This limb passes through the pump which milks it towards the
filter by a pre-determined flow rate.
• It has sensor for pressure called arterial pressure!! Which
measure the negative pressure exerted on the line to
withdraw blood which can be markedly negative if the line is
kinked or the Mahurker is obstructed or the shunt has low
flow

38. • The dialysis filter (The Dialyzer)
• It is the site where the two circuits meet
• It receives blood from above which passes through the thin
tubules formed of semipermeable membrane to exit from the
other side
• It also receives dialysate which come from the machine which
exit from the other side to be discarded
• Different types and sizes are available

39. • Size is determined by the surfaced area af the dialysis
membrane
• Type is determinred by type of membrane and size of its pores
• The machine excerts negative pressure between the blood
and the dialysate to do suction of water across the membrane
(filtration) to extreact excess water. This is measured by the
machine as trans membrane pressure (TMP) Which is
increased in cases the filter have clotting or the desired
amount of ultrafiltrate is too much
• We can determine the amount of fluid to be removed and the
time of the session from the ultrafiltration button

40. Dialyzer

41. Dialyzerin place
Notetheattachedbloodlinesand
dialysatelines

42. • The exit limb or venous limb!!
• It begin from the dialyzer filter and end by entering the
patient AV fistula
• It have a filter for trapping and a sensor for detection of air
bubbles which can be fatal if reached the patient
• It also have a sensor for pressure as increasing pressure can be
due to kinked lines or extravasation of blood from fistula site
and dropping of pressure can be due to dislodgment of the
venous line from fistula site which causes massive bleeding
• Any sensor alarm in the blood circuit causes the machine to
stop completely till it is solved

43. • The dialysate circuit:
• It combines water from the water treatment unit with the
dialysate concentrate in a ratio of 34: 1 to produce a near
physiologic dialysate
• Bicarbonate is often supplied as a separate bag containing dry
salts that is dissolved by the machine and added to the
dialysate
• We can determine the dialysate flow through the dialyzer and
the sodium concentration of it either through fixed
concentration or by sodium profiling through the session
• We also can determine bicarbonate concentration

44. • The machine cant measure the dialysate concentration but
can do it by measuring its electrical conductivity which reflect
its concentration
• When there is high or low conductivity alarm the machine is
still running but the dialysate circuit is stopped till the
conductivity normalize (mean that if conductivity is alarming
we see the machine running but actually the patient is off
dialysis)
• We can stop the dialysate circuit if we only need to do
ultrafiltration by using flow-off button.
• Dialysate circuit also has a sensor for blood leak if the filter
lines were leaking.

45. Dialysismachinepanel

48. Hemodiafiltration (HDF)

49. • Removal of wastes occur by two methods;
• Diffusion which means that solutes move through the dialysis
membrane by concentration gradient
• Convection which means filtration of water which is
accompanied by removal of the contained solutes
• For slightly larger molecules like cytokines (called middle
molecules) we need to use a larger pores dialyzers and more
convection to remove it. Hence the idea for hemodiafiltration
arises.

50. • To remove a large amount of fluid by convection
(hemofiltration), we need to replace this fluid minute by
minute, so the idea of giving replacement fluid which is
produced by the dialysis machine immediately (online) but the
machine uses extra filters (Diasafe) to ensure ultra pure water
to be injected to the blood circuit
• The replacement fluid can be introduced to the blood circuit
either before the filter (pre-dilution) or after the filter (post-
dilution)
• Pre-dilution makes the filter less liable to coagulate but gives
less efficient dialysis and vice versa.

51. Diffusionand convection

54. TheHDFmachinecontainsan
extrapumpforthereplacement
fluid

56. • So HDF provide more efficient dialysis with removal of the
middle molecules, less liable for clotting so we need less
anticoagulation and can be run on lower pump rate, but it is
more expensive.

57. CRRT (continousrenalreplacementtherapy)

58. • We use hemofiltration only with very low blood pump rate in
a lengthy dialysis session that can last 24-72 hours
• It is suitable for patients with hemodynamic instability who
cant tolerate the conventional pump rate.
• Very expensive as it uses pre-prepared dialysate with no need
for water unit

59. SchemeforCRRT

60. CRRT Machine
Notethetwoscalesabovethemachinetomeasurethedeliveredandremovedamount

61. Plasmapheresis
• We use only filtration by using large pore filters that can
filtrate plasma with all large molecules such as
immunoglobulin and albumin
• We use it in certain immunologic disorders to remove
offending antibodies or in toxicology to remove toxins and
drug that are protein bound
• The removed plasma is replaced by plasma or ringer and
albumin
• Also can be done using centrifugation

62. Plasmapheresis

63. Thank you