Principles of hemodialysis final 2017

1. Dr. Osama El-Shahat
Consultant Nephrologist
Head of Nephrology Department
New Mansoura General Hospital (international)
ISN Educational Ambassador

2.  Basics of hemodialysis:
◦ Definition.
◦ Technique of hemodialysis:
◦ Main principles:
 Diffusion.
 Osmosis.
 Filtration.
 Convection.
◦ 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. blood
membrane
dialysate

5. directiondialysatebloodsolute
To DxzerohighUREA
To DxzerohighOTHER TOXINS
NO135-140135-140Sodium
To Dx1.4-3.0Above 5Potassium
To Dx0.5-1.0Above 1Magnesium
+/-180 (10)+/-140 (8)glucose
NO100-119100-119chloride
+/-5-6 mg/dl
2.5-3 mEq/L
4.5-5 mg/dl
2-2.5mEq/L
Ionized Calcium

6.  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

7.  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)

8.  Attempts are made to increase the surface area of
contact between dialysate and dialyzer
◦ The Hollow fiber
◦ The parallel plate dialyzer

10.  Types
◦ Surface area.
◦ Low flux vs high flux.
◦ Biocompatibility.
◦ Technique of manufacture including hemo- adsorption.

11.  Cellulose membrane (Cuprophan)
◦ Is the first membrane to be used
◦ Contains free hydroxyl radicals
◦ They are bio-incompatible (BIC)
 They are able to activate complement a inflammatory reaction a
chronic inflammation a protein catabolism + anorexia + malnutrition
a Cardiovascular accidents
 Cause dialysis related Amyloidosis
 Increased incidence of infection
 Rapid loss of residual kidney function
◦ Cuprophan is BIC BUT this effect can be abolished after 2nd
use!!!

12.  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

13.  There is no definite techniques for biocompatibility
measurement
 There is no clear evidence for its superiority except in
AKI

14.  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

15.  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 number of ml/hour of water the dialyzer can remove
for every 1 mm Hg rise in TMP
 E.g. a HF with KUF of 1 can remove 100ml/hour with
TMP of 100
 For volumetric machines HF with KUF above 4 should be
used to give accurate results

19.  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

20.  ESRD patients are frequently oliguric
 If excess water is ingested a
accumulation of water in body a
edema, hypertension, pulmonary edema
 To remove water a Ultrafiltration
 Addition of hydrostatic force a 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)

21. 500 ml/min
700 ml/min
+ve
pressure
-ve
pressure
TMP

23.  Definition:
extracorporeal removal of waste products from the
blood of patient who has poorly functioning kidneys with
replacement of some materials deficient in the patient.

24.  Difussion:
The process by which particles, atoms or molecule move from
area of higher concentration to lower concentration across
semipermeable membrane.
Factors affecting :
Concentration gradient
MW of solutes.

28. 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

29.  Filtration:
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.

32.  Convection:
Transfer of heat and solute by
physical circulation or or movement
of parts of gas or liquid.
 Countercurrent circulation

34. 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.
.

35. 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.

38.  Varieties of hemodialysis techniques:
◦ Conventional hemodialysis.
◦ Online hemodiafilteration.
◦ SLEDD.
◦ CRRT.
◦ Hemo-adsorption.

39. Mode of
therapy
Principle method of
solute clearance
CVVH Convection
CVVHD Diffusion
CVVHDF Convection & Diffusion
SCUF Ultrafiltration (fluids)

40. HDF is a blood purification therapy combining diffusive
and convective solute transport using a high-flux membrane
characterized by an ultrafiltration coefficient greater than 20
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% 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.

43.  Kt/V is a number used to quantify hemodialysis and
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.

45. ©

46. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013
 Accumulation Of Waste products
◦ Urea, creatinine, others
◦ Hyperkalemia (increased potassium)
◦ Acidosis
 Water intoxication
◦ Volume overload, pulmonary edema
 Endocrinal Manifestations
◦ Anemia
◦ Osteodystrophy
◦ Hypertension

47. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013
 Main basics:

48. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013

49. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013
 Osmosis:
Movement of the solvent through semipermeable
membrane from area of low solute content to area of high
solute content and the difference between them is called
osmotic pressure gradient.
This pressure is affected by two powers, concentration of
solutes on both sides and the hydraulic pressure which
can increase or decrease the movement of the fluid.

50. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013

51. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013

52. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013
Post-dilution haemodiafiltration
Ultrafiltration followed by infusion of
replacement fluid
Pre-dilution haemodiafiltration
Infusion of replacement fluid followed by
ultrafiltration
Mid-dilution haemodiafiltration
Infusion of replacement fluid at the mid-point of
ultrafiltration (post-dilution followed by pre-
dilution)
Mixed-dilution haemodiafiltration
Infusion of replacement fluid before and after
ultrafiltration (pre-dilution followed by post-
dilution)

53. ©
ESNT-CNE 2nd Course, Cairo Jan 2-5, 2013
IHD SLEDD CRRT
Name Intermittent
hemodialysis
Slow low efficacy
daily dialysis
Continuous renal
replacement therapy
Mechanism &mol.
removed
HD mostly LMW Small & middle with
HD/F
Small &middle with
CVV HDF
Use Ambulatory CRF Critically ill CRF/
AKI
Critically ill
CRF/AKI
Blood flow rate 300-500 ml/min 200-300 ml/mi 50-200 ml/min
DFR 500-800 ml/min 1-2 L/h 2-3 L/h
Efficiency high Moderate low
HD stability Poor Good good
Duration 3-4hx3t/w 6-12 h/d Continuous
Anticoagulant Not needed According According
DDS May occur N/A N/A
Toxicology &drugs Risk of rebound Unclear Slower removal
logistics Less complicated Higher cost, low Ph costly