Dialysis

1
Dialysis
2
Definitions
Dialysis is the process of removing waste
products and excess fluids from the body
Dialysis is on of the primary modalities for pts
with RF
Dialysis can do two of the principal functions of
the kidney 1. removal of endogenous waste
products 2. maintenance of water balance
3
(No Transcript)
4
Dialysis is the process of separating elements in
a solution by diffusion across a semipermeable
membrane (diffusive solute transport) down a
concentration gradient
This is the principal process for removing the
end-products of nitrogen metabolism (urea,
creatinine, uric acid), and for repletion of the
bicarbonate deficit of the metabolic acidosis
associated with renal failure in humans
5
Cont
6
Indication for dialysis
A. Acute dialysis

• Normal renal function
• Poisoning
• Nephrotic syndrome with oedema
• Hypercalcemia

• Advanced renal failure with
• Hyperkalemia
• Fluid overload
• Severe metabolic acidosis (PHlt2)
• Pericarditis
• Encephalopathy
• Pulmonary oedema
• Peripheral neuropathy
• Uraemic symptoms

7
Cont
B. Acute dialysis

• ESRD with or without complications

8

• Signs of adequate dialysis
• Well looking
• Eats normal
• Normal BP
• No oedema
• Normal heart size
• HB gt10
• Albumin gt35

9
Hemodialysis
10
Cont

• Blood is removed from the body and pumped by a
  machine outside the body into a dialyzer
  (artificial kidney)
• The dialyzer filters metabolic waste products
  from the blood and then returns the purified
  blood to the person
• The total amount of fluid returned can be
  adjusted
• A person typically undergoes hemodialysis at a
  dialysis center
• Dialysate is the solution used by the dialyzer

11
Cont

• HD consists of perfusion of heparinized blood and
  physiologic salt solution on opposite sides of a
  semipermeable membrane
• Waste products (urea, creatinine,ets) move from
  blood into the dialysate by passive diffusion
  along concentration gradient
• Diffusion rate depends on
• The difference between solute concentrations in
  the blood and dialysate
• Solute characteristics
• Dialysis filter composition
• Blood and dialysate flow rate

12
Cont
Blood from the patient is circulated through a
synthetic extracorporeal membrane and returned to
the patient. The opposite side of that membrane
is washed with an electrolyte solution
(dialysate) contain- the normal constituents of
plasma water
13
Cont
14
(No Transcript)
15

• Dialysate
• Water
• Glucose
• Acetate
• Bicarbonate
• Calcium
• Sodium
• Potassium

16
Used 3 times a week Duration 4 hrs Complicated,
need to be done in a center Heparin required
Temporary arteriovenous access Permanent
arteriovenous access
17
Access
18
Cont
The access is where the needles are placed to
remove blood from the body and return it to the
body after it is filtered by the dialysis machine
Three types of accesses exist natural fistula,
artificial grafts, and jugular vein catheters A
vein and an artery are joined. Within 6 to 8
weeks, the vein becomes much bigger and is strong
enough to be used as an access for dialysis
19
Cont
How a fistula access works 1. During dialysis,
two needles are placed into the fistula. One
needle will remove the blood so it can be
cleaned. The other needle will return filtered
blood to the body 2. The needles are attached by
plastic tubing to a special filter called a
dialyzer (or artificial kidney) 3. A pump pushes
the blood through the dialyzer. Blood passes on
one side of the filter, and solution made by the
machine passes on the other side. The blood does
not mix with the solution. Instead, the solution
pulls extra fluid and waste out of the blood by a
process called dialysis 4. The "clean" blood
returns through the plastic tube. It passes back
into the patient's body through the second needle
20
Cont
A graft is another type of access, which is used
if a person's own veins are too small or weak to
create a fistula. Usually, a graft is a soft,
synthetic tube that connects to an artery at one
end and a vein at the other. It is placed under
the skin of the arm or thigh, like a natural
vein. The patient's blood flows through it, like
it flows through natural veins
21
Cont
Sometimes hemodialysis is needed right away, and
there is no time to create a fistula or graft. If
this happens, a tube called a catheter may be
inserted into a large vein in the neck (jugular
vein), behind the collarbone (subclavian vein) or
in the groin (femoral vein). The patient's blood
can flow through this tube
22

• Complications
• Vascular access
• Thrombosis
• infection
• Procedure related
• Decrease BP
• Headache
• Cramps
• Fever

• Long term
• Cardiovascular diseases
• Renal bone diseases
• Aluminum disease
• Social problems
• Chronic uraemia
• Anaemia
• Infection
• Gonadal dysfunction
• Increase BP

23
Cont
24
Cont
25

• Standard HD
• Characteristics
• Low permeability (low flux)
• Membranes are made of natural products
  (cellulose)
• Each session takes 4-5 hrs

26

• Rapid high efficiency HD (RHED)
• Characteristics
• Increase clearance of low molecular weight
  solutes (urea)
• Shorter procedure time
• Increase blood and dialysate flow rates
• Clearance of middle and high MW solutes including
  drugs is not increased

27

• High flux dialysis (HFD)
• Characteristics
• Shares the advantages of RHED
• Membrane pores are more open
• Higher clearance rate for middle molecules
• More expensive
• Needs experts to avoid large rapid fluid shift

28
Peritoneal Dialysis
29
Cont
30
Cont
The dialysis membrane is the person's own
peritoneum The dialysis fluid provides the
'container' in which waste products and excess
water can be removed from the body Dialysis
membrane acts as a filter It keeps the dialysis
fluid and the blood separate from each other, but
it allows certain substances and water to pass
through it During dialysis, waste toxins and
excess water pass from the blood into the
dialysis fluid, and this is drained out of the
body after a few hours A new bag of dialysis
fluid is drained in, and the process is repeated
Cont
31
Cont
PD needs to be done every day PD involves
draining dialysis fluid out of, and into the body
(known as an exchange), and leaving dialysis
fluid in the body while dialysis takes
place Draining fluid out usually takes around 20
minutes and draining fluid in takes around 5-10
minutes The 'used' dialysis fluid, containing
the water and waste (toxins) that the kidneys
would normally have passed into the urine, is
drained out of the body The person then needs to
drain between 1.5 and 3 litres of 'new' dialysis
fluid into their abdomen
32
Cont
The dialysis fluid is then left inside the
peritoneum to allow dialysis to take place. The
length of time it is left there varies (between 1
and 8 hours), depending on individual
requirements and the type of PD There are no
'set' times to carry out the exchanges It is
easy for people to adapt the timing of exchanges
to their own needs. For example, if a person
wants to go out for the day, they could delay the
mid-day exchange, and do two 'quick bags' (say, 3
hours apart) after they come home
33
Cont

• A four-bag regime 'fits' into a typical day
• For example,
• The first bag might be exchanged before breakfast
• The second before lunch
• The third before the evening meal
• The fourth before going to bed (leaving the
  fluid for the last exchange in through the night)

34
Cont
A plastic tube is permanently inserted into the
abdomen This tube is called a PD catheter It is
about 30 cm (12 in) long and as wide as a pencil
The PD catheter is placed through the lower
abdominal wall, into the peritoneal cavity Half
of the catheter lies inside the abdomen, and half
lies outside the body It comes out to one side of
the navel (belly button) The PD catheter acts as
a permanent pathway into the peritoneal cavity
from outside the body
35
Cont
36
Cont
The catheter is usually 'left alone' for 5 days
or more after the operation before it is used for
dialysis This allows it to 'settle in' and gives
the abdominal wound time to heal PD could be
done at home Much less efficient than HD, this is
why it is used more frequent
37
Cont
38

• Dialysate
• Water
• Glucose
• Dextrose 1.5-4.25
• Acetate
• Bicarbonate
• Calcium 3.5 or 2.5 mEq/l
• Chloride 102mEq/l
• Lactate 35mEq/l

1. Magnesium 1.5mEq/l
2. Sodium 132mEq/l to reduce the movement of sodium
   from the blood by gradient method
3. No potassium in PD
4. High osmolarity 350-480mOsm/L (serum280mOsm/l)
   to provide a drawing force from the blood into
   the peritonium

39

• PET peritoneal equilibrium test
• Is a diagnostic test that determines the
  peritoneal membrane clearance and ultrafiltration
  characteristics, and quantitates the ability to
  transfer solutes and water across the membrane
• PET results determine which type of PD is
  appropriate for each individual

40

• Indications
• DM
• No vascular access
• CVS unstable
• Children
• Old adults
• Pts unwilling to accept blood transfusion
• Severe anaemia
• Severe HD related symptoms e.g disequilibrium

41

• Contraindications
• Peritonea adhesion
• Severe lung disease
• Abdominal sepsis
• Massive polycystics

42
(No Transcript)
43

• Complications
• Malnutrition
• Peritonitis
• 70 Gm positive cocci
• IP antibiotic is preferred
• vancomicin or aminoglycosides. First dose in the
  first 2L exchange, scond dose at day 7
• Gentamicin 1.5 mg/kg IP in the first 2L exchange
  followed by 4-8 mg/L IP in each exchange for 10
  days

44
Cont
45
Cont
46
Cont
47
Pharmacokinetics of dialysis
48

• Factors affecting drug dialysability
• 1. Drug characteristics
• MW drugs with MW gt500 are not dialyzable in the
  conventional HD. E.g vancomicin, digoxin
• Using high flux HD the above mentioned drugs are
  dialyzable
• Water solubility solutes which are insoluble in
  water will not easily move into aqueous
  dialysate, e.g glutethimide

49
Cont

1. Volume of distribution drugs with large VD are
   not appreciably removed by HD, e.g digoxin,
   aminoglycosides
2. Protein binding only unbound drugs can pass
   through the dialyser membrane, e.g phenytoin,
   propranolol, oxacillin

50
Cont

• 2. Dialysis conditions
• Counter-current vs concurrent flow
• Blood flow rate
• Dialysate flow rate

• 3. Membrane characteristics
• Thickness
• Material type / pore size
• Surface area

51
Cont
Clearance of large MW drugs depends on pore size,
surface area and flow rate
52
Therapeutic considerations

1. Supplementary dose should be administered post
   dialysis. If the drug is administered at the
   beginning of HD, the fraction would be removed,
   since it is not yet distributed in the body
2. Drugs with NTW, plasma level should be monitored
   to verify the predicted estimation
3. Drugs with wide therapeutic window, decision
   based on pts clinical status

53

1. Blood sample should be drawn at least 1 hr post
   dialysis to allow redistribution from the tissue,
   other references recommend 6-12 hrs post dialysis
2. Drugs which plasma concentration can be measured
   but some times no published data on the
   pharmacokinetic of certain drugs. if the
   pharmacokinetics are known then replacement dose
   could be calculated
3. Drugs with wide therapeutic range and serum
   concentration cannot be measured single daily
   dose can be administered after dialysis

54

• Categories of drug dialyzability
• Dialyzable 50 - 100 removed
• Moderately dialyzable 20 - 50 removed
• Slightly dialyzable 5 - 20 removed
• Not dialyzable lt5 removed

55

• Estimating the supplementary dose in dialysis pt
• The supplementary doses can be calculated from
  the pharmacokinetic data reported in the
  literature
• The equations and pharmacokinetic utilized are
  based only on linear first order kinetics and one
  compartment model
• More complex kinetics seem to be unnecessary for
  general dosage recommendations for repeatedly
  administered drugs

56

• For pts on dialysis the total clearance of the
  drog from the plasma (ClT) can be defined as the
  sum of the pts residential endogenous clearance
  and the dialysis clearance (ClD)
• i.e ClT Cl ClD
• If ClD gtgtgtCl then the drug will be eliminated
  much more rapidly during dialysis

Clearance can be related to half life by the
following equation
0.693 X VD
t1/2

ClT
57
0.693 X VD
t1/2

Cl ClD
VD is the volume of distribution of the drug The
actual amount of drug removed by HD is the
product of the concentration of the drug in the
recovered dialysate and the dialysate volume
X
Amount in dialysate
drug conc. in dialysate

volume of the dialysate
58
It is not clinically feasible or analytically
practical to measure dialysate drug
concentration This value divided by total body
stores of drug prior to dialysis yield the actual
fraction of drug removed by dialysis (FD) FD
amount of dialysate drug / TBs TBS drug conc. X
VD
59
The following equation may be used to determine
the fraction of the total amount of drug in the
body removed during dialysis
FD

1 - e -(ClClD)(t/VD)
t is the duration of dialysis To use this
equation, the values of Cl, ClD must be obtained
from the literature Unfortunately, clearance dtat
are not always available Half life is more
available, so we use another equation
60
FD

1 - e -(0.693/t1/2 OD) X (t)
t1/2 OD is the half life during dialysis t is the
duration of dialysis This method can be used to
calculate the fractional drug removed but it is
inaccurate But it is useful in the clinical
setting when clearance data is not available
61
Example NN on amikacin, Wt 70 kg Estimated
amikacin Cl 5ml/min (endogenous clearance) Under
go 4 hr HD (t OD 4hrs) Calculate the
replacement dose for NN?? Assuming VD 0.2
L/Kg ClD 35 ml/min
62
Answer ClT Cl ClD 5 35 40 ml/min
2.4 L/hr
Then
0.693 X VD
t1/2

Cl ClD
0.693 X 0.2L/Kg X 70 Kg

2.4 L/hr

4 hrs
63
FD

1 - e -(ClClD)(t/VD)
Or
FD

1 - e -(0.693/t1/2 OD) X (t)
After we get the answer. It will be replaced
after dialysis