Dialysis 7

8/13/2019 Dialysis 7

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Dialysis


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Dialysis is the process of removing waste products

and excess fluids from the body

Definitions

Dialysis is on of the primary modalities for pts withRF

Dialysis can do two of the principal functions of the

kidney; 1.removal of endogenous waste products 2.maintenance of water balance


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Dialysis is the process of separating elements in a

solution by diffusion across a semipermeable

membrane (diffusive solute transport) down aconcentration 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


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Cont


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Advanced renal failure with:

1. Hyperkalemia

2. Fluid overload

3. Severe metabolic acidosis

(PH


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B. Acute dialysis

1. ESRD with or without complications

Cont


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Signs of adequate dialysis;

1. Well looking

2. Eats normal

3. Normal BP4. No oedema

5. Normal heart size

6. HB >=10

7. Albumin >35


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Hemodialysis


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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 adialysis center

Dialysate is the solution used by the dialyzer

Cont


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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;

1. The difference between solute concentrations in the

blood and dialysate2. Solute characteristics

3. Dialysis filter composition

4. Blood and dialysate flow rate

Cont


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Blood from the patient is

circulated through a syntheticextracorporeal 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

Cont


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Cont


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Dialysate;

1. Water2. Glucose

3. Acetate

4. Bicarbonate

5. Calcium

6. Sodium

7. Potassium


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Used 3 times a week

Duration; 4 hrsComplicated, need to be done in a center

Heparin required

Temporary arteriovenous access

Permanent arteriovenous access


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Access

C t


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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, andjugular 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

Cont

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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. Theother 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

Cont

Cont


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A graftis 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

Cont

Cont


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Sometimes hemodialysis is needed right away,

and there is no time to create a fistula or graft.

If this happens, a tube called a cathetermaybe 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

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Complications;

1. Vascular access

a. Thrombosis

b. infection

2. Procedure relateda. Decrease BP

b. Headache

c. Cramps

d. Fever

3. Long term

a. Cardiovascular diseases

b. Renal bone diseases

c. Aluminum disease

d. Social problems

4. Chronic uraemia

a. Anaemia

b. Infection

c. Gonadal dysfunction

d. Increase BP

Cont


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Cont

Cont


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Cont


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Standard HD

Characteristics:1. Low permeability (low flux)

2. Membranes are made of natural products

(cellulose)

3. Each session takes 4-5 hrs


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Rapid high efficiency HD (RHED)

Characteristics:1. Increase clearance of low molecular weight

solutes (urea)

2. Shorter procedure time

3. Increase blood and dialysate flow rates

4. Clearance of middle and high MW solutesincluding drugs is not increased


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High flux dialysis (HFD)

Characteristics:1. Shares the advantages of RHED

2. Membrane pores are more open

3. Higher clearance rate for middle molecules

4. More expensive

5. Needs experts to avoid large rapid fluid shift


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PeritonealDialysis

Cont


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Th di l i b i th ' itCont


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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 bodyDialysis membrane acts as a filter

It keeps the dialysis fluid and the blood separate from

each other, but it allows certain substances and water topass through it

During dialysis, waste toxins and excess water pass from

the blood into the dialysis fluid, and this is drained out ofthe body after a few hours

A new bag of dialysis fluid is drained in, and the process

is repeated

Cont

Cont


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PD needs to be done every day

PD involves draining dialysis fluid out of, and into

the body (known as an exchange), and leavingdialysis 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 havepassed 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

Cont


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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), dependingon 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 'quickbags' (say, 3 hours apart) after they come home

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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)

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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

Cont


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Cont


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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 abdominalwound time to heal

PD could be done at home

Much less efficient than HD, this is why it is used

more frequent

Cont


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Di l t


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Dialysate;1. Water

2. Glucose

3. Dextrose;1.5-4.25%

4. Acetate

5. Bicarbonate

6. Calcium;3.5 or 2.5 mEq/l

7. Chloride;102mEq/l

8. Lactate;35mEq/l

9. Magnesium;1.5mEq/l

10. Sodium;132mEq/l to reduce themovement of sodium from the blood by

gradient method

11. No potassium in PD

12. High osmolarity;350-480mOsm/L(serum=280mOsm/l) to provide a drawing force

from the blood into the peritonium

PET it l ilib i t t


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PET; peritoneal equilibrium test

Is a diagnostic test that determines the peritoneal

membrane clearance and ultrafiltrationcharacteristics, and quantitates the ability to transfer

solutes and water across the membrane

PET results determine which type of PD isappropriate for each individual

Indications;


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Indications;

1. DM

2. No vascular access

3. CVS unstable

4. Children

5. Old adults

6. Pts unwilling to accept blood transfusion

7. Severe anaemia

8. Severe HD related symptoms e.g disequilibrium


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Contraindications;

1. Peritonea adhesion

2. Severe lung disease

3. Abdominal sepsis

4. Massive polycystics


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Complications;


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Complications;

a. Malnutrition

b. Peritonitis:

c. 70% Gm positive cocci

d. IP antibiotic is preferred

e. vancomicin or aminoglycosides. First dose in

the first 2L exchange, scond dose at day 7

f. Gentamicin 1.5 mg/kg IP in the first 2L

exchange followed by 4-8 mg/L IP in each

exchange for 10 days

Cont


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Pharmacokinetics

of dialysis


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Factors affecting drug dialysability;

1. Drug characteristicsA. MW; drugs with MW >500 are not dialyzable in

the conventional HD. E.g vancomicin, digoxin

Using high flux HD; the above mentioned drugs are

dialyzable

B. Water solubility; solutes which are insoluble in

water will not easily move into aqueous dialysate,

e.g glutethimide

Cont


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D. Volume of distribution; drugs with large VD are

not appreciably removed by HD, e.g digoxin,

aminoglycosides

E. Protein binding; only unbound drugs can pass

through the dialyser membrane, e.g phenytoin,

propranolol, oxacillin

Cont


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2. Dialysis conditions

A. Counter-current vs concurrent flow

B. Blood flow rate

C. Dialysate flow rate

3. Membrane characteristics

A. Thickness

B. Material type / pore size

C. Surface area

Cont


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Clearance of large MW drugs depends on pore size,

surface area and flow rate

Therapeutic considerations


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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, decisionbased on pts clinical status

4 Bl d l h ld b d l 1 h


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4. Blood sample should be drawn at least 1 hr post

dialysis to allow redistribution from the tissue,

other references recommend 6-12 hrs postdialysis

5. Drugs which plasma concentration can be

measured but some times no published data onthe pharmacokinetic of certain drugs. if the

pharmacokinetics are known then replacement

dose could be calculated6. Drugs with wide therapeutic range and serum

concentration cannot be measured; single daily

dose can be administered after dialysis

C t i f d di l bilit


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Categories of drug dialyzability;

1. Dialyzable; 50% - 100% removed

2. Moderately dialyzable; 20% - 50%

removed

3. Slightly dialyzable; 5% - 20% removed

4. Not dialyzable;


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Estimating the supplementary dose in dialysis pt

1. The supplementary doses can be calculated

from the pharmacokinetic data reported in theliterature

2. The equations and pharmacokinetic utilized are

based only on linear first order kinetics and one

compartment model

3. More complex kinetics seem to be unnecessaryfor general dosage recommendations for

repeatedly administered drugs

4 F t di l i th t t l l f th d


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4. 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 thedialysis clearance (ClD)

i.e ClT= Cl + ClD

If ClD>>>Cl then the drug will be eliminated much

more rapidly during dialysis

t1/2 0.693 X VD

ClT=

Clearance can be related to half l i fe by the fol lowing equation


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t1/2 0.693 X VD

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

XAmount in

dialysate

drug conc. in

dialysate

volume of

the dialysate=


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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

The following equation may be used to determine the


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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 -(Cl+ClD)(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 alwaysavailable

Half life is more available, so we use another

equation

FD = 1 e -(0.693/t1/2 OD) X (t)


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FD = 1 - e (0.693/t1/2OD) X (t)

t1/2OD is the half life during dialysis

t is the duration of dialysis

This method can be used to calculate the fractionaldrug removed but it is inaccurate

But it is useful in the clinical setting when clearance

data is not available

Example:


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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

Answer:


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Answer:

ClT= Cl + ClD

= 5 + 35 = 40 ml/min = 2.4 L/hr

t1/2 0.693 X VD

Cl + ClD=

Then

=0.693 X 0.2L/Kg X 70 Kg

2.4 L/hr

= 4 hrs


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FD = 1 - e -(Cl+ClD)(t/VD)

Or

FD = 1 - e-(0.693/t

1/2OD) X (t)

After we get the answer. It will be replaced

after dialysis

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Dialysis 7