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Hemodialysis PowerPoint Presentation

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Description : A short illustrative review of dialysis modalities and principles

Tags : hemodialysis, dialysis, renal failure, renal replacement therapy, plasmapharesis, HDF, hemodiafiltration av fistula, central venous catheter, nephrology.

Published on : Jul 23, 2023 | Views : 4224 | Downloads : 17

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Hemodialysis By: Alaa ElDeen Mostafa Minia university
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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
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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…..
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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.
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Diffusion
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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
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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
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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
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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
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What we need for hemodialysis How to get sufficient blood Anticoagulants How to get dialysate Dialysis filters The machine
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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.
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Mahurker
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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.
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AV fistula
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Fistula needles
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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 !!!!
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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
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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
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Water treatment system
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There is also smaller units for home dialysis and most dialysis machines have extra purifying filters (Diasafe) to provide ultra pure water
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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
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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
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The dialysis machine
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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
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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
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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
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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
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Dialyzer
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Dialyzer in place Note the attached blood lines and dialysate lines
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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
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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
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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.
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Dialysis machine panel
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Hemodiafiltration (HDF)
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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.
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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.
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Diffusion and convection
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The HDF machine contains an extra pump for the replacement fluid
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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.
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CRRT (continous renal replacement therapy)
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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
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Scheme for CRRT
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CRRT Machine Note the two scales above the machine to measure the delivered and removed amount
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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
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Plasmapheresis
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Thank you