Hemodialysis: management of chronic kidney disease

Hemodialysis is a mechanical process of removing waste products (toxic nitrogenous substances) and replacing essential substances by the process of diffusion and removal of excess water from body by the process of osmosis by means of artificial kidney (made with modified cellulose or synthetic) through semi-permeable membranes.

1. Hemodialysis

2. Introduction H emodialysis is the most common renal replacement therapy used for ESRD. Involves use of an artificial kidney to remove waste products and excess water from patient’s blood. Doesnot cure renal disease and does not compensate for the loss of endocrine or metabolic activities of the kidney.

3. More than 90% of patients requiring long term renal replacement therapy are on maintenance hemodialysis. Most patients receive intermittent hemodialysis that involves treatments three times a week with the average treatment duration of 3-4 hours in an outpatient setting.

4. Definition Hemodialysis is a mechanical process of removing waste products (toxic nitrogenous substances) and replacing essential substances by the process of diffusion and removal of excess water from body by the process of osmosis by means of artificial kidney (made with modified cellulose or synthetic) through semi-permeable membranes.

5. History First dialysis machine was made by Willem Johan Kloff in 1943. M ade during World War II which used everyday materials as sausage skins, orange juice cans and washing machines. In 1945, treated a 67 year old woman in uremic coma who regained consciousness after 11 hours of dialysis.

6. P rofessor of medicine at the University of  Washington , Dr. Belding Scribner came up with the idea of connecting the patient to the dialyzer using plastic tubes, one inserted into an artery and one into a vein for circulatory access. In 1962, Scribner started the world’s first outpatient dialysis facility. 

7. In Nepal dialysis service was started in Bir Hospital from 1987. Estimated 221 HD machines in Nepal 46 dialysis centers provide free hemodialysis services

8. Principle of haemodialysis Diffusion Osmosis Ultrafiltration

9. Diffusion M ovement of toxins and wastes (urea, creatinine , uric acid and electrolytes) from an area of higher concentration in the blood to an area of lower concentration in the dialysate through semi-permeable membrane of dialyser .

10. Osmosis Water moves from an area of low concentration potential of solutes (the blood) to an area of high concentration potential (the dialysate bath ). It is the spontaneous net movement of solvent molecules through a semi-permeable membrane in the direction that tends to equalize the solute concentrations on the two sides.

11. Ultrafiltration Created by an increased pressure in the blood compartment. Water moves under high pressure to an area of lower pressure. Accomplished by applying negative pressure or a suctioning force to the dialysis membrane. Because patients with renal disease usually cannot excrete water, this force is necessary to remove fluid to achieve fluid balance. Usual ultrafiltration goal is total weight gain + 500 ml.

12. HD System The Hemodialysis system includes: Dialyzer Dialysate Vascular access routes HD machine

13. Dialyzer Dialyzers are hollow- fiber devices containing thousands of tiny cellophane tubules that act as semipermeable membranes. Blood flows through the tubules while the dialysate circulates around the tubule.

14. The artificial kidney or dialyzer has 4 parts: a blood compartment, a dialysate compartment, a semi-permeable membrane and an enclosed support structure

15. Dialysate Made from water and chemicals and is free of chemicals and waste products or drugs. The dialysate delivery system mixes electrolyte concentrate (Part A-5lts) with the mixture of purified water- RO water (9 lts )+ sodium bicarbonate HD solution (Part B) to approximate the chemical composition of ECF. The composition of dialysis fluid used varies according to clinical need (can be bicarbonate or acetate solution )

16. Acid concentrate NaHCO3 concentrate Pure H2O Final Dialysate

17. Final dialysate composition Sodium 137 meq /l Chloride 105 meq /l Calcium 3 meq /l Acetate 4.0 meq /l Potassium 2.0 meql / Bicarbonate 3.3 meq /l Magnesium 0.75 meq /l Dextrose 200 mg/dl A standard solution aims to allow a net outflow of potassium from the blood, at a rate below that to create hypokalemia, and a net inflow of calcium .

18. Vascular access Provides location for easy access to patient’s blood for dialysis Normal venous cannulation does not provide high rate of blood flow. H aemodialysis requires the availability of a large amount of blood flow: at least 250-300 ml/min, usually for a period of 3-4 hours for vascular access.

19. Types of vascular access Permanent AV fistula AV graft Temporary Dialysis catheter Tunnelled catheter

20. AV fistula AV fistula are formed by surgically connecting an artery to a vein. Most often used are radial or brachial artery and cephalic vein of non dominant hand. Fistula increases blood flow to 25-500 ml/min. As AV fistula matures after anastomosis, the increased pressure of arterial blood flow to vein causes the vessel walls to thicken which increases its strength and durability for repeated cannulation .

21. Dialysis catheter IJ most common Tunnelled under skin to reduce communication from skin flora with blood High infectious and high thrombosis risk

22. AV Graft Graft is created subcutaneously interposing a biologic, semibiologic or synthetic material between an artery and vein. Commonly used synthetic material is polytetrafluoroethylene . Created when patient’s vessels are not suitable for creating fistula (as in patients with vascular diseases)

23. Care of vascular access Check access before each treatment. Keep access clean at all times. Do not use cream or lotion over the site. Use access site only for dialysis. Be careful not to cut access. Don’t put a blood pressure cuff on access arm. Remove jewellery or tight clothes over access site. Don’t sleep with access arm under head or body. Don’t lift heavy objects or put pressure on access arm. Check the pulse in access every day.

24. HD machines This machine has three main jobs: pump blood and monitor flow for safety clean wastes from blood monitor blood pressure and the rate of fluid removal from body

25. Consists of 3 sections: Monitor section Module section- blood pump (300 ml/min); for patients with heart disease and according to condition of fistula- 200 ml/min Hydraulic section- connected to dialysate solution (part A and part B)

26. Anticoagulant Because the blood has tendency to clot in the extracellular circuit, an anticoagulant most commonly heparin is used. However, in patients with decreased hematocrit, thrombocytopenia or prolonged partial thromboplastin time (PTT), anticoagulant may not be used. Commonly used heparin dose in our dialysis unit- 5000 U in divided doses 1000 U – in circulation 2000 U- bolus/stat 2000 U- continuous

27. Procedure When haemodialysis is started, blood and dialysate (dialysing solution) flow in opposite directions across an enclosed semipermeable membrane. Dialysate contains a balanced mix of electrolytes and water that closely resemble human plasma. On the other side of the membrane is patient’s blood, which contains nitrogen waste products, excess water and excess electrolytes.

28. During dialysis, the waste products more from blood into the dialysate because of difference in concentrations (diffusion) Some water is removed into dialysate by osmosis Electrolytes can move in either directions as needed Potassium and sodium typically move out of plasma into dialysate Bicarbonate and calcium generally move from dialysate into plasma

29. Complications Disequilibrium syndrome (neurologic signs) Muscle cramps and back pain Headache Itching Hypotension Cardiac arrhythmias Dialyzer hypersensitivity Haemorrhage Infection