Renal dialysis or renal replacement therapy

III-Pharm.d, renal dialysis or renal replacement therapy, pharmacotherapeutics-II, haemodialysis, haemofiltration, haemodiafiltration, peritoneal dialysis

1. RENAL DIALYSIS T. SOUJANYA 16DC1T0021 PHARM. D

2. INTRODUCTION: Renal replacement therapy is indicated in a patient with AKI (acute kidney injury) when kidney function is so poor that life is at risk. However, it is desirable to introduce renal replacement therapy early in AKI, as complications and mortality are reduced if the serum urea level is kept below 35mmol/L. Generally, replacement therapy is used in AKI to: 1. Remove toxins when severe symptoms are apparent. e.g. impaired consciousness, seizures, pericarditis. 2. Remove fluid resistant to diuretics to facilitate parenteral nutrition. e.g. pulmonary oedema.

3. Contd... 3. Correct electrolyte and acid-base imbalances. e.g. hyperkalaemia>6.5mmol/L or 5.5-6.5 where there are ECG changes, increasing acidosis (p H <7.1 or serum bicarbonate<10mmol/L) despite bicarbonate therapy or where bicarbonate is not tolerated because of fluid overload. 4. Control the effect of sepsis. e.g. to reduce temperature.

4. FORMS OF RENAL REPLACEMENT THERAPY: The common types of renal replacement therapy used in clinical practice are: Haemodialysis. Haemofiltration. Haemodiafiltration Peritoneal dialysis.

5. Contd... In all types of renal replacement therapy, blood is presented to a dialysis solution across some form of semi permeable membrane that allows free movement of low molecular weight compounds. The process by which movement of substances occur are as follows: Diffusion: Diffusion depends upon the concentration differences between blood and dialysate and molecular size. Water and low molecular solutes move through pores in the semi permeable membrane to establish equilibrium. Smaller molecules can be cleared from blood more effectively as they move more easily through pores in the membrane.

6. Contd... Ultrafiltration: A pressure gradient (either +ve or -ve) across a semi permeable membrane will produce a net directional movement of fluid from relative high to low pressure regions. The quantity of fluid dialysed is the ultrafiltration volume. Convection: Any molecule carried by ultrafiltrate may move passively with the flow by convection. Larger molecules are cleared more effectively by convection.

7. 1. Haemodialysis: The dialysis solution is essentially a mixture of electrolytes in water with a composition approximately to extracellular fluid into which solutes diffuse. The ionic concentration of the dialysis fluid can be manipulated to control the rate and extent of electrolyte transfer. Calcium and bicarbonate concentration can also be increased in dialysis fluid to promote diffusion into blood as replacement therapy.

8. Contd... B y manipulating the hydrostatic pressure of the dialysate and blood circuits, the extent and role of water removal by ultrafiltration can be controlled. Haemodialysis can be performed in either intermittent or continuous schedules. The latter regimen is preferable in the critical care situation. Providing 24 hours control and minimising swings in blood volume and electrolyte composition that are found using intermittent regimens.

9. Contd... The capital cost of haemodialysis is considerable, requires specially trained staff and is seldom undertaken outside a renal unit. It does, however, treat renal failure rapidly and is therefore essential in hypercatabolic renal failure where urea is produced faster than, for example, it could be removed by peritoneal dialysis. Haemodialysis can also be used in patients who have recently undergone abdominal surgery in whom peritoneal dialysis would be advised.

10. 2. Haemofiltration: Haemofiltration is an alternative technique to dialysis whose simplicity of use, fine control of fluid balance and low cost have ensured it's wide spread use in the treatment of AKI. A similar arrangement to haemodialysis is employed but dialysis fluid is not used. The hydrostatic pressure of the blood drives a filtrate similar to interstitial fluid across a high permeability dialyser by ultrafiltration. Solute clearance occurs by convection. Commercially prepared haemofiltration fluid may then be introduced into the filtered blood in quantities sufficient to maintain optimal fluid balance.

11. Contd... As with haemodialysis, haemofiltration can be intermittent or continuous. In continuous arteriovenous haemofiltration (CAVH), blood is diverted, usually from the femoral artery and returned to the femoral vein. In continuous venovenous haemofiltration (CVVH) blood is taken from a vein, usually the femoral, jugular or subclavian and returned via a double linear catheter, the process being assisted by a blood pump. In slow continuous ultrafiltration (SCU or SCUF), the process is performed so slowly that no fluid substitution is necessary.

12. Contd... I n addition to avoiding the expense and complexity of haemodialysis, this system enables continuous but gradual removal of fluid, thereby allowing very fine control of fluid balance in addition to electrolyte control and removal of metabolites. This control of fluid balance often facilitates the use of parenteral nutrition. Because of the advantage of haemofiltration over peritoneal dialysis and haemodialysis, continuous haemofiltration is now generally agreed to be most appropriate form of dialysis in the majority of patients with AKI.

13. 3. Haemodiafiltration: Haemodiafiltration is a technique that combines the ability to clear small molecules as in haemodialysis with the large molecule clearance of haemofiltration. It is however more expensive than traditional haemodialysis.

14. 4. Peritoneal dialysis: Peritoneal dialysis is now rarely used for AKI except in circumstances where haemodialysis is unavailable. A semi rigid catheter is inserted into the abdominal cavity. Warmed sterile peritoneal dialysis fluid is instilled into the abdomen, left for a period of about 30 minutes and then drained into a collecting bag. This procedure may be preformed manually or by semi automatic equipment. The process may be repeated upto 20 times a day, depending on the condition of the patient.

15. Contd... Peritoneal dialysis is relatively cheap and simple and doesn't require either specially trained staff or the facilities of a renal unit. It is only used rarely in the UK because it has the disadvantages of being uncomfortable and tiring of the patient producing a high incidence of peritonitis and also permitting protein loss as albumin crosses peritoneal membrane.

16. Reference: Clinical Pharmacy and Therapeutics – Roger and Walker, Churchill Livingstone publication