Q. What is dialysis ?

A. Dialysis is a procedure used to remove endogenous toxic metabolites as in uremia/renal failure, inborn errors of metabolism (with accumulation of organic acids) across a semipermeable membrane. It is also useful in removing exogenous poisons like ethanol, aspirin, barbiturates, and boric acid from the blood in cases of poisoning.

What is Hemodialysis (HD)?

A. Hemodialysis is a method of dialysis where vascular access is used along with an artificial semipermeable membrane pack in a dialyser and controlled by a dialysis machine, so that transfer of solutes and fluid from blood to the dialysate fluid takes place in a controlled manner, by extracorporeal perfusion. (Fig. of a dialyser)

Q. How is hemodialysis given? What are the indications for giving hemodialysis?

A. For hemodialysis, 3 components are required:

• Vascular access :- arteriovenous connection
 
• Dialyser :- a disposable equipment, which holds a bundle of semipermeable membranes either polymerized or made of cellulose acetate cuprophane. The size of the dialyser varies according to the surface area of the patient. For children, pediatric size dialysers should be used. One end of the dialyser is connected to the arterial end and the other end to venous side of vascular access and the access for dialysate fluid. The semipermeable membrane separates the blood compartment and dialysate compartment and allows the transfer of solute from blood to the dialysate, which is drained out after dialysis is completed. The programmed removal of nitrogenous waste products, excess potassium, sodium and water is controlled by computerized dialysis machine.
 
• Dialysis machine :- It controls the flow of blood, dialysate fluid (which is prepared by adding water to the purified concentrate) and the amount of water, sodium and other noxious substances which need to be removed during 3-4 hours of dialysis. Advances in bioengineering and technical aspects of dialysis machines have made hemodialysis a safe and effective procedure.

Indications of hemodialysis are acute renal failure or poisoning, chronic renal failure/ end stage renal disease and rarely inborn errors of metabolism, cardiac failure.

Q. How frequently is hemodialysis given?

A.Chronic maintenance hemodialysis (CMHD) is given 3 times a week. Each session of dialysis is for 3-4 hours.

Q. What is the difference between A-V shunt, A-V Fistula & A-V grafting? Which is done when?

A. A-V. Shunt - Surgically, a silastic catheter is placed which connects radial artery to cephalic vein or femoral artery to femoral vein. The arterial and venous ends of the shunt are connected to arterial and venous ends of the dialyser when dialysis is to be commenced. This type of vascular access is rarely used because of high rate of blocking of the shunt.

A-V fistula - The radial artery is surgically anastomosed to cephalic vein in forearm. Ulnar-Basilic or saphenous vein loop are other fistulae used for hemodialysis. Two needles are introduced once the fistula matures and is functionally ready to connect the dialyser to fistula. In this method of vascular access, no foreign material is used.

A-V. graft - Teflon/PTFE graft is used to connect arterial to venous or veno-venous anastomosis. The major problem in young children are the small sized vessels, which are responsible for failure of vascular access. This graft is expensive and not available in India.

Currently dual lumen venous catheters, which can be introduced in subclavian, jugular or femoral veins are commonly used as vascular access for hemodialysis.

Q. What are the complications of hemodialysis?

A.Complications of hemodialysis are inadequate dialysis which results in malnutrition, growth failure, anemia, bone disease, hypertension. All of these require medical treatment. Blockage, bleeding and infection of vascular access are additional complications.

Q. What is peritoneal dialysis?

A.Peritoneal dialysis (PD) is the type of dialysis when peritoneal membrane is used as a semipermeable membrane for transfer of solutes and fluid from blood to the dialysate fluid which is infused by special peritoneal dialysis catheters and tubes and periodically removed after the dialysis procedure is completed.