Health Information

Introduction

Removal of waste materials and toxic substances and restoration of normal volume and composition of body fluid by means of an artificial kidney is called dialysis or hemodialysis.

Artificial Kidney

Severe dysfunction of kidney is treated by dialysis of patient’s blood. A machine called artificial kidney carries out dialysis. The artificial kidney is used in acute renal failure due to circulatory shock or mercury poisoning. It is also used in chronic or permanent renal failure.

Mechanism of function of artificial kidney

The word dialysis refers to the diffusion of solutes from an area of higher concentration to the area of lower concentration through a semi permeable membrane. This forms the principle of artificial kidney. Patient’s arterial blood is made to flow continuously or intermittently through the artificial kidney and then back to the body through the vein. Heparin is used as an anticoagulant while passing the blood through the machine.

Inside the artificial kidney, the blood passes through a hemofilter, which contains minute channels interposed between two cellophane membranes. The cellophane membranes are porous in nature. The dialyzing fluid baths the outer surface of these membranes. Urea, creatinine, phosphate and unwanted substances from the blood pass into the dialyzing fluid by concentration gradient. The essential substances required by the body diffuse from the fluid into blood. Almost all the substances except plasma proteins are exchanged between the blood and dialyzing fluid through the cellophane membranes.

At a time, about 500 ml of blood is passed through the artificial kidney. Dialysis is done usually thrice a week in severe uremia. Each time the artificial kidney is used for about 6 hours.

Uremia

This is the condition developed due to excessive accumulation of products of protein metabolism. There is increased level of blood, urea, nitrogen and creatinine. There is also accumulation of other toxic substances like organic acids and phenols, which produce the symptoms of uremia. The artificial kidney can excrete more than double the amount of urea that could be excreted by both the normal kidneys. About 200 to 250 ml of plasma could be cleared of urea per minute by the artificial kidney. But, the urea clearance by normal kidney is only about 70 ml per minute.