Dialysis and types of dayalysis

DIALYSIS

Dialysis is the procedure to remove waste materials and toxic substances and to restore normal volume and composition of body fluid in severe renal failure. It is also called hemodialysis.

 

DIALYSIS

ARTIFICIAL KIDNEY

Artificial kidney is the machine that is used to carry out dialysis during renal failure. It is used to treat the patients suffering from:

1. Acute renal failure

2. Chronic or permanent renal failure.

MECHANISM OF FUNCTION OF ARTIFICIAL KIDNEY

The term dialysis refers to diffusion of solutes from an area of higher concentration to the area of lower concentration, through a semipermeable membrane. This forms the principle of artificial kidney. Patient’s arterial blood is passed 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 dialyzer called hemofilter, which contains minute channels interposed between two cellophane membranes. The cellophane membranes are porous in nature.

The outer surface of these membranes is bathed in the dialyzing fluid called dialysate. The used dialysate in the artificial kidney is constantly replaced by fresh dialysate. Urea, creatinine, phosphate and other unwanted substances from the blood pass into the dialysate by concentration gradient. The essential substances required by the body diffuse from dialysate into blood. Almost all the substances, except plasma proteins are exchanged between the blood and dialysate through the cellophane membranes.

In addition to the dialyzer, the dialysis machine has several blood pumps with pressure monitors, which enable easy flow of blood from the patient to the machine and back to the patient. It also has pumps for flow of fresh dialysate and for drainage of used dialysate. Total amount of blood in the dialysis machine at a time is about 500 mL. The rate of blood flow through the dialysis machine is about 200 to 300 mL/minute. The rate of dialysate flow is about 500 mL/minute.

FREQUENCY AND DURATION OF DIALYSIS

The frequency and duration of dialysis depends upon the severity of renal dysfunction. Dialysis is done usually thrice a week in severe uremia. Each time, the artificial kidney is used for about 6 hours.

DIALYSATE

The concentration of various substances in the dialysate is adjusted in accordance with the needs of the patient’s body. The fluid does not contain urea, urate, sulfate, phosphate or creatinine, so that, these substances move from the blood to the dialysate. The fluid has low concentration of sodium, potassium and chloride ions than in the uremic blood. But the concentration of glucose, bicarbonate and calcium ions is more in the dialysate than in the uremic blood.

PERITONEAL DIALYSIS

Peritoneal dialysis is the technique in which peritoneal membrane is used as a semipermeable membrane. It is also used to treat the patients suffering from renal failure.

A catheter is inserted into the peritoneal cavity through anterior abdominal wall and sutured. The dialysate is passed through this catheter under gravity. The required electrolytes from dialysate pass through vascular peritoneum into blood vessels of abdominal cavity. Urea, creatinine, phosphate and other unwanted substances diffuse from blood vessels into dialysate. Later, dialysate is drained from peritoneal cavity by gravity. Peritoneal dialysis is a simple, convenient and lessexpensive technique, compared to hemodialysis. Patients themselves can change the fluid on an outpatient basis. However, it has few drawbacks. It is less efficient in removing some of the toxic substances and it may lead to complications by infections.

UREMIA

 Blood level of urea, nitrogen and creatinine increases during uremia. Toxic substances such as organic acids and phenols also accumulate in blood. 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 off urea per minute by the artificial kidney. But, the urea clearance by normal kidney is only about 70 mL/minute.

COMPLICATIONS OF DIALYSIS

Complications of dialysis depend upon the patient’s condition, age, existence of diseases other than renal

failure and many other factors. Common complications of dialysis in individuals

having only renal dysfunction are:

1. Sleep disorders

2. Anxiety

3. Depression

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