When the kidneys fail to maintain the body in a healthy state, the condition is called chronic renal failure. In advanced stages of chronic renal failiure, symptoms arise. These are called uremic symptoms and may consist of one or more of the following:-
Weakness, decreased appetite, nausea, vomiting, hiccups, breathlessness, swelling of the body, decreased amount of urine etc. Later on a person may develop fits or increasing drowsiness, unconsciousness, extreme weakness, muscle paralysis etc. Initially these symptoms are mild but later on they do not allow a person to live a normal life and still later they will kill a person unless treated.
The process of taking over of failed kidney functions by treatment is called Renal Replacement Therapy (RRT). This mainly comprises of Dialysis and Renal Transplant.
Dialysis is the process through which the accumulated waste products are removed. It also removes extra water salt, potassium, acid, phosphorus and molecules of middle size. Thus it attempts to return the body to a healthy state.
Dialysis is mainly of two types:- Hemodialysis and Peritoneal dialysis.
In this a membrane called dialysis membrane is used as a filter. It is folded many times over to increase its area to about .5 sq meters to 2 sq meters (for children and adults of various sizes). This membrane allows only small molecules to move from one side to the other.
Blood flows on one side of the membrane and dial sate fluid flows on the other. The dialysate fluid is produced in the dialysis machine by diluting commercial concentrates. The composition of the dialysate is similar to Blood without cells, proteins, fats and other larger molecules.
Smaller molecules present in high concentration in blood and dialysate move across because of difference in concentration (called electrochemical gradient) from a higher concentration to lower concentration. Pressure can be applied across the membrane to create pressure to push water and salt across as well.