How dialysis worksOctober 21, 2007
The human blood is a solution in which water is the solvent and substances, such as electrolytes, urea, glucose, and others are all solutes. The blood of a patient with kidney failure has excess fluid and substances that should be removed by dialysis using the principles of diffusion, osmosis and ultrafiltration.
To perform dialysis, every patient should have a vascular access. The vascular access is necessary to connect the patient’s blood with the dialysis machine. This is the place where a dialysis delivery system enters the bloodstream in a patient’s body (3). The vascular access can be one of two types:
Arterio-Venous Fistula (AVF), created by surgery, is an internal native anostomosis or connection between a patient’s artery and vein, “allowing arterial blood to flow directly into the vein”. (3) The vessels of the arm are the most common location for fistula.
Arterio-Venous Graft (AVG) is an artificial synthetic connection between an artery and a vein. The graft is used for patients who have vessel problems (diabetes, elderly). The graft can be long enough to connect vessels in different parts of the body: arm or thigh. ( 3 )
External devices or catheter.
- Subclaviar catheter
- Jugular catheter
- Femoral catheter
The catheter is a hollow tube inserted into the subclaviar or jugular, or femoral veins which has “direct access to the heart”. The catheter is a temporal vascular access . It is used when internal access is not ready for treatment, and a patient needs emergency dialysis. (3 )
Internal AVF and AFG are preferable to use than catheters because they decrease the possibility of infection , which is very important for dialysis patients who have low immunity.
1. Hoenich, Ncholas A., Woffindin, Celia, and Ward, Michael K: �Diaysers.� Replacement of Renal Function by Dialysis. Ed. John F. Manner. Boston Klumer Academic Publishers, 1989. 144-1762. Keshavian, Prakash R, and Shaldon, Stanley: Hemodialysis Monitors and Monitoring. Replacement of Renal function by Dialysis. Ed. John F. Manner. Boston : Klumer Academic Publishers, 1989. 276-299.
3. Kidney Dialysis Foundation. Dialysis Related Care. Vascular access. 2004 http://www.kdf.org.sg/vascular.htm
4.Stewart, William K.: �The Composition of Dialysis Fluid.� Replacement of Renal Function by Dialysis. Ed. John F. Manner. Boston : Klumer Academic Publishers,1989. 200-217.
5. Terrill, Bobbee. Renal Nursing- A Practical Approach. Ausmed Publications: Mebourne,2001.99-150.
6. Wang, Michael B. : General Physiology: Membrane and Cellular Physiology. Physiology. Ed. John Bullock. Philadelphia: Williams @ Wilkins, 1995.2-6.