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How dialysis works

October 21, 2007

Blood
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.

Vascular access
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:

Internal devices

1.gifArterio-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.

2.gifArterio-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

3.gif
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.

References :

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.

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