Dialysis Procedure in Hemodialysis

There are three types of dialysis: Hemodialysis, peritoneal dialysis and hemofiltration.

One of the vital aspects of hemodialysis is the establishment and maintenance of adequate blood access. Without it, hemodialysis cannot be done. The major routes of access are external arteriovenous shunts and subclavian catheters for acute dialysis and internal arteriovenous fistulae and grafts for chronic dialysis.

The external arteriovenous shunt requires surgical placement of two rubber-like silicone cannulas into the forearm or leg. The two cannulas are connected to form a U shape. Blood flows from the client’s artery through the shunt into the vein.

When the client is to be connected to the hemodialyzer, a tube leading to the membrane compartment is connected to the arterial cannula. Blood then fills the membrane compartment and flows back to the client by way of a tube connected to the venous cannula. When dialysis is completed, the arterial cannula is clamped. Once the blood in the membrane compartment has been returned to the body, the venous cannula is clamped and the ends of the two cannulas are reattached to form their U. This access can be created quickly and thus is particularly suitable when dialysis must be started immediately.

The internal arteriovenous fistula is the access of choice for clients receiving chronic dialysis. The fistula is created through a surgical procedure in which an artery in the arm is anastomosed to a vein in an end-to-side, side-to-side, or end-to-end fashion. The result is an opening or fistula between a large artery and a large vein. The flow of arterial blood into the venous system causes the veins to become engorged. These fistulae require up to 6 weeks to mature before they can be used.

The internal arteriovenous graft is used primarily for chronic dialysis. In this approach, an artificial graft made of water-repellent fabric or a bovine carotid artery is used to create an artificial vein for blood flow. One end of the artificial graft is anastomosed to an artery, tunneled under the skin and anastomosed to a vein. The graft can be used 2 weeks after insertion.

Once the fistula graft is placed and ready for use, two 15- or 16-gauge needles are placed in the access at each dialysis treatment. A pump pulls arterial blood out by way of the fistula and into the hemodialyzer. Besides the arm, the subclavian, thigh and ankle areas may be used as sites for hemodialysis access.

Subclavian, jugular and femoral catheters can be inserted at the bedside for vascular access or surgically placed in the operating room. Double-lumen catheters are usually used to provide access for both removal and return of blood. These catheters are usually a temporary source of vascular access and must be replaced frequently to prevent infection. Strict aseptic technique must be used during insertion and dressing changes are usually performed by a limited number of trained nurses.

By Dr.N.Dave