[ Home ] [ Instructions ] [ Program Menu ] [ Form and Evaluation ] [ Faculty ] [ Accreditation ]
|
ALTERNATIVE HEMODIALYTIC TECHNIQUES
The major alternative hemodialytic therapies that have evolved are the slow continuous renal replacement therapies. These therapies were devised in an attempt to improve the treatment of acute renal failure in critically ill patients in intensive care unit settings. The potential advantages of slow continuous therapy in treating this patient population are:
- It does not cause hemodynamic instability since there is little change in plasma osmolarity.
- Allows better control of electrolyte and acid-base balance
- It is very effective in removing fluid which may help patients in pulmonary edema or acute respiratory distress syndrome.
- The procedure is simple and does not require highly technical equipment.
Convection-Based Therapy
CAVH (continuous arteriovenous hemofiltration) - Blood circulates with or without a blood pump through a small hollow-fiber hemofilter. Access to the circulation is by the femoral artery and vein. Heparin is infused continuously proximal to the dialyzer. The patient's blood circulates through the hemofilter wherein the plasma and water is filtered and collected in the collection bag. Replacement fluid is infused into the venous return line.
CVVH (continuous venovenous hemofiltration) - This therapy is pump assisted and achieves higher clearance. Because of its greater effectiveness, this technique is replacing the pumpless CAVH mode. Blood access is achieved by placing a double lumen catheter in the femoral, subclavian, or internal jugular vein. Continuous diffusive solute transport is achieved by infusing a dialysis fluid that runs counter-current to blood at a flow rate of 15 ml/min or 1 L/hr.
Diffusive Therapy
CAVHD (continuous arteriovenous hemodialysis) - This technique uses an infusion pump, hemodialysis membrane and dialysate solution as well as the same blood access circuitry as the CAVH technique. An infusion pump pushes a continuous trickle of sterile dialysis fluid into the dialysate compartment of a hemodialyzer membrane. The blood/dialysate interface is the hemodialysis membrane. CAVHD uses the process of continuous diffusion dialysis to rid the body of fluid, electrolytes, and nitrogenous wastes. The preferred arterial access site is the common femoral artery.
CVVHD (continuous venovenous hemodialysis) - This technique uses an infusion pump, hemodialysis membrane and dialysate solution as well as the same blood access circuitry as the CVVH technique. As with the CAVHD system, adding the dialysis membrane and the dialysate solution increases the efficiency of the procedure. The process of continuous diffusion dialysis in CVVHD is less effective than the CAVHD because the lower pressure venous system does not filter as much blood per unit of time.
A = double-lumen subclavian vein access; B = venous air trap; C = venous pressure monitor; D = air detector; E = dialyzer; x,y,z = blood and dialysate pumps.
