The Basics of Renal Replacement Therapy
Renal replacement therapy (RRT) is divided into two main types: peritoneal, performed primarily in emergency rooms and in developing countries, and hemodialysis, which is practiced at dialysis centers. Techniques include intermittent hemodialysis, continuous hemofiltration and hemodialysis, and peritoneal dialysis. All modalities exchange solute and remove fluid from the blood, using dialysis and filtration across permeable membranes.
During dialysis, serum solute diffuses passively between fluid compartments down a concentration gradient (diffusive transport). During filtration, serum water passes between compartments down a hydrostatic pressure gradient, dragging solute with it (convective transport). The two processes are often used in combination (hemodiafiltration). Hemoperfusion is a rarely used technique that removes toxins by passing blood over a bed of adsorbent material.
Dialysis and filtration may be performed either intermittently or continuously. Continuous therapy, employed exclusively for acute kidney injury, is sometimes better tolerated than intermittent therapy in unstable patients, because solute and water are removed more slowly. All forms of RRT except peritoneal dialysis require vascular access; continuous techniques require a direct arteriovenous or venovenous circuit.
The choice of technique depends on several factors, including the primary need (solute or water removal or both), underlying indication (poisoning or acute or chronic kidney failure), vascular access, hemodynamic stability, availability, local expertise, and patient preference and capability (e.g., for home dialysis).