Renal replacement therapy is indicated when the kidney transiently or persistently loses its function to remove toxins, metabolites, and water from the body. It is also used in certain cases of poisoning/overdose when the kidney cannot clear the toxin fast enough. There are three main modalities used to replace the renal function: dialysis (either hemodialysis or peritoneal dialysis), hemofiltration, and kidney transplant (see “Renal transplantation” in ). Dialysis is based on the diffusion of molecules across a semipermeable membrane, which separates blood on one side and the dialysate on the other. Hemofiltration is based upon the principles of filtration and convection, (as opposed to diffusion) and mimics the function of the glomerular system. An ultrafiltrate is excreted, and the replacement of electrolytes with a specific solution is essential. Kidney transplantation is indicated for patients with end-stage renal disease (ESRD). In those cases, it is associated with a greater long-term survival rate and a better quality of life than dialysis.
- of pH < 7.1
- Refractory ,
- Toxic substances (e.g., , )
- Refractory fluid overload
- Signs of , including pericarditis, encephalopathy, and asterixis on exam
Hemodialysis and hemofiltration
Large-bore venous catheter for hemodialysis
- Insertion and catheter are similar to a central venous catheter
- Generally used either as a bridging measure until an AV fistula or graft has been created or if these are contraindicated.
- Nontunneled hemodialysis catheter: central venous catheter that is not tunneled and does not include a cuff (usually short-term use only)
- Tunneled hemodialysis catheter: Tunneling and the use of a cuff reduce the risk of infection and increase stability, allowing longer usage.
Arteriovenous fistula: anastomosis of an artery and a vein as a safe, large-bore vascular access
- Preferred location: radiocephalic fistula (Cimino fistula; anastomosis between radial artery and cephalic vein in the distal forearm)
- Should be provided early to ensure availability when needed
- Usually constructed in the nondominant arm (less impairment)
- Indication: maintenance dialysis in chronic kidney disease
- Molecules diffuse across a semipermeable membrane down their concentration gradient and are removed from the blood.
- Superior at removing low-weight molecules; (e.g., urea, protein-bound drugs, ammonia)
- Requires either a catheter (short-term option) or the creation and maturation of a fistula (long-term option)
- Common in the United States
- Molecules are filtered out by a semipermeable membrane, whereas fluid passes through freely and re-enters the body (as “ultrafiltrate”).
- Superior at removing middle-weight molecules (e.g., TNF, IL-8, IL-6)
- Replacement fluid is required because significant amounts of fluid are wasted in this process (“effluent”).
- More common in Europe than the United States
- Arteriovenous fistulas
- Rarely: allergic reactions to the equipment ,
Dialysis disequilibrium syndrome
- Pathophysiology: Because of the (rapid) extraction of osmotically active substances (e.g., urea, NaCl) during dialysis, patients (especially when they start on dialysis for the first time) can develop acute cerebral edema.
- Prevention: regular and slow hemodialysis
A catheter is surgically placed into the peritoneal cavity.
- Similar to hemodialysis, but utilizes the patient's own peritoneal membrane as the semipermeable membrane
- Can be done at home (as opposed to a dialysis center)
- Preferred for highly adherent patients because of the potential complications which can occur if maintained incorrectly (see “Complications” below).
- Exit-site infections and catheter tunnel infections
- Bacterial peritonitis
- Metabolic disturbances