• Clinical science

Renal replacement therapy

Abstract

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 Transplantation). 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.

Indications

Indications for dialysis: A-E-I-O-U → Acidosis, Electrolyte abnormalities (hyperkalemia), Ingestion (of toxins), Overload (fluid), Uremic symptoms

References:[1][2]

Hemodialysis and hemofiltration

Preparation

  • Large-bore venous catheter: insertion and catheter are similar to a central venous catheter
  • 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

Procedure/application

  • Hemodialysis
    • 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
  • Hemofiltration
    • 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

Complications

Cardiovascular disease is the leading cause of death in dialysis patients and in kidney transplant recipients.

References:[3][4]

Peritoneal dialysis

Preparation

A catheter is surgically placed into the peritoneal cavity.

Procedure/application

  • 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).

Complications

  • Infections
    • Exit-site infections and catheter tunnel infections
    • Bacterial peritonitis
  • Metabolic disturbances

References:[5]