Clinical meaning
Hemodialysis is a form of renal replacement therapy used to perform the essential functions of the kidneys when they can no longer adequately filter waste products, regulate fluid and electrolyte balance, or maintain acid-base homeostasis. In hemodialysis, the patient's blood is pumped through an extracorporeal circuit to a dialyzer (artificial kidney) containing a semipermeable membrane that separates the blood compartment from the dialysate compartment. Three physical principles govern solute and fluid removal: diffusion (movement of solutes from an area of higher concentration to lower concentration across the membrane -- urea, creatinine, potassium, and other waste products move from blood into dialysate), osmosis (movement of water across the membrane driven by osmotic gradients), and ultrafiltration (removal of excess fluid by applying hydrostatic pressure across the membrane, controlled by the transmembrane pressure gradient). Vascular access is required for hemodialysis and may be an arteriovenous fistula (AVF -- preferred, surgically created anastomosis between an artery and vein, requires 6-12 weeks to mature), arteriovenous graft (AVG -- synthetic conduit between artery and vein, usable in 2-4 weeks), or central venous catheter (CVC -- for acute or temporary access, highest infection risk). The practical nurse in dialysis settings must understand the principles of hemodialysis, vascular access assessment and care, monitoring during treatment, and recognition of complications.