This requires direct access to the circulation, either via a native arteriovenous fistula (the preferred method of vascular access), usually at the wrist (a “Brescia-Cimino” fistula); an arteriovenous graft, usually made of polytetrafluoroethylene; a large-bore intravenous catheter; or a subcutaneous device attached to intravascular catheters. Blood is pumped though hollow fibers of an artificial kidney (the “dialyzer”) and bathed with a solution of favorable chemical composition (isotonic, free of urea and other nitrogenous compounds, and generally low in potassium). Dialysate [K⁺] is varied from 1 to 4 mM, depending on predialysis [K⁺] and the clinical setting. Dialysate [Ca²⁺] is typically 2.5 mg/dL (1.25 mM), [HCO₃^-] typically 35 meq/L, and dialysate [Na⁺] 140 mM; these can also be modified, depending on the clinical situation. Most pts undergo dialysis thrice weekly, usually for 3-4 h. The efficiency of dialysis is largely dependent on the duration of dialysis, blood flow rate, dialysate flow rate, and surface area of the dialyzer.

Complications of hemodialysis are outlined in Table 140-1. Many of these relate to the process of hemodialysis as an intense, intermittent therapy. In contrast to the native kidney or to PD, both major dialytic functions (i.e., clearance of solutes and fluid removal, or “ultrafiltration”) are accomplished over relatively short time periods. The rapid flux of fluid can cause hypotension, even without a pt reaching “dry weight.” Hemodialysis-related hypotension is common in diabetic pts whose neuropathy prevents the compensatory responses (vasoconstriction and tachycardia) to intravascular volume depletion. Occasionally, confusion or other central nervous system symptoms will occur. The dialysis “disequilibrium syndrome” refers to the development of headache, confusion, and rarely seizures, in association with rapid solute removal early in the pt's dialysis history, before adaptation to the procedure; this complication is largely avoided by an incremental induction of chronic dialytic therapy in uremic pts, starting with treatments of short duration, lower blood flows, and lower dialysate flow rates.