Harrison’s Manual of Medicine
Initiation of dialysis usually depends on a combination of the pt’s symptoms, comorbid conditions, and laboratory parameters. Unless a living donor is identified, transplantation is deferred by necessity, due to the scarcity of cadaveric donor organs (median waiting time 2–5 years at most transplant centers). Dialytic options include (in order of prevalence in U.S.): in-center hemodialysis, continuous ambulatory peritoneal dialysis (PD), nocturnal cycled PD, and home-hemodialysis. Roughly 75% of U.S. pts are started on hemodialysis.
Absolute indications for dialysis include: severe volume overload refractory to diuretic agents, severe hyperkalemia and/or acidosis, encephalopathy not otherwise explained, and pericarditis or other serositis. Additional indications for dialysis include symptomatic uremia (Chap. 139) (e.g., intractable fatigue, anorexia, nausea, vomiting, pruritus, difficulty maintaining attention and concentration), and protein-energy malnutrition/failure to thrive without other overt cause. No absolute serum creatinine, BUN, creatinine or urea clearance, or glomerular filtration rate (GFR) is used as an absolute cut-off for requiring dialysis, although most individuals experience, or will soon develop, symptoms and complications when the GFR is below ~10 mL/min.
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). Most pts undergo dialysis thrice weekly, usually for 3–4 h. The efficiency of dialysis is largely dependent on the duration of dialysis, the blood flow rate, dialysate flow rate, and surface area of the dialyzer. More intense dialysis is generally associated with reduced morbidity and mortality.
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 CNS 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.
Table 140-1 Complications of Hemodialysis
This does not require direct access to the circulation; rather, it obligates placement of a peritoneal (“Tenckoff”) catheter that allows infusion of a dialysate solution into the abdominal cavity, which allows transfer of solutes (i.e., urea, potassium, other uremic molecules) across the peritoneal membrane, which serves as the “artificial kidney.” This solution is similar to that used for hemodialysis, except that it must be sterile, and uses lactate, rather than bicarbonate, to provide base equivalents. PD is far less efficient at cleansing the bloodstream than hemodialysis and therefore requires a much longer duration of therapy. Pts generally have the choice of performing their own “exchanges” (2–3 L of dialysate, 4–5 times during daytime hours) or using an automated device at night. Compared with hemodialysis, PD offers the major advantages of (1) independence and flexibility, and (2) a more gentle hemodynamic profile.
Complications are outlined in Table 140-2. Peritonitis is the most important complication. In addition to the ill effects of the systemic inflammatory response, protein loss is magnified severalfold during the peritonitis episode. If severe or prolonged, an episode of peritonitis may prompt removal of the Tenckoff catheter or even discontinuation of the modality (i.e., switch to hemodialysis). Gram-positive organisms (especially Staphylococcus aureus and other Staph spp.) predominate; Pseudomonas or fungal (usually Candida) infections tend to be more resistant to medical therapy. Antibiotic administration may be intravenous or intraperitoneal when intensive therapy is required.
Table 140-2 Complications of Peritoneal Dialysis
For a more detailed discussion, see Singh AK, Brenner B: Dialysis in the Treatment of Renal Failure: Chap. 271, p. 1562, in HPIM-15.