Dialysis Indications and Hemodialysis

Indications for Dialysis

• Dialysis decisions depend on patient symptoms/signs, not just blood urea nitrogen or serum creatinine levels.
• Patients starting dialysis with higher residual kidney function have lower morbidity and mortality.
• Early dialysis avoids malnutrition, fluid overload, and the harmful effects of prolonged uremic toxin buildup (phosphorus, beta-2-microglobulin, etc.).

Hemodialysis

• Hemodialysis replaces two kidney functions: solute removal and fluid removal.
• Solute removal in hemodialysis is mainly through diffusion (solutes move from blood to dialysate).
• Blood circulates through a semi-permeable membrane (dialyzer) in the machine.
• Heparin is used to prevent clotting in the extracorporeal circuit.
• Dialysate flows counter-currently to blood through the dialyzer.
• The machine controls dialysate temperature, electrolytes, and hydrostatic pressure.
• Solute diffusion across the dialyzer membrane happens based on concentration differences.
• Dialysate potassium levels are kept low (0-1.5 mEq/L) to prevent potassium buildup.
• Dialysate sodium and calcium are kept within normal ranges.
• Two types of dialysate are used:
  • Acetate dialysate: easier to prepare but can cause hypotension/headache and is less common now.
  • Bicarbonate dialysate: preferred for elderly and unstable patients.
• Fluid removed during dialysis is accumulated between sessions.
• This is achieved by ultrafiltration (using pressure differences across membrane).
• Vascular access is a critical requirement for hemodialysis.
  • Arteriovenous fistulas (e.g., radial artery/cephalic vein or ulnar artery/basilic vein) are common.
• Hemodialysis sessions usually last 4-6 hours, 3 times per week.
• Hypertension control is achieved through gradual salt/water removal.
• Dietary protein is increased to about 1.2 g/kg/day to avoid malnutrition.
• Anemia is treated with iron and erythropoietin, targeting a hemoglobin level of 11-12 g/dL.

Peritoneal Dialysis (CAPD)

• Continous Ambulatory Peritoneal Dialysis (CAPD) is a favored choice for some chronic renal failure patients.
• A soft silicon catheter (Tenckhoff) is surgically implanted into the abdomen.
• Usually, 2 liters of dialysate are run into the peritoneum.
• 3-5 exchanges are usually needed daily.
• Peritoneal dialysis solute/electrolyte removal principles are similar to hemodialysis, but potassium-free dialysate is used.
• Ultrafiltration is based on osmosis (hypertonic glucose dialysate).
• Dietary protein is increased to about 1.3 g/kg/day in CAPD to compensate for protein loss.
• Anemia correction is easier compared to hemodialysis.
• Recombinant erythropoietin is the primary treatment.
• Target hemoglobin level is 11-12 g/dL.

Advantages of CAPD

• Easy to perform and widely available
• Removal of large fluid volumes is possible, useful in hemodynamically unstable patients.
• Gradual correction of acid-base and electrolyte imbalances is possible.
• Easy access placement (especially for children).
• No arterial/venous punctures/anticoagulation needed.
• Biocompatible

Disadvantages of CAPD

• Peritonitis, weight gain, and occasional hernias are possible.

Complications of Hemodialysis

• Circulation Access Problems:
  • Infection (local or systemic)
  • Thrombosis/thrombophlebitis
  • Poor peripheral circulation (especially in elderly/diabetics)
• Kidney Machine/Dialyzer Problems:
  • Membrane bio-incompatibility
  • Fluid contamination & complement activation
  • Hypersensitivity to sterilization agents (Type I first-use syndrome).
• Dialysis Complications (Acute):
  • Hypotension/cramps
  • Bleeding/blood clot issues
  • Air embolisms
  • Chest/back pain (possible hypersensitivity)
  • Hemorrhage
  • Disequilibrium syndrome (rapid urea reduction causing brain edema)
• Dialysis Complications (Chronic):
  • Hepatitis
  • Psychogenic disorders
  • Accelerated atherosclerosis
  • Carpal tunnel syndrome (beta-2 microglobulin amyloidosis)
• Inadequate Dialysis Complications:
  • Uremia symptoms, neuropathy, pericarditis
• Dialysate-related Complications:
  • Hemolysis
  • Acidosis
  • Aluminum toxicity (avoided by purified water for dialysate preparation)