What are the basic principles of hemodialysis (HD) in patients with end-stage renal disease (ESRD)?

Basic Principles of Hemodialysis in ESRD

Hemodialysis removes uremic toxins and excess fluid from blood through diffusion dialysis and ultrafiltration across a semipermeable membrane, with conventional therapy consisting of 3 sessions per week for 3-5 hours each, though more intensive regimens may improve mortality and quality of life. 1, 2

Core Physiological Mechanisms

Hemodialysis operates through two fundamental processes:

• Diffusion dialysis removes uremic toxins by concentration gradient across the semipermeable membrane 2
• Ultrafiltration removes excess fluid through pressure gradient, and can be performed independently of diffusion dialysis with newer membranes 2
• The dialysate bath composition resembles plasma water with electrolytes adjusted to compensate for ESRD abnormalities 2

Standard Dialysis Prescription

Conventional Hemodialysis Schedule

• Frequency: 3 times per week 1
• Duration: 3-5 hours per session 1
• Minimum treatment time: 3 hours per session for patients with residual kidney function <2 mL/min 1

Adequacy Targets

• Target single pool Kt/V (spKt/V): 1.4 per hemodialysis session for thrice weekly treatment 1
• Minimum delivered spKt/V: 1.2 1
• For alternative schedules, target standard Kt/V of 2.3 volumes per week with minimum delivered dose of 2.1 1

Vascular Access Hierarchy

Arteriovenous access (fistula or graft) is strongly preferred over central venous catheters due to lower infection risk and better outcomes. 3

• Arteriovenous fistula (AVF): Preferred first choice, requires several months to mature before use 4
• Arteriovenous graft (AVG): Can be used in as few as 24 hours depending on graft material 4
• Central venous catheter (CVC): Usable immediately but carries highest infection risk; should use "closed connector" devices to reduce infection 3, 4
• For buttonhole cannulation with AVF, mupirocin antibacterial cream reduces infection risk 3

Intensive Hemodialysis Options

More frequent or longer dialysis sessions demonstrate superior outcomes for specific patients:

Short Daily Hemodialysis

• Definition: ≥5 sessions per week with <3 hours per session 1
• Benefits: Improved quality of life, regression of left ventricular hypertrophy, better blood pressure control, reduced intradialytic hypotension 1
• Risks: Increased vascular access procedures and potential for hypotension during dialysis 1

Long Hemodialysis

• Definition: ≥5.5 hours per session, 3-4 times per week 1
• Long-frequent: ≥5.5 hours per session for ≥5 sessions per week 1
• Home long hemodialysis: 6-8 hours, 3-6 nights per week for lifestyle considerations 1
• Risks: Increased vascular access complications, caregiver burden, accelerated decline in residual kidney function 1

Physiological Advantages of Intensive Regimens

• Enhanced clearance of urea, β2-microglobulin, and phosphate 1
• Patients can discontinue fluid, sodium, and phosphate restrictions including phosphate binders 1
• Improved patient survival with longer, more frequent hemodialysis 1
• Reduced overall cost in North American health care systems 1

Special Considerations for Intensive Hemodialysis

Dialysate Composition

• Calcium: Use dialysate calcium ≥1.50 mmol/L to maintain neutral or positive calcium balance 3
• If hypophosphatemia develops, consider phosphate dialysate additives after stopping phosphate binders and liberalizing diet 3

Pregnancy

• Women with ESRD during pregnancy should receive long frequent hemodialysis either in-center or at home 1

Urgent Dialysis Indications

Immediate hemodialysis is required for:

• Persistent hyperkalemia unresponsive to medical therapy 3
• Severe metabolic acidosis 3
• Volume overload unresponsive to diuretics in patients with residual function 3
• Overt uremic symptoms including pericarditis and severe encephalopathy 3
• Severe progressive hyperphosphatemia (>6 mg/dL) or symptomatic hypocalcemia 3

Volume Management and Ultrafiltration

• Consider additional sessions or longer treatment times for patients with large weight gains, high ultrafiltration requirements 1
• Patients with low residual kidney function require careful attention to ultrafiltration rate to prevent intradialytic hypotension 1

Common Pitfalls

• Do not assume achieving dialysis adequacy (Kt/V targets) means comprehensive patient care is complete - patients require management of anemia, nutrition, metabolic bone disease, diabetes, and cardiovascular disease independent of dialysis prescription 1
• Avoid relying solely on kidney function level to initiate dialysis - base the decision primarily on uremic signs/symptoms, protein-energy wasting, and inability to manage metabolic abnormalities with medical therapy 1
• Do not underestimate the importance of vascular access planning - catheter use is associated with decreased short-term and long-term survival 5