Why is an Arteriovenous (AV) fistula needed for hemodialysis?

Why AV Fistula is Needed for Hemodialysis

Arteriovenous (AV) fistulas are the preferred vascular access for hemodialysis due to their superior patency rates, lower risk of infection, and decreased mortality compared to other access types like arteriovenous grafts (AVGs) and central venous catheters (CVCs). 1

Advantages of AV Fistulas

• AV fistulas provide the most reliable, complication-free access that facilitates adequate dialysis and supports each patient's specific care needs 1
• They have the best 4-5 year patency rates and require fewer interventions compared to other access types 1
• AV fistulas have significantly lower infection rates (4.1% overall) compared to other access types 2
• They are associated with decreased mortality compared to other vascular access options 3
• AV fistulas create optimal conditions for increasing blood flow through the venous system, which reduces the risk of turbulence and endothelial injury 4

Technical Requirements for Hemodialysis Access

• Hemodialysis requires a vascular access that can:
  • Provide reliable high blood flow rates (typically >600 mL/min) 1
  • Allow repeated needle puncture for dialysis sessions 4
  • Have minimal depth (ideally <0.6 cm) for easy cannulation 1
  • Have adequate vein diameter (minimum 6 mm) for successful dialysis 1
  • Withstand the high-pressure system needed for efficient dialysis 1

Limitations of Alternative Access Types

• Central venous catheters (CVCs):

  • Associated with higher infection rates 1
  • Provide lower blood flow rates compared to AV access 1
  • Can compromise dialysis adequacy without appropriate adjustments in treatment duration 1
  • Increase risk of central venous stenosis, which may preclude future permanent access options 1
  • Should be limited to <10% of chronic maintenance hemodialysis patients 1

• Arteriovenous grafts (AVGs):

  • Have higher rates of thrombosis compared to AV fistulas 1
  • Require more frequent interventions to maintain patency 1
  • Have higher infection rates than native fistulas 1
  • Should be considered only when AV fistula creation is not possible 5

Timing and Planning for AV Fistula Creation

• AV fistulas should ideally be created 3-4 months before anticipated need for hemodialysis to allow proper maturation 1
• Early referral of patients with progressive kidney disease to nephrologists increases the probability of successful AV fistula formation 1
• Patients should be referred for hemodialysis access when their estimated glomerular filtration rate progressively decreases to 15-20 mL/min 6
• The 2019 KDOQI guidelines recommend a "Patient Life-Plan, Access Needs" (P-L-A-N) approach rather than simply "Fistula First" 1

Common Challenges and Complications

• Maturation failure occurs in 20-60% of cases, with only 26% of created fistulas reported as mature at 6 months 2
• Mean time to maturation is approximately 3.5 months 2
• About 21% of fistulas are abandoned without use 2
• Major complications include:
  • Stenosis due to neointimal hyperplasia (most common cause of access failure) 4
  • Thrombosis (primary cause of loss of vascular access patency) 1
  • Infection (though at lower rates than other access types) 4
  • Aneurysm formation 4
  • Steal syndrome (1-8% of patients) 6

Monitoring and Maintenance

• Regular monitoring of AV fistulas is essential to detect dysfunction early 1
• Physical examination can identify abnormal clinical signs like changes in thrill or bruit, with up to 90% of accesses with abnormal physical examinations having clinically significant findings on imaging 1
• Periodic surveillance using noninvasive and invasive methods to assess blood flow rate, access recirculation, and dialysis venous pressure is recommended 1
• Early detection and intervention for stenosis can prevent thrombosis and extend access lifespan 1

AV fistulas remain the gold standard for hemodialysis access despite their limitations, as they provide the best long-term outcomes in terms of morbidity, mortality, and quality of life for most patients requiring chronic hemodialysis 1, 6.