How to manage elevated Blood Urea Nitrogen (BUN) in patients undergoing dialysis?

Managing Elevated BUN in Dialysis Patients

The most effective approach to managing elevated BUN in dialysis patients is to optimize dialysis adequacy by ensuring proper blood flow rates, dialyzer function, and adequate treatment time, while addressing potential causes of recirculation and sampling errors. 1

Initial Assessment of Elevated BUN

When encountering elevated BUN in a dialysis patient, follow this systematic approach:

1. Assess Dialysis Adequacy

• Evaluate fistula/access integrity to identify potential recirculation issues:

  • Perform hydraulic compression test during next dialysis
  • Review arterial/venous needle placement and orientation
  • Verify graft flow configuration 1

• Review dialysis treatment parameters:

  • Compare prescribed versus actual blood flow rate (Qb)
  • Check dialysate flow rate (Qd)
  • Verify hemodialyzer type and total cell volume (TCV) if reusing dialyzers
  • Examine extracorporeal pressures (arterial/venous) 1

2. Evaluate Treatment Time

• Confirm effective hemodialysis treatment time matches prescription
• Investigate potential causes of reduced treatment time:
  • Patient arriving late for treatment
  • Early termination requests
  • Clinical events (hypotension, muscle cramps) causing interruptions
  • Technical issues (blood leaks, needle problems) 1

3. Review BUN Sampling Technique

Improper sampling is a common cause of misleading BUN results:

• For predialysis samples:

  • Must be drawn before dialysis begins
  • Avoid dilution with saline or heparin
  • For AV fistula/graft: obtain blood from arterial needle before connecting blood tubing
  • For venous catheters: withdraw heparin/saline first, then draw sample 1

• For postdialysis samples:

  • Use slow flow/stop pump technique to prevent dilution with recirculated blood
  • Avoid sampling immediately after dialysis when access recirculation may be present 1

Secondary Investigations

If initial assessment doesn't identify the cause, proceed with:

1. Clearance (K) assessment:

   • Measure recirculation in fistula using slow flow/stop pump technique
   • Review dialyzer clotting and anticoagulation protocol
   • Check blood pump calibration
   • Review extracorporeal pressures 1

2. Treatment time verification:

   • Review patient arrival patterns and transportation needs
   • Evaluate reasons for early terminations
   • Ensure proper understanding of treatment components by patient and staff 1

Clinical Implications of BUN Management

The National Cooperative Dialysis Study established that elevated time-averaged BUN concentration (TACurea) is associated with increased morbidity in dialysis patients 2, 3. Patients with higher BUN levels experience:

• Greater withdrawal from dialysis for medical reasons
• Increased hospitalization rates
• Higher overall morbidity 2

Importantly, in critically ill patients with acute kidney injury, initiation of dialysis at higher BUN concentrations (>76 mg/dl) has been associated with an increased risk of death compared to starting at lower BUN levels 4.

Optimizing Dialysis Prescription

To effectively manage elevated BUN:

1. Target appropriate clearance metrics:

   • Aim for Kt/V of at least 1.0 (equivalent to midweek predialysis BUN of 60-80 mg/dL)
   • Monitor time-averaged BUN concentration (TACurea) 3

2. Balance dialysis efficiency with safety:

   • While high-efficiency dialysis can achieve BUN clearances up to 240 ml/min, this may increase risk of complications like hypotension and neuropathy 5
   • Adjust prescription based on patient tolerance

3. Ensure adequate nutrition:

   • Maintain dietary protein intake of approximately 1.0 g/kg/day
   • Monitor protein catabolic rate as an indicator of nutritional status 3

Common Pitfalls to Avoid

1. Misinterpreting elevated BUN:

   • In adequately dialyzed patients with good nutrition, moderately elevated BUN may actually indicate improved protein metabolism rather than inadequate dialysis 6
   • Focus on trends rather than absolute values

2. Sampling errors:

   • Diluted predialysis samples can falsely lower BUN readings
   • Improper postdialysis sampling timing can miss rebound effects 1

3. Overlooking access recirculation:

   • Significant recirculation can dramatically reduce effective clearance
   • Always assess access function when BUN is persistently elevated 1

By systematically addressing these factors, elevated BUN in dialysis patients can be effectively managed to improve outcomes and reduce morbidity.