What does a positive 1155 mL cumulative ultrafiltration balance in temporary peritoneal dialysis indicate?

What Does +1155 mL Cumulative Ultrafiltration Balance Mean in Temporary PD?

A positive 1155 mL cumulative ultrafiltration balance means the patient has successfully removed a net total of 1155 mL of fluid from their body through peritoneal dialysis—this represents the difference between fluid drawn into the peritoneal cavity osmotically and fluid absorbed by tissues/lymphatics during the dialysis session.

Understanding Net Ultrafiltration

Net ultrafiltration in PD is not simply the fluid you instill minus what you drain out. The actual physiology is more complex 1, 2:

• Osmotic ultrafiltration draws fluid from blood capillaries into the peritoneal cavity (driven by glucose concentration)
• Fluid loss occurs simultaneously through:
  • Direct absorption into peritoneal tissues (75-95% of losses) driven by hydrostatic pressure (2-8 mmHg)
  • Lymphatic drainage (5-25% of losses)

The +1155 mL represents what remains after accounting for these losses—this is actual fluid removal from the patient's body.

Clinical Significance

Is This Adequate?

For a temporary/acute PD session, 1155 mL is generally acceptable ultrafiltration, though context matters:

• Minimum adequacy threshold: Guidelines emphasize achieving ≥400 mL with a 4-hour dwell using hypertonic (4.25%) dextrose to avoid ultrafiltration failure 3
• Your patient exceeded this significantly, suggesting:
  • Adequate peritoneal membrane function
  • Appropriate osmotic gradient maintenance
  • No ultrafiltration failure

What Affects This Number?

The cumulative balance is influenced by 4, 5:

1. Dwell time and frequency - Longer dwells allow more equilibration
2. Dextrose concentration - Higher concentrations drive more osmotic ultrafiltration
3. Intraperitoneal pressure (IPP) - Higher volumes create higher IPP, which paradoxically can reduce net ultrafiltration by driving more fluid into tissues 6, 7
4. Patient factors:
   • Peritoneal transport status (high transporters lose osmotic gradient faster)
   • Body habitus (obesity increases IPP)
   • Residual kidney function

Monitoring Implications

Total fluid removal (ultrafiltration + urine volume) is a strong predictor of survival (RR 0.90 for every 100 mL/24h increase, P<0.01) 4. Therefore:

• Track this cumulative balance at each session
• Combine with urine output for total fluid removal assessment
• Monitor for volume status clinically (edema, blood pressure, weight)
• Adjust dextrose concentration in subsequent exchanges if inadequate

Common Pitfalls

1. Negative ultrafiltration with long dwells should be avoided—adjust prescription and dextrose concentration 5
2. Don't assume linear ultrafiltration across cycles—later cycles in automated PD typically achieve higher UF volumes than early cycles 8
3. High intraperitoneal volumes don't always mean better UF—excessive IPP can reduce net ultrafiltration, particularly in men, obese patients, or those with polycystic kidneys 7

In summary: +1155 mL is successful fluid removal that should be documented, trended over time, and combined with clinical volume assessment to guide ongoing PD prescription adjustments.