What determines the optimal dialysis prescription for a patient with Impaired renal function?

Determining the Optimal Dialysis Prescription

The optimal dialysis prescription is determined by measuring residual kidney function (RKF) and body surface area (BSA), then targeting a minimum weekly Kt/Vurea of 2.0 (or 1.8 if RKF is absent), with adjustments based on peritoneal equilibration testing, volume status, and monthly clinical assessments.

Initial Assessment Framework

Step 1: Measure Baseline Kidney Function

• Obtain a 24-hour urine collection for urea and creatinine clearance to quantify residual kidney function before prescribing dialysis 1
• Calculate the patient's body surface area (BSA) and total body water (V) using sex-specific equations 1
• For males: TBW = 0.010 · (height · weight)^0.68 – 0.37 · weight 1
• For females: TBW = 0.14 · (height · weight)^0.64 – 0.35 · weight 1

Step 2: Set Clearance Targets Based on RKF Status

For patients WITH residual kidney function (urine Kt/Vurea >0.1/week):

• Target a minimum total (peritoneal + kidney) Kt/Vurea of 1.8 per week 1
• The peritoneal dialysis dose can be reduced proportionally to the contribution from RKF 1
• Remeasure RKF every 3 months since it contributes to total clearance 1

For patients WITHOUT residual kidney function (urine Kt/Vurea <0.1/week):

• Target a minimum peritoneal Kt/Vurea of 1.8 per week 1
• Use continuous 24-hour dwells rather than intermittent schedules to maximize middle-molecule clearance 1

Empiric Initial Prescription Algorithm

For Peritoneal Dialysis Patients with GFR <2 mL/min:

CAPD (Continuous Ambulatory PD):

• BSA <1.7 m²: Start with 2.0 L exchanges, 4 times daily 1
• BSA 1.7-2.0 m²: Start with 2.5 L exchanges, 4 times daily 1
• BSA >2.0 m²: Start with 3.0 L exchanges, 4 times daily 1

CCPD (Continuous Cycling PD):

• BSA <1.7 m²: 2.0 L overnight (9 hours) + 2.0 L daytime dwell 1
• BSA 1.7-2.0 m²: 2.5 L overnight (9 hours) + 2.0 L daytime dwell 1
• BSA >2.0 m²: 3.0 L overnight (9 hours) + 3.0 L daytime dwell 1

For Pediatric Patients:

• Prescribe instilled volumes of 1,100-1,200 mL/m² BSA as the starting point, with maximum tolerance up to 1,400 mL/m² 1

Mandatory Monitoring Schedule

Within First Month:

• Perform peritoneal equilibration testing (PET) at approximately 1 month to determine membrane transport characteristics 1
• Measure delivered Kt/Vurea within the first month after initiating dialysis 1
• Obtain 24-hour dialysate and urine collections for actual clearance calculations 1

Ongoing Monitoring:

• Remeasure total solute clearance every 6 months minimum 1
• For patients with RKF contributing to clearance targets, remeasure urine volume and clearance every 3 months 1
• Review clinical status monthly, assessing volume status, nutritional parameters, and drain volumes 1

Prescription Optimization Strategies

Increase Dialysis Dose When:

• Patient shows uremic symptoms (pericarditis, neuropathy, encephalopathy) despite adequate measured clearance 1
• Nutritional status deteriorates (declining serum albumin, protein-energy malnutrition) 1
• Volume overload persists despite current prescription 1
• Patient is not thriving without other identifiable cause 1

Volume Optimization Hierarchy:

1. First: Increase instilled volume per exchange (target 1,000-1,200 mL/m² BSA, maximum 1,400 mL/m²) before increasing exchange frequency 1
2. Second: Optimize drain volumes, particularly from overnight CAPD dwells and daytime CCPD dwells 1
3. Third: Use diuretics in patients with RKF rather than increasing dialysate dextrose concentration 1
4. Fourth: Ensure positive ultrafiltration for all exchanges in hypertensive or volume-overloaded patients 1

Critical Pitfalls to Avoid

Do not rely on GFR alone to determine dialysis adequacy - clinical symptoms, nutritional status, and volume control are equally important outcomes 1, 2

Do not use NIPD (nightly intermittent PD with dry days) at dialysis initiation unless the patient has significant RKF providing supplemental clearance 1

Do not measure clearances during clinical instability - wait at least 1 month after peritonitis resolution before assessing adequacy 1

Do not ignore residual kidney function preservation - avoid nephrotoxic medications (especially aminoglycosides), maintain adequate perfusion, and address pre-renal and post-renal causes of RKF decline 1

Do not prescribe fixed dialysate sodium without individualization - adjust based on patient's volume status, plasma sodium level, and hemodynamic response to prevent interdialytic weight gain and hypertension 3

When Standard Targets Are Insufficient

If a patient fails to thrive despite achieving minimum Kt/Vurea targets of 1.8-2.0 per week and no other cause is identified, empirically increase the dialysis dose 1. This clinical judgment supersedes numerical targets, as adequacy encompasses more than small-solute clearance alone - it includes middle-molecule removal, volume control, and quality of life 1.