What are the differences in the settings of sustained low‑efficiency dialysis (SLED) versus sustained low‑efficiency dialysis‑filtration (SLED‑F)?

Technical Differences Between SLED and SLED-F Settings

SLED-F (sustained low-efficiency dialysis-filtration) adds a convective component through hemofiltration with replacement fluid administration to standard SLED, which relies primarily on diffusive clearance alone. 1

Core Operational Distinctions

SLED (Standard Configuration)

• Operates purely by diffusion using countercurrent flow of blood and dialysate through the dialyzer membrane, maximizing concentration gradients for small solute removal 2
• Blood flow rates: Typically 200-300 mL/min (lower than conventional hemodialysis) 3
• Dialysate flow rates: 100-300 mL/min (substantially lower than intermittent hemodialysis which uses 500-800 mL/min) 2, 3
• Treatment duration: 6-12 hours per session, usually delivered 5-7 days per week 4, 5
• Primary clearance mechanism: Diffusion-dependent, most efficient for small molecular weight solutes (urea, creatinine, potassium) 3

SLED-F (Hybrid Configuration)

• Combines diffusion AND convection by adding hemofiltration with replacement fluid administration during the same treatment session 1
• Requires replacement fluid: Pre-dilution or post-dilution replacement fluid must be administered, typically at rates lower than pure CVVHF (which uses 20-35 mL/kg/hour) but higher than zero 1
• Enhanced middle molecule clearance: The convective component improves removal of middle and larger molecular weight solutes (beta-2 microglobulin, inflammatory mediators) that diffusion handles poorly 1, 6
• Blood and dialysate flows: Similar to standard SLED (200-300 mL/min blood, 100-300 mL/min dialysate), but with added ultrafiltration and replacement fluid circuits 3

Practical Implications for Prescription

Dose Calculation Differences

• SLED dose: Expressed as equivalent Kt/V or single-pool Kt/V targets borrowed from maintenance hemodialysis, aiming for delivered spKt/V ≥1.2 per session 7
• SLED-F dose: Must account for BOTH diffusive clearance (Kt/V) AND convective clearance (effluent volume), with total dose often expressed as continuous equivalent of 20-25 mL/kg/hour when combining both components 1, 4

Fluid Management

• SLED: Net ultrafiltration is prescribed based on volume removal goals; typical daily ultrafiltration ranges 1,500-4,500 mL depending on patient needs 5
• SLED-F: Requires careful balance of ultrafiltration, replacement fluid administration, and net fluid removal; the convective component necessitates higher ultrafiltration rates with partial replacement to achieve desired net fluid balance 1

Anticoagulation Requirements

• SLED: Regional citrate anticoagulation is first-line when not contraindicated; intermittent heparin dosing (median 4,000 U/day) is substantially lower than CRRT requirements 4, 5
• SLED-F: Anticoagulation needs may be slightly higher than standard SLED due to increased filter surface area exposure from convective flow, but still lower than 24-hour CRRT (which requires median 21,100 U/day heparin) 5

Nutritional and Metabolic Considerations

Protein and Amino Acid Losses

• SLED: Removes approximately 10-15 g of amino acids per treatment session; protein requirements are 1.3-1.5 g/kg/day 1, 4
• SLED-F: Higher amino acid and protein losses due to convective removal (similar to CVVHF patterns); protein requirements increase to 1.5-1.7 g/kg/day to compensate for continuous losses 7, 1

Energy Considerations

• SLED: Minimal caloric contribution from dialysate glucose (100-300 kcal/day when using citrate anticoagulation with glucose-containing solutions); allows increased citrate removal by the diffusive process itself 7
• SLED-F: Potentially higher caloric contribution if glucose-containing replacement fluids are used, though this depends on replacement fluid composition and rate 7

Clinical Selection Algorithm

Choose standard SLED when:

• Primary goal is small solute removal (uremia, hyperkalemia, metabolic acidosis) 3
• Hemodynamic stability allows 6-12 hour sessions without minute-to-minute fluid adjustments 4
• Resources for replacement fluid management are limited 7
• Cost containment is a priority (SLED is more cost-effective than convective therapies) 7

Choose SLED-F when:

• Middle molecule clearance is clinically important (sepsis with inflammatory mediator accumulation, tumor lysis syndrome) 7, 3
• Patient has both azotemia requiring diffusive clearance AND volume overload requiring aggressive convective removal 1
• Attempting to replicate CRRT benefits (hemodynamic stability, continuous solute removal) while maintaining SLED's operational advantages 1

Common Pitfalls

• Underdosing: Prescribed doses often exceed delivered doses by 20-25% due to treatment interruptions; monitor actual effluent volume and increase prescription accordingly for both modalities 4
• Inadequate protein supplementation: Failing to increase protein intake to 1.5-1.7 g/kg/day with SLED-F leads to negative nitrogen balance and malnutrition 7, 1
• Electrolyte depletion: Both modalities cause continuous losses of potassium, phosphate, and magnesium; check electrolytes every 2-6 hours initially and supplement aggressively 4
• Medication underdosing: Beta-lactam antibiotics and other dialyzable drugs require therapeutic drug monitoring and dose adjustment for both SLED and SLED-F 4