What is the difference between SLED (Sustained Low-Efficiency Dialysis) and CVVHF (Continuous Veno-Venous Hemofiltration) in treating critically ill patients with acute kidney injury?

SLED vs CVVHF in Critically Ill Patients with Acute Kidney Injury

Direct Comparison and Recommendation

Both SLED (Sustained Low-Efficiency Dialysis) and CVVHF (Continuous Veno-Venous Hemofiltration) are equally effective modalities for treating critically ill patients with acute kidney injury, with no significant difference in mortality, renal recovery, or hemodynamic stability. 1 The choice between these modalities should be based on institutional resources, nursing expertise, and specific clinical scenarios rather than superiority of one over the other.

Key Technical Differences

SLED Characteristics

• Duration and Schedule: Runs 8-12 hours per session, typically performed nocturnally, allowing unrestricted daytime access for procedures and tests 2
• Mechanism: Uses standard hemodialysis equipment with reduced dialysate (100-300 mL/min) and blood flow rates (100-200 mL/min) 2, 3
• Classification: Considered a "hybrid" or Prolonged Intermittent Kidney Replacement Therapy (PIKRT), combining features of both intermittent and continuous modalities 4
• Solute Removal: Primarily diffusion-based, achieving mean delivered Kt/V of 1.36 per completed treatment 2

CVVHF Characteristics

• Duration: Runs continuously 24 hours per day 4
• Mechanism: Pure convective therapy using hemofiltration with replacement fluid administration 5
• Effluent Rate: Typically prescribed at 20-35 mL/kg/hour 4, 5
• Solute Removal: Convection-based, more efficient for middle and large molecular weight solutes (though without proven clinical benefit) 5

Clinical Outcomes: The Evidence

Mortality

No significant difference exists in mortality between SLED and CRRT modalities. 1 A meta-analysis of 1,564 patients from 18 studies showed a marginal statistical favor for SLED (RR 1.21,95% CI 1.02-1.43), but this difference disappeared when analyzing only randomized controlled trials (RR 1.25,95% CI 1.00-1.57) 1

Renal Recovery

Both modalities demonstrate equivalent renal recovery rates. 1 Meta-analysis revealed no statistically significant difference in overall proportion of renal recovery (RR 0.87,95% CI 0.63-1.20) or time to renal recovery (mean difference 1.33 days, 95% CI 0.23-2.88) 1

Hemodynamic Stability

SLED provides comparable hemodynamic control to CRRT in critically ill patients. 6 In a cohort study of 223 RRT sessions, hemodynamic instability occurred in 56.4% of SLED sessions versus 50.0% of CRRT sessions (p = 0.51), with an adjusted odds ratio of 1.20 (95% CI 0.58-2.47) 6

Practical Advantages and Disadvantages

SLED Advantages

• Cost-effectiveness: Lower costs than CRRT while using existing dialysis equipment 3
• Treatment flexibility: Nocturnal scheduling permits unrestricted daytime patient access for procedures, imaging, and rehabilitation 2, 3
• Nursing efficiency: Requires less intensive nursing supervision than 24-hour CRRT 3
• Adequate detoxification: Achieves excellent small solute clearance with mean phosphate removal of 1.5 g per treatment 2

SLED Disadvantages

• Session interruptions: 28.2% of SLED sessions may be interrupted (compared to 34.9% for CRRT) 6
• Circuit clotting: Majority of premature discontinuations occur due to extracorporeal circuit clotting 2
• Electrolyte disturbances: Mild hypophosphatemia and/or hypokalemia requiring supplementation occurred in 17% of treatments 2
• Limited efficacy at high vasopressor doses: Hemodynamic tolerability and efficacy may be compromised in patients requiring high vasopressor support 7

CVVHF Advantages

• Continuous therapy: Provides 24-hour solute and fluid removal with slower, more gradual shifts 4
• Better fluid removal tolerance: Slower ultrafiltration rates may be better tolerated in severely hemodynamically unstable patients 4
• Middle molecule clearance: More efficient removal of larger molecular weight substances (though clinical benefit unproven) 5

CVVHF Disadvantages

• Higher costs: Significantly more expensive than SLED 3
• Limited patient access: Continuous therapy restricts patient mobility and access for procedures 2
• Intensive nursing requirements: Requires dedicated nursing supervision 24 hours daily 3
• Amino acid losses: Prolonged CRRT results in amino acid losses of 11.8-17.4 g/day, necessitating higher protein intake (1.5-1.7 g/kg/day) 4

Clinical Decision Algorithm

Choose SLED When:

• Institutional resources favor intermittent modalities with experienced dialysis nursing staff 3
• Daytime procedures are anticipated requiring unrestricted patient access 2
• Cost containment is a priority without compromising patient outcomes 3
• Hemodynamic stability is adequate with low-to-moderate vasopressor requirements 7

Choose CVVHF When:

• Severe hemodynamic instability exists requiring very gradual fluid removal 4
• Institutional preference and expertise favor continuous modalities 3
• Specific clinical scenarios such as severe hyperammonemia (though CVVHD would be preferred over CVVHF) 5

Important Caveats

Guideline consensus indicates no clear advantage for CRRT over PIKRT (including SLED) in hemodynamically unstable patients. 4 The 2021 ESPEN guidelines explicitly state: "No clear advantage has been demonstrated so far for CKRT over PIKRT" 4

Nutritional considerations differ: Patients on CVVHF require higher protein intake (1.5-1.7 g/kg/day) compared to those on SLED (1.3-1.5 g/kg/day) due to continuous amino acid and protein losses 4

Anticoagulation strategy: Regional citrate anticoagulation is recommended as first-line for CRRT when no contraindications exist 5, while SLED may use intermittent heparin dosing similar to conventional hemodialysis 4

Delivered dose matters: Both modalities frequently fall short of prescribed doses, supporting the need for frequent assessment of actual delivered therapy 4 Target doses should be at least 20-25 mL/kg/hour effluent for CRRT 4, 5 and Kt/V of 1.2-1.3 per session for SLED 2