Sustained Low-Efficiency Dialysis (SLED): Definition and Indications
SLED is a hybrid renal replacement therapy modality that uses standard hemodialysis equipment with reduced blood flow (100-200 mL/min) and dialysate flow rates (200-300 mL/min) over extended treatment durations (8-12 hours), and is indicated as a safe and effective alternative to continuous renal replacement therapy (CRRT) for hemodynamically unstable critically ill patients with acute kidney injury.
What is SLED?
SLED represents a middle ground between conventional intermittent hemodialysis and CRRT 1. The technique employs:
- Extended treatment duration: Typically 8-12 hours, often delivered nocturnally 2
- Reduced flow rates: Blood flow 100-200 mL/min, dialysate flow 200-300 mL/min 3
- Standard hemodialysis equipment: Can use conventional HD machines or batch dialysis systems 4
- Flexible scheduling: Usually daily or alternate-day treatments 3
By definition, SLED is classified as an intermittent therapy (prescribed for ≤12 hours) rather than continuous therapy, distinguishing it from CRRT which aims for 24-hour application 5.
Clinical Indications
Primary Indication: Hemodynamically Unstable Patients
SLED should be used preferentially for hemodynamically unstable critically ill patients with AKI who require renal replacement therapy 1. The KDOQI guidelines specifically recognize that SLED can be safely used in hemodynamically unstable adult patients and requires additional clinical research to compare outcomes with other RRT modalities 1.
Specific Clinical Scenarios Where SLED Excels:
- Hemodynamic instability: Provides excellent hemodynamic tolerability comparable to CRRT 2, 3
- When CRRT is unavailable or limited: Particularly valuable in resource-limited settings 4
- Patients requiring daytime procedures: Nocturnal SLED allows unrestricted daytime access for tests and interventions 2
- Septic shock patients: Demonstrated efficacy in sepsis management 6
- Intraoperative RRT: Can be used during complex procedures like liver transplantation 6
- Recalcitrant volume overload: Effective in heart failure patients with resistant fluid overload 6
Advantages Over Other Modalities:
Hemodynamic stability: Studies show SLED maintains hemodynamic stability during most treatments, with intractable hypotension causing premature discontinuation in only a minority of cases 2. The mean ultrafiltration goal shortfall was only 240 mL per treatment 2.
Adequate solute clearance: SLED provides efficient small solute removal with delivered Kt/V of approximately 1.36-1.43 per treatment 2, 3, and an equivalent renal urea clearance (EKRc) of 35.7 ± 6.4 mL/min 3, meeting established adequacy standards for both CRRT and intermittent hemodialysis.
Cost-effectiveness: Healthcare studies indicate SLED has emerged as a cost-effective alternative to CRRT 4.
Nursing autonomy: Can be delivered autonomously by ICU nursing personnel without requiring dedicated nephrology staff presence 3.
Clinical Outcomes
Mortality and Renal Recovery
The most recent comparative study found no difference in 90-day mortality between SLED and CRRT recipients (adjusted hazard ratio 0.90,95% CI 0.64-1.27) 7. However, a notable caveat: among 90-day survivors, a higher proportion of SLED recipients remained dialysis-dependent (23% vs 10% for CRRT, adjusted RR 2.82) 7. This difference disappeared by one year, suggesting no long-term disadvantage 7.
Observed hospital mortality with SLED (46-62%) was not significantly different from expected mortality based on APACHE II scores 3, 2, indicating SLED does not worsen outcomes in critically ill patients.
Technical Considerations and Pitfalls
Anticoagulation
Regional citrate anticoagulation (RCA) can be safely used with SLED, though the KDOQI guidelines note that FDA-approved citrate solutions for CRRT are not available in the United States, limiting formal recommendations 1. Recent studies demonstrate that simplified RCA protocols for SLED are safe and effective with appropriate monitoring 8.
Common Complications to Monitor:
- Electrolyte disturbances: Hypophosphatemia and hypokalemia requiring supplementation occur in approximately 25% of treatments 3, 8
- Circuit clotting: Represents the majority of premature treatment discontinuations 2
- Calcium requirements: May be needed in about 23% of sessions when using citrate anticoagulation 8
Dosing Targets
Based on the ATN and RENAL trials, target a delivered Kt/V of at least 1.3 per treatment when performing SLED three times weekly 1. The KDOQI guidelines emphasize that delivered dose often falls short of prescribed dose, supporting frequent assessment of actual delivered therapy 1.
Practical Algorithm for SLED Use
Use SLED when:
- Patient has AKI requiring RRT AND hemodynamically unstable
- CRRT is unavailable or resource-limited setting
- Need for daytime procedures/testing access
- Standard intermittent HD causes intolerable hypotension
Monitor closely:
- Phosphate, potassium, calcium, magnesium levels (check after each session)
- Circuit patency and clotting
- Actual delivered dose vs. prescribed dose
- Hemodynamic parameters throughout treatment
Avoid in:
- Pediatric patients (limited data, though emerging evidence supports use in resource-limited settings) 4
- When specific CRRT advantages are critical (e.g., acute brain injury with increased intracranial pressure—CRRT preferred due to slower solute shifts) 1
The evidence strongly supports SLED as a legitimate first-line option for hemodynamically unstable critically ill patients with AKI, with outcomes comparable to CRRT and practical advantages in many clinical settings.