What are the differences between Hemodialysis (HD), Sustained Low-Efficiency Dialysis (SLED), and Continuous Renal Replacement Therapy (CRRT) for a patient with impaired renal function?

Differences Between Hemodialysis, SLED, and CRRT

No single modality demonstrates survival superiority over the others, so continuous and intermittent renal replacement therapies should be used as complementary therapies with selection based on hemodynamic stability, local expertise, and cost considerations. 1

Key Technical Differences

Intermittent Hemodialysis (IHD)

• Duration: 3-4 hours per session, typically 3 times weekly 2
• Blood flow rate: 300-400 mL/min (standard) 3
• Dialysate flow rate: 500-800 mL/min (standard) 3
• Solute removal mechanism: Primarily diffusion with rapid clearance 4
• Hemodynamic impact: Rapid fluid shifts can cause hypotension in unstable patients 2, 5

Sustained Low-Efficiency Dialysis (SLED)

• Duration: 8-12 hours per session, typically performed nocturnally 6 days/week 3, 2
• Blood flow rate: 200 mL/min (reduced) 6, 3
• Dialysate flow rate: 300-350 mL/min (reduced) 3, 2
• Solute removal mechanism: Diffusion with gradual clearance, achieving weekly Kt/V of 8.4±1.8 3
• Hemodynamic impact: Gradual fluid removal provides stability comparable to CRRT 1, 6

Continuous Renal Replacement Therapy (CRRT)

• Duration: 24 hours continuous 7
• Blood flow rate: 150-200 mL/min 7
• Effluent flow rate: Target 20-25 mL/kg/hour 8, 7
• Solute removal mechanism: Combination of diffusion, convection, and ultrafiltration 7
• Hemodynamic impact: Minimal fluid shifts provide maximal stability 1

Clinical Selection Algorithm

For Hemodynamically Stable Patients

Use IHD as the first-line modality because it provides equivalent mortality outcomes to CRRT while being more cost-effective and practical. 1, 8

For Hemodynamically Unstable Patients

SLED should be viewed as interchangeable with CRRT rather than an inferior alternative because studies demonstrate comparable hemodynamic stability between the two modalities. 1, 8, 6, 5

• SLED provides hemodynamic stability through gradual fluid removal comparable to CRRT 1
• Hemodynamic instability occurs in 56.4% of SLED sessions versus 50.0% of CRRT sessions (not statistically different) 5
• The adjusted odds ratio for hemodynamic instability with SLED is 1.20 (95% CI 0.58-2.47) compared to CRRT 5

For Specific Clinical Scenarios

Use CRRT for patients with acute brain injury, increased intracranial pressure, or cerebral edema because gradual continuous therapy minimizes osmotic shifts that could worsen cerebral edema. 8

Cost and Resource Considerations

Direct Cost Comparison

• SLED: $1,431 per week 3
• CRRT with heparin: $2,607 per week 3
• CRRT with citrate: $3,089 per week 3

SLED represents a cost-effective alternative to CRRT by using existing dialysis infrastructure and reducing solution costs by approximately 45-54%. 1, 3

Anticoagulation Requirements

• IHD: Often performed without anticoagulation due to short duration 4
• SLED: 65% of treatments can be performed heparin-free with acceptable filter clotting rates (29% without heparin vs 18% with heparin, not statistically different) 3
• CRRT: Typically requires continuous anticoagulation, with regional citrate as first-line 7, 9

Personnel and Infrastructure

• IHD: Requires dialysis-trained nurses for 3-4 hours 4
• SLED: Requires dialysis capability but can be performed in centers without CRRT infrastructure, though longer treatment hours may strain personnel availability 1
• CRRT: Requires 24-hour ICU nursing supervision and specialized equipment 1

Solute Clearance Comparison

Small Solute Removal

• SLED: Achieves equivalent renal clearance (EKRjc) of 29±6 mL/min, similar to CRRT, with delivered double-pool Kt/V of 1.36 per treatment 3, 2
• CRRT: Target effluent volume of 20-25 mL/kg/hour provides adequate solute clearance 8, 7
• IHD: Rapid but intermittent clearance with potential for rebound 4

Middle and Large Molecule Removal

CRRT (particularly CVVH) removes middle and large molecular weight solutes more efficiently than SLED or IHD, though this has not proven to improve clinical outcomes. 7

Common Pitfalls and How to Avoid Them

Pitfall 1: Assuming CRRT is Always Superior for Unstable Patients

The totality of evidence does not support an advantage of CRRT over IHD or SLED with respect to patient-relevant outcomes including survival. 1, 8 Select modality based on local expertise and resources rather than defaulting to CRRT. 1

Pitfall 2: Inadequate Dose Delivery

Frequently assess actual delivered dose and adjust prescription upward to account for downtime and filter efficiency decline. 8 CRRT in routine clinical practice is often interrupted for imaging, surgery, and circuit clotting, reducing delivered dose below prescribed levels. 1

Pitfall 3: Inappropriate Fluid Composition

Use bicarbonate-buffered (not lactate-buffered) dialysate for all patients, especially those with circulatory shock, liver failure, or lactic acidemia. 7, 9 Lactate-buffered solutions can worsen metabolic acidosis in these populations. 9

Pitfall 4: Electrolyte Derangements with SLED

Monitor for hypophosphatemia and hypokalemia requiring supplementation, which occurred in 25 of 165 SLED treatments in one study. 2 The prolonged duration of SLED increases risk of electrolyte depletion. 2

Pitfall 5: Vascular Access Selection

Avoid subclavian veins for dialysis catheter placement due to increased risk of thrombosis and late stenosis. 7, 9 Use this order of preference: right internal jugular vein, femoral vein, left internal jugular vein, then subclavian as last resort. 9

Mortality and Clinical Outcomes

No modality demonstrates mortality benefit over the others. 1, 8

• 30-day mortality: 54% with SLED versus 61% with CRRT (adjusted OR 1.07,95% CI 0.56-2.03) 6
• Risk of RRT dependence at 30 days: adjusted OR 1.36 (95% CI 0.51-3.57) for SLED versus CRRT 6
• Risk of early clinical deterioration: adjusted OR 0.73 (95% CI 0.40-1.34) for SLED versus CRRT 6

Practical Implementation

When to Choose IHD

• Hemodynamically stable patients 1, 8
• Need for rapid solute removal in acute life-threatening conditions (severe hyperkalemia, toxic ingestions) 4
• Limited ICU nursing resources 4

When to Choose SLED

• Hemodynamically unstable patients when CRRT is unavailable or cost-prohibitive 1
• Centers with dialysis capability but not CRRT infrastructure 1
• Desire to minimize anticoagulation exposure 3
• Need for daytime access to patient for procedures (nocturnal SLED allows unrestricted daytime access) 2

When to Choose CRRT

• Acute brain injury, increased intracranial pressure, or cerebral edema 8
• Severe hemodynamic instability requiring maximal stability 1
• Need for precise hourly fluid balance control 7
• Hyperammonemia management (CVVHD mode provides higher ammonia clearance) 7