What are the clinical indications for different renal replacement therapies, including Hemodialysis (HD), Continuous Venovenous Hemofiltration (CVVH), Continuous Venovenous Hemodialysis (CVVHD), Continuous Venovenous Hemodiafiltration (CVVHDF), Slow Continuous Ultrafiltration (SCUF), Sustained Low-Efficiency Dialysis (SLED), and Peritoneal Dialysis (PD) in patients with Acute Kidney Injury (AKI) or Chronic Kidney Disease (CKD)?

Clinical Indications for Renal Replacement Therapy Modalities

General Principles for Modality Selection

The choice of RRT modality should be primarily determined by hemodynamic stability, with continuous therapies (CRRT) preferred for hemodynamically unstable patients and intermittent hemodialysis (HD) reserved for stable patients, while all modalities achieve similar mortality outcomes when appropriately matched to patient status. 1

Absolute Indications for Any RRT (Regardless of Modality)

• Life-threatening hyperkalemia with ECG changes requires emergent RRT initiation 2, 3
• Severe metabolic acidosis unresponsive to medical therapy 2, 3
• Uremic complications including pericarditis, encephalopathy, or bleeding diathesis 2, 3
• Refractory fluid overload causing pulmonary edema or respiratory compromise 2, 3
• Severe volume overload that cannot be controlled with diuretics 1

Intermittent Hemodialysis (HD)

HD is the preferred modality for hemodynamically stable patients with AKI or CKD requiring rapid correction of electrolyte abnormalities, particularly severe hyperkalemia. 3

Primary Indications:

• Hemodynamically stable patients with AKI or AKD requiring RRT 1
• CKD stage G5 requiring maintenance dialysis (typically 3 times weekly for 3-4 hours) 1
• Severe hyperkalemia requiring rapid correction in stable patients (faster potassium clearance than continuous modalities) 3
• Patients without hemodynamic instability who can tolerate rapid solute and fluid shifts 1

Dosing Requirements:

• Kt/V of at least 1.2 per treatment, 3 times weekly for maintenance 1
• Kt/V of 3.9 per week for adequate intermittent RRT 3

Key Contraindications:

• Hemodynamic instability or vasopressor requirement 1, 2
• Increased intracranial pressure (higher risk with intermittent vs. continuous RRT) 1
• Severe 3-vessel coronary artery disease with instability (rapid fluid shifts can precipitate cardiac ischemia) 2

Continuous Renal Replacement Therapy (CRRT)

CRRT encompasses CVVH, CVVHD, and CVVHDF, and is the preferred modality for hemodynamically unstable patients requiring vasopressor support, providing superior hemodynamic stability through slower solute shifts and better fluid removal tolerance. 1, 2

Primary Indications:

• Hemodynamic instability requiring vasopressor support 1, 2
• Severe 3-vessel coronary artery disease with AKI (superior hemodynamic stability) 2
• Increased intracranial pressure (lower risk compared to intermittent HD) 1
• Massive fluid overload requiring gradual, controlled removal 1
• Hypercatabolic states requiring continuous metabolic control 2

Dosing Requirements:

• Effluent volume of 20-25 mL/kg/h should be delivered 1, 3
• Higher prescription may be needed to achieve target delivery 1

Anticoagulation:

• Regional citrate anticoagulation is recommended for patients without contraindications 1, 3
• Minimal or no anticoagulation for trauma or bleeding-prone patients 3

CVVH (Continuous Venovenous Hemofiltration)

CVVH achieves solute clearance predominantly through convection and is particularly suited for patients with cardiovascular dysfunction or problematic arterial access. 4, 5

Specific Indications:

• Hemodynamically unstable patients with acute renal failure and volume overload 5
• Impaired cardiovascular function where arterial access is problematic 5
• Patients requiring individualized ultrafiltration and solute clearance 5

Mechanism:

• Convective solute clearance as the predominant mechanism 4

CVVHD (Continuous Venovenous Hemodialysis)

CVVHD utilizes predominantly diffusive solute clearance and is appropriate for hemodynamically unstable patients requiring continuous therapy. 4

Specific Indications:

• Hemodynamically unstable patients requiring continuous RRT 4
• Patients where diffusive clearance is preferred over convective 4

Mechanism:

• Diffusive solute clearance as the predominant mechanism 4

CVVHDF (Continuous Venovenous Hemodiafiltration)

CVVHDF combines both dialysis and hemofiltration, providing both convective and diffusive clearance, and may offer survival advantage in patients with multiple organ failures. 4, 6

Specific Indications:

• Severely ill patients with APACHE III scores >103 (may provide survival benefit where HD cannot) 6
• Patients with failure of three or more organs (36% survival vs. 9% with HD) 6
• Hemodynamically unstable patients requiring both convective and diffusive clearance 4
• Patients requiring prolonged ventilator support 6

Mechanism:

• Combined convective and diffusive clearance 4

Evidence Considerations:

• CVVHDF was applied to more severely ill patients with higher organ failure numbers and APACHE III scores in comparative studies 6
• Despite higher baseline mortality risk, CVVHDF provided survival opportunities in the most critically ill subset 6

SCUF (Slow Continuous Ultrafiltration)

SCUF is primarily indicated for isolated fluid removal in patients with refractory volume overload who do not require significant solute clearance. [General medical knowledge]

Primary Indications:

• Refractory fluid overload without significant uremia or electrolyte abnormalities
• Cardiorenal syndrome requiring gentle, continuous fluid removal
• Patients with preserved solute clearance but impaired fluid balance

SLED (Sustained Low-Efficiency Dialysis)

SLED is a hybrid therapy combining characteristics of intermittent and continuous RRT, providing comparable outcomes to CRRT in hemodynamically unstable patients while reducing resource demands. 7, 8

Primary Indications:

• Hemodynamically unstable patients with AKI (acceptable alternative to CRRT) 7
• Resource-limited settings where CRRT demands are prohibitive 7, 8
• Patients requiring prolonged treatment duration (8-12 hours) with better hemodynamic tolerance than standard HD 1

Technical Specifications:

• Target 8 hours per session 7
• Blood flow 200 mL/min 7
• Predominantly without anticoagulation (in studied protocols) 7

Outcomes Evidence:

• 30-day mortality comparable to CRRT (54% SLED vs. 61% CRRT, adjusted OR 1.07) 7
• RRT dependence at 30 days similar to CRRT (adjusted OR 1.36) 7
• Early clinical deterioration rates equivalent to CRRT (adjusted OR 0.73) 7
• Survival rates similar across all four modalities (IHD, CRRT, PD, SLED) in resource-limited settings 8

Peritoneal Dialysis (PD)

PD is rarely used in adult ICU settings in Western countries but remains an acceptable modality in resource-limited settings and for hospitalized patients previously on chronic PD. 1, 8

Primary Indications:

• Patients already on chronic ambulatory PD (CAPD) who become hospitalized 1
• Resource-limited settings where extracorporeal therapies are unavailable 8
• Hemodynamically stable patients with AKI in select circumstances 8

Dosing:

• 0.3 Kt/V per session suggested for AKI (though more research needed) 1

Limitations:

• Not routinely utilized for critically ill adult patients in ICU in Western countries 1
• Comparable survival to other modalities when appropriately selected 8

Critical Decision Algorithm for Modality Selection

Step 1: Assess Hemodynamic Status

• Hemodynamically unstable or on vasopressors → CRRT, CVVHDF, or SLED 1, 2
• Hemodynamically stable → Intermittent HD 1

Step 2: Assess Specific Clinical Scenarios

• Severe 3-vessel CAD → CRRT or SLED preferred over intermittent HD 2
• Increased intracranial pressure → CRRT preferred over intermittent HD 1
• Severe hyperkalemia requiring rapid correction in stable patient → Intermittent HD 3
• Multiple organ failure (≥3 organs) → Consider CVVHDF 6
• APACHE III >103 → Consider CVVHDF over HD 6

Step 3: Consider Resource Availability

• Limited CRRT resources or expertise → SLED is acceptable alternative 7
• Severely resource-limited setting → PD may be considered 8

Step 4: Transition Planning

• Transition from CRRT to intermittent HD when vasopressor support discontinued, hemodynamic stability achieved, and fluid balance controlled 1, 3

Common Pitfalls to Avoid

• Do not delay dialysis initiation waiting for hemodynamic optimization when absolute indications present (increases mortality) 2
• Do not use standard intermittent HD in hemodynamically unstable patients with severe CAD (rapid fluid shifts precipitate cardiac ischemia or arrhythmias) 2
• Do not assume modality choice affects mortality when appropriately matched to patient status (all modalities achieve similar outcomes) 8
• Do not use lactate-based buffers in patients with circulatory shock or lactic acidemia (use bicarbonate-based solutions) 2, 3
• Do not forget to monitor for post-obstructive diuresis in postrenal AKI after obstruction relief (may require massive fluid replacement) 3