# Renal Replacement Therapy for AKI — KDIGO 2012

## Timing of Initiation

- Initiate RRT **emergently** when life-threatening changes in fluid, electrolyte, and acid-base balance exist (Not Graded).
- Consider the **broader clinical context**, the presence of conditions that can be modified with RRT, and **trends** (rather than single values) of laboratory tests when making the decision to start RRT (Not Graded).

### Indications for Urgent/Emergent RRT

- Refractory hyperkalemia
- Refractory metabolic acidosis
- Refractory volume overload (pulmonary edema unresponsive to diuretics)
- Uremic complications (encephalopathy, pericarditis, neuropathy)
- Certain drug intoxications (e.g., lithium, methanol, ethylene glycol)

## Discontinuation of RRT

- Discontinue RRT when it is **no longer required**, either because intrinsic kidney function has recovered to the point that it is adequate to meet patient needs, or because RRT is no longer consistent with the goals of care (Not Graded).
- Suggest **not using diuretics to enhance kidney recovery** or to reduce the duration or frequency of RRT (Grade 2B).

## Modality Selection

### CRRT vs. Intermittent RRT

- Suggest using **CRRT rather than standard intermittent RRT** for hemodynamically unstable patients (Grade 2B).
- Suggest using **CRRT rather than intermittent RRT** for AKI patients with acute brain injury or other causes of increased intracranial pressure or generalized brain edema (Grade 2B).
- Use **continuous and intermittent RRT as complementary therapies** in AKI patients (Not Graded).

### Modality Summary

| Modality | Indication | Key Features |
|---|---|---|
| **CRRT** | Hemodynamically unstable patients; acute brain injury/raised ICP | Continuous solute and fluid removal; better hemodynamic tolerance |
| **IHD** | Hemodynamically stable patients; rapid solute removal needed (e.g., acute hyperkalemia) | Intermittent sessions; higher solute clearance per unit time |
| **SLED/Hybrid** | Intermediate hemodynamic stability | Extended daily dialysis; combines features of IHD and CRRT |

## Dosing of RRT

### CRRT Dosing

- Recommend delivering an effluent volume of **20-25 mL/kg/h** for CRRT in AKI (Grade 1A).
- A **higher prescribed dose** may be required to ensure delivery of this target dose, as prescribed and delivered doses frequently differ due to treatment interruptions.
- This recommendation is based on the ATN and RENAL trials, which demonstrated no benefit from higher-intensity CRRT (35-40 mL/kg/h).

### Intermittent RRT Dosing

- Recommend delivering a **Kt/V of 3.9 per week** when using intermittent or extended RRT in AKI (Grade 1A).

## Buffer Selection

- Suggest using **bicarbonate rather than lactate** as a buffer in dialysate and replacement fluid for RRT in AKI patients (Grade 2C).
- Recommend using **bicarbonate rather than lactate** as a buffer in dialysate and replacement fluid for RRT in AKI patients with **circulatory shock** and/or **liver failure** and/or **lactic acidosis** (Grade 1B).

## Anticoagulation

### General Principles

- For patients who do not have an increased bleeding risk or impaired coagulation and are not already receiving systemic anticoagulation, recommend **anticoagulation during RRT** (Not Graded).

### CRRT Anticoagulation

- Suggest using **regional citrate anticoagulation** rather than heparin in patients who do not have contraindications for citrate (Grade 2B).
- Citrate is contraindicated in patients with severe liver failure or shock with impaired citrate metabolism (risk of citrate accumulation).
- For patients with contraindications for citrate, suggest using either **unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH)** rather than other anticoagulants (Not Graded).

### Intermittent RRT Anticoagulation

- For patients without increased bleeding risk, recommend using either **UFH or LMWH** rather than other anticoagulants during intermittent RRT (Grade 1C).

### Patients with Increased Bleeding Risk

- For patients with increased bleeding risk who are not on anticoagulation, suggest performing RRT **without anticoagulation** (Grade 2C) for CRRT.
- For patients with increased bleeding risk on intermittent RRT, suggest performing **anticoagulant-free dialysis** (saline flushes) or using regional citrate (Grade 2C).

### Heparin-Induced Thrombocytopenia (HIT)

- Recommend **stopping all heparin** and using **direct thrombin inhibitors (e.g., argatroban) or Factor Xa inhibitors (e.g., danaparoid, fondaparinux)** rather than other or no anticoagulation during RRT (Grade 1A).
- Do not use LMWH in patients with HIT.

## Vascular Access

### Catheter Type

- Suggest initiating RRT in patients with AKI via an **uncuffed, nontunneled dialysis catheter**, rather than a tunneled catheter, as first choice (Not Graded).

### Insertion Site

When choosing a vein for insertion of a dialysis catheter in patients with AKI, the guideline recommends the following order of preference (Not Graded):

1. **Right internal jugular vein** (first choice)
2. **Femoral vein**
3. **Left internal jugular vein**
4. **Subclavian vein** (last choice, dominant side preferred)

- **Avoid subclavian vein catheterization** when possible, as subclavian stenosis may compromise future arteriovenous fistula creation.
- Recommend using **ultrasound guidance** for dialysis catheter insertion (Grade 1A).
- Recommend obtaining a **chest radiograph** promptly after placement of an internal jugular or subclavian dialysis catheter and before its use (Grade 1B).

### Catheter Design

- Suggest using **dialysis catheters with the minimum necessary lumen size** (Not Graded).
- For CRRT, suggest longer catheters (at least 20 cm for right internal jugular; at least 24 cm for femoral) to ensure adequate blood flow rates.

## Membranes

- Suggest using RRT with **biocompatible membranes** for IHD and CRRT in patients with AKI (Grade 2C).

## Decision Algorithm — RRT in AKI

1. **Does the patient have life-threatening indications for RRT** (refractory hyperkalemia, acidosis, volume overload, uremic complications)?
   - If **yes:** Initiate RRT emergently (Not Graded).
   - If **no:** Assess trends and broader clinical context.
2. **Modality selection:**
   - If **hemodynamically unstable** or acute brain injury: use CRRT (Grade 2B).
   - If **hemodynamically stable:** IHD or SLED acceptable.
3. **Dosing:**
   - CRRT: Target effluent 20-25 mL/kg/h (Grade 1A).
   - IHD: Target Kt/V 3.9 per week (Grade 1A).
4. **Anticoagulation:**
   - If CRRT and no contraindication to citrate: regional citrate (Grade 2B).
   - If CRRT and citrate contraindicated: UFH or LMWH (Not Graded).
   - If IHD: UFH or LMWH (Grade 1C).
   - If increased bleeding risk: anticoagulant-free or regional citrate (Grade 2C).
   - If HIT: argatroban or Factor Xa inhibitor (Grade 1A).
5. **Buffer:** Use bicarbonate (Grade 2C; Grade 1B if shock/liver failure).
6. **Access:** Right internal jugular preferred; use ultrasound guidance (Grade 1A).
7. **Monitor for recovery:** Discontinue RRT when kidney function recovers sufficiently (Not Graded).

## Limitations

- The optimal timing of RRT initiation remains one of the most debated topics in nephrology. The guideline does not specify absolute SCr, BUN, or urine output thresholds for initiating RRT, instead emphasizing clinical judgment and trend assessment.
- Evidence comparing CRRT to IHD does not demonstrate a mortality benefit for either modality; the preference for CRRT in hemodynamically unstable patients is based on physiological rationale rather than high-quality RCT evidence.
- The anticoagulation recommendations, particularly for citrate, require careful monitoring of ionized calcium, total calcium, and acid-base status to avoid citrate accumulation toxicity.
