Renal Replacement Therapy (RRT) in Critical Care
📌 Indications for RRT (AEIOU Mnemonic)
Indication | Description |
A – Acidosis | Severe metabolic acidosis (pH <7.1) refractory to medical therapy |
E – Electrolyte imbalance | Refractory hyperkalemia (K⁺ >6.5 mEq/L or ECG changes) |
I – Intoxications | Dialyzable toxins (e.g., lithium, methanol, ethylene glycol, ASA) |
O – Overload | Volume overload unresponsive to diuretics → pulmonary edema |
U – Uremia | Pericarditis, encephalopathy, bleeding, nausea/vomiting due to azotemia |
🚨 Initiation should be based on clinical criteria, not serum creatinine or urea alone.
⏱️ Timing of RRT in ICU: Early vs Late
- Early (proactive) RRT:
- Before overt complications
- May improve fluid/electrolyte control
- May reduce ICU LOS in select patients
- Delayed (reactive) RRT:
- Wait for classic indications
- Avoids unnecessary dialysis
📚 Trials: AKIKI, ELAIN, STARRT-AKI → no consistent mortality benefit of early RRT; individualize decision.
🧪 Modalities of RRT
Type | Description | Setting |
IHD (Intermittent Hemodialysis) | 3–4 hours, high blood & dialysate flow | Stable ICU, outpatient |
CRRT (Continuous RRT) | 24-h, slow, gentle | Hemodynamically unstable patients |
SLED (Sustained Low-Efficiency Dialysis) | 6–12 h hybrid | Intermediate option |
PD (Peritoneal Dialysis) | Uses peritoneum as membrane | Less used in ICU; anuric, pediatric, or resource-limited settings |
🔬 CRRT Modalities Explained
Modality | Mechanism | Solute Clearance |
CVVH (Hemofiltration) | Convection | Middle molecules |
CVVHD (Hemodialysis) | Diffusion | Small molecules (urea, K⁺) |
CVVHDF (Hemo-diafiltration) | Both | Broad clearance |
📌 CVV-Continous Venovenous
⚖️ CRRT vs IHD vs SLED: Comparison
Feature | IHD | CRRT | SLED |
Duration | 3–4 h | 24 h | 6–12 h |
Hemodynamic tolerance | Poor | Best | Good |
Solute clearance | Rapid | Slow-continuous | Intermediate |
Fluid removal | Rapid | Gradual | Controlled |
Cost/resource | Less | More | Intermediate |
ICU use | Selective | Preferred in unstable | Good alternative |
💉 Vascular Access for RRT
Site | Preferred Use |
Right IJV | First-line (straight to RA, less stenosis risk) |
Femoral vein | Easy to access, especially in emergencies |
Left IJV | More tortuous path, use if right unavailable |
Subclavian vein | Avoid (risk of stenosis, esp. if transplant candidate) |
Catheter types:
- Non-tunneled: Temporary (used in ICU)
- Tunneled cuffed: For long-term dialysis (not first choice in ICU)
💊 RRT Dose in CRRT (KDIGO)
- Effluent rate: 20–25 mL/kg/h
- For a 70-kg patient: 1400–1750 mL/h
- Pre-dilution may require increasing to 25–30 mL/kg/h
📌 No added benefit above 35 mL/kg/h, per ATN trial
📋 RRT in Special Scenarios
Condition | Approach |
Sepsis + AKI | CRRT preferred; may remove cytokines |
Liver failure (HRS) | CRRT to manage volume, acidosis |
Raised ICP (e.g. hepatic encephalopathy) | Avoid IHD (risk of cerebral edema); prefer CRRT |
Tumor lysis syndrome | CRRT/SLED for gradual correction |
Rhabdomyolysis | CVVH or CVVHDF to clear myoglobin (esp. high-volume) |
🚫 Complications of RRT
Category | Examples |
Mechanical | Catheter-related infection, bleeding, malposition |
Hemodynamic | Hypotension (IHD), arrhythmias |
Metabolic | Hypokalemia, hypophosphatemia, alkalosis/acidosis |
Hematologic | Coagulopathy, heparin-induced thrombocytopenia |
Other | Dialyzer reactions, filter clotting, loss of nutrients (esp. in CRRT) |
💉 Anticoagulation in CRRT
Type | Notes |
Systemic heparin | Common, but ↑ bleeding risk |
Citrate regional anticoagulation | Preferred in bleeding risk; complex to manage |
No anticoagulation | For high bleeding risk; short filter life |