What are the guidelines for Renal Replacement Therapy (RRT) in patients undergoing Extracorporeal Membrane Oxygenation (ECMO)?

Guidelines on Renal Replacement Therapy During ECMO

Continuous renal replacement therapy (CRRT) is the most appropriate modality for patients undergoing extracorporeal membrane oxygenation (ECMO) due to their hemodynamic instability and sensitivity to fluid overload. 1

Indications for RRT during ECMO

• The indications for RRT in ECMO patients are generally similar to those for other critically ill patients, with fluid overload being particularly important 1
• Common indications include:
  • Persistent anuria 2
  • Metabolic acidosis 2
  • Fluid overload (patients on ECMO are particularly sensitive to this) 1
  • Hyperkalemia 2
• Earlier initiation of RRT may be required in ECMO patients specifically for preventing and managing fluid overload compared to non-ECMO patients 1

Modality Selection

• CRRT is strongly preferred over intermittent hemodialysis for ECMO patients (used in 97% of cases according to surveys) 2, 3
• Continuous veno-venous hemofiltration (CVVH) is the most commonly used CRRT technique (64%) followed by continuous veno-venous hemodiafiltration (CVVHDF) at 21% 2
• The hemodynamic instability typical in ECMO patients makes CRRT physiologically more appropriate than intermittent modalities 1, 3

Circuit Configuration Options

• Two main approaches exist for combining RRT with ECMO 2, 3:
  1. Integrated approach (preferred by 40% of centers): RRT device connected directly to the ECMO circuit
     • Most commonly connected with inlet and outlet lines after the ECMO pump (58% of cases) 2
     • May experience pressure alarms (reported by 60% of users) 2
  2. Parallel system (used by 30% of centers): Separate ECMO and RRT circuits with independent vascular access 2, 3
• The decision between integrated vs. parallel configuration should be based on institutional expertise, available technology, and a multidisciplinary approach 1
• There is no evidence that different methods of combining ECMO and CRRT impact mortality 3

Anticoagulation Management

• Anticoagulation for RRT circuits when ECMO is already running is not standardized 1
• Options include:
  • Unfractionated heparin (most common, used in 61% of cases) 2
  • Regional citrate anticoagulation (used in 16% of cases) 2
  • No dedicated anticoagulation for the RRT circuit if already anticoagulated for ECMO (possible unless frequent clotting occurs) 1
• The choice depends on patient factors (bleeding risk), circuit setup, and institutional protocols 1
• Citrate anticoagulation during RRT with ECMO is possible but its comparative effectiveness remains untested 1

Dosing and Delivery

• When using CRRT, an effluent volume of 20-25 ml/kg per hour should be delivered 1
• Higher prescription may be required to achieve this target delivery 1
• Fluid management is critical - a positive fluid balance at 72 hours is independently associated with mortality in ECMO patients receiving CRRT 4

Practical Considerations

• Vascular access for RRT (if using a parallel configuration):
  • First choice: right jugular vein or femoral vein 1
  • Femoral site is inferior in patients with increased body mass 1
  • Alternative options: left jugular vein followed by subclavian vein 1
• An uncuffed non-tunnelled dialysis catheter of appropriate length and gauge should be used initially 1
• Consider a cuffed catheter for patients expected to need prolonged RRT 1

Monitoring and Discontinuation

• RRT should be discontinued when kidney function has recovered or when RRT becomes inconsistent with shared care goals 1
• Transition from CRRT to intermittent hemodialysis should be considered when:
  • Vasopressor support has been stopped 1
  • Intracranial hypertension has resolved 1
  • Positive fluid balance can be controlled by intermittent hemodialysis 1
• Monitor for renal recovery - approximately 80% of survivors can recover renal function after combined ECMO/CRRT 4

Caveats and Pitfalls

• Knowledge of intra-circuit pressure changes, risks of air entrapment, and hemolysis is essential when using integrated CRRT-ECMO systems 3
• Complications to watch for include clots in the filter and excessive ultrafiltration 5
• Current evidence is limited by practice variability and lack of standardized protocols 2, 6
• The KDIGO guidelines note that more research is needed on optimal approaches to patient selection, techniques, timing/indications, circuit integration, and monitoring for ECLS with concomitant blood-purification techniques 1