Hemolysis on Ecmo

ECMO and Hemolysis: Pathophysiology, Risk Factors, and Management

Extracorporeal Membrane Oxygenation (ECMO) is a life-saving intervention that provides cardiac and/or respiratory support. However, one of its significant complications is hemolysis, which occurs due to mechanical trauma to red blood cells (RBCs) as they circulate through the ECMO circuit. Hemolysis can lead to organ dysfunction, coagulopathy, and increased mortality.

Pathophysiology of Hemolysis on ECMO

Hemolysis in ECMO patients occurs primarily due to mechanical shear stress and turbulence in the circuit, leading to RBC fragmentation and the release of free hemoglobin (fHb) into the plasma. The free hemoglobin can contribute to:

• Acute Kidney Injury (AKI) – Free hemoglobin is nephrotoxic, leading to tubular damage.

• Hyperbilirubinemia and Jaundice – Excess hemoglobin breakdown increases indirect bilirubin.

• Thrombosis and Coagulopathy – Free hemoglobin scavenges nitric oxide, increasing platelet aggregation and clot formation.

• Hemoglobinuria – Dark urine due to excessive RBC destruction.

Risk Factors for Hemolysis on ECMO

1. Pump and Circuit-Related Factors

• Centrifugal Pumps – Operate at 2500-4500 RPM; excessive speeds (>4000 RPM) increase shear stress.

• High Circuit Pressures – Excessive negative pressures in the venous line (< -50 mmHg) or high post-oxygenator pressures (>250 mmHg) increase hemolysis risk.

• Oxygenator Dysfunction – Clot formation within the oxygenator can create areas of turbulence and shear stress.

2. Cannula-Related Factors

• Small Cannula Size – Smaller cannulas (e.g., 17-21 Fr arterial, 21-25 Fr venous) require higher RPMs to maintain flow, increasing shear stress.

• High Blood Flow Rates – VA-ECMO typically runs at 3.5-5.0 L/min, and VV-ECMO at 4.0-6.0 L/min. Higher flow rates can exacerbate hemolysis if the cannula is undersized.

• Cannula Malposition – Improper positioning can cause recirculation, leading to increased shear forces.

3. Clot Formation

• Thrombosis in the ECMO Circuit – Fibrin deposits in the oxygenator or tubing create high-resistance zones, contributing to hemolysis.

• Inadequate Anticoagulation – Low heparin levels can promote clot formation, increasing turbulence.

4. Patient-Specific Factors

• Pre-existing Hemolysis – Conditions like sickle cell disease, mechanical heart valves, or pre-ECMO hemolysis can exacerbate RBC destruction.

• Hyperinflammatory States – Sepsis or shock can increase endothelial dysfunction, worsening hemolysis.

• Low Hematocrit – Anemia increases RBC susceptibility to mechanical damage.

Diagnosis of Hemolysis on ECMO

Laboratory Findings

• Plasma Free Hemoglobin (fHb) > 50 mg/dL – A direct indicator of hemolysis.

• Lactate Dehydrogenase (LDH) > 1000 U/L – Suggests RBC destruction.

• Low Haptoglobin (<25 mg/dL) – Due to hemoglobin binding and clearance.

• Indirect Hyperbilirubinemia – Resulting from RBC breakdown.

• Hemoglobinuria (Dark Urine) – Indicates severe hemolysis

Management of Hemolysis on ECMO

1. Optimize ECMO Circuit Settings

• Reduce RPM if Possible – Lowering pump speed decreases shear stress.

• Optimize Flow Rates – Adjust blood flow to maintain perfusion while minimizing turbulence.

• Monitor and Adjust Negative Pressure – Keep venous pressures above -50 mmHg to prevent excessive suction forces.

2. Evaluate and Adjust Cannulation

• Use the Largest Possible Cannula – Reduces resistance and shear stress.

• Reposition Cannula if Needed – To minimize recirculation and turbulence.

3. Check for Clots and Circuit Dysfunction

• Inspect Oxygenator and Tubing – Look for fibrin deposition or clot formation.

• Consider Circuit Change – If hemolysis is persistent and due to thrombosis.

4. Manage Free Hemoglobin and Organ Dysfunction

• Plasmapheresis or Hemodialysis – If severe hemolysis causes AKI.

• Volume Management – Avoid volume overload to prevent kidney injury.

• Monitor and Treat Hyperbilirubinemia – Support liver function.

5. Consider Alternative Anticoagulation

• Heparin Monitoring (Anti-Xa Goal 0.3-0.7 IU/mL) – Ensures proper anticoagulation.

• Direct Thrombin Inhibitors (e.g., Argatroban, Bivalirudin) – Used if heparin-induced thrombocytopenia (HIT) is suspected.

Hemolysis on ECMO is a serious complication with multiple contributing factors, including high shear stress, circuit thrombosis, and inappropriate cannulation. Early detection through laboratory markers and careful management of ECMO settings can help reduce its impact and improve patient outcomes.