What are the risks associated with Extracorporeal Membrane Oxygenation (ECMO)?

Risks of ECMO

ECMO carries substantial risks of both bleeding and thrombotic complications, with bleeding being the predominant concern—occurring in 45.1% of VV-ECMO and 62.1% of VA-ECMO patients, with intracranial hemorrhage associated with the highest mortality rates. 1

Major Hemorrhagic Complications

Bleeding Incidence and Sites

• Bleeding complications exceed thrombotic events in contemporary ECMO practice, with recent registry data showing 37% of patients experiencing bleeding events during ECMO support 1
• Common bleeding sites include:
  • Cannulation/surgical insertion sites 1
  • Intracranial hemorrhage (most feared complication—rapidly fatal, occurs in up to 11% within 24 hours of ECPR) 2
  • Pulmonary hemorrhage (may cause irreversible lung damage) 3
  • Gastrointestinal tract 3
  • Thoracic and abdominal cavities 3

Mechanisms of Bleeding Diathesis

• Acquired von Willebrand Syndrome (AVWS) develops in almost all ECMO patients within hours of device implantation due to high shear stress causing loss of high-molecular-weight VWF multimers 1
• Additional coagulopathy mechanisms include thrombocytopenia, platelet dysfunction, consumptive coagulopathy, and hyperfibrinolysis 1
• Systemic anticoagulation required to prevent circuit thrombosis paradoxically increases bleeding risk 1
• Higher anti-Xa activity levels (>0.46 IU/mL) are associated with increased bleeding probability 1

Thrombotic Complications

Incidence and Types

• Thrombotic events occur in 25.3% of VV-ECMO patients and 20% of VA-ECMO patients 1
• Recent analysis shows 42% of VV-ECMO patients experience thrombotic events, with 21% experiencing both bleeding and thrombosis simultaneously 1
• Circuit-related thrombosis is the most common thrombotic complication, potentially requiring equipment exchange 4
• Patient thrombotic events include:
  • Venous thromboembolism/pulmonary embolism 2
  • Arterial thromboembolism 4
  • Coronary embolism leading to cardiac arrest 2
  • Cerebral venous sinus thrombosis 1

Thrombosis Mechanisms

• Blood contact with artificial, pro-thrombotic surfaces in the circuit 5
• High shearing forces in the pump and membrane oxygenator 5
• Platelet activation despite anticoagulation 3

Cardiovascular Complications

VA-ECMO Specific Risks

• Left ventricular distension occurs due to increased LV afterload in peripheral VA-ECMO, leading to ventricular stasis, pulmonary congestion, and myocardial ischemia 2
• Harlequin syndrome (differential upper/lower torso oxygenation) occurs in approximately 10% of peripherally cannulated patients, causing inadequate coronary and cerebral oxygenation 2
• Inadequate coronary perfusion can precipitate myocardial ischemia and cardiac arrest, particularly in patients with underlying coronary artery disease 2

Neurological Complications

Acute Neurological Events

• Intracranial hemorrhage carries the highest mortality among all ECMO complications in both VV and VA configurations 1
• Ischemic stroke can occur despite anticoagulation 1
• Cerebral venous sinus thrombosis presents with non-specific symptoms (headache, seizure, encephalopathy) making diagnosis challenging 1
• Dual-lumen VV ECMO cannulas may be associated with intraventricular hemorrhage, possibly due to venous hypertension and cannula-related thrombosis 1

Management Challenges

• Neurosurgical interventions (external ventricular drain, decompressive craniectomy) carry extremely high procedural bleeding risk due to coagulopathy and anticoagulation requirements 1
• Tissue plasminogen activator (tPA) is contraindicated for acute ischemic stroke during ECMO due to prohibitive bleeding risk 1

Metabolic and Organ Dysfunction

• Acid-base disorders (metabolic acidosis or severe alkalosis) can precipitate cardiac arrest post-ECMO 2
• Renal injury is common during ECMO support 6
• Inadequate oxygenation can lead to myocardial hypoxia and end-organ damage 2

Infectious Complications

• Bloodstream infection is independently associated with bleeding events (adjusted OR 2.76, p=0.047) 7
• Ventilator-associated pneumonia risk increases with prolonged mechanical ventilation during ECMO 6
• Cannulation sites serve as potential portals for infection 6

Technical and Mechanical Complications

• ECMO circuit thrombosis requiring equipment exchange occurs in approximately 13.4% of patients managed without continuous anticoagulation 4
• Hemolysis can occur from mechanical shear stress 6
• Oxygenator dysfunction from thrombus formation 1

Risk Factors for Complications

Bleeding Risk Factors

• Lower fibrinogen levels (adjusted OR 0.56 per unit increase, p=0.009) 7
• Longer duration on ECMO (adjusted OR 1.14 per day, p=0.018) 7
• Bloodstream infection 7
• Higher anticoagulation intensity (aPTT increase of 10 seconds associated with adjusted HR 1.14 for hemorrhage) 1

General Risk Factors

• Prolonged mechanical ventilation (>9.6 days) before ECMO initiation is associated with worse outcomes 8
• Lower institutional volume (<20-25 cases/year) correlates with worse outcomes 8

Long-Term Complications

• Physical, functional, and neurologic sequelae of critical illness persist after ECMO 6
• Delayed lung recovery or worsening lung injury from suboptimal ventilator management 6

Critical Pitfalls

• No coagulation test reliably predicts bleeding or thrombotic risk in ECMO patients, making anticoagulation management empirical and challenging 1
• The extent to which AVWS contributes to bleeding cannot be determined by current evidence, and data supporting VWF concentrate use remain limited 1
• Premature decannulation can lead to clinical deterioration, while delayed decannulation unnecessarily prolongs exposure to complications 6