Femoral arterial cannula thrombosis in patients undergoing extracorporeal membrane oxygenation: a case series

Technical Summary: Femoral Arterial Cannula Thrombosis in Patients Undergoing Extracorporeal Membrane Oxygenation

Problem Statement
Extracorporeal Membrane Oxygenation (ECMO) is a critical short-term cardiopulmonary support technology, yet thrombosis within the ECMO circuit remains a frequent and severe complication. While circuit thrombosis generally affects approximately 17.2% of ECMO patients, thrombosis specifically localized to the femoral arterial cannula is less documented despite its potential to cause catastrophic systemic embolisms, including cerebral infarction, mesenteric embolism, and distal limb ischemia. The etiology, optimal diagnostic workflow, and management strategies for femoral arterial cannula thrombosis remain poorly understood, necessitating a systematic analysis of clinical cases to improve patient outcomes.

Methodology
This study presents a retrospective case series of seven patients who developed femoral arterial cannula thrombosis while receiving ECMO support at Fuwai Central China Cardiovascular Hospital between January 2022 and December 2024. The study was approved by the hospital's Ethics Committee (Approval Number: 2024-24), with a waiver of informed consent due to the retrospective nature of the de-identified data.

The analysis focused on:

• Patient Characteristics: Including admission diagnoses (e.g., AMI with cardiogenic shock, post-cardiac surgery), ECMO configuration (VA vs. VAV), cannula sizes, and duration of support.
• Coagulation Monitoring: Review of Activated Clotting Time (ACT), Activated Partial Thromboplastin Time (APTT), platelet counts, fibrinogen, and D-dimer levels from ECMO initiation until thrombosis detection.
• Diagnostic Workflow: Implementation of a rapid diagnostic algorithm based on hemodynamic parameters, specifically analyzing flow-speed mismatches and pressure gradients (pre-pump P1, post-pump/pre-membrane P2, and post-membrane P3).
• Intervention Strategies: Evaluation of three primary management approaches: direct ECMO weaning, thrombus aspiration via the cannula side port, and in-situ guidewire placement followed by cannula exchange.

Key Contributions and Clinical Findings

• Diagnostic Indicators: The study identifies specific hemodynamic signatures of arterial cannula thrombosis. A sudden drop in flow to near zero or a significant decrease (e.g., to ~0.3 L/min) accompanied by a pressure gradient where the post-membrane pressure (P3) is significantly higher than the mean arterial pressure is indicative of arterial occlusion. Conversely, a flow-speed mismatch with specific pressure readings helps localize the obstruction.
• Thrombus Pathology: Pathological examination of the retrieved thrombi revealed they were predominantly "white thrombi" (platelet-rich) with mixed components, often originating or growing within the side ports of the femoral arterial cannula.
• Management Outcomes:
  • Case 6: A patient meeting weaning criteria was successfully weaned and discharged.
  • Case 7: Thrombus aspiration via the side port restored flow, but the patient suffered a postoperative cerebral infarction and died.
  • Cases 1–5: These patients underwent in-situ guidewire placement and cannula exchange to restore flow. While hemodynamic stability was temporarily achieved, all five patients subsequently developed Multiple Organ Dysfunction Syndrome (MODS) and persistent cardiac dysfunction, leading to death after treatment withdrawal.
  • Overall Survival: Only one of the seven patients (Case 6) survived to discharge.
• Anticoagulation Insights: The study highlights that relying solely on ACT may be insufficient. Several patients developed thrombosis despite ACT values within or near the target range (160–220s), provided their APTT remained low (<40s) or platelet counts were severely depressed. This suggests a need for comprehensive coagulation monitoring, potentially incorporating anti-Xa levels, rather than relying on a single metric.
• Risk Factors: The authors note that thrombocytopenia, low-flow states in side ports, and turbulent flow at cannula bends are significant contributors. Additionally, in post-cardiac surgery patients, the intentional reduction or temporary cessation of anticoagulation due to bleeding concerns was a precipitating factor.

Significance and Claims
The paper asserts that femoral arterial cannula thrombosis is a life-threatening complication that requires immediate recognition and intervention. The authors claim that:

1. Timely Intervention is Critical: Rapid restoration of ECMO flow via safe cannula replacement (often utilizing in-situ guidewire techniques) is essential to maintain hemodynamic stability, though this carries a risk of thrombus dislodgement and systemic embolism.
2. Precision in Anticoagulation: Effective prevention requires precise anticoagulation management that integrates ACT, APTT, and platelet counts, rather than relying on isolated parameters.
3. Real-Time Monitoring: Continuous monitoring of ECMO circuit pressures (P1, P2, P3) and transmembrane gradients is vital for the early identification of thrombus formation before total occlusion occurs.
4. Clinical Guidance: The study provides a diagnostic workflow and management algorithm for clinicians facing this specific complication, emphasizing that while direct thrombus aspiration can restore flow, it may lead to severe embolic events, necessitating a careful risk-benefit assessment.

The authors conclude that while the mortality rate in this specific series was high, the systematic approach to diagnosis and the emphasis on comprehensive anticoagulation monitoring and circuit pressure surveillance are key to preventing such complications and improving the prognosis of ECMO-supported patients.