Algorithmic Approach to Membrane Lung Dysfunction in ECMO: A Practical Guide

September 8, 2024

Clot formation in an ECMO oxygenator

Since I began working in ECMO, one article that consistently seems to come up in discussions is “How I Approach Membrane Lung Dysfunction in Patients Receiving ECMO” by Bishoy Zakhary et al. It’s become a foundational piece of my ECMO education. It is frequently referenced in ECMO classes and caught me off guard in a quiz I took. Most recently, it was referenced in a Simulation Class, so, recognizing how often this article resurfaces, I felt it was worth delving into and providing a detailed breakdown.

Membrane lung dysfunction is a common yet complex issue during ECMO therapy, and Zakhary’s article offers a well-structured algorithmic approach for evaluating and managing it. Whether you’re troubleshooting hematologic abnormalities, pressure changes, or gas transfer issues, a systematic approach helps ensure that membrane lung problems are identified early and addressed promptly. In this article, I’ll look at the main points of Zakhary’s work and offer insights into how to apply these principles in daily practice.

Mechanisms of Membrane Lung Dysfunction

The membrane lung in an ECMO circuit serves two primary functions: oxygenation and carbon dioxide removal. However, exposure to the non-biologic surfaces of the membrane lung can activate inflammatory and coagulation pathways, leading to clot formation and increased resistance within the circuit. Over time, protein buildup, cellular debris, and moisture can impair gas exchange, leading to inadequate oxygen uptake and carbon dioxide removal. This dysfunction generally falls into three categories:

Hematologic profile abnormalities (coagulopathy or hemolysis).
Blood flow obstructions (increased resistance).
Impaired gas exchange (decreased O2 uptake or CO2 clearance).

1. Hematologic Abnormalities: Coagulopathy and Hemolysis

Coagulopathy

Coagulopathy can arise from the interaction between blood and the ECMO circuit. Activation of the coagulation system within the circuit can lead to increased clotting times, hypofibrinogenemia, thrombocytopenia, and elevated D-dimer levels, all signs of circuit-related coagulopathy.

Signs: Elevated clotting times, reduced fibrinogen levels (< 200 mg/dL), high D-dimer (> 25-30 mg/dL), and thrombocytopenia without another explanation.
Management: Adjust anticoagulation therapy based on monitoring results. If abnormalities persist despite optimal anticoagulation, consider exchanging the membrane lung or entire circuit, especially in the case of circuit-related coagulopathy.

Hemolysis

Hemolysis occurs when red blood cells are mechanically damaged as they flow through the circuit, possibly due to shear forces or circuit malfunction.

Signs: Increased plasma-free hemoglobin (> 50 mg/dL) and elevated lactate dehydrogenase (LDH), indicating hemolysis.
Management: If hemolysis markers remain high, assess the circuit for excessive pump speeds or clots and consider replacing the oxygenator to reduce mechanical stress on red blood cells.

2. Pressure Monitoring: Blood Flow Obstruction

An increasing pressure gradient across the membrane lung (ΔP) is one of the most direct indicators of obstruction, often due to clot formation. Monitoring the ΔP relative to the blood flow rate (BFR) allows for earlier detection of membrane lung resistance (RML).

Signs: A progressive increase in ΔP, even without changes in gas exchange, suggests increasing clot burden. A higher pump speed required to maintain stable BFR also indicates rising resistance in the circuit.
Management: If the ΔP continues to rise rapidly, it’s often a warning sign of imminent membrane lung failure. Prompt membrane lung exchange should be considered to avoid acute failure.

3. Membrane Lung Gas Transfer: Oxygen and CO2 Exchange Issues

Decreased Oxygen Uptake

Membrane lung dysfunction often manifests as impaired oxygenation. When the membrane lung can no longer meet the patient’s oxygenation demands, assessing the oxygen transfer capacity (V′O2) is critical.

Signs: Persistent low post-ML oxygen levels (PPost-ML O2 < 200 mmHg) despite adequate circuit settings or a V′O2 below 100-150 mL/min at maximal effective Blood Flow Rate and FiO2.
Management: Increase blood flow through the oxygenator to maximize oxygen transfer and ensure it functions at capacity. If the V′O2 remains below 100-150 mL/min and cannot meet oxygen demands, membrane lung exchange is warranted.
Critical Note: A colleague pointed out that while the document suggests V’O2 < 100-150 mL/min as a potential indicator, it’s crucial to recognize that average adult oxygen consumption is typically higher (around 280-350 mL/min for a 70 kg adult). The specific threshold for inadequate oxygen transfer should be evaluated in the patient’s overall clinical picture, including their weight, metabolic demands, and the degree of native lung function.

Inadequate Carbon Dioxide Clearance

CO2 clearance can also become impaired with membrane lung dysfunction. A typical indicator is persistent hypercapnia despite high sweep gas flow rates.

Signs: A post-membrane lung CO2 level (PPost-ML CO2) > 40 mmHg and a minimal CO2 gradient (< 10 mmHg) between pre- and post-ML gases, despite high sweep gas flows (> 10 L/min).
Management: First, ensure sweep gas flow is not restricted. If the gas exchange does not improve and CO2 clearance remains inadequate, membrane lung replacement may be required.

Sudden Membrane Lung Failure

While most cases of membrane lung dysfunction develop gradually and can be addressed electively, sudden failure can occur and pose a life-threatening risk. It is critical to have emergency protocols in place to exchange the membrane lung rapidly in such cases. Regular monitoring of pressure gradients and gas transfer can help preempt sudden failure, allowing for elective exchanges before an emergency arises.

Critical Considerations for ECMO Practitioners

Context is King: The provided cut-off values are based on the author’s experience and should be interpreted within the patient’s clinical context and ECMO dependence level. This is particularly crucial when assessing oxygen transfer adequacy.
Adult-Centric Guidance: This approach is tailored for adult ECMO patients and may not apply to pediatric or neonatal cases. Remember that oxygen consumption varies significantly with body size and metabolic state.
Lab Monitoring Variability: The extent and frequency of coagulation and hemolysis lab monitoring vary between centers. Not all labs are necessary for diagnosing coagulopathy or hemolysis.
Circuit Exchange Strategies: Consider switching the entire ECMO circuit, not just the ML, if: a) The ML and pump head are fused, b) ML dysfunction occurs alongside circuit-related coagulopathy c) ML dysfunction appears in an older circuit (>2 weeks) This approach aims to mitigate the risk of ongoing or new circuit-related coagulopathy.
Individualized Oxygen Transfer Assessment: Consider the patient’s specific oxygen requirements when evaluating ML function. Factors such as body weight, metabolic rate, fever, sepsis, and native lung function influence the oxygen demand and should be factored into interpreting V’O2 values.

To sum it up for the TLDR subscribers:

Membrane lung dysfunction in ECMO is a common yet complex issue that requires a structured and algorithmic approach for diagnosis and management. By regularly monitoring the hematologic profile, pressure differentials, and gas exchange efficiency, clinicians can detect dysfunction early and act before catastrophic failure occurs. Understanding the various causes of dysfunction, such as coagulopathy, obstruction, and inadequate gas transfer, allows for targeted interventions and ensures better patient outcomes.

Note: This article reflects my learning journey in ECMO and is intended for educational purposes only. It should not be used as a substitute for professional medical advice or guidance. Always consult with qualified healthcare professionals for clinical decisions and patient care.

Acknowledgments:

I developed three custom GPTs, “AI ECMO Expert,” “ECMO Specialist Handover Practice,” and “Micro Definitions (MD-GPT),” for specialized research. These tools draw primarily from the ELSO Redbook (6th Edition), the ELSO Specialist Training Manual (4th Edition), various research papers, and articles. Additional research was supported by GPT-4o/o1, Claude 3.5 Sonnet/Opus, and Perplexity. Editing was performed with Grammarly. A.I. images and charts were created using Leonardo AI, DALL-E3 AI Image Generator, Microsoft Designer, and Adobe Express. Content for all articles sourced from Extracorporeal Life Support: The ELSO Red Book, 6th Edition, and ECMO Specialist Training Manual, 4th Edition.