VV ECMO Part 1 of 3: Indications and Rationale for Use
Extracorporeal Membrane Oxygenation (ECMO) has emerged as a vital intervention in managing severe respiratory conditions, particularly Venovenous (VV) ECMO, which provides advanced respiratory support without directly influencing cardiac function. This article is part one of a three-part series. Here, we explore the comprehensive reasons for initiating VV ECMO. In part two, I will discuss what I have learned about working with patients while they are on VV ECMO. Part three will cover the weaning process, including a surprising but common method to reduce FdO2 without using the blender.
VV ECMO: A Learning Tool for Novice ECMO Specialists
As a novice ECMO specialist, I found that initially, VV ECMO was easier to understand than VA ECMO. It is an excellent way to get a foundation in hemodynamics, cannulation, anticoagulation, and the various labs necessary to monitor. It also helped me understand the ECMO machine, including blood flow, sweep, FDO2, and various pressures and interventions. It provided me with a solid knowledge base to build upon as I progressed to more complex scenarios such as VA ECMO. This hands-on experience was invaluable in developing the confidence and competence needed to manage patients on ECMO effectively.


How VV ECMO Works
VV ECMO works by drawing deoxygenated blood from the venous system, passing it through an oxygenator where it is oxygenated and carbon dioxide is removed, and then returning the oxygenated blood back to the venous system. The heart then pumps this blood to the lungs and the rest of the body. Unlike VA ECMO, VV ECMO does not provide direct cardiac support, but it can indirectly reduce pulmonary vascular resistance (PVR) by normalizing blood gases and reducing hypoxic pulmonary vasoconstriction.
Reasons for Placing a Patient on VV ECMO
1. Severe Hypoxemic Respiratory Failure
The number one indication for VV ECMO is severe hypoxemic respiratory failure. Patients who cannot maintain adequate oxygenation despite maximal conventional therapies, such as high levels of positive end-expiratory pressure (PEEP) and high fraction of inspired oxygen (FiO2), are candidates for VV ECMO. This extracorporeal support ensures adequate oxygen delivery to tissues while minimizing further lung damage.
2. Hypercapnic Respiratory Failure
VV ECMO is crucial for patients with hypercapnic respiratory failure when mechanical ventilation cannot effectively remove carbon dioxide. Conditions such as chronic obstructive pulmonary disease (COPD) exacerbations or severe asthma can lead to refractory hypercapnia. However, for some instances, extracorporeal carbon dioxide removal (ECCO2R) may be a less invasive alternative to VV ECMO. ECCO2R can effectively clear carbon dioxide, allowing for lower ventilator settings and reducing the risk of further lung injury.
3. Lung-Protective Ventilation Strategy
VV ECMO facilitates lung-protective ventilation strategies. High ventilator pressures and volumes are necessary to maintain oxygenation, and ventilation in severe cases can cause volutrauma (overdistension of alveoli), barotrauma (pressure-related injury), and atelectrauma (continuous opening and closing of alveoli). By taking over the gas exchange function, VV ECMO allows the use of lower ventilator settings, reducing the risk of ventilator-induced lung injury (VILI).
4. Bridge to Recovery or Lung Transplant
VV ECMO serves as a bridge to recovery for patients with end-stage lung disease awaiting a lung transplant. VV ECMO maintains adequate gas exchange, providing critical support until donor lungs become available.
5. Management of Refractory ARDS
ARDS presents a significant challenge with its profound hypoxemia and impaired gas exchange. One crucial metric used to assess the severity of ARDS is the PF ratio, calculated as the ratio of arterial oxygen partial pressure (PaO2) to the fraction of inspired oxygen (FiO2). ARDS is classified based on the PF ratio: mild (200-300), moderate (100-200), and severe (less than 100). When conventional therapies, including prone positioning and steroids, fail, VV ECMO offers an alternative.
PaO2/FiO2 ratio < 50 mmHg for > 3 hours despite optimized mechanical ventilation (FiO2 ≥ 80%, tidal volume = 6 cc/kg, and trial of PEEP ≥ 10 cmH2O).
PaO2/FiO2 ratio < 80 mmHg for > 6 hours despite optimized mechanical ventilation (as listed above).
Arterial blood pH < 7.25 with PaCO2 ≥ 60 mmHg for > 6 hours despite an optimized respiratory rate of at least 35 breaths per minute and optimization of ventilation settings to maintain a plateau pressure ≤ 32 cmH2O.
By assuming the role of the lungs in gas exchange, VV ECMO reduces the strain on the lungs, allowing time for recovery from the underlying condition. The decision to initiate VV ECMO involves evaluating the severity of hypoxemia, duration of mechanical ventilation, overall health status, and potential contraindications. VV ECMO can significantly improve oxygenation and provide a bridge to recovery for patients with severe ARDS. Making an early referral for ECMO is crucial, ideally within the first 7 days of invasive mechanical ventilation.
6. Post-Lung Transplant Support
VV ECMO can be critical post-lung transplant in cases of primary graft dysfunction, providing respiratory support while the transplanted lungs recover and stabilize. This allows for adequate oxygenation and ventilation without putting additional stress on the newly transplanted lungs.
7. Pulmonary Hemorrhage
In cases of severe pulmonary hemorrhage, VV ECMO can be life-saving. While this is not something I have seen, VV ECMO allows the lungs to rest and heal while providing continuous gas exchange, thus stabilizing the patient and giving time for other medical or surgical interventions to control the hemorrhage.
8. Severe Infections Leading to Respiratory Failure
Severe respiratory infections, such as viral pneumonia (e.g., COVID-19) and bacterial infections leading to sepsis and acute respiratory failure, may necessitate using VV ECMO. This support ensures adequate oxygenation and ventilation while the patient is treated for the underlying infection.
Conclusion
VV ECMO is a critical tool against severe respiratory and some non-respiratory conditions, providing life-saving support when conventional therapies fall short. VV ECMO ensures optimal patient outcomes by enabling lung-protective ventilation strategies, bridging patients to recovery or transplantation, and managing conditions such as ARDS, pulmonary hemorrhage, and post-lung transplant support. Understanding VV ECMO allows healthcare providers to make informed decisions, ensuring timely and effective intervention.
References:
Extracorporeal Life Support: The ELSO Red Book, 6th Edition. Published by the Extracorporeal Life Support Organization (ELSO), this comprehensive text is a key resource for understanding the principles and practices of ECMO.
ECMO Specialist Training Manual, 4th Edition. This manual provides in-depth training protocols and guidelines for ECMO specialists, covering cannulation techniques, patient management, and emergency procedures.
Various Other Source Materials. Additional insights and guidelines on ECMO practice, including hospital patient care practices.
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.
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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.