“Awake” extracorporeal membrane oxygenation (ECMO): pathophysiology, technical considerations, and clinical pioneering

Langer, T., Santini, A., Bottino, N. et al. “Awake” extracorporeal membrane oxygenation (ECMO): pathophysiology, technical considerations, and clinical pioneering. Crit Care 20, 150 (2016). https://doi.org/10.1186/s13054-016-1329-y

Summary of “Awake” Extracorporeal Membrane Oxygenation (ECMO): Pathophysiology, Technical Considerations, and Clinical Pioneering

Abstract

Venovenous extracorporeal membrane oxygenation (vv-ECMO) has traditionally been a rescue therapy for patients with respiratory failure unresponsive to conventional mechanical ventilation. Recently, the approach to ECMO has shifted towards earlier intervention and even as a first-line treatment in awake, non-intubated patients with respiratory failure. This method, known as "awake" ECMO, circumvents the complications associated with sedation, intubation, and mechanical ventilation. Despite its benefits, this approach presents challenges related to patient-ECMO interactions, respiratory monitoring, and the management of awake patients on extracorporeal support.

Background

ECMO has been used to manage respiratory failure, especially in cases where mechanical ventilation is insufficient. Traditionally, ECMO is initiated in the later stages of acute respiratory distress syndrome (ARDS) to mitigate the adverse effects of mechanical ventilation. However, ECMO is now being considered earlier and as an alternative to mechanical ventilation in awake, spontaneously breathing patients. This approach could avoid ventilation-related side effects but involves significant challenges in patient management.

Pros and Cons of Spontaneous Breathing

Pros:

1. Optimal Ventilation-Perfusion Matching: Spontaneously breathing patients optimize ventilation-perfusion matching by primarily moving the dorsal part of the diaphragm, directing ventilation to better-perfused lung areas.
2. Maintenance of Functional Residual Capacity: Awake patients maintain respiratory muscle tone, ensuring chest wall expansion and preventing atelectasis.
3. Diaphragm Function Preservation: Avoiding mechanical ventilation reduces the risk of ventilator-induced diaphragm dysfunction.
4. Enhanced Venous Return and Lymphatic Drainage: Spontaneous breathing favors venous return and pulmonary lymphatic drainage, improving cardiac output.
5. Reduced Risk of Ventilator-Associated Pneumonia: Avoiding intubation preserves natural airway defenses.

Cons:

1. Risk of Lung Injury: Spontaneous breathing can generate positive transpulmonary pressure, potentially causing lung injury.
2. Increased Oxygen Consumption: High respiratory muscle effort can lead to increased oxygen consumption, worsening hypoxemia.
3. Need for Emergency Intubation: Equipment failure might necessitate emergent intubation and mechanical ventilation.

Pros and Cons of Keeping Patients Awake

Pros:

1. Reduction of Delirium: Avoiding sedatives can reduce delirium risk, decreasing ICU/hospital stay and mortality.
2. Rehabilitation Opportunities: Awake patients can participate in physical therapy, reducing neuromuscular disorders.
3. Enhanced Communication: Awake patients can interact with relatives and communicate their symptoms to medical staff.

Cons:

1. Risk of Device Displacement: Awake patients must be monitored to prevent self-harm from removing invasive devices.
2. Patient Discomfort and Anxiety: Awake patients require analgesics and experience stress from the ICU environment.

Physiology and Pathophysiology of the Control of Breathing

Spontaneous breathing is primarily controlled by carbon dioxide (CO2) levels. Hypoxic ventilatory response is usually activated at low oxygen levels, while CO2 plays a critical role in respiratory drive. Understanding the control of breathing in patients with acute lung disease remains limited, with lung receptors potentially influencing respiratory patterns during disease.

Technical Considerations

Cannulation Approaches

Venous cannulation for vv-ECMO is often done percutaneously using the Seldinger technique. Two approaches are used:

1. Single Site Cannulation: Involves bicaval dual-lumen catheters, freeing femoral veins for physical therapy and reducing infection risk.
2. Dual Site Cannulation: Performed in awake patients with local anesthesia, though it limits physical therapy options.

Physiology of Extracorporeal Gas Exchange and Patient–Machine Interactions

Extracorporeal gas exchange follows the same principles as pulmonary gas exchange. CO2 removal depends on membrane lung ventilation and blood flow, while oxygen transfer relies on extracorporeal blood flow and hemoglobin saturation. Interactions between the patient and ECMO can affect blood flow, especially during respiratory distress.

Monitoring During Awake ECMO

Respiratory monitoring in awake ECMO patients is challenging due to the lack of airway pressure and tidal volume data. Clinicians must rely on signs of respiratory distress, such as dyspnea and rapid breathing. Esophageal pressure monitoring can help assess pleural pressure swings and potential lung injury.

Clinical Pioneering

Bridge to Lung Transplantation

Awake ECMO has been used as a bridge to lung transplantation, offering benefits in preoperative physical rehabilitation. Studies show improved survival and reduced postoperative mechanical ventilation time compared to traditional approaches.

Exacerbation of Chronic Obstructive Pulmonary Disease (COPD)

Extracorporeal CO2 removal systems may reduce intubation rates in COPD exacerbations, offering a promising strategy to avoid mechanical ventilation-related side effects.

Acute Respiratory Distress Syndrome (ARDS)

Although data are scarce, awake ECMO is being explored as an alternative to mechanical ventilation in ARDS patients, despite their complex treatment needs.

Conclusions

Awake ECMO presents a viable option for managing respiratory failure, avoiding many side effects associated with traditional methods. However, it poses challenges in monitoring and management. More research is needed to understand the pathophysiology and evaluate potential benefits compared to standard care.

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Discussion Questions

1. What are the potential benefits and drawbacks of using "awake" ECMO compared to traditional mechanical ventilation in managing respiratory failure?
2. How can ICU staff be trained to effectively manage the unique challenges of awake ECMO in spontaneously breathing patients?
3. What additional research is needed to better understand the pathophysiology and optimize the use of awake ECMO in clinical practice?

Javier Amador-Casta?eda, BHS, RRT, FCCM

Interprofessional Critical Care Network (ICCN)

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