What are the mechanics of venovenous Extracorporeal Membrane Oxygenation (ECMO)?

From the Guidelines

VV ECMO (Veno-Venous Extracorporeal Membrane Oxygenation) is a life-support therapy used to support patients with severe respiratory failure, and its mechanics involve draining deoxygenated blood from the venous system and returning oxygenated blood to the venous system 1.

Key Components of VV ECMO

• Cannulation: A large catheter is inserted into a major vein, typically the femoral or internal jugular vein, to drain deoxygenated blood from the body 1.
• Blood Pumping: The drained blood is then pumped through a membrane oxygenator, which removes carbon dioxide and adds oxygen to the blood 1.
• Oxygenation: The oxygenated blood is then returned to the body through a separate catheter, typically inserted into the same vein, using a centrifugal pump.
• Gas Exchange: The membrane oxygenator facilitates gas exchange, allowing for the removal of carbon dioxide and the addition of oxygen to the blood.
• Anticoagulation: Patients on VV ECMO require anticoagulation to prevent clotting, typically with heparin, to maintain a target activated partial thromboplastin time (aPTT) of 60-80 seconds.

Key Parameters to Monitor

• Blood flow rate: 2-4 L/min
• Sweep gas flow rate: 2-4 L/min
• FiO2: 0.21-1.0
• Oxygen saturation: > 90%
• Carbon dioxide removal: monitored through arterial blood gas analysis

Medications Used

• Heparin: 10-20 units/kg/hour
• Sedatives: such as propofol or midazolam, to maintain patient comfort and minimize agitation
• Analgesics: such as fentanyl or morphine, to manage pain

The duration of VV ECMO support varies depending on the underlying condition and patient response, but typically ranges from several days to several weeks.

Circuit Components

All circuits contain an oxygenator, pump, and heat exchanger 1.

• The oxygenator is commonly a hollow fiber design.
• The pump may be either a roller pump or a centrifugal pump. VV ECMO is used for patients with isolated respiratory failure with preserved cardiac function 1.

From the Research

Overview of Venovenous Extracorporeal Membrane Oxygenation (ECMO)

• Venovenous (VV) ECMO is a form of mechanical life support that provides full respiratory bypass in patients with severe respiratory failure 2.
• It allows for an artificial mechanism for oxygenation and decarboxylation of native blood, enabling safer mechanical ventilatory care and treatment of underlying respiratory pathologies 2.

Mechanics of VV-ECMO

• VV-ECMO provides complete respiratory support by allowing extracorporeal gas exchange, which can replace the patient's lung function for weeks or even years 3.
• The technique involves the cannulation of two vessels (double cannulation) in its classic configuration, but single cannula and triple cannulation approaches are also possible 4.
• Ultrasound-guided vessel puncture, double lumen single bicaval cannulations, and triple cannulation are important considerations in VV-ECMO 4.

Indications and Outcomes

• VV-ECMO is indicated for patients with severe acute respiratory failure refractory to mechanical ventilation with conventional therapy 5.
• The efficacy of VV-ECMO has been demonstrated in various studies, with overall survival rates ranging from 68% to 94% in certain patient populations 6, 5.
• Early use of VV-ECMO therapy has been shown to improve outcomes in patients with severe respiratory failure, particularly in trauma patients 5.

Complications and Management

• VV-ECMO is associated with substantial risks, including bleeding, thromboembolic events, and infection 4.
• Close vigilance and management of complications during ECMO, as well as identification of strategies post-ECMO, are critical to successful ECMO support 2.
• Ambulatory ECMO has been shown to be safe and effective in preventing critical illness neuropathy and myopathy during prolonged treatments in the intensive care unit 3.