Extracorporeal membrane oxygenation (ECMO) is a life support technique that assists individuals whose heart and lungs are severely compromised and unable to function. Specifically, venovenous (VV) ECMO provides temporary support solely for the lungs. This method works by circulating a patient’s blood outside their body through an artificial lung, which adds oxygen and removes carbon dioxide. The connection to this external circuit involves cannulation, where specialized tubes are inserted into large blood vessels.
The Purpose of VV ECMO
VV ECMO is employed when a patient’s lungs are so severely diseased or injured that conventional treatments, such as mechanical ventilation, are no longer sufficient to maintain adequate oxygen levels or remove carbon dioxide. It acts as an external lung, allowing the patient’s own lungs to rest and heal by reducing the strain. This temporary support can span days to weeks, providing a window for recovery.
Conditions that necessitate VV ECMO include severe Acute Respiratory Distress Syndrome (ARDS) resulting from viral or bacterial pneumonia, including cases related to COVID-19. It is also utilized for respiratory failure characterized by low oxygen levels (hypoxemia) or high carbon dioxide levels (hypercapnia) that do not respond to other therapies. For some patients, VV ECMO serves as a bridge to a lung transplant or as support while awaiting lung recovery.
Understanding Cannulation
VV ECMO cannulation involves inserting specialized tubes, known as cannulas, into large veins to connect with the ECMO circuit. This procedure is performed in a controlled environment, such as an operating room or an intensive care unit (ICU), to ensure sterility and equipment access. Patients undergoing cannulation receive sedation, often including general anesthesia, to ensure comfort and stillness during insertion.
Medical professionals use ultrasound guidance during cannulation to visualize blood vessels and guide cannula insertion. This imaging ensures cannulas are placed correctly within the vein and avoids surrounding structures. The procedure is performed under sterile conditions to minimize infection risk.
Strategic Cannula Placement
For VV ECMO, cannulas are placed in veins, in the neck or groin. Common sites are the internal jugular vein in the neck and the femoral veins in the groin. One cannula drains deoxygenated blood from the patient to the ECMO machine, and another returns oxygenated blood to the patient.
There are two configurations for VV ECMO cannulation. One uses two separate single-lumen cannulas: a drainage cannula in the femoral vein, with its tip near the junction of the inferior vena cava and the right atrium, and a return cannula in the internal jugular vein, with its tip extending into the superior vena cava. The other option uses a single dual-lumen cannula, a tube with two internal channels, inserted into the right internal jugular vein. This dual-lumen cannula allows blood to be drawn out and returned through one entry site, offering advantages like increased patient mobility. Careful positioning of the cannulas maximizes blood flow efficiency and minimizes recirculation, where oxygenated blood is drawn back into the drainage cannula.
Initial Patient Care After Cannulation
Following insertion of the cannulas and connection to the ECMO circuit, attention shifts to securing the cannulas and initiating support. The cannulas are secured to the patient’s skin to prevent accidental dislodgement, which could lead to complications. This securing involves sutures and dressings to maintain their position.
Once connected, initial checks confirm proper blood flow through the circuit and verify the ECMO machine effectively oxygenates blood and removes carbon dioxide. Continuous monitoring of the patient’s vital signs, blood gas levels, and ECMO circuit parameters begins. This observation takes place within the intensive care unit, where nurses and ECMO specialists assess the patient’s response and system performance to make adjustments.