Extracorporeal circulation (ECC) is a medical procedure where a machine temporarily supports the function of the heart and lungs outside the body. This technique diverts a patient’s blood through an external circuit for gas exchange and circulation. ECC provides temporary assistance to maintain blood flow and oxygenation during complex medical interventions or when organs are not performing adequately.
Essential Components of the Circuit
Cannulas, specialized tubes, are inserted into the patient’s blood vessels to divert blood to and from the machine. A pump then acts as the circuit’s mechanical heart, moving blood through the system, with common types including roller and centrifugal pumps. The oxygenator serves as an artificial lung, adding oxygen to the blood and removing carbon dioxide, mimicking the natural process of the lungs. A heat exchanger regulates the blood’s temperature, warming or cooling it as needed. Filters and reservoirs collect blood, remove air bubbles, and capture debris to maintain blood purity within the circuit. All these components are interconnected by tubing, creating a continuous pathway for blood outside the body.
Blood Collection and Initial Processing
Deoxygenated blood is carefully collected from the patient, typically from a large vein such as the vena cava, and flows into the extracorporeal circuit. Drainage often occurs through gravity, directing the blood into a reservoir. Upon entering the reservoir, the blood undergoes initial processing. This collection point allows for temporary storage, helps remove air bubbles, and acts as a preliminary filter, capturing larger particles before the blood proceeds further into the circuit and reaches the pump. This initial phase is crucial for establishing a stable flow and protecting the blood’s integrity as it enters the external system.
Gas Exchange and Temperature Control
After collection, blood moves into the oxygenator. Here, deoxygenated blood contacts a gas mixture rich in oxygen. Oxygen diffuses into the blood, while carbon dioxide, a waste product, diffuses out, effectively replicating the gas exchange function of healthy lungs. This process is achieved through a semipermeable membrane within the oxygenator, preventing direct contact between blood and gas. Simultaneously, the blood’s temperature is precisely controlled by the heat exchanger, often integrated within the oxygenator unit. This device can either warm or cool the blood, which is important for maintaining the patient’s body temperature during surgical procedures and helps protect organs and tissues. Throughout this phase, sensors within the circuit continuously monitor blood gases and flow to ensure optimal function and patient safety.
Blood Return to the Body
Once oxygenated and temperature-adjusted, the blood is returned to the patient’s arterial system, typically through a large artery like the aorta or femoral artery. This arterial return ensures oxygen-rich blood is delivered efficiently to the patient’s tissues and organs, thereby maintaining systemic circulation. Continuous monitoring of the patient’s blood pressure, flow rates, and other vital signs is maintained as the blood re-enters the body. This monitoring helps confirm that the patient’s cardiovascular system is adapting appropriately to the re-introduced blood flow.
When Extracorporeal Circulation is Used
Extracorporeal circulation is utilized in various medical situations where temporary support for heart and lung function is necessary. A common application is during cardiopulmonary bypass (CPB) for open-heart surgeries, allowing surgeons to operate on a still, bloodless heart. This technique is employed for procedures such as coronary artery bypass grafting, heart valve repair or replacement, and the correction of congenital heart defects. Another important use is Extracorporeal Membrane Oxygenation (ECMO), which provides life support for individuals experiencing severe heart or lung failure. ECMO can be used for conditions like acute respiratory distress syndrome, severe pneumonia, or cardiogenic shock, offering temporary support while the patient’s organs rest or recover. Beyond these primary uses, ECC may also be considered in certain organ transplant procedures or for inducing deep hypothermia to protect organs during complex surgeries.