An extracorporeal membrane oxygenation (ECMO) machine pumps and oxygenates a patient’s blood outside the body. It takes over the functions of the heart and lungs, allowing those organs to rest and recover. ECMOs are often used to aid patients awaiting open-heart surgery or a lung transplant. ECMOs are now being used to support late-stage coronavirus patients suffering from reduced respiratory function and organ failure.
An ECMO does not fix a patient’s underlying medical problem. It serves as a supportive measure while doctors anticipate how to treat the patient. An ECMO is usually used for about five days. A patient who is on an ECMO for a long period, such as 25 days or longer, is at risk of suffering from various complications, including septic shock and stroke.
An ECMO’s Basic Functions
An ECMO works by drawing blood through tubing to an artificial lung in the machine, which adds oxygen and removes carbon dioxide. The ECMO warms the blood to the body temperature and pumps it back into the body. There are two types of ECMOs. They include a veno-arterial (VA) ECMO, which is connected to a vein and an artery and when there are problems with the heart and lungs, and a veno-venous (VV) ECMO, which is connected to one or more veins, usually near the heart, and used when the problem is only in the lungs.
Cannulas are plastic tubes set directly into a patient’s heart or bloodstream. They are an important part of an ECMO. The size of cannulas varies depending on the patient’s size, age, weight and the reason for the ECMO’s use. Other significant components of the machine include large-bore catheters with soft hollow tubes with a wide diameter; [MG1] and external pumps, which combine with the cannulas. Sensors that regulate the amount of blood pushed and pulled into the cannulas are also critical to an ECMO’s success.
Improvements in ECMOs
The past few years have seen a number of significant developments in ECMOs. These include an alternative smaller, portable ECMO that can be carried by one person and easily transported in an ambulance or helicopter. The development of ultrasound equipment that provides real-time visual guidance to medical professionals inserting the cannulas has also been helpful.
There are now ECMOs that are better designed to treat children. Children have a range of weights and dimensions, from 4.25kg (9.4lb) to 60kg (132.27lb). Doctors need to use different ECMO circuits and cannulas that meet the needs of children in a range of weight categories.
Medical device designers have also created tubing circuits that are smaller and coated with an anticoagulant. The anticoagulant helps break up blood clots. Blood clots present an issue because small clots of blood can develop in ECMOs. This issue often arises in the oxygenator. When a clot enters the body, it can obstruct blood flow to a vital organ like the heart. The obstruction can cause part or all of the organ to fail.
How Engineers Can Help
Engineers interested in contributing to progress on ECMOs and associated technologies should review a diagram of the ECMO and understand technologies associated with its use. These include X-rays to check the location of the cannulas and observe inflation of the lungs. They also include ultrasound equipment to monitor the head for complications related to bleeding, particularly in the brain, and the heart to ensure regular heart function.
Common concerns with ECMOs include the potential for air bubbles and clots to develop in the tubing, varying pressures in the ECMO machine and creating leaks, kinks and other wear that impair the machine’s function. Technologies to assess, adjust and repair components of an ECMO are welcome.