ECMO, the last line of defense for life

As of now, the number of COVID-19 infections worldwide has reached nearly 50 million. The World Health Organization (WHO) has announced that the world has entered the COVID-19 pandemic stage, with a sharp increase in severe, critical and death cases. The COVID-19 virus is highly contagious, has a long incubation period, a high mortality rate, and even asymptomatic infections. These characteristics make the COVID-19 virus known as a "cunning virus", and its characteristics make it very difficult to prevent and control the epidemic itself. In this war against the epidemic, countless white-clad warriors have charged backwards to protect every life; countless ordinary people have rushed to the front line to protect every city. At the same time, countless scientific researchers have actively engaged in research related to the fight against the epidemic, providing the most advantageous weapons to the frontline fighters and tens of millions of Chinese people to fight the epidemic.

I believe that everyone has heard the term ECMO in recent news reports, especially in some cases of treating patients with COVID-19. Now I will give you some basic information about extracorporeal membrane oxygenation ECMO.

Extracorporeal membrane oxygenation (ECMO) is a type of extracorporeal life-support technology, which is mainly used to partially or completely replace the patient's cardiopulmonary function, so that the heart and lungs can fully rest, thereby buying time for the treatment of the primary disease. It is suitable for various cardiogenic and pulmonary diseases, such as cardiogenic shock, massive cardiac hemorrhage and trauma, severe pneumonia, acute respiratory distress syndrome, neonatal lung disease, etc.

In this COVID-19 outbreak, severe and critically ill patients have severe lung lesions and respiratory failure. Under the premise that conventional methods such as endotracheal intubation and ventilators cannot meet the patient's oxygenation requirements, the ECMO system is needed to maintain oxygen supply to various organs, so that the patient's lungs can fully rest and buy precious time for the recovery of lung function. As early as the beginning of the outbreak, Wuhan University Zhongnan Hospital successfully treated a new coronavirus patient with ECMO. In the subsequent rescue of severe and critical COVID-19 patients, ECMO played an important role, and this foreign word gradually entered the field of vision of the general public.

(Using ECMO to treat patients with COVID-19)

On March 4, 2020, the Ministry of Industry and Information Technology said at a press conference that since the outbreak of the COVID-19 epidemic, with the increase in confirmed and critically ill patients, the demand for ECMO in Wuhan, Hubei has continued to increase. At present, the domestic ECMO inventory is about 400 units, distributed in tertiary hospitals and heart centers with better medical conditions. Although the country actively purchases ECMO systems from abroad, it still cannot meet the demand for the COVID-19 epidemic. Putting aside public emergencies such as COVID-19, the National Health Commission counted the number of ECMO centers and ECMO-assisted cases in China as early as 2017, and it is expected that the number of ECMO-assisted cases will reach more than 5,000 by 2020. Affected by the epidemic, the number of patients in need of ECMO assistance has also continued to increase worldwide. Due to the serious shortage of ECMO production capacity, there are many cases of patients in many countries dying due to lack of timely assistance.

(Data source: National Health and Family Planning Commission and Cardiac Surgery White Paper)

At present, almost all ECMO in China are imported products, and there are no similar products with independent intellectual property rights. And because of the high cost of ECMO and the scarcity of ECMO resources, not all patients in need can use it. Depending on the brand, the cost of ECMO host is between 2 million and 3 million, but more expensive are ECMO consumables, a set of consumables costs between 60,000 and 120,000. ECMO consumables are in direct contact with human blood, so they are disposable consumables, and generally a set of consumables can be used for a maximum of 7-14 days. The high cost of use makes many patients discouraged.

The main components of ECMO are the blood pump and the oxygenator (membrane lung). The blood pump can replace or partially replace the human heart to provide the power required for life activities; the oxygenator (membrane lung) can replace or partially replace the human lungs to ensure oxygenation, allowing various organs to function normally. At present, many well-known domestic universities and research institutes such as Tsinghua University, Peking University, and the Chinese Academy of Sciences are actively developing independent research and development of ECMO.

How does ECMO replace or partially replace the work of our heart and lungs?

ECMO inserts a cannula into the patient's vein and then connects it to a sterile plastic tube to draw out the body's venous blood and transport it to the oxygenator (membrane lung) on ​​the ECMO for oxygenation. The oxygenator removes carbon dioxide from the blood and simultaneously adds oxygen to it, turning it into arterial blood. The blood is then pumped through the blood pump on the ECMO and then pumped back through the tube to the patient's arterial or venous cannula, thereby assisting circulation and breathing.

(ECMO operation principle diagram)

The current oxygenator is a membrane oxygenator

The membrane oxygenator is filled with hollow fiber membranes, and the mixed gas passes through the hollow fibers, while blood (venous blood) passes between the hollow fibers. There are holes in the membrane that allow gas molecules to pass through, while blocking water molecules and various cellular components in the blood. Due to the different partial pressures of oxygen and carbon dioxide on both sides of the hollow fiber membrane, gas diffusion exchange occurs, that is, the high concentration of carbon dioxide gas in the venous blood diffuses into the mixed gas, and the oxygen mixed in it diffuses into the blood, thereby completing the oxygenation process of the blood in the oxygenator (membrane lung), and the dark red venous blood also becomes oxygen-rich arterial blood.

(Schematic diagram of gas exchange in membrane lung)

The blood pump is a centrifugal magnetically coupled blood pump

The centrifugal magnetically coupled blood pump is a pump that transports liquid by the centrifugal force generated by the rotation of the impeller.

(ECMO principle machine)

At present, the COVID-19 epidemic in China has been basically under control, but at the same time, the uncontrolled outbreak of COVID-19 in countries and regions outside China is also worrying. ECMO is the hope for patients with severe pneumonia, and it is also the gospel for many patients with cardiogenic and pulmonary diseases. The research and development and application of domestic ECMO equipment and consumables with excellent performance and relatively low prices are crucial.

During the critical period of the global COVID-19 outbreak, the demand for ECMO products in various countries has increased dramatically. However, the high cost of host and consumables has restricted the introduction of ECMO in many countries and has also restricted the use of ECMO by many patients. Scientific researchers from all over the world still have a long way to go.