Extracorporeal Membrane Oxygenation (ECMO) is a treatment that uses artificial heart and lung to support the body when a patient’s heart and/or lung have failed.
Extracorporeal Membrane Oxygenation (ECMO) is a treatment that uses artificial heart and lung to support the body when a patient’s heart and/or lung have failed. It can provide the cardiac and respiratory support for up to a few weeks, allowing time for the heart and/or lung to be treated and recover. ECMO may be an option only after all other conventional treatments have failed.
By Asst Prof Jose Chakaramakkil Mathew, Consultant, Department of Cardiothoracic Surgery
ECMO uses a modified “heart-lung machine” that is routinely used for open-heart surgery. It involves the use of a centrifugal pump (artificial heart) which takes over the work of the heart and an oxygenator (artificial lung) which takes over the work of the lungs. Large bore cannula is placed in a large vein to draw venous blood out into the ECMO circuit. This venous blood is oxygenated and decarboxylated by the oxygenator in the circuit. The treated blood is warmed up using a heat-exchanger in the circuit and pumped back into the patient using the centrifugal pump.
There are two types of ECMO - Venoarterial (VA) ECMO, which provides the heart and lung support, and venovenous (VV) ECMO, which provides only lung support.
VA ECMO supports the function of the patient's heart and lungs by diverting most of a person's blood to the ECMO circuit without the blood flowing through the patient's heart and lungs. VA ECMO draws out blood from a large vein and into the ECMO circuit. The venous blood in the ECMO circuit is oxygenated and returned into a large artery, allowing oxygen-rich blood to circulate through the body. In adults, VA ECMO is commonly used in conditions causing cardiac arrest and cardiogenic shock such as heart attack, myocarditis, cardiomyopathy, pulmonary embolism and primary graft failure after heart transplant. It is also used in conditions like poisoning, endocrine emergencies, sepsis, trauma, and organ donation. Most commonly, patients are on VA ECMO for 5-10 days.
VV ECMO supports the function of patient’s lungs only, hence a persons’ heart must still function well to meet the body's needs. It draws most of the patient’s venous blood out of a large vein and into the ECMO circuit. The venous blood in the ECMO circuit is oxygenated and returned to the right atrium and the patient's own heart pumps the blood throughout the body. It is therefore important the patient’s heart is strong enough to pump the oxygenated blood in the right atrium, through the non-functioning lungs, to the rest of the body. In adults, common indications for VV ECMO is lung failure due to pneumonia and adult respiratory distress syndrome. It is also used in aspiration, drowning, respiratory burns, lung trauma, airway obstruction, and post lung transplantation. Most commonly, patients are on VV ECMO for 10-14 days.
ECMO treatment is a high-risk procedure with significant complications including bleeding, stroke, sepsis and limb ischemia, and should only be used when all other conventional treatments such as mechanical ventilation (breathing machine), inotropes (medications that help with heart's contractions), intraaortic balloon pump (device that helps the heart pump more blood), have failed. In this group of critically ill patients, ECMO can save approximately, 60% with respiratory failure, 40% with cardiogenic shock and 30% with cardiac arrest.
Eligibility Criteria for Adult ECMO
NHCS has been performing ECMO since 2001 and is the largest ECMO centre in Singapore; performing about 75 procedures per year. NHCS has a mobile unit that can be activated to initiate ECMO at peripheral hospitals and bring the patient back to NHCS for management.
ECMO is generally contraindicated if patient is/has:
a. Age > 65-70 years old
b. Presence of advanced multi-organ failure
c. Severe chronic organ failure (e.g. kidney, liver, lung)
d. Advanced malignancy
e. Severe brain injury
f. Pre-existing ‘DO NOT RESUSCITATE’ order
g. Uncontrolled bleeding
Nonetheless, decisions on ECMO initiation are made based on the risks and benefits it could bring to individual case. When a patient is identified to be requiring ECMO, the referring physician will discuss with the ECMO centre on the treatment plan.
Venoarterial ECMO (VA ECMO) for medically refractory cardiogenic shock
In addition to the conditions listed above, factors which may influence the decision to provide VA ECMO include whether the patient:
a. is a transplant and/or ventricular assist device candidate
b. has severe peripheral vascular disease
c. has severe thrombocytopenia
a. Aortic dissection
b. Moderate to severe aortic valve egurgitation
Venovenous ECMO (VV ECMO) for acute respiratory failure
VV ECMO should be reserved for patients who are at a high risk of death despite maximal conventional therapy, including those with:
a. Severe hypoxaemia (eg. PaO2/FiO2 < 80 on FiO2 >90%) despite optimal positive end-expiratory pressure, oxygen, and adjunct therapies (e.g. paralysis, prone positioning)
b. Severe hypercapnic respiratory acidosis (pH < 7.15)
c. Inability to achieve lung protective ventilation (e.g. tidal volume ≤6ml/kg, plateau pressure≤30cmH2O)
d. Significant air leak/barotrauma Triggers for VV ECMO activation should take into account the trajectory of illness (e.g. rate of deterioration) and safety of the hospital transfer (time and logistics).
General contraindications for VV ECMO in acute respiratory failure:
a. Immediately following cardiac arrest
b. Patients with chronic immunosuppression
c. Invasive mechanical ventilation for ≥7 days prior to referral