Introduction 

Severe Acute Respiratory Distress Syndrome (ARDS) is a critical life-threatening condition characterised by inflammation in the lungs, leading to fluid buildup and difficulty in breathing. Clinically, it presents with sudden shortness of breath, coughing, choking, and low blood oxygen levels. It can happen in several cases such as pneumonia, COVID-19, sepsis, severe trauma, inhalation of foreign substances like smoke, and drug overdose. 

Usually, in the case of ARDS, the first priority is to support breathing and oxygenation with the help of oxygen masks and mechanical ventilation (breathing machines). In severe cases, Extracorporeal Membrane Oxygenation or ECMO may be used where it acts as a temporary life support system. 

Understanding ECMO

ECMO is used for cardiac (heart) or lung failure when conventional methods, like CPR, are not successful. It is a machine that provides oxygen to the blood and takes out carbon dioxide, functioning as an artificial lung for the body. A specialised tube (cannula) is inserted into a vein in the body to drain out blood and send it to the machine. Once the machine has oxygenated the blood, a returning cannula brings the oxygenated blood back into the body, and this process repeats. 

• Extracorporeal means “outside the body” where blood is pumped and circulated out of the body to the ECMO machine
• Membrane oxygenation: the machine has a membrane that acts as an artificial lung, exchanging gases by adding oxygen and removing carbon dioxide

Types of ECMO

Depending on the organ that needs support, there are two kinds of ECMO: Veno-venous (VV) ECMO for respiratory (lung) support and Veno-arterial (VA) ECMO for both the heart and lungs in cases of cardiac failure. The majority of ARDS cases involve lung failure alone, for which veno-venous VV ECMO is required. 

In ARDS, the lungs can worsen to a point that it causes blood vessels in the lungs to clamp down, overloading the right side of the heart. The right side of the heart struggles to pump blood into the lungs and it happens due to very low oxygen levels (hypoxemia) or high carbon dioxide levels (hypercapnia). When this happens, doctors are afraid of heart failure and sometimes opt for VA ECMO, that supports both the heart and lungs but it is a more invasive option. VV ECMO alone can actually relieve this pressure by improving the oxygen and carbon dioxide levels which then relaxes the lung vessels and takes the strain off the heart. 

Indications for ECMO Use in ARDS

Criteria for consideration¹ 

• Severe hypoxemia (very low blood oxygen levels)
• Uncompensated hypercapnia with acidemia which means high levels of carbon dioxide (CO2) in the blood (hypercapnia) and a low blood pH (acidemia). If the blood becomes too acidic (pH < 7.15) because CO₂ is building up, it’s dangerous
• Unsafe pressure needed to ventilate the lungs: If doctors have to use very high pressures (plateau pressure > 35–45 cmH₂O) on the ventilator to inflate the lungs, that can cause lung damage
• Patients who do not improve with other advanced interventions

Contraindications: When not to use ECMO²

Absolute conditions: 

• Patient refuses ECMO
• Advanced stage of cancer
• Severe, fatal brain injury 
• Irreversible lung damage with no option for lung transplant
• Any condition that rules out lung transplantation

Relative conditions: 

• Advanced age
• Obesity 
• Weakened immune system (from disease or medication like immunosuppressants)
• On harmful or high intensity ventilator settings for more than 7 days before ECMO
• Right side heart failure
• Blood cancers (especially after bone marrow transplant)
• High severity illness scores (markers of poor progression of disease) 
• “Do Not Resuscitate” (DNR) status

VV ECMO procedure in ARDS

When carrying out the VV ECMO procedure, there are two main ways of placing the tubes (cannulas) that carry blood in and out. The dual-site method uses two separate veins where blood is taken through a large vein in the leg (femoral vein) and returned through a vein in the neck (internal jugular) or the other leg.¹ Another option is using single-site method, which uses a special dual-lumen cannula placed through one vein, usually in the neck. A dual-lumen cannula has two “channels” (lumens) inside one cannula that is designed to both remove blood from the body and return oxygenated blood through the same tube. It avoids using the leg veins and allows the individual to stay mobile, however, this method requires advanced imaging tools to guide it into the perfect position.

Monitoring and management during ECMO

After placing a patient on ECMO, careful monitoring and supportive care are critical. Doctors first watch the ECMO circuit blood flow, because a sudden drop can signal serious problems such as internal bleeding in the chest or abdomen, heart compression (cardiac tamponade), or the left side of the heart becoming overloaded with blood, which can cause lung congestion. If dangerous heart rhythms occur, they can be treated with electric shocks. Oxygen and carbon dioxide levels are constantly monitored and controlled to avoid clots and reduce bleeding risk. Since blood clots can form in the ECMO circuit, patients also need anticoagulation (blood-thinning treatment) and are usually given heparin. It is essential to monitor for clots, bleeding, infection, or device malfunction. 

Heart rhythm is continuously monitored for irregularities. Mechanical ventilation is also adjusted to reduce strain on the heart and lungs. Body temperature is managed with a target of 33–36°C for the first 24 hours before slowly rewarming to normal (37°C). Supportive care, including management of fluids, nutrition, sedation are essential to provide overall care to the individual being treated. 

Duration on ECMO

There is no fixed duration that an individual is on ECMO. It depends on how fast their lungs can improve function. Typical duration lasts 1-2 weeks but it can last for several weeks if healing is slow. Decisions are individualised based on recovery and risk of complications. 

Weaning and decannulation

VV ECMO is gradually weaned off when lung function improves, which includes better oxygen levels, carbon dioxide removal, and lung compliance. Recovery is checked by reducing the ECMO sweep gas flow (the oxygen/air mix) usually between 5–65%. A sign that the lungs are improving is when the body maintains oxygenation with reduced ECMO flow, rising oxygen levels in the blood, good chest X-ray findings. 

Timing and safety of removal is essential. If the ECMO is weaned off too early, then it can lead to collapse, and if it is removed too late, then it risks complications. If all goes well, then decannulation (removal of tubes) is performed carefully. The individual can continue on ventilator support, whilst careful monitoring via blood tests and scans are carried out by healthcare professionals. Any sudden drop in oxygen level must be identified. 

Complications of ECMO in ARDS

• Bleeding - the most common complication with ECMO and it can occur in the brain, lungs, or gastrointestinal (GI) tract. 
• Clotting or thrombosis 
• Gas Embolism: Gas embolism may occur if air enters the circuit.Neurological issues: stroke, seizures, or intracranial (brain) hemorrhage due to clotting or anticoagulation.
• Renal failure: acute kidney injury may require dialysis
• Infection/sepsis: ECMO circuits increase infection risk
• Cannula Complications: wrong positioning, vessel injury, reduced blood flow to limb (limb ischemia)
• Hypoxia

Outcomes and prognosis 

ECMO is a life-saving treatment for severe ARDS cases, especially when conventional treatments have failed. Studies report mortality rates ranging from 22% to 62.6%in cases of using ECMO for ARDS.⁴ The variability is due to patient-related factors such as age, cause of ARDS, severity of hypoxia, and extent of organ damage that determine mortality rate.⁴ However, 90-day mortality is significantly lowered by ECMO compared to conventional treatment, where individuals who underwent ECMO treatment had more days alive out of the ICU, with no respiratory, cardiovascular, renal and neurological failure. 

Summary 

Severe ARDS is a highly critical condition where one has difficulty breathing. ECMO is a last resort life-saving treatment when other conventional forms of treatment for ARDS have failed. ECMO temporarily takes over lung function, allowing the lungs to rest and heal while maintaining oxygenation and removing carbon dioxide. This is done via a machine that circulates blood through tubes attached to the body. Success depends on careful patient selection, timely initiation, and close monitoring to manage complications such as bleeding, infection, or clotting. Outcomes vary based on factors like age, underlying health, and disease severity, but studies show ECMO can significantly improve survival and recovery compared to standard care. With ongoing advances, ECMO continues to be a vital option for critical lung support.