ECMO

ECMO or Extracorporeal Membrane Oxygenation

WHAT IS ECMO?

ECMO or Extracorporeal Membrane Oxygenation is a modality derived from the heart & lung machines now used in selected advanced ICU’s in a much miniaturized and user friendly format. It can be used as a ventilator /oxygenation support (Veno -Venous; V-V ECMO) or as a mechanical (Cardiac; Veno -Arterial; V-A ECMO) support.

One needs to remember that ECMO is a support modality which maintains the cardiac and/or respiratory functions of the body allowing the lungs and the heart to rest and therapies to act without causing adverse effects of conventional ventilation on the lungs and high dose vasopressors/ inotropes on the heart and other organs

ECMO is a life saving modality for patients with severe organ dysfunction.

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TECHNIQUES

There are two basic types which are described by the site of drainage & where the blood returns

Veno-venous

  • Deoxygenated blood is drained from venous circulation into the ECMO circuit

  • Blood is oxygenated via the oxygenator and is returned to the right atrium

  • Drains from major vein & returns to a major vein

  • Supports only the lungs

  • Adequate circulation is provided by the native cardiac output

Veno-arterial

  • Deoxygenated blood is drained from venous circulation into the ECMO circuit

  • Passes through the oxygenator and is returned directly to the arterial circulation

  • Drains from major vein & returns to major artery

  • Supports heart & lungs

WHEN IS ECMO INDICATED?

ECMO is not usually the first line therapy. It needs to be considered when first line modalities start failing or start causing unwanted effects. A patient deteriorating even after best of mechanical ventilatory efforts for the lungs OR after highest possible doses of inotropes/vasopressors, needs to be considered for ECMO provided the organ failure has a reversible cause.

The choice for the type of ECMO is determined by the predominant failure: V-A ECMO if cardiac and V-V ECMO if respiratory.

INDICATIONS OF V-V ECMO

Lung disease that is:Acute, Life threatening, Reversible, Unresponsive to conventional /alternative therapy for Example:

ARDS

Pneumonia

Trauma

Status asthmaticus

Severe COPD exacerbations

Trauma/Drowning/inhalational injuries

Auto immune diseases

Broncho-pleural fistulas/post-operative

WHEN DOES A RESPIRATORY FAILURE BECOMES AN ECMO CANDIDATE?

If 2 or more of the following criteria exist even after four-six hours of maximal conventional ventilation in a reversible disease.

Pa02/Fi02 ratio < 100 with Fi02 1.0

Murray score > 3

Respiratory acidosis pH < 7.2 or PaCO2 > 100

A-a gradient > 600mm Hg

Lung compliance < 0.5 ml/cm of H20/Kg

INDICATIONS OF V-A ECMO

Failure to wean from bypass

Myocarditis: toxic (aluminium phosphide, beta blockers, CCB) or viral

Cardiogenic Shock: Acute MI and its complications

Pulmonary embolism

Sepsis with profound cardiac depression

Trauma

WHEN DOES A CARDIAC FAILURE BECOMES AN ECMO CANDIDATE?

If 2 or more of the following criteria exist even after four-six hours of maximal conventional support in a reversible disease

Cardiogenic shock on high vasopressors (>=0.2mcg/kg/min of noradrenaline or equivalent vasopressors)

Lactate> 5 mmol/L

ScV02 < 65%

Low cardiac output with Organ failure: AKI, Hepatic, pulmonary edema)

Life threatening arrhythmias unresponsive to medical therapy

HOW IS ECMO HELPFUL?

The body is primarily dependent on oxygen from the lungs and its transport to various organs by the pumping of the heart. Moreover, lungs also remove carbon dioxide. If any of these functions fail because of a disease process, external support is required: conventional ventilation for the lungs and vasopressors/inotropes for the heart. Mostly these modalities are helpful, but in some cases high pressure of ventilation and high levels of oxygen delivery to the lungs can cause more harm than good. Likewise, high doses of vasopressors/inotropes can damage the heart and end organs like kidney, peripheries, gut etc.

Putting such patients on ECMO support allows us to turn down the high degree of support thus preventing their side effects while allowing the heart/lungs to rest and heal without hampering the body physiology.

RISK INVOLVED

  • Risks involved in ECMO can be due to the initiation and placement of cannula eg. damage to blood vessels and heart, hematomas, pneumothorax etc. but these are very uncommon and further minimized by using ultrasound and echocardiographic guidance for placement of cannulas.
  • On ECMO, there is a risk of bleeding: externally or internally; as patient needs to be administered heparin as an anticoagulant so that blood does not clot in the ECMO circuit, which can be fatal. Most of the bleeding is minor and non-life threatening and easily manageable. Rarely, internal bleeds into the abdomen and brain can occur which can be fatal. These events are minimized by close monitoring of heparin dose.
  • Acquired infections on ECMO are also a possibility due to the foreign invasive devices.