Medicine is a continually evolving science. One of the most important offshoots of medicine is emergency medicine. The actual practice of emergency care is as old as medicine itself. Year by year we are evolving in this science and newer and better technologies are coming up. One of such technologies is “Extra Corporeal Membrane Oxygenation” (ECMO).
We are more than aware that hypoxic respiratory failure and/or cardiogenic shock are two of the most difficult cases that can present in the intensive care unit (ICU) and put patients at high risk for ICU mortality. The use of cardiopulmonary bypass technologies such as ECMO allows for more aggressive lung rest strategies and cardiovascular support than could be provided otherwise.
WHAT IS ECMO?
Whereas standard cardiopulmonary bypass is designed to ensure minutes to hours of support for patients undergoing surgery, extracorporeal membrane oxygenation (ECMO) provides support to patients with respiratory, cardiac, or combined failure for days to weeks.
Working Principle– The basic principle of ECMO is to oxygenate a patient’s blood outside her/his body.
- Deoxygenated blood is drained via a venous cannula.
- CO2 is removed, O2 is added through an “extracorporeal” device.
- The blood is then returned to systemic circulation via another vein (VV ECMO) or artery (VA ECMO).
Uses– ECMO serves as a BRIDGING THERAPY not as a curative therapy. It’s used as a
- Bridge to recovery- Buying time for patient to recover
- Bridge to decision- Provide temporary support to the patient and allow clinicians to decide on the next step.
- Bridge to transplant- Provide support to the patient while awaiting suitable donor organ.
COMPONENTS, TECHNIQUES AND TYPES
ECMO circuit and components- Basic components of ECMO circuit includes-
- A blood pump
- Membrane oxygenator (for oxygenation of extra corporeal blood) and heat exchanger (for temperature regulation of extra corporeal blood)
- Aortic- Single outlet hole
- Venous- Multiple inlet holes
- Double lumen single cannula
Tubings- Depending on heparin coating- regular and heparin coated.
Different configurations in ECMO-
1. Veno-Venous ECMO (VV- ECMO)
- Used to support patients with severe respiratory failure refractory to conventional therapy.
- Blood is drawn from a central vein, passed through the ECMO machine and then returned back via central vein.
- 4 types of configurations depending on cannulation site-
- High flow
- Double lumen single cannula
2. Veno-Arterial ECMO (VA-ECMO)
- Used to support patients with severe cardiac failure with or without respiratory failure.
- Blood is drawn from a central vein, passed through the ECMO machine and then returned back via a central artery.
- Different configurations are-
- Standard femoro-femoral
- Emergency femoro-femoral (similar to standard but smaller cannula used)
- High flow
- Central- specialised cannula
- Central- bypass cannula
3. Arterio-Venous ECMO (AV ECMO)
- This circuit uses the patient’s own arterial pressure or incorporates a pump to drive blood across an oxygenator.
- Can partially support the respiratory system by effectively removing the carbon dioxide.
INDICATIONS AND CONTRAINDICATIONS
Indications for ECMO can be divided into three categories according to the supported organ- cardiac, respiratory or a combination of the two.
ECMO Indications for cardiac support
1. Cardiogenic shock; severe cardiac failure due to any cause
- Acute coronary syndrome
- Cardiac arrhythmic storm refractory to other measures
- Sepsis with profound cardiac depression
- Drug overdose/ toxicity with profound cardiac depression
- Pulmonary embolism
- Isolated cardiac trauma
- Acute anaphylaxis
2. Post cardiotomy- inability to wean from cardiac support.
3. Post heart transplant- primary graft failure after heart or heart lung transplantation.
4. Chronic cardiomyopathy
5. As a bridge to longer term ventricular assist device (VAD) support
6. Or as a bridge to decision
7. Periprocedural support for high risk percutaneous cardiac interventions.
8. Bridge to transplant.
ECMO indications for respiratory support
1. Acute respiratory distress syndrome
- Severe bacterial or viral pneumonia
- Aspiration syndromes
- Alveolar proteinosis
2. Extracorporeal assistance to provide lung rest
- Airway obstruction
- Pulmonary contusion
- Smoke inhalation
- Primary graft failure after lung transplantation
- Bridge to lung transplant
- Intraoperative ECMO
4. Lung hyperinflation- status asthmaticus
5. Pulmonary hemorrhage or massive hemoptysis
6. Congenital diaphragmatic hernia, meconium aspiration
Contraindications to ECMO
- unrecoverable heart and not a candidate for transplant
- Disseminated malignancy
- Known severe brain injury
- Unwitnessed cardiac arrest
- Prolonged CPR without adequate tissue perfusion
- Unrepaired aortic dissection
- Severe aortic regurgitation
- Severe chronic organ dysfunction
- Compliance (financial, cognitive, psychiatric or social limitations to the patient)
- Peripheral vascular disease- contraindication for VA ECMO
- Cardiogenic failure- contraindication for VV ECMO
2. Relative- anticoagulation, advanced age, obesity
Complications on ECMO are very common and are associated with significant increase in morbidity and mortality. These complications could be related to the underlying pathology needing ECMO, or of the ECMO itself (surgical insertion, circuit tubing, anticoagulation etc.). The ECMO inserted for pulmonary support has less complications than the ECMO inserted for cardiogenic support.The worst outcomes are reported when ECMO is used after ECPR (extracorporeal cardiopulmonary resuscitation). VV ECMO has fewer complications than VA ECMO, the children have less complications than adults except for neurologic complications.
Following are few complications encountered-
- Bleeding at the surgical or cannulation site
- Pulmonary hemorrhage
- Intracerebral hemorrhage or infarction
- Systemic thromboembolism
- Heparin induced thrombocytopenia
- Neurologic complications
- Septic complications
- The harlequin syndrome (saturation of upper part of body is less than lower half)
ORGAN MANAGEMENT AND WEANING OFF OF ECMO
Organ management is very critical in obtaining good survival outcomes with better quality of life, better general health, physical health, and social functioning. The aim of organ management is to avoid multiorgan failure in a patient who is suffering from primary failure of the heart, lung or both.
- Cardiovascular system management: systemic perfusion and intravascular volume should be maintained. Volume status can be assessed clinically by urine output, central venous pressure, physical signs of perfusion, and body weight.
- Pulmonary system management: Pulmonary hygiene is strict and requires frequent positional changes, endotracheal suctioning every 4 hours depending on secretions, a daily chest radiograph, and flexible bronchoscopy when needed.
- Renal system management: during the first 24-48 hours ECMO patients experience an oliguric phase as the ECMO circuit triggers an acute inflammatory reaction. If oliguria persists for 48-72 hours, diuretics are often required.
- CNS management: complications related to hypoxia and acidosis should be watched for.
- Infection control: strict aseptic precautions are required
- Hematologic considerations: to optimize oxygen delivery, the patient’s hemoglobin should be maintained at higher than 8 g/dL.
- Fluids, Electrolytes and Nutrition: patients on ECMO require close monitoring of fluids and electrolytes (potassium, magnesium, phosphorus and ionized calcium).
Following are the indications for weaning off of ECMO-
- For patients with respiratory failure, improvements in radiographic findings, pulmonary compliance and arterial oxyHb concentration.
- With cardiac failure, improved aortic pulsatility correlating with improved left ventricular output.
One or more trials of taking patient off ECMO should be performed before discontinuing ECMO permanently.
This new technology has proved itself to be a breakthrough in life support and this is confirmed by various trials. CESAR study for acute respiratory failure demonstrates that referral to an ECMO center significantly improves recovery and survival from severe ARDS. ECMO performed for cardiac arrest was associated with increased survival with minimal neurologic impairment compared to conventional cardiopulmonary resuscitation.
Veno-venous extracorporeal membrane oxygenation (V-V ECMO) may serve as life-saving rescue therapy for refractory respiratory failure in the setting of acute respiratory compromise such as that induced by SARS-CoV-2.
The outcomes of ECMO are better when compared to ventilatory support or any other life saving technology, as it has low mortality rates with better survival rates and majority patients are able to meet primary endpoints. Despite various challenges, ECMO is a vital lifesaving modality in patients with respiratory and cardiorespiratory failure. The success of such technologies give us a hope for an advanced future in the scope of medicine.