Original Article
Review of ECMO (Extra Corporeal Membrane Oxygenation) Support in Critically Ill Adult Patients

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Mechanical circulatory support has evolved markedly over recent years. ECMO (extra corporeal membrane oxygenation) is instituted for the management of life threatening pulmonary or cardiac failure (or both), when no other form of treatment has been or is likely to be successful. Most commonly, it is instituted in an emergency or urgent situation after failure of other treatment modalities. It is used as temporary support, usually awaiting recovery of organs, or can be used as a bridge to a more permanent device or cardiac transplantation.

ECMO can be deployed in a veno-arterial configuration (either peripheral or central cannulation) for the treatment of cardiogenic shock. This is usually seen post-cardiotomy, post-heart transplant and in severe cardiac failure due to almost any other cause (e.g. cardiomyopathy, myocarditis, acute coronary syndrome with cardiogenic shock). Veno-venous ECMO is used for respiratory failure and usually involves peripheral cannulation using the femoral veins ± internal jugular vein if required. The indications for veno-venous ECMO are respiratory failure, most commonly due to adult respiratory distress syndrome (ARDS), pneumonia, trauma or primary graft failure following lung transplantation. ECMO is also used for neonatal and paediatric respiratory support. Its use in premature neonates is the mainstay of treatment for immature lungs and insufficient surfactant.

In this review, the technical aspects of ECMO cannulation, maintenance and weaning are outlined. Complication rates and outcomes are reviewed and our experience at The Epworth Hospital is summarized.

Introduction

Mechanical circulatory support has evolved markedly over recent years. In particular, the use of ECMO (extra corporeal membrane oxygenation) has become more reliable with improving equipment, and increased experience, which is reflected in improving results. ECMO is instituted for the management of life threatening pulmonary or cardiac failure (or both), when no other form of treatment has been or is likely to be successful. It is used as temporary support, usually awaiting recovery of organs.

ECMO is essentially a modification of the cardiopulmonary bypass circuit which is used routinely in cardiac surgery. Blood is removed from the venous system either peripherally via cannulation of a femoral vein or centrally via cannulation of the right atrium, oxygenated, has its carbon dioxide extracted and then returned back to the body, either peripherally via a femoral artery or centrally via the ascending aorta.

Although ECMO remains a short-term support device, the use of such a circuit for extended periods (days to weeks) has required some modifications. Essentially the circuit is smaller than a standard cardiopulmonary bypass circuit, transportable and closed to the atmosphere. The cannulae are also specifically designed for ECMO. The duration of support with ECMO has greatly increased with improving oxygenators and medical management, and whereas support was previously in the order of days, patients can now be maintained on ECMO for weeks. In most patients the duration of support required is approximately 1 week. Most commonly, it is instituted in an emergency or urgent situation after failure of other treatment modalities.

Section snippets

Indications for ECMO

In terms of cardiac failure, the most common indications for ECMO are post-cardiotomy (that is unable to get the patient off cardiopulmonary bypass following cardiac surgery) [1], post-heart transplant (usually due to primary graft failure) [2] and severe cardiac failure due to almost any other cause (e.g. decompensated cardiomyopathy, myocarditis, acute coronary syndrome with cardiogenic shock, profound cardiac depression due to drug overdose or sepsis). In terms of respiratory failure, the

Configurations for ECMO

ECMO can be inserted in a veno-venous (VV) configuration which provides oxygenation (and thus is used for respiratory failure not responding to mechanical ventilation), or can be used in a veno-arterial (VA) configuration (providing both respiratory and cardiac support). VA-ECMO can be instituted peripherally or centrally.

The term VV ECMO refers to blood being drained from the venous system and returned to the venous system. This mode only provides respiratory support and is achieved by

Maintenance and Weaning of ECMO

The basic function of VA-ECMO in supplying mechanical circulatory support is to drain blood from the venous circulation, oxygenate it and then return it to the arterial circulation at physiologic perfusion pressures. Although ECMO does a very good job of unloading the right ventricle, it does not do as good a job of unloading the left ventricle, even though left ventricular preload is significantly reduced by the diminished return from the lungs. For this reason, attempts to improve left

Complications of ECMO

Not surprisingly, ECMO does have an attendant myriad of possible complications. The most common of these is bleeding, which can rapidly become life threatening and appears to be out of proportion to the degree of coagulopathy and patient platelet count. For this reason, attempts should be made to avoid or minimise all non-urgent invasive procedures. Operative interventions in patients on ECMO can be particularly hazardous because of the risk of bleeding and should be avoided if at all possible

Outcomes of ECMO

The results of ECMO support are fairly consistently related to the indication for institution of such therapy. In one of the largest published series to date, 1000 patients supported on ECMO at the University of Michigan were reviewed [19]. VV-ECMO for respiratory failure provided survival to discharge in 88% of 586 cases of respiratory failure in neonates, 70% for 132 cases of respiratory failure in children and 56% for 146 cases of respiratory failure in adults. Their experience with cardiac

Results at the Epworth

Since 1998, 17 patients have been treated with ECMO at The Epworth. The details and outcomes of these patients are outlined in Table 1. As can be seen in the table, all patients received VA-ECMO. One patient received mechanical support in an RVAD (right ventricular assist device) configuration for right ventricular failure following a pulmonary embolectomy (patient 9). All of the patients had cardiac failure except for one patient with respiratory failure who also developed cardiac instability.

Conclusion

ECMO is a very useful treatment modality for acute severe cardiac or respiratory decompensation. Although generally restricted to quaternary referral or specialist centres, internationally comparable results can be achieved in the private sector where cardiothoracic and intensive care services exist.

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