Extracorporeal Membrane Oxygenation in Cardiogenic shock – A Review

INTRODUCTION

There are various modalities to manage cardiogenic shock. Mechanical support to heart and lung is still considered to be mainstay of the treatment. When there is evidence of inadequate tissue oxygen delivery despite intra-aortic balloon counterpulsation, invasive ventilation, and inotropes, full circulatory support is found to have a significant impact on the patient outcome. Extracorporeal membrane oxygenation (ECMO) can subsume the function of both heart and lungs.

ECMO was first used successfully for life-threatening respiratory failure in an adult in 1971^[1] and in a neonate with meconium aspiration in 1975.^[2] ECMO has been used in adult in cardiogenic shock due to myocardial infarction, myocardiopathy, myocarditis, or inability to come off cardiopulmonary bypass after cardiac surgery^[3] ECMO can provide partial or total support, but it is temporary. It is not a definitive treatment but a life support system that allows time for evaluation, diagnosis, and treatment of the condition that causes heart failure [Figure 1].

Close

Figure 1:

Cardiogenic shock-sequence of events.

Export to PPT

This modality requires a high level of care and traditionally has remained underutilized. ECMO team should consider the patient condition, prognosis of the disease, and weaning strategies before embarking on the task of putting an ECMO as it has lot of implications.

CARDIOGENIC SHOCK AND ECMO

ECMO controls gas exchange and perfusion, stabilizes the patient physiologically, decreases the risk of on-going iatrogenic injury, and allows ample time for diagnosis, treatment, and recovery from primary injury or disease of the heart.

It can be broadly categorized into two types:

1. Venovenous ECMO (VV-ECMO)

2. Venoarterial ECMO (VA-ECMO).

VV-ECMO is appropriate only for respiratory failure.

VA-ECMO is used for cardiogenic shock and is currently the fastest growing indication for ECMO worldwide.^[4]

In ECMO, the right atrial venous blood is drained through a large cannula, pumped through an artificial lung (oxygenator), and back into the patient either into the aorta (venoarterial and VA mode) or into right atrium (venovenous, VV mode). Venoarterial access puts the oxygenator in parallel with native lung and substitutes for both heart and lung functions. Venovenous access puts at artificial lung in series with the native lung.

In adults, blood is usually removed through a femoral vein and returned through a femoral artery (peripheral ECMO). Occasionally, other cannulation strategies, such as directly cannulating the right atrium and aorta (central ECMO), may be employed. For total support, the blood flow required is 60–100 mL/kg/min (equal to cardiac output) [Figure 2]. The target MVO₂ is 60–80% and avoid full flows as far as possible [Tables 1 and 2].

Close

Figure 2:

The Downfall Spiral.

Export to PPT

Peripheral ECMO is less invasive, is easier to place, and can be placed percutaneously by surgeons or intensivists. It can be initiated quickly, making it more appropriate in emergencies. However, the cardiac output of the failing heart competes with retrograde ECMO flow from the femoral aortic cannula, producing admixing in the thoracic aorta and an increase in left ventricular wall tension. If there is concomitant respiratory failure, this can result in the delivery of inadequately oxygenated blood to the coronary and cerebral circulations and hinder recovery.^[5]

Central ECMO is not associated with this problem but is slower to initiate and may have a higher complication rate with bleeding and infection. It is usually confined to the support of patients after surgical revascularization and is initiated often in the operating room.

Cardiopulmonary resuscitation along with ECMO (E-CPR) is yet another emerging use of VA-ECMO in restoring the circulation during cardiac arrest when used in conjunction with advanced life support strategies. Data show improved in hospital survival with fairly good neurological outcomes for up to 2 years when VA-ECMO is used along with CPR in highly selected patients.^[6] As per a systematic review and meta-analysis done by Wilson-Smith et al. the survival rates in VA-ECMO for refractory cariogenic shock at 1–5 years were 36.7%, 33.8%, 31.7%, and 29.9%, respectively.^[7]

Peripheral VA-ECMO is adequate for most forms of cardiogenic shock, but frequent echocardiography is necessary to monitor for progressive ventricular dilatation and, increased left ventricular end diastolic pressure which can put strain on the left venticle, leading to pulmonary edema and increase in myocardial oxygen consumption. If this develops, the left atrium can be vented either by changing the ECMO circuit configuration or by performing a percutaneous atrial septostomy. Use of LEFT ventricular assist devices, Impella, also has proven to be an effective strategy to unload such ventricle.^[8-11]

The clinical and echocardiographic contraindications are as mentioned in [Tables 3 and 4]. In septic patient, initiation of ECMO is controversial even in the presence of cardiogenic shock due to presence of conduit bacteremia, inflammation, and bleeding diathesis in septic patients with disseminated intravascular coagulopathy. However, advancement in extracorporeal technology and clinical practice might minimize these complications and that potential benefits may outweigh the risks. A prospective trial found that preexisting sepsis is not a contraindication for ECMO; however, in septic patient, VA ECMO should be used with caution [Tables 5 and 6].^[12]

European Society of Cardiology guidelines for the diagnosis and treatment of acute and chronic heart failure recommend short-term mechanical circulatory support (as a “bridge to recovery”) in patients remaining severely hypoperfused despite inotropic therapy and with a potentially reversible cause (e.g., viral myocarditis) or a potentially surgically correctible cause (acute inter ventricular septal rupture).^[13]

COMPLICATIONS

CONCLUSION

ECMO has proven to be an effective therapeutic modality in managing cardiovascular collapse as a bridge to recovery or more definitive treatment options. Early initiation is the key to a successful outcome in cardiogenic shock. A well-coordinated ECMO team is the core factor of management of ECMO. As with any technology used in critically ill patients, end of life discussion and target of therapy and prognosis are essential. Daily update to the family members of the patient with regard to the patient’s condition is crucial due to the financial burden associated with it in the modern health-care scenario. Palliative care consultations when available also should be initiated early.