Extracorporeal Cardiopulmonary Support in Acute High-risk Pulmonary Embolism

Still Waiting for Solid Evidence

Nazzareno Galiè; Massimiliano Palazzini; Alessandra Manes

Disclosures

Eur Heart J. 2018;39(47):4205-4207. 

In This Article

Extracorporeal Membrane Oxygenation

ECMO is a rapidly growing procedure for both respiratory and cardiac failure in adult patients.[6] Relevant advances in technology, have made ECMO devices easier to implement, safer, and more effective.[7] However, the increased use of ECMO and the expanded availability of ECMO-related literature have still not provided sufficient evidence in different aspects of this procedure including indications, appropriateness in the individual patients, thresholds for initiation, type of ECMO to implement, duration, and weaning procedures.

ECMO is a circuit that oxygenates and removes carbon dioxide from blood through an extracorporeal gas exchange device constituted by a semi-permeable membrane that separates a blood compartment from a gas compartment, allowing only gas molecules to diffuse between compartments. Special cannulas for blood drainage and reinfusion are positioned in central vessels. An external pump provides the dynamic force to drain the deoxygenated blood, to pass it through the membrane oxygenator, and to reinfuse it back to the patient. According to the central vessels engaged by the drainage and reinfusion cannulas, ECMO is defined as veno-venous or veno-arterial: veno-venous ECMO provides a gas exchange function[8] only, while veno-arterial ECMO provides both gas exchange and circulatory support (Take home figure).[9]

Take Home Figure.

Schematic representation of veno-arterial extracorporeal membrane oxygenation (ECMO): venous blood is drained from a cannula inserted through the femoral vein into the inferior vena cava and oxygenated blood is reinfused by a cannula inserted through the femoral artery into the thoracic descending aorta. According with the level of cardiac function, the location of the border between antegrade blood flow and retrograde blood flow from the aortic cannula will vary, and the reinfused oxygenated blood may not reach the cerebral and coronary vascular beds.

Veno-venous ECMO is mainly indicated in cases of severe respiratory failure and can be configured with two distinct access points or using single cannulas with two lumens inserted typically into an internal jugular vein which can achieve both drainage and reinfusion.[7] Indications of veno-venous ECMO for severe respiratory failure, when gas exchange is refractory to conventional ventilation, include acute respiratory distress syndrome, acute hypercapnic respiratory failure, bridge to lung transplantation, and primary graft dysfunction post-lung transplantation.[7]

Veno-arterial ECMO is usually indicated in cases with severe impairment of cardiac function, and the preferred approach includes femoral venous drainage and femoral arterial reinfusion. However, this strategy may increase the left ventricular afterload and may limit the amount of well oxygenated blood reaching the aortic arch and perfusing the coronary and cerebral circulations. These drawbacks are particularly relevant in cases of concomitant impaired lung gas exchange and delivery of deoxygenated blood to the aortic arch. Arterial reinfusion sites closer to the aortic arch (e.g. the subclavian arteries) may limit this problem.[10] Indications for veno-arterial ECMO in cardiopulmonary diseases include the following conditions (Take home figure): myocardial infarction-associated cardiogenic shock, myocarditis-associated cardiogenic shock, post-cardiotomy cardiogenic shock, bridge to ventricular assist devices (VAD) implantation, prevention of acute right ventricular failure after left VAD implantation, bridge to heart transplantation, primary graft failure after heart transplantation, pulmonary hypertension and acute or decompensated right heart failure, high-risk acute pulmonary embolism, extracorporeal cardiopulmonary resuscitation, and sepsis-associated cardiac failure.[9]

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