Perioperative management of adult surgical patients on extracorporeal membrane oxygenation support.

XTRACORPOREAL MECHANICAL support devices are used as an adjunct in the management of critically ill patients who are refractory to more conventional modes of therapy. Extracorporeal membrane oxygenation (ECMO) is one such device that has been used mainly in the management of patients in cardiogenic shock or respiratory failure who failed therapy on maximal ventilator settings and maximal pharmacologic support. ECMO has the advantage of being rapidly deployable, both at the bedside and in the operating room, and can be initiated without the need for general anesthesia. ECMO has been used as a bridging device to recovery or to more definitive therapy. In patients who are awaiting lung transplantation, ECMO has been used as a bridge to transplant when decompensation occurs and also as an adjunct in physical rehabilitation before transplant. The science and instrumentation of ECMO are direct outgrowths of the development of cardiopulmonary bypass (CPB) technology that reached its full potential in support of cardiac surgery in the latter half of the 20th century. This is a fascinating history in itself and has been reviewed thoughtfully at key points by physician-scientists directly involved in the process. 1-3 Over the last decade, the design and reliability of components of the ECMO circuit have improved markedly from earlier iterations, and clinical teams have gained experience with a multidisciplinary approach to the management of patients on ECMO. These advancements have led to more prolonged and widespread use of ECMO as an alternative for support in patients with otherwise nonsurvivable respiratory or cardiopulmonary failure. Outcomes also have improved from what is reported in the older medical literature. With the increase in the use of ECMO, anesthesiologists have become more involved in the perioperative management of these critically ill patients, and an understanding of the physiologic changes that occur in patients on ECMO is essential for perioperative management. In addition, a number of issues remain controversial, mainly regarding risk/benefit differentials in pediatric versus older age groups, end-stage versus acute disease, and the timing and duration of therapy. This review addresses the practical clinical problems during the perioperative management of adult patients on ECMO. TYPES OF ECMO Three major configurations of ECMO are available. Venovenous (VV) ECMO is used in the management of patients with refractory pulmonary failure and stable cardiovascular status. Venoarterial (VA) ECMO is used in patients with refractory cardiogenic shock or cardiorespiratory failure. The third configuration, arteriovenous (AV) ECMO, also known as the “artificial lung,” can be used in patients with acute lung injury presenting with stable cardiovascular status. In this review, the term “inflow cannula” refers to the cannula that carries blood from the patient into the ECMO system, and “outflow cannula” refers to the cannula that carries oxygenated blood from the ECMO system back to the patient. In VV ECMO, the inflow and outflow ECMO cannulae run in and out of the venous system in the patient. In VA ECMO, the inflow cannula is from the patient’s venous system, but the outflow cannula runs into the arterial system. Conversely, in AV ECMO, the inflow cannula is from the patient’s arterial system with the outflow cannula from the oxygenator running into the patient’s venous system. AV ECMO differs from VA and VV ECMO in that the AV ECMO circuit does not incorporate a pump to maintain blood flow in the circuit. Blood flow in this type of circuit is a function of systemic blood pressure, cardiovascular stability, the resistance of the membrane oxygenator, the size and length of the conducting circuit, and blood viscosity. Adequate blood pressure and cardiovascular stability are required to maintain blood flow in this form of circuit. Commonly used inflow cannulation sites during VV and VA ECMO are the femoral vein, the inferior vena cava, the superior vena cava, and the right atrium. Outflow during VV ECMO may be into any of these sites. In patients on VA ECMO, inflow usually is into the femoral artery, axillary artery, ascending aorta, or the pulmonary artery. Inflow during AV ECMO may