An Overview of Extracorporeal Membrane Oxygenation: The Principles of ECMO for Adults
Extracorporeal membrane oxygenation (ECMO) is now several decades into use, yet is still a somewhat controversial procedure in adults despite being a well-established practice for infants and some older children (Mielck & Quintel 2005). New technologies have greatly improved the process and made it a standard part of severe cardiopulmonary derangement due to disease or injury, but only after the exhaustion of other interventions (Mielck & Quintel 2005; Yang 2011). There are different forms of ECMO with different direct impacts and specific variations from techniques such as cardiopulmonary bypass, but in the most common ECMO types blood still passes through the lungs (and in some types part of the heart) after passing through an external pump and oxygenator, while in cardiopulmonary bypass the heart and lungs are entirely bypassed (Yang 2011). Acute respiratory distress syndrome, alveolar capillary dysplasia, and many other causes of severe pulmonary failure that is thought to be reversible warrant the use of ECMO (Schuerer et al. 2008; Yang 2011).
Certain congenital defects and other conditions that render the cardiopulmonary irreversible are grounds for exclusion of an ECMO intervention, otherwise the procedure is deemed appropriate as a final attempt intervention and is routinely used on infants and older adults (Schuerer et al. 2008; Yang 2011). In typical ECMOs, blood is taken from the venous system and pushed through an extracorporeal gas exchanger that mimics the lungs, removing carbon dioxide and adding oxygen to the blood, after which the blood is returned wither to the right side of the heart or directly into the arterial system (Yang 2011). Silicone membrane gas exchangers are being replaced by hollow fiber oxygenators, which are more efficient, and other technological changes including centrifugal pumps, inline pumps, and improved carbon-dioxide removal methods that decrease ventilator resource needs are all improving the technique (Yang 2011; Mielck & Quintel 2005). These newer pumps, especially centrifugal pumps, are more appropriate for adult ECMO procedures (Yang 2011).
VA (venoarterial) ECMO, which places the blood directly into the arterial system with the pressure of the external pump behind it, is indicated in cases where the heart itself if impaired and/or blood pressure is dangerously low, while VV (venovenous) ECMO allows the heart to function normally (Yang 2011). It is the inclusion or the bypassing of the heart and/or lungs that constitutes the major difference between VA and VV ECMO. Cannulation typically occurs in the right internal jugular vein and the femoral vein, with two cannulas often required in adult ECMO to achieve necessary levels of venous drainage; anticoagulation methodologies are standard as for most surgical procedures (Yang 2011). ECMO requires constant monitoring and assessment in order to maintain proper oxygen saturation levels, blood pressure, and circulatory activity (Schuerer et al. 2008; Mielck & Quintel 2005).
Institutional experience and multidisciplinary focus are both of extreme importance in determining patient outcome following ECMO, as technological innovations and the high-risk of the procedure make an ongoing knowledge base and expertise level a major determiner of outcome (Schuerer et al. 2008). As serious complications including infection, instability of oxygenation, thrombosis, and volume requirements can all occur, patients should be treated in a manner comparable to an acute stroke response — increased risk for disrupted blood flow is a definite result of an ECMO procedure (Yang 2011). ECMO can only last a few days, and decreased fluid requirements and increased pulmonary function are both indicators that the weaning process should begin (Yang 2011). Mortality rates for ECMO vary significantly depending on the specific diagnosis, but range from fifty to seventy percent; though these numbers are high, it should be stressed that as an intervention of last resort ECM is often use din cases that ultimately prove incurable, which contributes to this mortality rate (Yang 2011). Employing ECMO interventions can also be cost effective in modern institutions as such procedures can be less costly than other external oxygenation equipment and can reduce recovery times, as well (Mielck & Quintel 2005).
Healthcare administrators must find a balance between ensuring aggressive treatment, which can include ECMO interventions, and ensuring that treatments do not overtake symptoms in harm caused to the patient. Implications for perioperative nursing are quite extensive, as these procedures can be used during times of surgically necessary or contributed cardiopulmonary distress or loss of function, and as the procedure itself constitutes an initial (and in some views, an ongoing) surgery, perioperative nursing procedures are an essential part of the support and successful carrying out of an ECMO intervention (Mielck & Quintel 2005; Schuerer et al. 2008). Qulaity improvement in ECMO support trhough the identification of specific support strategies has been a major cause of improvement to the procedure (Schuerer et al. 2008).
Mielck, F. & Quintel, M. (2005). Extracorporeal membrane oxygenation. Current Opinion n Critical Care 11(1): 87-93.
Schuerer, D., Kolovos, N., Boyd, K. & Coopersmith, C. (2008). Extracorporeal Membrane Oxygenation Current Clinical Practice, Coding, and Reimbursement. Chest 134(1): 179-84.
Yang, E. (2011). Extracorporeal membrane oxygenation. In Fundamentals of Pediatric Surgery, P. Mattei, editor. New York: Springer.