Extracorporeal membrane oxygenation (ECMO) is an adaptation of the conventional cardiopulmonary bypass system for use as prolonged pulmonary and cardiopulmonary support. ECMO is generally instituted at specialized centers as a last resort for patients with respiratory or cardiac failure unresponsive to conventional therapies. The term ECMO is considered a broad ranging term for the range of methods for extracorporeal blood oxygenation and carbon dioxide removal. Other similar terms in current use include those listed in Table 61-1. This is considered a closed circuit system, which differentiates it from cardiopulmonary bypass (CPB) circuits, in that there is no blood reservoir and no arterial filter.
TABLE 61-1Artificial Cardiac or Pulmonary Support Acronyms ||Download (.pdf) TABLE 61-1 Artificial Cardiac or Pulmonary Support Acronyms
|Extracorporeal membrane oxygenation
|Extracorporeal life support
|Extracorporeal carbon dioxide removal
|Partial extracorporeal carbon dioxide removal
|Arteriovenous carbon dioxide removal
|Extracorporeal lung assist
The early 1970s brought the introduction of ECMO as a treatment modality for acute respiratory distress syndrome (ARDS). Early advances in the design included improvements in the membrane lung, the access catheters, and bladder systems. Additionally, the concept of anticoagulation titration of the system with heparin reduced bleeding complications. The year 1976 brought the first neonatal survivor of ECMO by Dr Robert H. Bartlett for the treatment of a chemical pneumonitis secondary to meconium aspiration. Further research and monitoring of the state of ECMO was advanced in the 1980s by the introduction of multiple registries and finally by the charter of the Extracorporeal Life Support Organization (ELSO), which houses the largest registered case series and promotes multi-institutional research.
ECMO use is generally limited to those neonatal, pediatric, and adult patients with failing respiratory and/or cardiac systems who do not respond to maximal medical therapy or those patients with inability to wean from cardiopulmonary bypass. The institution of ECMO is often considered a last resort and is predicated on the fact that there is no underlying lung damage caused by mechanical ventilation or that the cardiac insult is reversible. Mortality is increased with increasing lung injury patterns whether related to volutrauma, barotrauma, or oxygen toxicity. Several indices of refractory hypoxemia are used to qualify patients for ECMO, all of these estimating a predicted mortality of > 80% without the treatment. These indices are listed in Table 61-2 and are generally gained from looking at retrospective data, and thus should be assessed in concert with other patient factors. The primary goals gained from an ECMO run are to remove CO2 and oxygenate the lung; improve oxygen delivery to tissues; provide lung rest and/or cardiac offloading; and to allow the normal physiologic metabolic environment to function at tissue levels.
TABLE 61-2ECMO Indication Indices for > 80% Predicted Mortality