Extracorporeal membrane oxygenation for acute cardiopulmonary failure

History

As with many innovative and unconventional therapies, ECMO has had a challenging history and still continues to face widespread skepticism of its clinical utility, particularly in the context of its invasiveness, cost, and tremendous demand for hospital resources. In the backdrop of the increasing use of cardiopulmonary bypass in the operating room for cardiac surgical procedures in the 1960s, there was an initial enthusiasm for applying similar extracorporeal technologies outside of the operating room for prolonged applications following acute cardiopulmonary injury. The typical patient considered for ECMO was the cardiac surgical patient who could not be successfully weaned from cardiopulmonary bypass in the operating room and was felt to require longer support in the intensive care unit pending cardiopulmonary recovery. Other early applications included patients with severe acute cardiac or respiratory failure of various etiologies in which, only after all other salvage therapies were considered, was ECMO attempted. Unfortunately, as predicted, early applications of ECMO in these critically ill patients resulted in poor outcomes and only limited reports of recovery and survival. With growing enthusiasm in the context of isolated successful cases, especially in neonates with correctable congenital defects, a trial was sponsored by the United States National Institutes of Health in the late 1970s. Unfortunately, preliminary results from this trial were catastrophic with survival rates of less than 10%, which resulted in abandoning the trial. The reasons for the poor outcomes were clearly multifactorial and were attributed to poor or limited experiences in managing these complex patients at most of the centers, concern for difficulties with patient selection and lack of established management guidelines and protocols, technological deficiencies of the ECMO circuit and oxygenators that were available at the time, and an overall concern that such advanced therapies were not quite scientifically mature enough and developed for widespread clinical application. In general, it became apparent that the cardiopulmonary bypass technologies that were being utilized for short-term physiologic support in the operating room were not suitable for longer-term support of the critically ill patient in the intensive care unit. The inflammatory response of blood interacting with the primitive and evolving extracorporeal circuits were yet to be understood in a manner that would result in the desired goal of using extracorporeal support to facilitate cardiopulmonary recovery and ultimately lead to improved patient survival.

Fortunately, many of the early setbacks only fostered a greater sense of enthusiasm to better understand the complex biomechanical interactions of ECMO. In the 1980s and 1990s, mainly under the leadership of Dr. Robert Bartlett at the University of Michigan who established the first extracorporeal life support service and worked tirelessly to better understand and advance the technology, ECMO started to gain momentum as being a viable therapy. His landmark publication published in the Journal of the American Medical Association in 2000, which outlined the results of over 250 adult and pediatric patients supported with ECMO for cardiac and pulmonary indications, still serves as the foundation and benchmark that programs strive for today. In addition, the establishment of the Extracorporeal Life Support Organization (ELSO) at the university of Michigan facilitated the development of an international registry of the clinical data related to ECMO cases. Centers worldwide could better understand the potential role for this therapy, including benchmarking their results against international outcomes and being part of a growing community dedicated to establishing standards, guidelines, and protocols, which facilitated the scientific advances that contributed to a much broader international application. With growing international experience, centers of excellence rapidly emerged that helped better our understanding not only regarding the technical aspects of the management of the ECMO patient but, just as importantly, of the critical components necessary for establishing and maintaining a program at the institutional level.

Components of an ECMO team

ECMO is a very complex and resource-intensive therapy, and, as such, it requires tight integration of a multidisciplinary team combined with strong administrative and institutional leadership support. As with many therapies that are aimed toward critically ill patients, it requires an understanding that, even in the best of circumstances, outcomes might be less than ideal and reimbursement is often a challenge.

While there are a variety of different models of care, it is not uncommon for a variety of different medical and surgical disciplines to be involved in the management of the ECMO patient. As isolated respiratory failure is typically in the domain of the pulmonary critical care team, regardless of whether those individuals are trained under a medical, surgical, or anesthesia model, they tend to be the first to identify potential candidates. Likewise, as initiation of ECMO is a technical task that requires placement of large-bore cannulas and close coordination with perfusionists or “ECMO specialists” who prepare (i.e., prime) and manage the ECMO circuit, it is not uncommon for cardiothoracic surgeons to take the lead in this role. Nevertheless, with appropriate training, experience, and institutional credentialing, cannulation can be performed by a variety of disciplines, ranging from cardiothoracic surgeons, vascular surgeons, trauma and or critical care physicians, interventional cardiologist, emergency room physicians, pulmonary critical care doctors, and even physician assistants or advanced practice providers. Regardless of the specific backgrounds of the individuals specifically performing the cannulation, such individuals must be comfortable and proficient in basic wire handling, cannulation skills and the management of cannulas, access site problems, initiation of extracorporeal support, and the technical aspects of decannulation and potential vascular repair. Few data exist regarding what type of provider is best suited for this role, and national or professional society guidelines have yet to be established other than recommending some degree of technical proficiency as outlined previously. Therefore, it is imperative that each institution develop its own guidelines and competencies to ensure safe and appropriate credentialing.

Another key component of developing an ECMO team is identifying those providers with expertise and interest in the management of these critically ill and complex patients. Bedside critical care nursing requires specialized skills, as these patients often require other forms of therapy that push the limits of many individuals’ background and training. Often programs will designate ECMO specialists who are solely responsible for monitoring and maintaining the extracorporeal circuit. Various models exist and depend upon the resources and skill sets available at each program. Because of the similarities of the ECMO circuit to the cardiopulmonary bypass technologies that are used in the operating room for cardiac surgery, it is not uncommon for perfusionists to take a leadership role in the management of the ECMO pump. However, staffing limitations may challenge the ability to maintain a robust cardiac surgery program if perfusionists are also called upon to be at the bedside of an ECMO patient around the clock. Therefore, other models can have critical care nursing or respiratory therapists with advanced ECMO training serving in this bedside role. Hybrid models can also be developed in which oversight is provided by the perfusionists, with bedside management and circuit supervision being provided by other disciplines.

Because of the complexity of ECMO patients, it is also not unusual to identify physician champions in other specialties who understand the nuances of these patients and some of the unique challenges that they experience. Having access to neurology critical care, infectious disease, advanced heart failure, and nephrology are important, as they are often called upon to lend their expertise to the ECMO patient. Even in the best of circumstances, poor outcomes are not unusual and early involvement of a palliative care specialist can facilitate what might be challenging social and family circumstances. It has clearly been established that the outcomes of ECMO patients are improved with early and timely referral to centers with broader specialization in acute cardiopulmonary failure. Additionally, an ECMO team requires close collaboration with other hospital disciplines, such as pharmacy, the blood bank, respiratory therapy, and social work.

While the financial and reimbursement issues that surround ECMO are dynamic and vary considerably based upon indications, payor status, and geography, suffice it to say that ECMO is expensive and reimbursement remains a challenge. As such, close collaboration with administrative leaders to better track and understand program finances in the setting of broader goals and expectations from the very beginning is of the utmost importance—especially since compensation and reimbursement for ECMO is constantly in flux. Likewise, the establishment of a working group that meets periodically to review outcomes, opportunities for program improvement, and the development of guidelines and protocols is also necessary for program success.

Patient selection

As with any therapy, optimal outcomes are often grounded in initial patient selection. Patient selection in ECMO remains a challenge, as there is a delicate balance between offering highly invasive therapy to patients that might have indications for ECMO but could potentially be more appropriately treated medically as they are not sick enough for such an aggressive intervention versus those patients that have already deteriorated to irreversible end-organ damage or have experienced major life-threatening complications (e.g., anoxic brain injury) that may inherently preclude a good outcome. Nevertheless, it is a difficult balance. Existing guidelines typically focus on the severity of isolated lung injury, degree of cardiac failure, or specific circumstances, such as acute cardiopulmonary arrest in which early initiation of ECMO therapy has been associated with better outcomes. As with many invasive therapies, initiation of support might limit further disease-specific injury, barotrauma, or ischemic complications from impaired oxygen delivery. It is also important to recognize that ECMO is fundamentally a supportive tool to support the acutely failing lungs and/or heart to allow for optimal therapies for recovery. ECMO does not treat the primary problem, but it may allow for effective definitive treatment and recovery. Because longer durations of support on ECMO are correlated with worse complications and outcomes, it becomes imperative that early and timely recognition and management of the precipitating problem(s) is crucial. While ECMO may serve as a temporary bridge to more advanced end-organ replacement therapies such as transplant or ventricular assist devices, the expectation is appropriate and timely management of the physiologic insult precipitating the need for ECMO. ECMO is not a substitute for targeted antibiotics for advanced pneumonias and appropriate therapies for other pulmonary insults, uncorrected structural or coronary cardiac problems, or secondary causes of respiratory failure such as pancreatitis, undrained intra-abdominal abscesses, or other unusual systemic problems. Nevertheless, ECMO can serve as a means of stabilizing a patient both immediately and during the recovery phase, while primary causes of cardiopulmonary injury are identified and definitively treated.

To facilitate patient selection, various scoring systems have been developed over the years to help identify and risk stratify patients based upon whether the primary indication for ECMO is for respiratory or cardiac failure. Such systems, including the Respiratory ECMO Survival Prediction (RESP) score for respiratory failure and Survival After Veno-Arterial ECMO (SAVE) score for cardiac failure may help identify patients who are either optimal candidates or whose predicted outcome may be so poor that initiating therapy may be viewed as potentially futile in the context of institutional programmatic risk tolerance and experience. Nevertheless, each clinical case must be thoroughly evaluated by a multidisciplinary team before therapy is either initiated or potentially withheld, because while risk scores may help identify patients, it would be inappropriate to exclude any patient who may be potentially salvageable based upon their predicted survival alone.

Indications

For isolated respiratory failure, even in the setting of evolving cardiac and end-organ dysfunction, the basic principles behind the indications for ECMO are focused on the severity of impaired oxygenation, ventilation, and acid-base abnormalities in the context of maximal optimization of mechanical ventilatory support in patients who have often failed short trials of other established salvage therapies. While specific indications may vary, criteria based upon ELSO guidelines combined with an assessment of the degree of respiratory failure (i.e., “The Murray Score”) and those used for the CESAR and ELIOA trials often provide a good foundation ( Tables 1 and 2 ).