ethics of randomised controlled trials in the face of such impressive changes in outcome. The impressive outcomes in neonates and children, primed the larger critical care, cardiac and cardiac surgery community to take notice; and over the past four to five years, we have a seen a proliferation in ECMO use. Two recent events have provided the largest driving force – the H1N1 pandemic in 2009-2010 and the concomitant reporting of a trial where adult patients with ARDS were randomised to conventional ventilator therapy or transfer to an ECMO centre. This trial, also called the “CESAR” trial, found that ARDS patients referred to an ECMO centre were not only more likely to survive, but also had less disability following their critical illness (Figure 3). At about the same time, the Australian and New Zealand Intensive Care Society (ANZICS) published their ECMO experience in H1N1 patients. They reported a 71% survival in patients who were failing conventional mechanical ventilation after they were placed on ECMO. Similarly, an elegant study in England reported that H1N1 patients with severe ARDS were more than twice as likely to survive their critical illness if they received ECMO. The reason for this survival benefit in patients with refractory respiratory failure is the opportunity VV-ECMO provides for complete lung rest. It is well-recognised that mechanical ventilation can perpetuate the underlying lung injury and damage that resulted in the critical illness in the first place. This has been described as ventilator induced lung injury. Patients on VV-ECMO are no longer dependent on their lungs for gas exchange, allowing use of “rest” ventilator settings. Indeed, in some centres, patients are taken off the ventilator altogether once they are stabilised on ECMO.
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Unfortunately, the equipment necessary to allow ECMO patients to be managed off the ventilator is currently unavailable in Singapore, but NUHCS is primed to take this next leap once it becomes available. At NUHCS, we supported several patients with VV-ECMO during the H1N1 epidemic. In addition, we have supported many patients with cardiogenic shock using VA-ECMO. Cardiogenic shock patients fall into two groups – those who need support after complex open heart surgery, including children after correction of congenital heart abnormalities, and those who have had a large myocardial infarction. The role of VA-ECMO in these patients is to maintain organ perfusion with oxygenated blood and off-load the heart while it recovers from major surgery or a massive myocardial infarction. VA-ECMO allows the heart to “rest” because these patients would otherwise need high levels of inotropes and vasopressors if they were managed without ECMO. Paradoxically, such medications increase oxygen consumption in the struggling heart, perpetuating cardiac ischaemia. The majority of patients experience a recovery in cardiac function within a few hours or days of commencing VA-ECMO, allowing discontinuation of ECMO as recovery ensues. However, some patients will experience a delayed recovery requiring placement of a more permanent cardiac assist device, once they are stabilised on ECMO. In some patients, the heart may not recover at all resulting in a heart transplant. ECMO is not without complications, and complications resulting from bleeding are of particular concern. There are two reasons for this; firstly, blood coming into contact with the foreign surface of the ECMO has a tendency to clot. This results in consumption of clotting components and can create a diffuse
References 1. Zapol WM, Snider MT, Hill JD et al. Extracorporeal membrane oxygenation in severe acute respiratory failure.A randomized prospective study. JAMA. 1979;242:2193-2196. 2. Peek GJ, Mugford M, Tiruvoipati R et al. Efficacy and economic assessment of conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR): a multicentrerandomised controlled trial. Lancet. 2009;374:1351-1363.
intravascular coagulation type of picture. Secondly, in order to prevent blood from clotting within the circuit, these patients are subjected to anticoagulation with heparin. These factors place patients at risk of hemorrhagic complications. Bleeding complications have been as high as 60% in some reports, and range from simple cannula exit site bleeding to the much feared intracranial bleeds, which affect up to 12% of patients. Improvements in biocompatibility are reducing the bleeding risks, but they still remain significant. Other complications include failure of circuit components, infection and problems related to the underlying critical illness. NUHCS has built a team of cardiac surgeons and intensivists who have a special interest in ECMO. In addition, we have a team of specially trained nurses and perfusionists to support the programme. We also run bi-annual workshops to train and accredit staff who work with ECMO patients. As a result, the number of patients receiving ECMO has increased from 0-2 per year to 20-25 per year over the past five years. We are proud that we can provide this support to respiratory failure patients and cardiac patients of all ages. As our team grows, and our outcomes continue to improve, we anticipate that many providers in the community will come across our ECMO survivors within their practice in the community.
Published on Aug 16, 2013