Blood oxygenation: understanding ECMO

Dr Julian Barker knows a thing or two about impaired lung function and, in particular, what it feels like to be hypoxic himself – having experienced this when he recently climbed Mount Kilimanjaro as part of a charity fund raising effort. Dr Barker trained in anaesthesia in North-West England, before commencing as a consultant at the University Hospital of South Manchester, Wythenshawe (UHSM) in 2003, where he has been lead clinician for cardiothoracic critical care and cardiothoracic anaesthesia for the last five years. However, it is in his role as director of the ECMO programme that Dr Barker now spends an increasing amount of his time, as he explained: “The ECMO service was commissioned by the DH in 2011 in response to the swine flu outbreak. ECMO stands for Extra Corporeal Membrane Oxygenation and is basically the use of cardiopulmonary bypass technology to oxygenate blood outside the body. “Depending on where the cannulae are placed, the system can provide support for the lungs, or the heart and lungs. It is often thought that this is a new technique, but what has really improved in recent years is the technology involved. It is now extremely small, portable, efficient and much ‘kinder’ to the blood, resulting in fewer complications and, additionally, the actual circuit itself is very simple, far more so than a full cardiopulmonary bypass circuit that is used for routine cardiac surgery.”

ECMO development

In terms of ECMO systems, there are two distinct types, although they utilise exactly the same kit. ‘Respiratory’ or veno-venous ECMO (VV) whereby blood is taken from, and returned to, the venous system and ‘cardiac’ or veno-arterial ECMO (VA), where the blood is taken from the venous side of the circulation and returned to the arterial side. However, it is respiratory ECMO in particular that has made the news in the last 2-3 years because of its role in treating swine flu, Dr Barker commented: “Respiratory ECMO has been used increasingly over the last decade or so to treat ‘Adult Respiratory Distress Syndrome’ (ARDS). This is a final common pathway of many severe respiratory or systemic illnesses, characterised by a profound failure of the lungs to get oxygen into the blood; the lungs then become very stiff as a result of the air-spaces becoming occupied by inflammatory fluid. “ARDS can be caused by a range of conditions including pneumonia, major trauma, pancreatitis and septic shock. The history of the development of ECMO will say that two important events occurred that really made people sit up and take notice. First was the publication in the Lancet of the ‘CESAR’ trial and the second was the success in treating swine flu patients with ECMO.” He explained that the CESAR trial was conducted by the ECMO group at Glenfield Hospital, Leicester, which for many years was the only UK adult ECMO centre. The pioneering work undertaken at Leicester led them to conducting the CESAR study which compared ECMO treatment with conventional ventilation for ARDS and showed that ECMO could be beneficial. The publication of this trial preceded the more widespread use of ECMO in the treatment of swine flu, both here in the UK and in Australia. “The results on both sides of the world were impressive,”Dr Barker continued. “Many young patients made good recoveries despite being critically ill with lung failure, more so than would have been possible with conventional ventilator treatment. The success of, and the consequent need for, ECMO meant that the DH had to increase the number of ECMO beds in the UK. “First this needed to be done in a hurry during the swine flu crisis, a couple of years ago, and then subsequently in a more planned way to cope with the increasing demand for a treatment that was becoming more and more successful. UHSM had a track record for using ECMO technology to treat lung failure and heart failure that occasionally ensues for a few days after transplantation surgery. This experience meant that we were one of the first UK centres that the DH asked to help provide ECMO treatment for swine flu.” So how does Dr Barker explain the remarkable success that ECMO has had with swine flu patients? “In a few susceptible individuals swine flu causes a severe viral pneumonia leading to ARDS. Many of these patients were previously well and had little in the way of underlying health issues. We knew that if we rested the lungs by oxygenating the blood with ECMO then recovery would be possible,” he commented, adding: “A question frequently asked is: ‘how does ECMO actually treat the lungs?’ The answer is that it doesn’t treat the lungs directly, but it allows the lungs to rest. An often cited analogy is that of a broken leg – a broken leg does not heal well if the patient continues to run on it. Similarly, the lungs do not recover well by being made to work harder by being exposed to high pressures and high oxygen tensions by mechanical ventilation.” Dr Barker explained that, after the swine flu experience of the 2010/11 winter, the DH decided to commission more ECMO centres. Hospitals were then asked to bid for the contracts and this process was overseen by the National Specialist Commissioning Team (NSCT). The successful institutions were Guys’ and St Thomas’ Hospital and the Royal Brompton in London, Glenfield, Papworth and UHSM, Wythenshawe. The new contracts started in December 2011 and have now been operational for over a year.