Sophisticated European-style ECMO in the Louvre, with Zeng Fanzhi’s 1830 Until Now in the background
What is ECMO?
Extracorporeal Membrane Oxygenation or ECMO is a type of cardiopulmonary bypass for providing prolonged cardiac and respiratory support to persons whose heart and lungs are unable to provide an adequate amount of gas exchange or perfusion to sustain life. The key differences between ECMO and the traditional forms of cardiopulmonary bypass used in cardiac surgery are that the latter requires transthoracic cannulation typically done under general anaesthesia and for only a few hours during surgery, whilst the former can be done with more peripherally sited central access (i.e. femoral or cervical vessels) and can remain in place for several days allowing for intrinsic recovery of damaged lungs and heart. ECMO at its simplest is a pump and oxygenator working in tandem to supply the patient’s circulation with oxygenated blood. It exists in two broad forms with venovenous (VV-ECMO) providing only lung support and venoarterial (VA-ECMO) providing both respiratory and haemodynamic support with the circuit connected in parallel to the heart and lungs.
ECMO’s development throughout the 70s was largely driven by the need to temporarily support infants with respiratory failure due to congenital heart defects. Since then, the scope of its use has continued to grow to the point now that in some European cities it has been routinely being taken out into the prehospital environment to support selected patients in cardiac arrest.
The Parisian Model
In cardiac arrest, VA-ECMO (in this setting more commonly referred to as ECPR- Extracorporeal cardiopulmonary resuscitation) is performed. The setup in Paris, (which has become the benchmark for out-of-hospital ECPR for over 10 years) is perhaps the most widely known. The Parisian EMS known as SAMU (Service d'Aide Médicale Urgente) regularly dispatch Mobile ICU units (MoICU) to scenes where advanced medical care and patient stabilisation are required, be that a suspected aortic dissection, major stroke or cardiac arrest. The MoICU team typically comprises an emergency physician/anaesthetic-intensivist, a nurse and a paramedic. Having been deployed to the scene by a dispatch physician screening emergency calls at the EMS control centre, the MoICU take over the resuscitation started by the regular fire department EMS who are usually first on the scene. If after 10 minutes ROSC is not achieved, and the patient is deemed suitable for ECPR (i.e. witnessed cardiac arrest in a patient aged under 70) the MoICU will call for the ECPR team who themselves will have already been on standby from the initial emergency call. The ECPR team has a similar setup to the MoICU with an anaesthetist-intensivist, an anaesthetic nurse and paramedic typically on the team. The ECPR and MoICU teams work in tandem (physicians doing the cut-down/Seldinger hybrid technique to gain femoral vascular access, nurses priming the ECMO and drawing up drugs, paramedics assisting the physicians and handling kit). This is the very antithesis of ‘scoop and run’. And the results speak for themselves with survival and good neurological outcome reported in almost third of out of hospital cardiac arrests. Prospective studies in cities such as London (in collaboration with London’s Air Ambulance) are ongoing to establish the wider feasibility and likely outcomes of pre-hospital ECPR.
ECMO in trauma
The traditional role of ECMO in trauma since the 1970s has been VV-ECMO for the adjunctive treatment of refractory respiratory failure in ARDS, TRALI and the like. The use of VA-ECMO/ECPR in the haemorrhagic shock and traumatic arrest patient is a much more novel and controversial proposition. The AAST stance on the matter remains fairly equivocal, essentially leaving it up to individual ECMO centres to do as they please. There have been a number of case reports and series from Asia of successful ECPR as a bridge to definitive surgery in patients who have arrested from traumatic ventricular rupture, cardiac tamponade and tension pneumothoraces. When we think about traumatic coagulopathy and vicious cycles it seems intuitive that ECMO has an important role to play. Simultaneous extracorporeal warming of blood, transfusion of blood products and depleted clotting factors can all take place with the patient on ECMO as part of the damage-control resuscitation continuum. The reduction in venous pressure from large bore cannulation may help to reduce bleeding and as techniques and technology continue to advance there may be scope for selective anatomical exclusion of injured solid organs from the patient’s circulation pending surgical repair. Indeed, ECMO in trauma is intrinsic to the success of suspended animation, a topic discussed in this very blog only a few months ago. Unanswered questions remain about the ideal candidate for ECMO in trauma. Consider also that a large percentage of blunt polytrauma that leads to arrest has a concomitant traumatic brain injury, which as with resuscitative thoracotomy would be a contraindication for specialist resource-intensive interventions such as ECMO.
A further consideration is the question of anticoagulation. In the non-trauma setting, systemic anticoagulation is generally a given due to the risk of thromboembolic events in the patient and the ECMO machinery itself. However, in trauma ECMO, given the inherent injury-related bleeding risk several strategies have been employed including full heparin systemic anticoagulation, a heparin-minimised strategy, all heparin-free, initially heparin-free and delayed heparin-free treatments. Whilst several series have reported no thromboembolic complications with heparin-free ECMO, hope remains that technological advancements including the use of more efficient membrane oxygenators, centrifugal pumps, miniaturisation of circuits, and heparin-bonded circuitry will eventually allowed ECMO use with little or no anticoagulation.
The Future
The inevitable next stage in ECMO’s evolution is its incorporation into prehospital trauma care. Perhaps as a last-ditch salvage technique when thoracotomy and even REBOA may prove futile. One would imagine the results could be promising. On the whole trauma patients are younger and fitter than the stereotypical medical cardiac arrest patients who come with their usual cardiovascular and lifestyle risk factors. Furthermore, trauma patients are likely to sustain their injuries in a public urban setting (e.g. road traffic accident or a witnessed assault violent incident) and therefore help will be summoned quickly, minimising downtime and thus increasing the likelihood of success. Further prospective studies are needed, not least because traumatic arrest has often been an exclusion criteria in the few ECPR studies to date. The clinical and technical skills involved can be easily taught. As ever it is likely to be the financial and political will that proves the rate-limiting step.
Obi Nnajiuba is a British surgical resident with a specialist interest in trauma, acute care, prehospital care, triage, mass casualty events and trauma systems. His postgraduate qualifications include an MSc in Trauma Sciences and membership of the Royal College of Surgeons of England. He is also a registered Motorsport UK physician, providing trackside advanced trauma care to competitors at world famous motor-racing circuits such as Brands Hatch, Goodwood and Silverstone.
