To establish whether a pre-hospital advanced physician/ paramedic cardiac arrest team that is ECMO capable can establish ECMO flow within 30 minutes of collapse. The Sub30 study will investigate the technical and logistical feasibility of instituting pre-hospital Extracorporeal Cardiopulmonary Resuscitation (ECPR) within 30 minutes of collapse for selected patients (n=6) in a geographical sector of Greater London. It will achieve this through a unique collaboration between the primary emergency dispatch and response services (London Ambulance Service NHS Trust, LAS), pre-hospital practitioners (LAS and London Air Ambulance) and clinicians in ECMO (Barts Health NHS Trust).

Every year, in London, the ambulance service treats over 4,000 patients who have a had a cardiac arrest (or their heart has stopped). Less than 1 in 10 patients survive to get home. Some of those who survive have severe brain damage since their brains did not receive blood and oxygen when their heart was stopped. The ambulance service in London manages to get to a patient, on average, 7 minutes following a 999 call. The paramedics are very skilled in restarting people's hearts and often manage this in less than 10 minutes. However, sometimes it can take much longer or not be possible. The risks of a patient dying or suffering brain damage increase the longer it takes to restart the heart, particularly after about 20-30 minutes. An extracorporeal membrane oxygenation (ECMO) machine may reduce these risks by pumping a patient's blood through an artificial lung and to their vital body organs - temporarily replacing the function of the heart and lungs. The ECMO is used in normal care to support patients after a cardiac arrest once a patient reaches the hospital, but in this study we want to see if the ECMO can be used very soon after the cardiac arrest is reported via the 999 call.

In the Sub30 study, the ECMO team and machine to travel immediately to where the patient collapses rather than wait for the patient to be moved to a hospital. The study hypothesis is that the ECMO will be started faster and that this may improve patient survival and outcomes.

The ECMO team consists of three senior doctors and a paramedic. They attend patients who have collapsed and start ECMO if standard advanced resuscitation techniques fail to restart the heart in 20 minutes. The team will aim to have the ECMO machine started within 30 minutes of the 999 call. The team have achieved this in training and the current study will assess whether it is possible to do this in six patients in real-life.

A target of thirty minutes to achieve ECMO flow or return of spontaneous circulation (ROSC) is less than in published series to date. This can be achieved by:

• integration into an established pre-hospital emergency response services that aggressively pursue ROSC through optimised Advanced Life Support
• immediate deployment of an ECPR-capable cardiac arrest team as a primary resource, as opposed to delayed secondary deployment. Dispatch will be done by the established Advanced Paramedic Practitioner (APP) desk of London Ambulance Service, with the objective to reach the patient within 8-10 minutes of the 999 call.
• early placement of guide-wires into the femoral vessels during on-going conventional CPR, a procedure with low complication risk that does not commit the team to ECPR but will minimise the delay to ECPR support if conventional resuscitative techniques are not successful within 20 minutes
• facilitated guide-wire placement through real-time wireless ultrasound delivered to the operator through augmented reality smart glasses.

Some out of hospital cardiac arrests (OHCA) are irreversible in nature and ECPR would not provide benefit to these patients. The ECPR team will not be task fixated on providing ECPR, but also supportive of the APP primary responders and provide ECPR only in settings of refractory cardiac arrest that fulfils the study criteria, that have been chosen based on best available evidence to identify those patients in whom ECPR is likely to be of benefit.

If pre-hospital ECMO is feasible within 30 minutes of chest compressions starting, then a larger randomised controlled study of clinical and cost effectiveness is merited. Optimisation of the delivery of ECPR is vital, prior to a controlled study, in order to maximise any potential benefits for patients.

Data from Sub30 will inform the design of such studies enabling an estimation of the size of any potential outcome benefits and the likely affordability for a healthcare service.

Inclusion Criteria:

Adult patients who:

• have a witnessed out-of-hospital cardiac arrest
• a presumed cardiac aetiology to their cardiac arrest
• receive bystander chest compressions within 3 minutes
• remain in cardiac arrest at 20 minutes following the call to the emergency services or fail to sustain ROSC in the pre-hospital setting

Exclusion Criteria:

The following patients will not be suitable for entry into the study:

• Known to be are visibly appear younger than 18 years old or older than 65 years.
• Known or visible advanced pregnancy (when resuscitative hysterotomy should be performed)
• No signs of life (physical movement or breathing) AND evidence of ineffective chest compressions suggested by:
• absence of electrical activity at 20 minutes time out OR
• end tidal carbon dioxide level of less than 1.3 kPa (10 mmHg)
• Evidence from others present at the scene or patient examination that ECMO unlikely to benefit patient (e.g. advanced malignancy, severe frailty).

There is no plan to share study participant data