Pre-hospital ECMO in Advanced Resuscitation in Patients With Refractory Cardiac Arrest. ( SUB30 )

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).