It is unknown whether this evolved strategy (Pre-Hospital Zone I P-REBOA) is feasible and with an acceptable safety profile. This study will address this question, therefore informing the design of a prospective multicentre exploratory cohort study followed by a pilot/feasibility multicenter RCT (IDEAL 2B). The IDEAL Framework is an internationally recognised standard, that describes the stages through which interventional therapy innovation normally passes, the characteristics of each stage and the study design types recommended for each

Haemorrhage (bleeding) is the most common cause of preventable death after injury and is responsible for approximately one-third of trauma deaths (of which between 16-29% of such deaths are thought to be preventable).

Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) is a minimally invasive damage control procedure for life-threatening abdominal and/or pelvic haemorrhage. It involves temporary occlusion of the aorta with an endovascular balloon, providing proximal control to the site of vascular injury whilst supporting cerebral and myocardial perfusion.

Emergency Department (ED) use of REBOA appears to be feasible and associated with improved outcomes. However, bleeding trauma patients die quickly and it's evident that the peak death rate from haemorrhage occurs within 30 minutes of injury. This is well before the majority of patients can reach hospital, it's therefore likely this resuscitation strategy may have greatest benefit for patients when used in the pre-hospital environment.

We have demonstrated that Pre-Hospital Zone III REBOA (distal aortic occlusion) for exsanguinating pelvic haemorrhage is a feasible resuscitation strategy that significantly improves blood pressure and may reduce the risk of hypovolaemic cardiac arrest and early death due to exsanguination.

To evolve this resuscitation strategy, it is important to establish whether it can be delivered in patients with more proximal haemorrhage in the abdomen (Zone I REBOA). However, this development may be associated with increased risk of harm due to the visceral ischaemia that is created. The use of a technique called Partial REBOA (P-REBOA) may offer a solution by mitigating the ischaemia/reperfusion injury created.

It is unknown whether this evolved strategy (Zone I P-REBOA) is feasible in the pre-hospital setting. This study therefore aims to establish via an Observational Cohort of eight adult trauma patients whether Zone I P-REBOA can be achieved in pre-hospital resuscitation of adult trauma patients with exsanguiunating sub-diaphragmatic haemorrhage at risk of imminent hypovolaemic cardiac arrest or recent hypovolaemic cardiac arrest.

Inclusion Criteria -

• Adult trauma patients (aged, or believed to be aged 16 years or older) attended by LAA;
• assessed to have exsanguinating sub-diaphragmatic haemorrhage and imminent risk of hypovolaemic cardiac arrest, or recent hypovolaemic cardiac arrest;
• which is thought to be amenable to treatment with Zone I REBOA;
• and an attempt is made at femoral arterial access (percutaneous access or open surgical approach to insert 8Fr REBOA access sheath)

Exclusion Criteria -

• Age < 16 years
• Injuries deemed clinically unsurvivable
• Known or visible advanced pregnancy

8 Patients cannulated for REBOA (+ all other patients meeting the inclusion criteria during the study period where there was a failed attempt at femoral arterial access).