Background and objectives
Studies have shown that in-hospital cardiac arrests are usually preceded by a period of physiological deterioration that has often gone unnoticed. We proposed that the same might be true for out-of-hospital cardiac arrests (OOHCA) attended by the ambulance service. Approximately 50% of patients assessed at home by ambulance paramedics following an emergency call are left at home rather than conveyed to hospital. 
We therefore assessed a cohort of known OOHCA patients to assess if any had been reviewed by ambulance crews but then left at home in the 48 hrs prior to their subsequent cardiac arrest.
Methods
Retrospective cohort study using data from a SCAS database. All adult patients (≥18) who suffered OOHCA and were seen by SCAS within the preceding 48 hours were included. The NEWS2 scores at the time of their initial assessment were calculated and mitigating circumstances recorded. 
Results
Of 1960 OOHCA patients, 184 (9.4%) had been seen within the previous 48 hours. 43 of these were taken to hospital and discharged home before their subsequent cardiac arrest and discounted. 39 declined hospital transfer. 23 were on an end-of-life pathway, 4 had incomplete data, and 75 (55%) were left at home through crew discretion. 33/75 (44%) patients not conveyed had either a NEWS 2 score of 3 in a single parameter or a score of 5+, which in hospital would mandate an urgent medical review. The most over looked observation was respiratory rate. 
Conclusions	
Based on deteriorating physiology, 1.7% OOHCA have been inappropriately left at home by ambulance crews. NEWS 2 scoring is has the potential to improve prehospital triage of these patients. This study also identifies the need for further research into paramedic decision-making and more guidance on who can be safely left at home.

5 - Service review focusing on non-conveyance of patients who proceed to suffer out of hospital cardiac arrests in the South Central Ambulance Service (SCAS): A Missed Opportunity?