Table 1 Study secondary outcomes

Study feasibility outcomes (formulae detailed summary in Additional file 1)

• Proportion of patients randomised outside of weekday daytime hours).

• Device deployment time- measured as the pause in chest compressions associated with device deployment.

• Proportion of patients/consultees providing agreement to ongoing study participation.

• Success of study blinding procedures.

• Proportion of patients with complete follow-up data.

• Proportion of patients with analysable chest compression quality data.

Patient outcomes

• Return of spontaneous circulation- defined as the return of a spontaneous circulation for at least twenty minutes.

• Duration of critical care and hospital stay.

• Survival- measured at hospital discharge, 30-days, and 6-months.

• Quality of life- measured using EQ-5D-5 L (EuroQOL- 5 dimensions- 5 levels) and SF-12 (12-item short form survey) questionnaires at hospital discharge and 6-months.

• Good neurological outcome measured using cerebral performance category (CPC) at discharge and the modified Rankin score (mRS) at discharge and at six-months. Good neurological outcome will be defined as a CPC of 1 or 2 or return to baseline (pre-admission) CPC, or mRS of 0–3 or return to baseline (pre-admission) mRS.

Process outcomes

• Cardiopulmonary resuscitation (CPR) quality (chest compression rate, chest compression depth, flow-fraction, pre-shock pause, post-shock pause, peri-shock pause).

Safety outcomes

• Device related adverse events