Compression Only CPR Versus Standard CPR in Out-Of-Hospital Cardiac Arrest - A Randomized Survival Study

This is an interventional, prospective, randomized, 1:1 open label, multicenter trial comparing two different methods of bystander CPR in witnessed cases of OHCA. Since CO-CPR is a simplified form of CPR that could lead to a higher rate of bystander-CPR by itself, a non-inferiority design for the primary outcome has been chosen. Superiority testing will also be performed to demonstrate a potential increase in survival with CO-CPR. Witnessed cases of OHCA with a non-asphyctic aetiology will be the principal study population. According to current guidelines, an unresponsive patient with no or agonal breathing is treated as a suspected case of OHCA at the dispatch centre. These cases are eligible for screening for inclusion. If the case is witnessed, the bystander has previous knowledge in CPR, and no exclusion criteria are present, the case can be included in the study. If included, it will be randomly assigned to either CO-CPR (intervention) or S-CPR (control). The intervention consists of instructions from a dispatcher at the dispatch center to bystanders to perform either CO-CPR (intervention) or S-CPR (control). * Instructions to bystanders on how to perform CO-CPR include continuous chest compressions without interruptions or rescue breaths. * Instructions to bystanders on how to perform S-CPR in the control group include information on giving chest compressions and rescue breaths in a 30:2 ratio. This is a national study where all dispatch centers in Sweden participate, and since 2025, selected sites in northern Italy. The overall study project is conducted in three different phases: 1. RUN-IN period, for establishing logistical and technical study procedures (completed) 2. PILOT STUDY, with focus on feasibility, logistics, and safety (completed) 3. MAIN STUDY will focus on 30-day survival (primary end point) and other important clinical outcomes (secondary outcomes) Objective for RUN-IN period: In order to test the technical inclusion procedures, logistics, feasibility, and data collection, a pre-study RUN-IN period started in Stockholm during 2015. Objective PILOT study: The PILOT study aimed to assess the safety and feasibility of the TANGO2 trial design, as well as intermediate clinical outcomes. The TANGO2 trial started recruitment of patients on January 1st, 2017, and the last patient was included on December 31st, 2018. All patients from the PILOT study will be included in the MAIN STUDY in a seamless design. Objective MAIN study: The MAIN study aims to evaluate whether survival to 30 days following instructions to perform CO-CPR is non-inferior to instructions to perform S-CPR in witnessed OHCA where the bystander has previous CPR training.