An interventional study of Chest Compression Only CPR (CO-CPR) performed by trained bystanders after instructions from dispatchers and Standard CPR (S-CPR) performed by trained bystanders after instructions from dispatchers in Out-Of-Hospital Cardiac Arrest, Cardiac Arrest and Cardiopulmonary Resuscitation, sponsored by Karolinska Institutet. Recruiting at 2 sites in 2 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-05-08.
Sponsored by Karolinska Institutet · Not applicable, Interventional, and Treatment
Out-of-hospital cardiac arrest (OHCA) is one of the leading causes of mortality in the industrialized world. Bystander CPR before arrival of the Emergency Medical Service (EMS) is associated with an increased chance of survival.
During the last decade, the best form of bystander CPR has been debated. Chest Compression Only CPR (CO-CPR) has been advocated as a preferable method in situations where the bystander has no previous knowledge in CPR, both because its believed to be equally efficient but also a simplified form of CPR that could lead to a higher incidence of bystander-CPR.
In an initiative to increase CPR rates the American Heart Association has launched public campaigns such as the "hands-only CPR" promoting CO-CPR as an option to S-CPR for adult non-asphyxic cardiac arrest. In the 2015 updates of the European resuscitation council guidelines it states that the confidence in the equivalence between the two methods is not sufficient to change current practice.
Whether CO-CPR leads to a survival rate no worse than, or even superior to standard CPR in situations where the bystander has previous CPR training remains unclear. This clinical question remains unanswered while millions of people are trained in CPR worldwide each year.
To investigate whether CO-CPR is non-inferior to standard CPR (S-CPR) when performed by a bystander with previous CPR training in witnessed, non-asphyxic cases of OHCA. Superiority testing will also be performed for the purpose of demonstrating a possible increase in survival with CO-CPR.
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).
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:
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.
323 studies on the registry are indexed under Out-of-Hospital Cardiac Arrest; 89 are open to participants now.
This study's planned enrollment of 3,260 is above the median of 218 across 183 interventional studies indexed under Out-of-Hospital Cardiac Arrest.
Browse Out-of-Hospital Cardiac Arrest studies →Karolinska Institutet is the lead sponsor of 1,113 studies on the registry; 267 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Exclusion Criteria:
Post randomisation exclusion Criteria from data analysis:
Instructions from a dispatcher at the dispatch center to trained bystanders to perform CO-CPR with chest compressions only.
Other: Chest Compression Only CPR (CO-CPR) performed by trained bystanders after instructions from dispatchers
Instructions from a dispatcher at the dispatch center to trained bystanders to perform S-CPR with chest compressions and rescue breaths in a 30:2 ratio.
Other: Standard CPR (S-CPR) performed by trained bystanders after instructions from dispatchers
Instructions by dispatcher to bystander to provide CPR with chest-compressions only The instructions from the dispatcher in interventional arm include: * An ambulance is dispatched and is on it´s way to you * Do CPR with chest compressions only * Push hard on the chest with a pace of 100/minute without interruptions for rescue breathing.
Also known as: Chest compression only CPR, Compression only CPR, Hands-only CPR
Instructions by dispatcher to bystander to provide CPR with chest-compressions and rescue breaths in a ration of 30:2 The Instructions from the dispatcher in the control arm include: * An ambulance is dispatched and is on it´s way to you * Do CPR with chest compressions and rescue breathing * Push hard on the chest 30 times and give 2 rescue breaths. The pace of the compressions should be 100/minute.
Also known as: Standard CPR
30-day survival
Survival to 30 days after cardiac arrest
Time frame: 1 month
1-day survival
1-day survival will be derived from the date of death recorded in Swedish Cardiopulmonary Resuscitation Registry (SRCR). Because SRCR only provides the calendar date of death (and not the exact time), we cannot reliably determine the Utstein variable "survival to hospital admission". We therefore will use 1-day survival as a proxy. If the SRCR date of death is the calendar day after the event date, the patient will be classified as still alive after 1-day. Separating survival to hospital admission from early in-hospital death will not be possible with the available SRCR data.
Time frame: 1 day
1-year survival
Survival to 1-year after cardiac arrest
Time frame: 1 year
Survival with good neurologic outcome at discharge
Survival to hospital discharge with cerebral performance category (CPC) 1-2
Time frame: 30 days
Proportion of participants found with VT/VF at first rhythm analysis
Proportion of participants found with ventricular tachycardia (VT) or ventricular fibrillation (VF) at first rhythm analysis by the EMS or by an automated external defibrillator (AED)
Time frame: 1 day
Proportion of participants with return of spontaneous Circulation (ROSC)
Proportion of participants with return of spontaneous Circulation
Time frame: 1 day
Analysis of primary endpoint (30-day survival) in pre-defined subgroup
Subgroups will be analysed according to the following pre-defined variables: Sex, Age, Cause of OHCA, Initial rhythm, Location of cardiac arrest, Time to start of bystadner CPR, Time to arrival of EMS and Neurological severity classification (CPC).
Time frame: 30 days
Documents are hosted by the registry — open the source record to download them.
Plan to share: No — Data will be published on group level only
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