Performing chest compressions during the initial phase of out-of-hospital cardiac arrest: continuous vs. alternating (CALM) - a study protocol for prospective, randomised, monocentric, non-blinded, mannequin study with German emergency medical service personnel.

Introduction: Effective chest compressions are a core element of cardiopulmonary resuscitation (CPR). Current guidelines recommend exchanging the person performing chest compressions every two minutes to ensure high-quality chest compressions. However, this can lead to several task interruptions, which could result in a prolonged delay until other relevant tasks, such as securing the airway or administering adrenaline, are completed. Some studies have shown that a rescuer can perform sufficient CPR continuously for more than five minutes. Therefore, this study will investigate whether chest compressions without staff changes in the initial phase of CPR result in fewer task interruptions and an earlier completion of relevant tasks. Methods and analysis: To investigate this, a prospective, randomised, monocentric, non-blinded, mannequin study will be conducted. The 32 teams will perform CPR in two simulated settings. Each team consists of four members, according to the German emergency service standard. Before entering the scenario, they will be randomised to either CPR with or without staff changes or either a shockable or non-shockable rhythm. The scenario ends with the fourth rhythm analysis. After a 20-min break, they will enter the second scenario. Teams will be informed whether they should perform continuous or alternating CPR but will not know which rhythm they have been assigned to. The primary outcome will be the time it takes to complete all relevant tasks during the initial CPR phase. Secondary outcomes include chest compression quality, task load, and number of interrupted tasks. Ethics and dissemination: The protocol was approved by the ethics committee of the University of Heidelberg (S-252/2025, June 04, 2025). It is registered with the German Clinical Trials Register (DRKS00037157, June 10, 2025). Participation will be voluntary and based on informed consent. Data will be recorded only in a pseudonymised form. After completion, data will be kept on file for 10 years. The findings will be disseminated in a peer-reviewed academic journal. De-identified data from the case report form will be made publicly available within the first publication. The study will be conducted following the Declaration of Helsinki and relevant laws.