Out-of-hospital cardiac arrest (OHCA) remains a leading cause of mortality worldwide, with survival highly dependent on the immediate initiation of bystander cardiopulmonary resuscitation (CPR). Early recognition, prompt chest compressions, and rapid defibrillation are critical components of the chain of survival. Telephone-assisted CPR (T-CPR) provided by emergency dispatchers has been shown to significantly increase bystander intervention rates and improve outcomes. While the availability and use of automated external defibrillators (AEDs) further enhance survival, the optimal integration of AED use into dispatcher-guided, single-rescuer scenarios remains insufficiently studied.

This prospective, randomized, controlled simulation study aims to evaluate the effect of modified telephone cardiopulmonary resuscitation (T-CPR) instructions optimized for automated external defibrillator (AED) use on no-flow time and chest compression fraction (CCF) during single-rescuer resuscitation. Participants are randomized to receive either standard T-CPR instructions or enhanced instructions focusing on minimizing interruptions in chest compressions and reducing time to first compression during AED use.

Out-of-hospital cardiac arrest (OHCA) is a major public health problem associated with low survival rates despite advances in emergency care systems. Survival is critically dependent on early recognition, immediate initiation of high-quality chest compressions, and timely defibrillation. Bystander intervention plays a pivotal role in this process, and telephone-assisted cardiopulmonary resuscitation (T-CPR) has been demonstrated to substantially increase the likelihood of CPR initiation prior to the arrival of emergency medical services.

The increasing availability of automated external defibrillators (AEDs) in public spaces has further strengthened the chain of survival. Early defibrillation is a key determinant of favorable outcomes, particularly in shockable rhythms. However, the integration of AED use into dispatcher-assisted scenarios - especially when only a single rescuer is present - poses practical challenges. In such situations, the rescuer must balance multiple tasks, including chest compressions, AED retrieval, device preparation, and adherence to voice prompts, all of which may introduce interruptions in compressions and increase no-flow time.

While the benefits of T-CPR and AED use independently are well established, there is limited evidence on how dispatcher instructions can optimally coordinate these interventions in single-rescuer scenarios. In particular, it remains unclear whether modified, AED-optimized T-CPR instructions can reduce no-flow time and improve chest compression fraction (CCF) by minimizing unnecessary interruptions and optimizing task sequencing.

This prospective, randomized, controlled simulation study aims to evaluate the effect of modified telephone cardiopulmonary resuscitation (T-CPR) instructions optimized for automated external defibrillator (AED) use on no-flow time and chest compression fraction (CCF) during single-rescuer resuscitation. Participants are randomized to receive either standard T-CPR instructions or enhanced instructions focusing on minimizing interruptions in chest compressions and reducing time to first compression during AED use.

Inclusion Criteria:

• Adolescents and adults (≥16 years)
• Healthcare professionals or laypersons
• Voluntary participation

Exclusion Criteria:

• pregnant women
• people with cardio-pulmonary and musculoskeletal diseases or any other impairment that would risk harm for the volunteer while performing CPR
• physical and/or psychological disabilities
• technical issue during data collection

Participants will be informed about their group assignment post-randomization but will be blinded to the study's aims. The dispatcher will be briefed on their specific tasks but will remain blinded to the study hypotheses and outcomes.