Cardiac arrest in hospitalized children is a rare occurrence in general and for each healthcare professional in particular, making lack of routine in performing cardiopulmonary resuscitation a challenge. Mortality and morbidity following cardiac arrest depend on the technical (medical knowledge, procedures, etc.) and non-technical (team leadership, communication, etc.) skills performed by the medical team. Simulation-based team training is a well-known and effective method to improve team performance in high-stake and time-sensitive situations, without putting actual patients at risk. Unfortunately, studies show that skills obtained during simulation-based team training decline within a few months. However, recent observational studies have demonstrated improved technical pediatric basic life support skills after short simulation sessions with a high frequency of repeat. The healthcare professionals in these studies are limited to selected groups and tests are performed exclusively on skill stations.

In this study, the effects of a novel high-frequency training program will be investigated. A controlled intervention study in two comparable Danish regions will be conducted. Healthcare professionals in four pediatric departments in the intervention region will participate in the high-frequency training program. Healthcare professionals in four pediatric departments in the control region will continue simulation-based team training with no changes - "as usual" and at a two to three times lower frequency (based on unpublished data). Both groups consist of approximately 600 healthcare professionals, contributing to a total of 1,200 participants included in this project.

Hypotheses: high-frequency training will improve primary outcomes during in-situ simulated pediatric in-hospital cardiac arrest as specified:

1. Teamwork competencies measured by the team emergency assessment measure (TEAM),
2. Time (seconds) to recognition of cardiac arrest.
3. Time (seconds) to initiation of cardiopulmonary resuscitation.
4. Longest chest compression pause duration.

Data collection. To assess clinical performance in both regions unannounced in-situ (in own department with usage of own equipment) simulations of pediatric cardiac arrest will be performed and recorded on video.

Inclusion Criteria:

• Healthcare professionals (doctor or nurse) employed in one of the eight pediatric departments in Central Denmark Region og Southern Denmark Region during the project period April 1st 2023 to April 1st 2024.

Exclusion Criteria:

• Missing consent to be recorded