Out-of-hospital cardiac arrest (OHCA) remains a major cause of mortality, with low survival probabilities to hospital discharge. Despite the frequent use of airway management and mechanical ventilation during resuscitation, there is limited evidence regarding the optimal ventilation strategy to improve oxygen delivery and patient outcomes. The present study aims to investigate the effects of positive-end-expiratory-pressure (PEEP) set at 5 mbar compared to zero-end-expiratory-pressure (ZEEP) on the return of spontaneous-circulation (ROSC) in adult patients with OHCA.

This is a prospective, multicenter, cluster-randomized controlled trial conducted across emergency medical services (EMS) in the regions of Guetersloh, Minden-Luebbecke and Osnabrueck. Adult patients (>= 18 years) with OHCA who are undergoing mechanical ventilation through an airway device will be enrolled. The clusters (regional district) will be randomized into two groups: one group will receive ventilation with PEEP set at 5 mbar (intervention group), while the other group will receive ventilation with ZEEP (control group). The study's primary endpoint is the rate of ROSC. Secondary endpoints include rate of re-arrest, death during pre-hospital care phase, hospital admission during ongoing resuscitation, hospital admission with spontaneous circulation, peripheral oxygen saturation and end tidal CO2 at hospital admission.

Inclusion Criteria:

• Adults >= 18 years
• non-traumatic OHCA
• mechanical ventilation via airway device

Exclusion Criteria:

• Patients < 18 years,
• traumatic cause of OHCA,
• no cardiac arrest, withholding of resuscitation (e.g. Do-Not-Resuscitate orders)