Our study suggests that although the aetiology of arrest is rarely clear in the early stages of OHCA, even assuming that the OHCA is due to respiratory disease, EMS personnel may not need to adhere to pre-hospital advanced airway management as well as epinephrine administration. Further, although a bystander might persist in conventional CPR, rescue breathing may not always be required for favourable neurological outcomes even in OHCA caused by respiratory disease.