Overall survival of patients after out-of-hospital cardiac arrest (*OHCA*) is less than 10% worldwide and in Taiwan. Interventions provided by the emergency medical system (*EMS*) before arrival at the hospital are of paramount importance to patient outcomes after OHCA. Among those interventions, the pros-and-cons of different vascular accesses, including intraosseous (*IO*) access or intravenous (*IV*) access, remained the issue of most under debate.

The objective of this study is to determine the comparative effectiveness of IO access vs IV access in patients with OHCA by a randomized controlled trial (*RCT*) in Taipei EMS. To name in short, the investigators called it a "*VICTOR* trial" standing for "Venous Injection Compared To intraOsseous injection during Resuscitation of patients with out-of-hospital cardiac arrest".

Overall survival of patients after out-of-hospital cardiac arrest (*OHCA*) is less than 10% worldwide and in Taiwan. Interventions provided by the emergency medical system (*EMS*) before hospital care is of paramount importance to patient outcomes after OHCA. Among those interventions, the pros and cons of different vascular accesses, including intraosseous (*IO*) access or intravenous (*IV*) access, recently became the focus under debate.

Theoretically, IO access provides a rapidly established way to administrate medication and fluid to patients (Reference 1) and has been adopted in many acute care societies and organizations including current resuscitation guidelines (Reference 2). However, some of the recent publications questioned the outcomes of OHCA patients receiving the IO route comparing to the IV route (References 3-5). Studies showed non-different or negative outcomes of patients receiving the IO route has been severely biased through the inherent inadequacy of retrospective design (References 3-5). The three major problems of those studies were:

1. . Time to vascular access cannot be adjusted. In many EMS, IO access was allowed only after one or two failed attempts of IV route. This led to a significant selection bias.
2. . The location of vascular access was not accurately reported. As we know, medications through upper limbs arrive at the heart sooner than the lower limbs. Many paramedics tend to insert the IO needle in tibia but to inset IV catheters in the forearm vein.
3. . Post-hoc analysis with old data over 5 to 10 years. Two of the three studies were the post-hoc analysis from the data of previous studies which was conducted from 2007 to 2010 when cardiopulmonary resuscitation quality and teamwork (i.e. important confounding factors to OHCA survival) were not that emphasized and recorded.

Hence, the investigators designed the study to determine the comparative effectiveness of IO access vs IV access in patients with OHCA by a randomized controlled trial (*RCT*) in Taipei EMS. In this 2-year research plan, we will conduct a prehospital RCT to address the following question: In adult patients with non-traumatic cause of OHCA resuscitated by emergency medical technician paramedic in the prehospital setting, will receiving IO access cause a better chance of survival to discharge, sustained recovery of spontaneous circulation, and other survival outcomes like neurologically favorable status, comparing to those who receiving IV access.

To name in short, the investigators called it a "*VICTOR* trial" standing for "Venous Injection Compared To intraOsseous injection during Resuscitation of patients with out-of-hospital cardiac arrest".

Inclusion Criteria:

• Out-of-hospital cardiac arrest (OHCA) activated Taipei EMS ALS team (EMTP)
• Adult ≥ 20 years old

Exclusion Criteria:

• OHCA patients with signs of obvious death, e.g. rigor mortis
• Existing do-not-attempt-resuscitation order
• Patients with cardiac arrest en route to the hospital
• OHCA patients with successful vascular access before EMTP arrival
• OHCA patients with a canceled ambulance call or being transported to the hospital before EMTP arrival
• OHCA patients with known or suspected pregnancy
• OHCA patients with traumatic cause of cardiac arrest
• OHCA patients with known or suspected < 20 years old, or > 80 years old
• OHCA patients with contraindications to IO access or IV access

The intervention (IO vs IV route) on the patients with out-of-hospital cardiac arrest can not be masked.