Abstract Body: Introduction/Background
Out-of-hospital cardiac arrest (OHCA) in children and young adults is uncommon but devastating. While the etiology of OHCA shows unique features at each age group, it also follows a continuum with overlapping elements across ages. Cardiac arrest in infants and young children is most often the end result of progressive respiratory failure or shock. Adolescents and young adults share several common etiologies of cardiac arrest, including drug overdose, genetic heart disease and congenital structural abnormalities, highlighting different pathophysiological from other adults.

Research Questions
How does EMS utilization vary by age group in patients under 35 years with OHCA?
Is EMS use associated with improved clinical outcomes in pediatric and young adult populations?
Have the outcomes associated with EMS use changed over time in these age groups?

Aims
This study aimed to investigate patterns of EMS transport and evaluate its association with outcomes in non-traumatic pediatric and young adult OHCA.

Methods
A retrospective cohort study was conducted at the emergency department of a tertiary centre. Patients aged <35 years with OHCA who were treated from 1995 to 2019 were included. Exclusion criteria included referrals and newborns <24 hours old. Young adults were ≥18 years old and <35 years old. EMS use was defined as public-ambulance transport to the emergency department. The primary outcome was any return of spontaneous circulation (ROSC).

Results
Of 195 OHCAs, 109 (55.9%) were pediatric. EMS use increased with age, from 38.0% (0–5 years) to 82.6% (18 to <35 years). EMS was associated with higher ROSC and survival to hospital discharge (41.7% vs. 24.6%, p = 0.06, and 25.0% vs. 6.6%, p = .007, respectively) in pediatric group but not in the young adult group. However, EMS improved the ROSC rate in young adults from 30.8% during 1995–2002 to 65.7% during 2011–2019. The impact of EMS was not significant after multivariable adjustment.

Conclusion
The use of EMS for pediatric patients with OHCA was significantly lower compared to that for young adults. While rates of ROSC have improved significantly in recent years for young adults in the EMS transport group, no similar improvement has been observed for pediatric patients. Further research is needed to explore the underlying reasons for this lower utilisation and to identify effective interventions that could improve outcomes for pediatric patients with OHCA.