Background Most patients with out-of-hospital cardiac arrest (OHCA) have grave outcomes. The efficacy of emergency medical services (EMS) may affect outcomes. However, no data exists in Thailand.

Objectives To ascertain the prevalence of EMS utilisation in patients with OHCA transferred to Siriraj Hospital and also to elucidate the rates of return of spontaneous circulation (ROSC), hospital admission and survival to hospital discharge.

Methods This prospective cohort study was conducted in patients with OHCA at a university hospital in Bangkok, Thailand from May 2011 to February 2013. The data was gathered by interviewing bystanders. Data about the mode of transportation, reasons for EMS usage, response time, ROSC and 30-day mortality were collected. Patients with rigour mortis or livor mortis were excluded. The factors affecting ROSC and survival rate were determined by univariate analysis.

Results One hundred and fifty-two patients were included. The prevalence of EMS usage was 14.5% (95% CI 9.3 to 21.0). The most common cause of non-usage of EMS was not knowing or forgetting an EMS number (49.2%). The proportion of bystanders having known an EMS number and using EMS was 34%. The ROSC and 30-day survival rates were 53.3% and 10.5%, respectively. Non-cardiac causes and witnessed arrests were associated with ROSC (p<0.05).

Conclusions The prevalence of EMS utilisation in OHCA at Siriraj Hospital was very low. This may affect the outcomes of patients with OHCA. Improving the EMS system by publicity to increase public awareness and providing life-support education nationwide may improve outcomes of patients with OHCA in Thailand.