Purpose of the study. To evaluate epidemiology of out-of-hospital cardiac arrest (OHCA) and performance of emergency medical services (EMS) in the Crimea. 
Materials and methods. The Crimean Out-of-Hospital Cardiac Arrest and Resuscitation Registry (COHCARR) is designed as a prospective population-based registry of all EMS-attended OHCA with attempted resuscitation, occurring in the Republic of Crimea (population coverage: 1.91 million). The baseline data collected from January to June 2018 were analyzed descriptively following the Utstein methodology.
Results. A total of 6,391 OHCA were attended by EMS during the 6-month period, whereas resuscitation was commenced in 196 cases (3.1%). The incidence of OHCA with resuscitation attempted in the Republic of Crimea is calculated to be 20.5 per 100,000 population per year. The majority of OHCA patients were male (56%), median age – 65 years. OHCA mostly occurred at home (80%). Aetiology was considered to be medical in 92% cases. Most OHCA were witnessed by either the EMS (71%; n=139) or a bystander (24%; n=47). Out of the bystander-witnessed cases, resuscitation was initiated by a lay person in 19% (n=9). Shockable initial rhythm was registered in 16% OHCA. When excluding EMS-witnessed cases, mean EMS response time was 11 min, mean time to first defibrillation – 12 min, mean time to the first dose of adrenaline – 16 min. Thirteen patients (6.6%) gained return of spontaneous circulation (ROSC), and 5.6% had sustained ROSC until hospital admission. Out of 11 cases of bystander-witnessed OHCA with shockable initial rhythm, two patients (18%) achieved ROSC, and both survived to hospital arrival.
Conclusions. OHCA is a major health problem in the Crimea as evidenced by the high incidence, low rates of resuscitation commencement and dramatically low survival. The COHCARR would serve as a valuable tool for monitoring OHCA epidemiology and EMS performance, and prioritizing reasonable interventions to improve outcomes after OHCA.

7 - Establishing the Crimean Out-of-Hospital Cardiac Arrest and Resuscitation Registry (COHCARR): a baseline epidemiological analysis