We conducted a retrospective analysis of prospectively collected data from Kaunas EMS-attended OHCA cases in which resuscitation was attempted from 1 to 2016 to 31 December 2018.

We used four data sources to describe each OHCA event: (1) Kaunas EMS Dispatcher Centre data, (2) EMS data, (3) hospital data, and (4) death registry data. EMS dispatcher data and EMS recordings were collected from the Kaunas EMS digital databases. Each OHCA case in which EMS staff initiated CPR underwent an internal audit by a Kaunas EMS quality manager and was included in the study. EMS dispatcher calls were reviewed by the EMS dispatch quality manager. Hospital data were collected from both paper records and the hospital information system (started in June 2017). Hospital data were retrieved manually and collected in the study database. The 1-year survival of patients discharged alive from a hospital was retrieved from the Lithuanian Health Information Centre of Institute of Hygiene, which is responsible for national death statistics in Lithuania.

In 2018, Lithuania had a population of 2,808,901 and occupied an area of 65,300 km2. Approximately 70% of the Lithuanian population lives in cities. Kaunas is the second largest Lithuanian city, with a population of approximately 0.29 million. The Kaunas EMS Station is the only prehospital care provider in the city. The dispatch system is entirely protocol-based. In Kaunas, all the callers were instructed to perform dispatcher-assisted CPR (DA-CPR) using the standard MPDS ProQA® cardiac arrest (CA) protocol starting in 2011. The EMS is a two-tiered response system: a basic life support (BLS) tier with paramedics or a nurse and a paramedic who can apply an automated external defibrillator (AED) and an advanced life support (ALS) tier with ambulance teams including a physician and/or a nurse with advanced competencies in emergency medicine and a paramedic. In the case of presumed OHCA, a dispatcher always dispatches two EMS teams: the one closest to the victim and the ALS team. In Lithuania, CPR regulations are based on an order of the Ministry of Health, which was drafted under the European Resuscitation Council (ERC) guidelines. We do not have a do-not-resuscitate (DNAR) order in Lithuania.

All OHCA cases in which EMS staff initiated CPR were included in the study. OHCA was defined as the cessation of cardiac mechanical activities as confirmed by the absence of signs of circulation [3]. Patients who received bystander CPR but had a pulse when EMS staff arrived were not included in the study, except for one patient who received a shock from an AED before EMS arrival.

The exclusion criteria were age less than 18 years and obvious signs of death on EMS arrival.

The core study dataset complied with the Utstein definitions [3] and is presented in Tables 1 and 2. We collected and examined 27 core and supplemental variables: system (population served, number of CAs attended, number of resuscitation attempted and not attempted, system description), dispatcher (dispatcher identified presence of CA, dispatcher provided CPR instructions), patient (age, sex, witnessed arrest, arrest location, bystander response, first monitored rhythm, aetiology), process (response times, defibrillation time, provision of targeted temperature management (TTM), drugs, performance of coronary angiography, number of occluded arteries); outcomes (prehospital ROSC, survived event, survival to hospital discharge, 1-year survival, transport to hospital, neurological outcome at discharge and discharge location).

The primary outcome measure of this study was survival to hospital discharge in all patients and in the Utstein comparator subgroup which is defined as bystander-witnessed OHCA of medical/cardiac aetiology with an initial shockable rhythm. We selected these two groups because they reflect EMS system effectiveness and efficacy, respectively, according to the Utstein template [3]. 1-year survival was measured as a secondary outcome.

Age and EMS times were reported as the medians and interquartile ranges (IQRs). To compare the times of occurrence, the Mann-Whitney U and Wilcoxon tests were used. Categorical variables are reported as numbers and proportions and were compared by using the Pearson chi-square test. To assess the associations among patient (age, sex), arrest (location, first rhythm) and care (bystander CPR, defibrillation) characteristics and the odds of being alive at hospital discharge, logistic regression models were used. The log linearity was tested for continuous variables, and variables for which log linearity was not proven were converted into categorical variables. First, a univariate analysis was performed with all the descriptive variables, and the association between these variables and the survival rate was tested using the Wald test. Stratification was then performed on OHCA characteristics with adjustment for age and sex. Multivariate analysis was performed with adjustment for all the variables that were significant in the univariate analysis. To assess the impact of patient characteristics, odds ratios (ORs) and their 95% confidence intervals (95% CIs) and p-values are presented.

All tests were two-tailed, and p-values less than 0.05 were considered to indicate statistical significance.