INTRODUCTION
Out-of-hospital cardiac arrest (OHCA) is the leading cause of death worldwide, with low survival rates, and is a major public health problem [1,2]. Many studies have described the importance of bystander cardiopulmonary resuscitation, bystander defibrillation, and early emergency medical services (EMS) response to improve outcomes of OHCA [3,4], as well as the critical role of EMS first responders who provide Advanced Life Support (ALS) in addition to rapid Basic Life Support (BLS) [5,6]. Systemic EMS operations such as multitier response with predetermined team approaches are required to improve outcomes [7,8].
In addition to rapid BLS [7,9,10], there are reports that ALS is associated with good results [10], and some studies have reported that early advanced airway management (AAM) and early intravenous (IV) and epinephrine administration yield good results [11–13]. In Korea, AAM and IV can be performed by EMS crews treating patients with OHCA, but drug administration, such as epinephrine, is restricted by law. Therefore, the Korean National Fire Agency has implemented a dedicated ambulance ALS protocol, including epinephrine administration, as a pilot project.
These EMS resuscitation protocols can affect the rate and timing of resuscitation of patients with OHCA provided by EMS crews [14,15]. Despite recent improvements in patient outcomes due to various interventions for EMS constructs [7,16–18], it is unclear whether provision of prehospital return of spontaneous circulation (ROSC) and ALS differ according to the operation of OHCA-dedicated ALS protocols. We hypothesized that an OHCA-dedicated ALS ambulance protocol aiming to provide timely ALS would increase prehospital ROSC and ALS rates in patients with OHCA. Therefore, this study aimed to investigate the effects of an OHCA-dedicated ALS ambulance for patients with OHCA on the provision of prehospital ROSC and ALS.
METHODS
Ethics statement
This study was approved by the Institutional Review Board of the Korea National Institute for Bioethics Policy (No. 2022-0048-001). The requirement for informed consent was waived due to the retrospective nature of the study.
Study design and setting
An observational study was performed by the Korean National Fire Agency (NFA) using the OHCA registry. The NFA operates a single EMS system across the country, with 18 provincial offices targeting more than 50 million people in an area of 100,210 km2. The Korean EMS system is implemented by EMS crews at the US emergency medical technicians-intermediate (EMT-I) level who have completed 3 to 4 years of education, and the administration of ALS medication such as epinephrine is legally restricted.
Intervention program
There are three types of ALS-provided ambulances differentiated by protocols. The first type is a smartphone-based ALS ambulance (SALS). Since 2015, this protocol has been implemented in selected areas (four cities and provinces, 31 of 224 fire departments nationwide, covering 23.9% of the total population). The SALS protocol requires two ambulances and enables real-time feedback from EMS physicians using video calls as well as the use of a manual defibrillator and administration of ALS medications such as epinephrine and amiodarone [19]. If two ambulances are not available, BLS will be performed on-site for at least 5 minutes, and the patient will be transferred to a hospital. The SALS program has shown better results than that of single-tiered ALS (6.3% 6-month cerebral performance categories score 1 or 2 vs. 2.6%, P<0.01), but operated in a limited area [20,21].
The second type is a dedicated ALS ambulance (DA) consisting of two or more qualified EMS crews. This nationwide EMS intervention was initiated based on evidence that a better trained and experienced EMS crew can improve outcomes in patients with cardiac arrest [18,22,23]. There are 224 fire stations and 1,558 ambulances nationwide; among them, 193 ambulances (one for each fire station, except 31 SALS areas) were designated as DAs. Each DA unit was strategically assigned to fire stations based on the number of cardiac arrest cases.
The EMS crews in these DAs received 3 days of Advanced Cardiac Life Support training, enhancing their capability for handling complex emergencies. DA teams are dispatched with priority in cases of OHCA and are permitted to use epinephrine under direct medical oversight via video calls as part of a nationwide pilot project. When the dispatch center recognizes cardiac arrest, they dispatch the DA with priority, followed by another ambulance for a multitier response.
Specifically, the DA protocol allows the initiation of AAM and epinephrine administration even in the absence of a second ambulance when a fire engine (acting as a BLS team) is on scene. This is a significant protocol advantage over SALS, which requires the presence of two ambulances for ALS interventions (Fig. 1).
Data source and collection
OHCA data were drawn from the NFA EMS system database in Korea, which includes EMS activity, cardiac arrest, and EMS dispatch center information. The details of this database have been reported in previous studies [5].
Study population
This study included patients with OHCA aged >18 years with a presumed cardiac etiology treated by EMS crews between January 2020 and December 2020. We included individuals irrespective of prehospital ALS. Patients who had not undergone resuscitation or were witnessed by the EMS crew and a single ambulance dispatch were excluded from the analysis.
Outcome measures
The primary analytical factor was prehospital ROSC that was maintained until hospital arrival. The secondary analysis factors were the rates of AAM, IV, and epinephrine administration, defined as ALS.
Variable definitions and measurements
The following variables were recorded: (1) demographic factors of age and sex; (2) community factors of season, metropolitan area (patients categorized based on residential location, including 10 metropolitan cities and nine provinces), place (public, private, and other), witnessed, bystander cardiopulmonary resuscitation (CPR), and defibrillation; and (3) EMS factors of response time interval (RTI; from the time of the call to the time when the first vehicle arrives at the site), scene time interval (STI; from the time the first vehicle arrives at the site to the time the patient transport vehicle leaves the site), transport time interval (from the time of departure from the site to the time of arrival at the patient transport vehicle hospital), field primary electrocardiogram (shockable [ventricular fibrillation and pulseless ventricular tachycardia], pulseless electrical activity, and asystole), prehospital airway management (bag valve mask, endotracheal intubation, and supraglottic airway), advanced airway timing (from arrival time at the site to success time of advanced airway), EMS defibrillation, IV and epinephrine administration, epinephrine administration timing (from arrival time at the site to time of epinephrine administration), and ROSC upon arrival at the emergency department.
Statistical analysis
Statistical analysis was performed to determine differences among groups. Categorical variables were compared using the chi-square test. Continuous variables were expressed as median and quintile, and statistical tests were performed using the Wilcoxon rank sum test. A multivariate logistic regression model was used to estimate the relationships between key variables and study results and to adjust for potential disturbance factors. Model I was adjusted for demographic factors (age and sex). Model II was adjusted for model I demographic factors, community factors (season, witness, cardiac arrest location, metropolitan area, and bystander CPR), RTI, STI, initial electrocardiogram rhythms, and epinephrine administration. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were calculated for the key variables. All statistical analyses were performed using SAS ver. 5.2 (SAS Institute Inc). P-values less than 0.05 were considered statistically significant.
RESULTS
Demographic findings
Among 31,651 patients with OHCA treated by EMS between January and December 2020, 18,031 adult patients (56.97%) were included in the study. The number of patients transferred by group was 2,622 SALS, 7,520 DA, and 7,889 non-DA (Fig. 2).
The median age was 74 years for SALS, 73 years for DA, and 74 years for non-DA (P=0.09). The DA group included the largest number of metropolitan residents (SALS, 18.31%; DA, 56.58%; and non-DA, 39.83%; P<0.01). Public places were the highest location of response in the non-DA group (SALS, 9.57%; DA, 10.25%; and non-DA, 11.81%; P<0.01). Witnessed cases were highest in the non-DA group (SALS, 44.77%; DA, 43.34%; and non-DA, 44.78%; P<0.01) and bystander CPR cases were highest in the SALS group (SALS, 69.45%; DA, 65.85%; and non-DA, 67.22%; P<0.01) (Fig. 2 and Table 1).
Main analysis
Prehospital ROSC was the highest in the DA group (SALS, 11.17%; DA, 13.19%; and non-DA, 7.91%; P<0.01). In multivariable logistic regression model Ⅰ after adjusting for age and sex, the SALS and non-DA groups were associated with lower prehospital ROSC compared with the DA group (SALS: aOR, 0.83 [95% CI, 0.72–0.96]; non-DA: aOR, 0.56 [95% CI, 0.51–0.63]). In model II, after adjusting for all other confounders, there was no significant difference in the SALS group, and the non-DA group was associated with lower prehospital ROSC (SALS: aOR, 0.97 [95% CI, 0.82–1.15]; non-DA: aOR, 0.57 [95% CI, 0.50–0.65]) (Table 2).
For ALS, in regression model Ⅰ, the SALS and non-DA groups were associated with lower provision of AAM (SALS: aOR, 0.68 [95% CI, 0.58–0.79]; non-DA: aOR, 0.69 [95% CI, 0.62–0.78]), IV (SALS: aOR, 0.47 [95% CI, 0.43–0.52]; non-DA: aOR, 0.40 [95% CI, 0.38–0.43]), and epinephrine (SALS: aOR, 0.50 [95% CI, 0.46–0.55]; non-DA: aOR, 0.09 [95% CI, 0.08–0.10]) compared with the DA. In model Ⅱ, even after adjusting for all other confounders, the results were similar (Table 3 and Supplementary Table 1).
Secondary analysis
Prehospital ALS rate according to ALS protocol
Regarding the prehospital ALS rate, the DA group provided AAM at a higher rate (SALS, 89.70%; DA, 92.75%; and non-DA, 89.91%; P<0.01), and the median (interquartile range, IQR) time interval from EMS arrival at the scene to the application of AAM was similar in the three groups (6 minutes). DA showed the highest provision rate of IV (SALS, 45.77%; DA, 63.88%; and non-DA, 41.65%) and epinephrine (SALS, 31.50%; DA, 47.77%; and non-DA, 7.40%) (Table 4). A cumulative proportion ≥90% of patients had AAM within 12 minutes of EMS arrival at the scene to the application in all groups (SALS, 89.7%; DA, 92.8%; and non-DA, 89.9%). The cumulative rate of administering epinephrine to more than 90% of the patients was achieved slightly faster in the DA group compared with the SALS and non-DA groups (SALS, 20 minutes [IQR, 19–21 minutes]; DA, 19 minutes [IQR, 19–20 minutes]; and non-DA, 20 minutes [IQR, 20–22 minutes]) (Table 4).
The cumulative rate of prehospital epinephrine at 60 minutes was the highest in the DA group (epinephrine timing, 19 minutes) followed by the SALS and non-DA groups (epinephrine timing, both 21 minutes) (Supplementary Table 2 and Fig. 3).
The DA group had a slightly faster RTI (7 minutes [IQR, 6–9 minutes]) than that of the SALS group (8 minutes [IQR, 7–11 minutes]) and the non-DA group (8 minutes [IQR, 6–11 minutes]). The DA group (17 minutes [IQR, 14–21 minutes]) and the SALS group (18 minutes [IQR, 14–22 minutes]) had a longer STI than that of the non-DA group (14 minutes [IQR, 12–18 minutes]; P<0.01). The rate of use of defibrillation was highest in DA (SALS, 19.72%; DA, 21.57%; non-DA, 20.18%; P=0.04) (Table 1).
DISCUSSION
This nationwide observational study was conducted in Korea. When a DA is dispatched, there is a higher rate of prehospital ROSC and provision of prehospital ALS, such as AAM, IV, and epinephrine, than for other protocols.
Depending on the nature and circumstances of EMS, benefits may vary as well as their effects on patient outcomes [24,25]. More training and experience in the EMS crew increases survival after OHCA, and there is an association between the number of ALS procedures performed by a crew and successful applications [18,22,23]. A study in North East England showed a significant association between dedicated EMS operations and OHCA resulting in cardiac arrest [16]. In Korea, where an EMS protocol for dispatching a DA has been developed and applied, the same conclusions were reached in this study.
Early ALS response was associated with improved survival in a recent ALS study [10,26]. Early AAM delivery and epinephrine administration may improve outcomes in patients with OHCA [11,27]. There were differences in outcomes according to the time of epinephrine administration in OHCA, and decreases in survival have been reported in both shockable and nonshockable rhythms following administration delay [11,28]. In our study, the DA group showed a higher rate of prehospital ROSC, although ALS timing was not faster after arrival at the site compared with that of the non-DA group. This is consistent with previous studies showing that fast response time and provision of three-person team CPR within the DA for high-quality CPR are important for improving the prehospital ROSC to ALS ratio in patients with OHCA.
The strength of this observational study is that it investigated the effects of a new EMS protocol and operation implemented in Korea at the national level. To improve OHCA results, Korea has implemented interventions such as DA and EMS [5]. A high frequency of dispatch can increase experience using higher-risk ALS techniques (epinephrine administration and IV) among EMS crews providing ALS [17]. In a recent study, the cardiac arrest frequency of ambulance stations was related to ALS application rates and OHCA outcomes [29]. This effect was also observed in our study, where the operation of DA ambulances and case volume positively affected the outcomes of patients with OHCA, such as an increase in the out-of-hospital ROSC rate [23,29].
In our analysis, the DA group exhibited a higher rate of advanced AAM application compared to both SALS and non-DA groups. Notably, the time to administer AAM did not significantly differ across these groups, indicating that the efficiency of these EMS protocols is consistent across models. This suggests that EMS protocol implementation effectively standardizes care delivery without delaying interventions, showcasing its potential to enhance patient outcomes in OHCA scenarios (Table 4).
When designing an EMS system, various considerations are needed to improve EMS quality. To improve prehospital ROSC and ALS rates, there is a need to increase performance skills and self-efficacy through appropriate staffing of EMS providers and systematic training. In addition, it is necessary to maintain the experience of ALS providers to improve higher-risk ALS capabilities. Therefore, the operation of a DA-type EMS for patients with OHCA with high dispatch frequency can be especially effective [16,17,30].
This study has several limitations. First, this was a natural experimental study rather than a randomized controlled trial [31]. There may be unmeasured confounding factors, such as community, patient, and hospital characteristics. The study was conducted partly during the COVID-19 lockdown period, and we were unable to consider variables such as patient factors (fever and arrest due to COVID-19), EMS factors (delayed response due to personal protective equipment and increased transport time for finding an available hospital), and other unknown COVID-related factors [32–34]. Second, our primary outcome was prehospital ROSC rather than survival or neurological outcomes. The data from the NFA registry only included prehospital outcomes. However, compared with other factors, prehospital ROSC is more closely associated with survival in patients with cardiac arrest [35,36]. When we excluded the STI in our analysis (model II) as a possible mediator, we found that the exclusion did not alter the prehospital ROSC outcomes. Previous studies of prehospital epinephrine use have shown that survival to hospital discharge was lower in the epinephrine use group [37]. However, previous studies have been limited to data from the Korean Cardiac Arrest Research Consortium (KoCARC), which are not national data, but rather data from 32 hospitals with high quality and experienced medical staff. Our study uses nationwide data on OHCA, which provides a broader sample than the previous study. This includes a range of patient demographics, regional variations and treatment protocols across the country, increasing the generalizability of our findings and their applicability to the whole population. Third, we did not account for whether the DA EMS crews were more experienced, received more education, or had more actual case volumes than other protocols, because these data were not available. Such information about individual EMS crews is necessary to improve the quality of future research. Fourth, the quality of EMS crew resuscitation could not be measured, and feedback CPR was only available in some metropolitan areas. Finally, this study was based on a pilot project conducted during a transitional stage when the level of EMT transitioned from EMT-I to paramedics and is difficult to generalize to all countries.
In conclusion, ALS protocol interventions were associated with differences in prehospital ROSC rates. All societies should do their best to improve the survival of patients with cardiac arrest based on local characteristics.
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