Association between endotracheal intubation and outcomes of nonshockable out-of-hospital cardiac arrest in Japan

Abstract

Background

Patients with nonshockable out-of-hospital cardiac arrest (OHCA) have poor outcomes compared with those with shockable rhythm. The optimal strategy for advanced airway management (AAM) for these patients remains controversial. This study aimed to compare outcomes between prehospital endotracheal intubation (ETI) and supraglottic airway (SGA) for adults with witnessed and nonshockable OHCA.

Methods

We compared the outcomes according to airway management using a nationwide, population-based Japanese registry (All-Japan Utstein Registry) between 2005 and 2021. The study population included adults with witnessed, nontraumatic, nonshockable OHCA who received prehospital AAM by emergency medical service (EMS) personnel. The outcomes were return of spontaneous circulation (ROSC), 1-month overall survival, and 1-month survival with a favorable neurological outcome, defined as a Cerebral Performance Category score of 1 or 2. To adjust for confounding factors between the ETI and SGA groups, we used propensity score analysis with inverse probability of treatment weighting (IPTW) and performed a sensitivity analysis using overlap weighting.

Results

A total of 147,088 patients were included: 30,797 (20.9%) received ETI and 116,291 (79.1%) received SGA. After IPTW adjustment, patients receiving ETI had significantly higher rates of ROSC (19.3% vs. 11.1%; odds ratio [OR] 1.51; 95% confidence interval [CI] 1.48–1.54), 1-month survival (6.4% vs. 4.5%, OR 1.44; 95%CI 1.40–1.49), and 1-month survival with favorable neurological outcomes (1.0% vs. 1.0%, OR 1.11; 95%CI 1.04–1.20) than those receiving SGA. The sensitivity analysis confirmed robust associations for ROSC (OR 1.53; 95%CI 1.45–1.61) and 1-month survival (OR 1.48; 95%CI 1.36–1.60), but the association with favorable neurological outcome was not statistically significant (OR 1.11; 95%CI 0.93–1.34).

Conclusion

In this Japanese nationwide Utstein registry cohort study with IPTW adjustment, for adult witnessed OHCA patients with initial nonshockable rhythm, prehospital ETI was associated with significantly higher rates of ROSC and 1-month survival, compared to prehospital SGA. These findings suggest that ETI, when performed by EMS personnel, has the potential to improve outcomes in these patients with OHCA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12873-025-01341-6.

Introduction

Out-of-hospital cardiac arrest (OHCA) is a major public health burden worldwide. In 2010, Berdowski et al. reported that emergency medical service (EMS) treated OHCA occurred in 87.4, 96.5, 65.4, and 108.9 cases per 100,000 person-years in Europe, North America, Asia, and Australia, respectively [1]. A recent report has indicated that OHCA occurred in 143,507 adult patients and had a high incidence, occurring in 88.8 patients per 100,000 person-years annually in the United States [2]. Moreover, most adult patients with OHCA had an initial nonshockable rhythm (74.4%), and approximately 52.2% had an initial asystole rhythm [2].

Despite intensive efforts by the EMS over many years, adult patients with OHCA have a low survival rate to hospital discharge (9.3%) [2]. The outcomes of patients with OHCA treated by EMS vary according to the initial cardiac rhythm [2–5]. Patients with an initial nonshockable rhythm (pulseless electrical activity or asystole) have worse survival rates to hospital discharge than those with an initial shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia) [2–5]. The initial nonshockable rhythm is independently associated with worse outcomes in patients with OHCA [6]. The database of the United States indicated that the survival rates to hospital discharge were 26.6% and 5.7% in shockable and nonshockable rhythms, respectively [2]. A systematic review and meta-analysis revealed that the survival rates to hospital discharge or at 30 days were 20% and 6% in shockable and nonshockable rhythms, respectively, even among patients with EMS-witnessed OHCA [7]. Therefore, improving outcomes in OHCA with nonshockable rhythms is a major challenge worldwide.

Advanced airway management (AAM) and epinephrine administration can be performed simultaneously while continuing high-quality cardiopulmonary resuscitation (CPR) in the prehospital situation [8]. Globally, guidelines recommend AAM for OHCA during CPR [9–11]; however, the survival benefits of management are still controversial in OHCA. Although some studies have reported survival benefits regarding prehospital AAM, others have reported poor outcomes [12–17]. Actually, AAM can provide optimal oxygenation and airway protection in the early stages of CPR [18]. In contrast, positive pressure ventilation and technical errors in AAM can result in a reduction in the quality of chest compression and worsen OHCA outcomes [19, 20]. Based on the constructive controversy, AAM has been the focus of clinical research and device development in recent years, with the potential to complement existing strategies for patients with OHCA treated EMS.

AAM commonly consists of manual maneuvers with a bag-valve-mask (BVM), endotracheal intubation (ETI), and supraglottic airway (SGA) [21]. In addition, SGA devices include the laryngeal tube (LT), laryngeal mask, i-Gel, and combi-tube [22, 23]. ETI has long been considered the gold standard of AAM for patients with OHCA in most countries [24]. However, reports of ETI-related complications, including unrecognized esophageal intubation, iatrogenic hyperventilation, and aspiration pneumonia, have increased [25–27]. In addition, EMS personnel require proper training and competence in performing ETI [28]. Compared with ETI, SGA insertion is rapid, simple, and requires less training and has been gradually used despite its complications [22, 23].

In Japan, specially trained EMS personnel have been permitted to use ETI since 2004, which has gradually increased nationwide, and received instructions and training on the use [29]. In the cohort study conducted in Osaka Prefecture, Japan, in 2011, no difference in the outcome from witnessed OHCA was noted between ETI and SGA regardless of the initial rhythm [30]. In this current study, using the All-Japan Utstein Registry from 2005 to 2021, we evaluated the outcomes of witnessed adult patients with nonshockable OHCA according to AAM types (ETI versus SGA).

Methods

Study design and settings

This retrospective cohort study used data from the All-Japan Utstein Registry, as previously described [31]. In Japan, this registry is a prospective, population-based, nationwide registry of OHCA in which data are recorded with the internationally standardized Utstein template [32]. The cohort study was approved by the Wakayama Medical University Ethics Committee (Approval no. 4196, approved on July 16, 2024) and the Meiji University of Integrative Medicine Ethics Committee (Approval no. 2024-043, approved on January 30, 2025), and was performed in accordance with the Declaration of Helsinki. Due to the retrospective nature of the study and the use of publicly available de-identified data, the Wakayama Medical University Ethics Committee and the Meiji University of Integrative Medicine Ethics Committee waived the need of obtaining informed consent. This study was reported according to the Strengthening the Reporting of Observational Studies in Epidemiology guidelines [33]. Data are available through the submission of a proposal and completion of a data usage agreement with the Fire and Disaster Management Agency of Japan.

Study participants

This retrospective cohort study enrolled 786,670 patients, aged ≥ 18 years who suffered from witnessed OHCA, recorded in the Utstein Registry between January 1, 2005, and December 31, 2021. Among them, data on 616,410 patients with an initial nonshockable rhythm at EMS arrival were extracted. Then, 282,719 patients with traumatic or unknown causes were excluded, and 333,691 patients with nontraumatic causes were selected (Fig. 1). To mitigate the impact of treatment bias and potential confounding in the direct comparisons between patients who underwent ETI and those who underwent SGA, we excluded patients who did not receive prehospital AAM, and 147,088 were included in the primary analysis.

Fig. 1.

Flowchart of the study population

Study variables

The following variables were analyzed: age, sex, origin of arrest, place of occurrence, witness status, presence and type of bystander CPR, bystander automated external defibrillator (AED) use, first documented rhythm on EMS personnel arrival, interventions of EMS personnel (defibrillation, types of AAM, and epinephrine administration), and the time from collapse to arrival of EMS [31, 32]. The All-Japan Utstein Registry records SGA use with information on device type, including laryngeal tube and laryngeal mask airway. Information on the i-Gel is incorporated into the category of laryngeal mask. However, the registry does not capture whether ETI was performed using video or direct laryngoscopy. Moreover, the datasets included outcome measures, such as the return of spontaneous circulation (ROSC), 1-month overall survival, and 1-month survival with favorable neurological outcomes. Neurological outcomes were evaluated according to the Glasgow Cerebral Performance Categories (CPC) scale. Patients with CPC 1 or 2 were considered to have favorable neurological outcomes [31].

EMS system in Japan

The EMS personnel are highly trained in all aspects of prehospital emergency care and treat cardiac arrest based on the Japanese CPR guidelines [34]. EMS teams are not allowed to terminate resuscitation in the field unless postmortem signs such as rigor mortis or lividity are evident. In particular, certified personnel with advanced training are allowed to insert an intravenous line, administer adrenaline, and conduct ETI for patients with OHCA. With online medical guidance by a physician, they are permitted to perform these emergency life-saving technicians. Moreover, medical control is established as a regionally structured protocol for these technicians. During the COVID-19 pandemic, infection control notices were issued in Japan; however, there were no changes to the protocol regarding the selection of AAM methods.

In accordance with international recommendations, adrenaline administration for nonshockable OHCA is indicated without delay, and this practice is also followed in Japan [34]. However, Japan’s EMS protocol limits intravenous access attempts to a maximum of two. Consequently, vascular access is not always achieved before hospital arrival, preventing epinephrine administration in some cases.

Exposure and outcome measures

The main exposure was prehospital ETI or SGA by EMS personnel. The primary study outcome was 1-month survival with favorable neurological outcomes. The secondary outcomes were 1-month overall survival and ROSC.

Statistical analyses

In this analysis, 147,088 patients receiving AAM were divided into two subcohorts: ETI and SGA. Continuous variables are reported as means, and categorical variables are reported as counts and proportions. Standardized mean differences were calculated to determine differences in baseline patient characteristics.

Inverse probability of treatment weights (IPTW), which were calculated from the propensity score (PS) for ETI, was used to adjust for confounding factors. IPTW analysis was applied to the multiply imputed datasets using the within-imputation method [35], wherein PS estimation and weighted outcome modeling were conducted separately for each dataset and subsequently combined using standard methods. PS was estimated through conditional logistic regression on the covariates. These covariates included age, sex, bystander CPR, initial rhythm, administration of epinephrine, and the time from collapse to EMS arrival, consistent with the variables listed in Table 1. To evaluate the ability of the model to predict ETI, the C-statistic was calculated as the area under the receiver operating characteristic curve. To evaluate the balance of the baseline covariates between the two groups, absolute standardized differences were computed, with a threshold of < 25% considered acceptable [36]. Following the generation of the IPTW cohorts, weighted logistic regression analyses were conducted to compare the outcomes between the ETI and SGA groups: logistic regression analyses were performed for binary outcomes. OR and standard errors were calculated using Rubin’s rules [37].

Table 1.

Demographic and clinical characteristics of all patients and propensity-score inverse probability of treatment weighted patients

	Before Weighting			After Weighting
	ETI (N = 30,797)	SGA (N = 116,291)	SMD	ETI (N = 28,285)	SGA (N = 115,529)	SMD
Age, median, year	79.9	77.1	0.061	78.0	77.6	0.012
Sex, female, N (%)	13,664 (46)	48,373 (43)	0.215	13,539 (44)	49,058 (43)	0.026
Implementation of bystander CPR, N (%)	14,578 (41)	63,068 (47)	-0.115	13,263 (46)	51,503 (45)	0.013
Asystole as initial rhythm on EMS arrival, N (%)	17,534 (57)	59,860 (51)	0.112	16,871 (54)	61,568 (52)	0.053
Administration of Epinephrine, N (%)	16,291 (54)	59,145 (50)	0.098	13,155 (43)	61,637 (53)	-0.203
Collapse-EMS arrival, median, (seconds)	799.6	757.8	0.038	800.0	760.0	0.036
EMS arrival-AAM, median, (seconds)	600.0	540.0

Characteristics of the included patients in the cohort data. Data are presented as N (%) or median (interquartile range)

Abbreviation: CPR: cardiopulmonary resuscitation; EMS: emergency medical service; ETI: endotracheal intubation; N: number; SMD: Standardized mean difference; SGA: supraglottic airway

By stratifying patients into two groups based on the year, the subgroup analysis was performed to investigate whether the effect of ETI interacted with the outcomes. Weighted logistic regression analyses for the outcomes were performed using identical covariates.

For the sensitivity analysis, overlap weighting of the PS was applied as an alternative to IPTW to balance the baseline characteristics [38, 39]. The overlap weighting estimate represents the average treatment effect within the overlap population, comprising patients with a realistic likelihood of receiving either treatment. This method ensures an exact balance in the mean of all measured covariates [39].

All statistical analyses and data visualization were performed using R statistical software version 4.1.0 (The R Foundation for Statistical Computing, Vienna, Austria) and Stata/MP 16.0 (StataCorp, College Station, TX, USA). All p-values were two-sided, with p < 0.05 considered significant.

Results

In this study, 147,088 eligible patients who were treated with AAM by ESM personnel were analyzed and categorized into two distinct groups: 30,797 patients (20.9%) with ETI (ETI group) and 116,291 patients (79.1%) with SGA (SGA group). The mean ages of the ETI and SGA groups were 79.9 and 77.1 years, and female patients were 13,664 (46%) and 48,373 (43%), respectively. Moreover, we focused on the year of AAM implementation for patients with OHCA. Before matching, the mean time between EMS arrival and AAM was 1,200 s in the early (2005–2012) years and 626 s in the later (2013–2021) years (p < 0.001). Patients with OHCA in the ETI group were unlikely to receive bystander CPR and were likely to be female and receive epinephrine administration. Table 1 shows the patient demographics and clinical characteristics before and after the IPTW. The C-statistic was 0.605 in the PS models. The IPTW indicated that the patient distributions were well-balanced between the groups. Among the covariates used from the cohort, missing values ranged from 5.7 to 23.8% (Supplemental Table 1).

After imputing the missing data, the outcomes by the type of advanced airway are shown in Table 2. The proportions of the ROSC in the ETI and SGA groups were 19.3% and 11.1%, respectively. The proportions of 1-month survival of the ETI and SGA groups were 6.4% and 4.5%, respectively. The proportions of 1-month survival with favorable neurological outcomes in the ETI and SGA groups were 1.0% and 1.0%, respectively. The ETI group exhibited significantly higher rates of ROSC (OR, 1.51; 95% CI, 1.48–1.54), 1-month overall survival (OR, 1.44; 95% CI, 1.40–1.49), and 1-month survival with favorable neurological outcomes (OR, 1.11; 95% CI, 1.04–1.20). Table 3 indicates the results of the sensitivity analysis. The overlap weighting of the PS confirmed the relationship of ETI with ROSC (OR, 1.53; 95% CI, 1.45–1.61) and 1-month overall survival (OR, 1.48; 95% CI, 1.36–1.60). The relationship between the ETI group with 1-month survival and favorable neurological outcomes was not significant (OR, 1.11; 95% CI, 0.93–1.34).

Table 2.

Outcomes among endotracheal intubation versus supraglottic airway after propensity-score inverse probability of treatment weighted logistic regression analyses

	Overall (N = 147,088)	ETI (N = 30,797)	SGA (N = 116,291)	Odds ratio (95%CI) (IPW)*
ROSC, N (%)	18,895 (12.8)	5,931 (19.3)	12,964 (11.1)	1.51 (1.48–1.54)
One-month Survival, N (%)	7,238 (4.9)	1,986 (6.4)	5,252 (4.5)	1.44 (1.40–1.49)
CPC score 1 or 2, N (%)	1,508 (1.0)	307 (1.0)	1,201 (1.0)	1.11 (1.04–1.20)

Data are presented as N (%)

Abbreviations: CI: confidence interval; CPC: cerebral performance category; ETI: endotracheal intubation; ROSC: return of spontaneous circulation, SGA: supraglottic airway, IPW: inverse probability weighting. ^* IPW analysis was performed to balance the potential confounders

Table 3.

Outcomes among endotracheal intubation versus supraglottic airway after sensitivity analysis

	Odds ratio (95% confidence interval)
ROSC	1.53 (1.45–1.61)
One-month Survival	1.48 (1.36–1.60)
CPC score 1 or 2	1.11 (0.93–1.34)

Abbreviations: CPC: cerebral performance category; ROSC: return of spontaneous circulation

As for the year group, the differences in the effects of ETI on the outcomes were observed between the early (2005–2012) and later (2013–2021) years (Table 4). In the early years, although a significantly higher ROSC rate was observed (OR, 1.26; 95% CI, 1.21–1.30), no significant differences were detected in 1-month overall survival (OR, 1.03; 95% CI, 0.98–1.08) or 1‐month survival with favorable neurological outcomes (OR, 1.00; 95% CI, 0.91–1.10). Meanwhile, in the later years, the ETI group exhibited better outcomes consistent with the primary analyses for ROSC (OR, 1.54; 95% CI, 1.50–1.59), 1‐month overall survival (OR, 1.62; 95% CI, 1.55–1.70), and 1‐month survival with favorable neurological outcomes (OR, 1.17; 95% CI, 1.05–1.31).

Table 4.

Outcomes according to the year of advanced airway management implementation

	Odds ratio (95% confidence interval)
	2005–2012 years	2013–2021 years
ROSC	1.26 (1.21–1.30)	1.54 (1.50–1.59)
One-month Survival	1.03 (0.98–1.08)	1.62 (1.55–1.70)
CPC score 1 or 2	1.00 (0.91–1.10)	1.17 (1.05–1.31)

Abbreviations: CPC: cerebral performance category; ROSC: return of spontaneous circulation

Discussion

This observational study using the All-Japan Utstein Registry focused on adult patients with witnessed nontraumatic OHCAs and nonshockable rhythms on EMS arrival and assessed the difference between ETI and SGA outcomes. Patients with OHCA receiving ETI in the prehospital setting exhibited favorable outcomes than those receiving SGA.

In 2011, a prospective Utstein-style population cohort database conducted in Osaka, Japan, showed that these devices were not significant predictors of OHCA outcomes regardless of the initial rhythms [30]. Two multicenter randomized control trials (RCTs) of AAM for OHCA did not indicate a difference in the survival and neurological outcomes between ETI and SGA [23, 40]. An RCT by Wang et al. revealed that the initial LT insertion improved the 72-h survival compared with the initial ETI among adults with OHCA [22]. In two reports of systematic review and network meta-analysis, ETI did not contribute to improving survival to discharge compared with other devices for AAM [41, 42]. Furthermore, the subanalysis of the Target Temperature Management-2 trial showed that the choice of airway device, including ETI and SGA, was not independently associated with the outcomes of adult patients with OHCA [43]. In this study, the positive effect of ETI for OHCA did not align with these reports but may be due to focusing on some variables such as witnessed and initial nonshockable rhythm in the prehospital setting.

Some studies, including a meta-analysis, have indicated that compared with SGA, ETI is positively associated with outcomes among adults with OHCA [21, 44]. The ROC PRIMED study, a prospective clinical trial conducted in the North America, revealed the superiority of ETI over SGA in adult and nontraumatic OHCAs [21]. At that time, the Ministry of Health, Labour and Welfare issued a directive stating that ETI should be performed only in cases where SGA was ineffective or where ETI was expected to provide superior airway management [45]. As a result, patients who underwent ETI in the early period may have included those in whom SGA was not feasible or who had already experienced failed SGA attempts, introducing potential selection bias against ETI. More than 10 years have passed since this report of the Osaka registry, and prehospital medical care in Japan has changed. In our country, specially trained and certified EMS personnel have been permitted to perform ETI under medical direction, although the regional protocol varies [46, 47], and the number has been increasing. Early and increased performance of AAM including ETI and SGA at the prefecture level improved neurologically favorable survival following OHCA [46, 47]. Notably, even in the PS matching for OHCA, AAM was associated with favorable outcomes among patients with nonshockable rhythms [48]. However, SGA was preferred because of the low ETI success rate in these studies. In the RCT by Wang et al., the rate of unsuccessful first insertion was significantly higher in the ETI group (44.1%) than in the LT group (11.8%) [22]. For OHCAs receiving ETI attempts, the cumulative success rates for the first three attempts were 69.9%, 84.9%, and 89.9%, respectively, and the overall success rate was 91.8% after three attempts [49]. In this study, during prehospital CPR, conducting ETI improved the outcomes of nonshockable OHCA regardless of the timing and attempt. Moreover, high PaO2 and PaCO2 ≤ 45 mmHg by ETI were associated with favorable outcomes following OHCA [50, 51]. Therefore, the higher success of ETI by EMS personnel is needed for adequate training and practice, as in previous reports [52, 53].

For patients with OHCA, the use of a video laryngoscope for ETI during CPR was associated with better neurological outcomes than with a direct laryngoscope [54]. In addition, an observational study in Hiroshima (Japan) and the meta-analysis have recently shown that the video laryngoscope was associated with first-pass success for patients with OHCA; however, no differences in survival outcomes were found between the two approaches [55, 56]. The improvement in portability and price reduction led to the worldwide use of video laryngoscopy to assist ETI and promote effectiveness and safety. Therefore, the use of video laryngoscopy for OHCA is suggested to offer a promising option. Indeed, our subanalyses indicated that the ETI group in the later years shortened the mean time between EMS arrival and AAM and improved favorable outcomes compared with that in the early years. The improvement in outcomes observed in the later years may reflect not only enhanced EMS training systems but also the increasing adoption of video laryngoscopy, which has been reported to improve first-pass success during CPR [55, 56]. Unfortunately, the registry does not include data on laryngoscopy type, so stratified analyses could not be performed. The wide dissemination of video laryngoscopy for each team of Japanese EMS is important to increase the success rate of ETI and the survival rate of patients with OHCA.

In our study, the relatively low rate (54% in the ETI group and 50% in the SGA group) of epinephrine administration in the nonshockable OHCA is likely attributable to procedural constraints within Japan’s EMS system, where intravenous access attempts are limited to two per patient. Moreover, in Japan, vascular access placed by EMS personnel is not permitted via intraosseous route [31]. This can result in failed vascular access before hospital arrival, even when epinephrine is indicated. Similarly, a population-based study from the Osaka Utstein Registry reported that intravenous access was attempted in 42.0% of non-ventricular fibrillation cohort and succeeded in 45.7% of attempts (ventricular fibrillation cohort: 51.2% attempted; 53.5% successful among attempts) [57]. These findings should be interpreted in the context of Japan’s unique EMS system, which differs from those of other countries.

The interval in our study from EMS arrival to AAM attempt (median times: 600 s for ETI and 540 s for SGA) appears relatively longer than in a previous study, which reported the time from arrival to AAM as approximately 8 min for ETI and 6.5 min for SGA [30]. That study was conducted using the Osaka Utstein Registry database, reflecting Japan’s major metropolitan areas with a well-developed EMS system, whereas our study employed a nationwide database that also included rural regions. In addition, delays in AAM may have occurred in some cases due to EMS resource constraints and regional protocols that prioritize uninterrupted chest compressions [31]. These factors, inherent to Japan’s EMS system, likely contributed to the longer time to AAM observed in our study and should be considered when comparing our findings with those from other EMS systems. Importantly, prior research has suggested that survival outcomes may be adversely affected when the time to advanced airway exceeds 15 min [13]. Given that the median interval in our study was considerably shorter than this threshold, it is unlikely that the observed delay substantially altered our results. Nevertheless, our findings may not be directly generalizable to EMS systems operating under different regulatory and training frameworks, and extrapolation should be made with caution.

Limitations

This observational cohort study has several limitations. First, this study did not compare adults receiving AAM with those receiving BVM. Although previous studies have shown that BVM was associated with favorable outcomes compared with AAM, including ETI and SGA [15], the comparison between AAM and BVM is now controversial. The current 2024 AHA guidelines recommend both BVM and AAM for adult OHCA in the prehospital setting [58]. In this study, the effect of ETI relative to SGA for them was evaluated. Second, the choice of AAM techniques varied according to the local medical direction and EMS experience in Japan. Therefore, selection bias may occur in the AAM implementation content between regions. Third, the exact confounding variables could not be clarified because our database lacks detailed information such as intubation attempt counts, success rates, or complications. Moreover, whether ETI was performed using video or direct laryngoscopy were not recorded, limiting further device-specific analyses. This information could have potentially affected the outcomes. Fourth, the dataset analyzed did not include information regarding in-hospital interventions, such as induced targeted temperature management, extracorporeal CPR, percutaneous coronary intervention, and administration of some drugs [59]. These interventions may have contributed to the outcomes observed, but prior evidence suggests that excluding such patients does not materially change the associations [60].

Future registry iterations should incorporate such variables to enable a more comprehensive evaluation of the continuum of care from prehospital to in-hospital settings.

Conclusion

For adults with witnessed nontraumatic OHCA, the ETI strategy was positively associated with outcomes in nonshockable rhythms on EMS arrival. In Japan, improving training and protocols so that ETI can be performed accurately and quickly may improve outcomes for OHCA with nonshockable rhythms. Future studies on global cohort and RCT are required to address the impact of ETI for such patients.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

OHCA

Out-of-Hospital Cardiac Arrest

EMS

Emergency Medical Service

AAM

Advanced Airway Management

CPR

Cardiopulmonary Resuscitation

BVM

Bag-Valve-Mask

ETI

Endotracheal Intubation

SGA

Supraglottic Airway

LT

Laryngeal Tube

AED

Automated External Defibrillator

ROSC

Return of Spontaneous Circulation

CPC

Cerebral Performance Categories

IPTW

Inverse probability of treatment weights

PS

Propensity score

RCT

Randomized control trial

Author contributions

MN, AK, and ST contributed to study conception and design, and drafted the manuscript; MN, MU, AK and ST collected the data; AK, KK, TN, RH, SI, and MH contributed to methodology development; MN, MU, AK, and ST analyzed and interpreted the data; KK, TN, RH, SI, and MH provided supervision, critically reviewed the manuscript, and gave final approval. All the authors reviewed and approved the final version of the manuscript.

Funding

This work was supported by the JSPS KAKENHI (grant number: 23K07865) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and 2023 Wakayama Medical University Special Grant-in-Aid for Research Projects (grant number: K23TS03).

Data availability

The datasets used and analyzed in this study are available from the corresponding author (Shinobu Tamura, stamura@wakayama-med.ac.jp) upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Wakayama Medical University Ethics Committee (Approval no. 4196, approved on July 16, 2024) and the Meiji University of Integrative Medicine Ethics Committee (Approval no. 2024-043, approved on January 30, 2025). The study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. The requirement for informed consent was waived due to the retrospective design of the study and the use of use of publicly available de-identified data.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.