Association between prehospital airway management methods and neurologic outcome in out-of-hospital cardiac arrest with respiratory cause: a nationwide retrospective observational study

1. Introduction

Various etiologies are responsible for the occurrence of out-of-hospital cardiac arrest (OHCA) [1, 2]. Although majority of OHCA is caused by cardiac cause, respiratory problems resulting from hypoxia and hypoventilation in conditions such as ARDS, pneumonia, COPD and asphyxia also cause cardiac arrest [3, 4, 5]. For cardiac arrest caused by respiratory aetiology, resuming and providing oxygenation and ventilation during cardiac arrest is especially important for correcting the cause of arrest and minimizing neurological damage in the brain [6, 7].

Advanced airway placement is one of the key prehospital interventions performed by emergency medical service (EMS) providers during field resuscitation of OHCA [8]. The main purpose of advanced airway placement is to provide more effective oxygenation and ventilation than basic airway such as bag-valve-mask (BVM) [9, 10]. Various studies have compared the effects of prehospital advanced airway management methods on outcomes in OHCA, but they are mostly tested in cardiac arrest with presumed cardiac cause the results are still controversial [11, 12, 13, 14, 15].

However, little is known about the association of prehospital advanced airway management and outcome according to the cause of cardiac arrest.

In this study, we investigated the association between prehospital advanced airway method and neurologic outcome according to the presumed cause of cardiac arrest under the hypothesis that the effect of each advanced airway management type would be different when cause of arrest is suspected to be respiratory.

2. Methods

3. Results

In total, 145,003 OHCA patients in our registry were initially enrolled from January 2013 to December 2017. Patients aged less than 18 years (N = 3170), patients with OHCA not witnessed (N = 79,208), patients not treated by EMS providers (N = 4063), patients with cardiac arrests occurring during ambulance transport (N = 7203), patients treated by EMS teams without any level-1 EMTs capable of advanced airway placement (N = 5756), traumatic cause (N = 5062) and patients with unknown outcome (prehospital ROSC, survival and neurologic outcome) (N = 98) and were excluded (Fig. 1).

Fig. 1.Enrollment flow of study population. OHCA, out-of-hospital cardiac arrest; EMS, emergency medical service; EMT, emergency medical technician.

After serial exclusion, 40,443 OHCA patients were included in the final analysis. Regarding the presumed cause of arrest, 36,404 (90.0%) cases were cardiac, 3050 (7.5%) were respiratory and 989 (2.4%) were others. The demographic characteristics according to cause are summarized in Table 1. The proportion of advanced airway placement differed according to the group, and the rate of endotracheal intubation was highest in the respiratory cause group (6.7% vs. 8.1% vs. 5.1%, respectively, p $<$ 0.01). The neurologically favorable survival-to-discharge rates were 12.5% in the cardiac group, 9.6% in the respiratory group, and 12.1% in the others group (Table 1, p $<$ 0.01).

In the multivariable logistic regression analysis, there was no statistically significant association between type of airway management and good neurologic recovery (SGA as reference, aOR (95% CI) 1.01 (0.93–1.11) for BVM; 0.96 (0.81–1.14) for ETI) and survival to discharge (SGA as reference, aOR (95% CI) 0.96 (0.89–1.03) for BVM; 0.96 (0.83–1.11) for ETI) in the total population (Table 2). For multivariate model of good neurological outcome, p-value of Hosmer and Lemeshow goodness of fit test was less than 0.01 and C-statistics was 0.84. For multivariate model of survival to discharge, p-value of Hosmer and Lemeshow goodness of fit test was less than 0.01 and C-statistics was 0.78.

In the interaction analysis, the magnitude of the association between type of advanced airway and outcome measures was different according to the presumed cause of cardiac arrest. ETI was associated with significantly better neurological recovery than SGA (aOR 3.12 (95% CI 1.24–7.80)) and BVM (aOR 3.16 (95% CI 1.43–6.98)) when the cause of arrest was respiratory. Although the effect of ETI was nonsignificant, BVM was associated with lower survival to discharge than SGA when the cause of arrest was respiratory (aOR 0.70 (95% CI 0.52–0.94)) (Table 3). For interaction analysis model of good neurological outcome, p-value of Hosmer and Lemeshow goodness of fit test was less than 0.01 and C-statistics was 0.84. For interaction analysis model of survival to discharge, p-value of Hosmer and Lemeshow goodness of fit test was less than 0.01 and C-statistics was 0.78.

4. Discussion

In this analysis of a nationwide, population-based OHCA registry, we evaluated the association between prehospital advanced airway methods and clinical outcome of cardiac arrest. The magnitude of the association was different according to the presumed cause of cardiac arrest. There was no statistically significant difference in the effect according to the advanced airway type in total population and arrest with cardiac origin. However endotracheal intubation was associated with better neurologic outcome when the cause of arrest was respiratory. We believe more efficient oxygenation and ventilation through prehospital endotracheal intubation provides a rapid and effective solution to respiratory cause of cardiac arrest, as an antidote for drug intoxication. Although most of cardiac arrest cases receive endotracheal intubation eventually after hospital transport, faster reversal of hypoxia and hypoventilation by prehospital endotracheal intubation in the field might show an effect on minimizing hypoxic brain injury. Based on the results of our study, we suggest that endotracheal intubation might be considered as a first choice of method in OHCA patients whose cause of arrest is suspected to be respiratory, such as respiratory disease, asphyxia and strangulation.

Even after recent prospective clinical trials, defining the optimal choice of prehospital advanced airway methods in OHCA is controversial. Wang et al. [13] compared laryngeal tube and ETI as prehospital airway management methods for OHCA and showed that LT was superior to ETI when measuring 72-hour survival. Benger et al. [19] compared I-gel versus ETI, and there was no difference in survival to discharge or favorable neurologic outcome rate. Jabre et al. [12] compared BVM to ETI and obtained inconclusive results regarding 28-day survival with favorable neurologic outcome. Overall, the results showed no definite benefit of ETI over BVM or SGA. In a nationwide cohort study conducted in Japan, advanced airway management (ETI and SGA) was associated with better survival and more favorable neurologic outcomes compared with no advanced airway management in non-shockable (pulseless electrical activity and asystole) OHCA patients [20]. However, these studies did not consider the etiologies of arrest.

The supraglottic airway can be inserted blindly and therefore has a higher success rate than endotracheal intubation, even for those with low skills, such as EMS providers in Korea. However, compression of important structures such as carotid vessels has been suggested in animal studies in some SGAs due to its morphologic characteristics and mechanism [21, 22]. In severe hypoxia in respiratory arrest, carotid blood flow reduction caused by SGA insertion might be more critical than for other etiologies of cardiac arrest. One case reported ventilation failure of a drowned patient with supraglottic airways due to leakage from high pressure [23].

Several previous studies have reported negative effects of prehospital advanced airway placement on the outcome of respiratory cardiac arrest [15, 24]. However, these studies included only limited number of patients with medical intrinsic respiratory disease, excluding external causes of arrest, such as asphyxia or hanging. Additionally, the studies only tested the overall effect of prehospital advanced airway rather than the effect of each advanced airway method according to different etiologies, as in our study.

Only witnessed cardiac arrests were enrolled for analysis in our study. We opted not to include patients with arrest not witnessed by initial bystanders. Although our study was a retrospective observational study and there are currently no guidelines for EMS providers to consider cause of arrest when selecting the airway management method, we supposed it might be difficult for EMS providers to estimate the cause of arrest in unwitnessed cases. We believe that, for witnessed cardiac arrest, EMS providers can presume the cause of cardiac arrest based on a history taken from the bystander who witnessed the arrest or could at least determine whether the cause was respiratory or not. Based on the result of our study, we suggest that EMS providers might consider estimated cause when deciding the airway management method in the field.

A previous study reported negative association between pre-hospital advanced airway management and neurologic outcome of OHCA [15], we believe there are two different points between the study and our study. First, patient population of two studies was different because criteria used to define respiratory disease were different. Ohashi-Fukuda’s study was conducted on a population with the etiology of cardiac arrest as respiratory disease such as pneumonia, tuberculosis, chronic obstructive pulmonary disease, or asthma. Respiratory group in our study was categorized as cardiac arrests caused by obvious aggravation of respiratory disease, asphyxia (including foreign body airway obstruction), drowning(submersion) or hanging. Second, exposure of study performed by Ohashi et al. [15, 24] was advanced airway management, which combined laryngeal mask airway, oesophageal obturator airway, endotracheal tube. although subgroup analysis on methods of each airway devices shows poor neurological outcome consistently, laryngeal mask airway (aOR 0.35 (0.19–0.57)), oesophageal obturator airway (aOR 0.44 (0.35–0.55)), endotracheal tube (aOR 0.47 (0.30–0.69)) shows different effect between methods of each advanced airways. Our study analyzed each advanced airway method separately.

There are some limitations to our study. First, this was a retrospective observational study; therefore, careful interpretation is needed considering the unique characteristics of our EMS system. Second, we extracted cause of arrest by medical record review. For patients who did not achieve any ROSC and were pronounced dead after initial resuscitation, there might be few clues to estimate the cause of arrest. Third, the number of patients with favorable neurological outcome in the ETI group with respiratory arrest were very small (9 patients), which leading to wide confidence intervals and making results difficult to interpret. Furthermore, detailed diagnosis of respiratory disease or severity of trauma were not included in our database. Last, there might be unmeasured confounders not included in our registry that could affect both airway management method and outcome.

Also, there were some strengths in our study. First, this was a relatively large-scale nationwide study. Second, with Korea’s prehospital EMS system exclusively operated by national fire agency nationwide protocol was unified and EMS services were homogenous nationwide. Third, our study might suggest tailored therapy with prehospital stage information on treatment of OHCA.

Regarding the generalizability of our study, we can consider applying it to the Asian, scoop and run EMS model environment rather than the North American or European EMS model.

5. Conclusions

The association between prehospital advanced airway and the neurological outcomes of patients with witnessed non-traumatic OHCA was not significant. However, endotracheal intubation was associated with better neurologic recovery in cardiac arrest with respiratory cause. Endotracheal intubation may be considered initially by EMS providers when a respiratory cause is suspected for the pathogenesis of cardiac arrest.

Author contributions

YC and THK had full access to all of the data in the study and take responsibility for the integrity of the data as well as the accuracy of the data analysis. Study concept and design—YC, THK and SDS; acquisition, analysis, or interpretation of data—THK, KJH and KJS; drafting of the manuscript—YC; critical revision of the manuscript for important intellectual content—THK, KJS, and SDS; statistical analysis—THK and YC; administrative, technical, or material support—KJS and SDS; study supervision—SDS, KJS and THK; manuscript approval—all authors.

Ethics approval and consent to participate

The study was approved by the Seoul National University Hospital Institutional Review Board with a waiver of informed consent owing to its retrospective nature (IRB No. 1103-153-357). The first approval date was June 8th, 2011.

Acknowledgment

Not applicable.

Funding

This research received no external funding.

Conflict of interest

The authors declare no conflict of interest.