Abstract
Background:
Over 70% of patients with out-of-hospital cardiac arrest (OHCA) present with a non-shockable initial rhythm, asystole or pulseless electrical activity (PEA), which is associated with lower survival than a shockable initial rhythm. Advanced airway management and oxygen delivery are important OHCA interventions, but their impact based on different presenting rhythm groups are incompletely defined. Our objective was to determine if advanced airway strategy is associated with outcomes in shockable, PEA and asystolic OHCA.
Methods:
We performed a secondary analysis of data collected from the Pragmatic Airway Resuscitation Trial (PART), which assigned adults with OHCA to a strategy of either endotracheal intubation (ETI) or laryngeal tube (LT) for initial advanced airway management. We stratified patients by initial cardiac rhythm: shockable (ventricular fibrillation/pulseless ventricular tachycardia (pVT), AED shock), PEA or asystole. We excluded AED non-shockable and unknown rhythms. The primary outcome was 72-h survival. Secondary outcomes included return of spontaneous circulation (ROSC) at emergency department arrival, survival to hospital discharge, and survival with good neurological function (modified Rankin score ≤3). We used general estimating equations to determine the associations between airway strategy initial arrest rhythm and outcomes, adjusted for age, sex, witnessed status, and bystander CPR.
Results:
There were 3004 patients in the parent trial of which 2847 were included in this analysis. Of these 575 (20.2 %) were shockable, 671(23.6 %) were PEA, and 1601 (56.2 %) were asystole. Compared with ETI, LT airway use was not associated with improved 72-h survival in shockable rhythms (adjusted [AOR] 1.30 (0.91, 1.67)), PEA (AOR 0.97 (0.65, 1.45)), or asystole (AOR 1.13 (0.79, 1.64)). Similarly, we noted no significant interaction between airway strategy and initial rhythm for the secondary outcomes of ROSC, survival to discharge, and survival to discharge with good neurological function.
Conclusion:
Prehospital advanced airway management strategy (ETI vs. LT) was not significantly associated with outcomes regardless of initial cardiac rhythm.
Keywords: Out-of-hospital cardiac arrest, Airway management, PEA, Asystole, Shockable rhythm, Non-shockable rhythm
Introduction
Over 350,000 out-of-hospital cardiac arrests (OHCA) occur annually in the United States.1 Over 70 percent of patients experiencing cardiac arrest present with a non-shockable rhythm, including pulseless electrical activity (PEA) or asystole.2,3
Non-shockable rhythms have dismal survival to discharge with only 11 % and 2 % for PEA and asystole, respectively.2 Despite the poor prognosis of patients with non-shockable rhythms, little advancement has been made in evidence-based management of non-shockable cardiac arrest. However, airway management remains a central tenet of critical care and resuscitation. The American Heart Association (AHA), based on class 2b, weak evidence, recommends either a bag mask ventilation (BVM) or advanced airway strategy may be used in CPR for cardiac arrest in any setting.4 Similarly, the National Association of EMS Physicians (NAEMSP) recommends that either BVM, SGA or ETI may be considered as airway management strategies for OHCA based on clinician skill and available resources.5
The benefits of advanced airway management may vary by initial rhythm. Airway management may have a more prominent influence on PEA and asystole, where impaired oxygenation and ventilation may be more important contributing factors. In contrast, advanced airway management may be less important in ventricular fibrillation, where defibrillation is the preferred initial intervention. In two large population-based observational studies of OHCA from Japan, Okubo et al. and Izawa et al. reported that with initial non-shockable rhythms, advanced airway management was associated with survival.6,7 However, advanced airway management was not associated with survival in the shockable cohort.7 In a small prospective study of patients managed with ETI vs. SGA, Matic et al. found no significant difference in incidence of ROSC irrespective of initial cardiac arrest rhythm.8 There remains a gap in existing research regarding whether the approach to airway management should differ in shockable versus non-shockable rhythms.
The objective of our study was to determine if the association between advanced airway management and OHCA outcomes varies with different initial cardiac rhythm, with a focus on non-shockable rhythms, utilizing clinical trial data from the Pragmatic Airway Resuscitation Trial (PART).9
Methods
Design and setting
We performed a secondary analysis of data from the PART trial.9 The PART trial was approved by the Institutional Review Boards of participating centers under federal regulations for Exception from Informed Consent for Emergency Research (21 CFR 50.24). The current analysis was approved by the Ohio State University Office of Responsible Research Practices (Protocol No. 2021H0379).
The PART trial involved 27 emergency medical services (EMS) agencies from the Birmingham (Alabama), Dallas-Fort Worth (Texas), Milwaukee (Wisconsin), Pittsburgh (Pennsylvania) and Portland (Oregon) communities of the Resuscitation Outcomes Consortium (ROC). The PART study enrolled OHCA patients in these EMS systems from 2015 to 2017. The objective of the PART trial was to compare the effect of airway management strategies (initial LT vs. initial ETI) upon adult OHCA outcomes. The parent trial reported improved 72-h survival, hospital survival and hospital survival with favorable neurologic outcome with the initial LT strategy.
Participants
Patients were eligible for enrollment in the PART trial if they were adults (age ≥ 18 years or per local interpretation) experiencing a non-traumatic OHCA and requiring anticipated ventilatory support or advanced airway management.
Interventions
The cluster-crossover trial randomized EMS agencies to either of two initial advanced airway management strategies: initial Laryngeal Tube (LT) insertion or initial endotracheal intubation (ET). If the initial LT/ET insertion efforts were unsuccessful, EMS personnel were allowed to use all other available airway techniques for airway management. The complete protocol for airway management has been previously published (5).
Outcomes
The primary outcome was 72-h survival. Secondary outcomes included return of spontaneous circulation (ROSC) at emergency department arrival, survival to hospital discharge, and survival with good neurological function (modified Rankin score 3). Excluded AED non-shockable and unknown rhythms.
Statistical analysis
We compared baseline characteristics between LT and ETI groups, stratifying by initial rhythm (VF/pVT/AED-Shock, PEA, asystole, AED-non-shockable, and unknown). Because of this limited numbers, we excluded AED non-shockable and unknown rhythm groups from further analyses. We fit a series of regression models using Generalized Estimating Equations, accounting for randomization cluster. We created a separate models for each major outcome (72-h survival, ROSC, survival to hospital discharge and survival to discharge with good neurologic outcome). In each model we fit airway strategy (LT vs ET) and initial rhythm (VF/pVT/AED-Shock vs. PEA vs. asystole) as the main independent variables. We added an [airway X initial rhythm] multiplicative interaction term. We adjusted the models for age, sex, witnessed arrest, and bystander CPR. We repeated the analysis stratifying by initial rhythm.
Results
Of 3004 patients in the parent trial, initial rhythms were; shockable 575, PEA 671, asystole 1,601, AED non-shockable 95, and unknown 62 (Table 1). Mean patient age was 63.1 years (SD 16.9) (Table 1). Most subjects were male (60.9 %). Witnessed arrest rate was lowest in the asystole group. Bystander CPR was lowest in the PEA group. Assigned airway strategy was similar across initial rhythms. Time to first airway attempt and airway first pass success were similar across initial rhythms. ROSC, 72-h survival, hospital survival and survival with good neurologic function were higher for patients with an initial rhythm of VF/VT/AED shock than PEA or asystole.
Table 1 –
Characteristics of the study population.
| Initial Rhythm | |||||
|---|---|---|---|---|---|
| Characteristics | VF/pVT/AED Shock (N = 575) |
PEA (N = 671) |
Asystole N = 1601 |
AED No Shock (N = 95) |
Unknown (N = 62) |
| Age - mean (SD) | 61.6 (15) | 66.5 (16.3) | 62.3 (17.5) | 64.6 (18.2) | 59.4 (18.8) |
| Sex – male N-(%) | 404 (70.3) | 397 (59.2) | 937 (58.5) | 58 (61.0) | 33 (53.0) |
| Race/Ethnicity | |||||
| White N (%) | 329 (57.2) | 334 (49.8) | 799 (49.9) | 43 (45.3) | 37 (59.7) |
| Black | 120 (20.9) | 217 (32.3) | 466 (29.1) | 46 (48.4) | 14 (22.6) |
| Hispanic | 29 (5.04) | 32 (4.77) | 98 (6.12) | 0 (0.0) | 4 (6.5) |
| Other | 21 (3.65) | 13 (1.94) | 54 (3.37) | 2 (2.1) | 2 (3.2) |
| Witnessed Arrest – n (%) | 406 (70.6) | 448 (66.8) | 466 (29.1) | 48 (50.5) | 31 (50.0) |
| EMS witnessed - n (%) | 46 (8.00) | 190 (28.3) | 105 (6.56) | 6 (6.3) | 12 (19.4) |
| Bystander witnessed – n (%) | 360 (62.6) | 258 (38.5) | 361 (22.6) | 42 (44.2) | 19 (30.7) |
| Not witnessed – n (%) | 136 (23.7) | 183 (27.3) | 972 (60.7) | 44 (46.3) | 22 (35.5) |
| Unknown | 33 (5.7) | 40 (5.9) | 163 (10.2) | 3 (3.2) | 9 (14.5) |
| Bystander chest compressions – n (%) | 339 (58.9) | 220 (32.8) | 772 (48.2) | 41 (43.2) | 32 (51.5) |
| Time to First Vasopressor (min) – mean (SD) | 9.12 (5.2) | 11.22 (6.9) | 9.24 (4.9) | 9.8 (4.3) | 12.3 (8.2) |
| Field Termination of Resuscitation – n (%) | 79 (13.7) | 163 (24.3) | 914 (57.1) | 41 (43.2) | 12 (19.4) |
| Airway Strategy Assignment | |||||
| LT – n (%) | 307 (53.4) | 339 (50.5) | 790 (49.3) | 43 (45.3) | 31 (50.0) |
| ETI – n (%) | 268 (46.6) | 332 (49.5) | 811 (50.7) | 52 (54.7) | 31 (50.0) |
| Time to First Airway Attempt (min) – median(IQR) | 11 (7, 16) | 12 (9, 17) | 11 (8, 15) | 14 (11,20) | 15.5 (7, 23) |
| First Pass Airway Placement Success – n (%) | 336 (70.7) | 435 (69.8) | 961 (66.0) | 54 (70.1) | 27 (77.1) |
| ROSC | 238 (41.4) | 212 (31.6) | 281 (17.6) | 16 (16.8) | 38 (61.3) |
| 72-h Survival | 218 (38.0) | 129 (19.3) | 122 (7.6) | 6 (6.3) | 20 (49.2) |
| Survival to Hospital Discharge | 170 (29.6) | 55 (8.3) | 28 (1.8) | 1 (1.1) | 25 (41.7) |
| Survival to Hospital Discharge with Good Neurologic Function | 116 (20.4) | 24 (3.6) | 15 (0.9) | 0 (0.0) | 22 (36.7) |
Results of the multivariate analysis showed that the initial airway strategy was not associated with adjusted 72-h survival (Table 2). However, compared to asystole, initial PEA and VF/VT/AED Shock were associated with higher adjusted 72 h survival. The [airway X initial rhythm] interaction terms were not statistically significant. We observed similar associations with the outcomes of ROSC, hospital survival and hospital survival with favorable neurologic function. When stratified by initial ECG rhythm (asystole, PEA, VF/pVT/AED shock), initial airway strategy was not associated with 72-h survival, ROSC, hospital survival, or hospital survival with good neurologic function (Table 3).
Table 2 –
Associations of Airway Strategy with OHCA outcomes adjusted for age, sex, race, witnessed arrest, bystander CPR and [airway × initial rhythm] interaction.
| Exposures | 72 h Survival | ROSC | Hospital Survival | Hospital Survival with Favorable Neurologic Function |
|---|---|---|---|---|
| Airway Assignment (LT vs. ETI) | 1.17(0.81–1.69) | 1.21 (0.93–1.58) | 1.05(0.51–2.17) | 0.77(0.29–2.04) |
| Initial Rhythm | ||||
| Asystole | Reference | Reference | Reference | Reference |
| PEA | 2.52(1.69–3.75) | 2.20(1.62–3.00) | 3.68(1.85–7.31) | 2.18(0.90–5.31) |
| VF/pVT/AED shock | 5.14 (3.49–7.56) | 2.66 (1.94–3.71) | 13.00 (6.81–24.74) | 10.40(4.75–22.77) |
| [Airway × Initial Rhythm] Interaction | ||||
| LT × Asystole | Reference | Reference | Reference | Reference |
| LT × PEA | p = 0.46 | p = 0.06 | p = 0.97 | p = 0.65 |
| LT × VF/pVT/AED Shock | p = 0.71 | p = 0.87 | p = 0.50 | p = 0.31 |
Table 3 –
Associations of Advanced Airway Strategy (LT vs. ETI) with OHCA outcomes, stratified by initial rhythm. Data adjusted for age, sex, race, witnessed arrest, bystander CPR.
| Subgroups | 72 h Survival | ROSC | Survival Hosp Discharge | Survival with Good Neurologic Function |
|---|---|---|---|---|
| Asystole | 1.13(0.79–1.64) | 1.23(0.94–1.60) | 1.22(0.58–2.58) | 0.93(0.32–2.65) |
| PEA | 0.97(0.65–1.45) | 0.79(0.57–1.11) | 1.01(0.57–1.78) | 1.01(0.44–2.34) |
| VF/pVT/AED Shock | 1.30 (0.91–1.87) | 1.25(0.88–1.77) | 1.40(0.95–2.07) | 1.28 (0.82–1.99) |
Discussion
We observed no significant association between initial airway strategy and 72-h survival when stratified by initial rhythm. There was also no significant difference in ROSC, survival to discharge or neurologic status at discharge when stratified by assigned airway strategy method and initial rhythm.
While there are well-characterized differences in outcomes between shockable vs. non-shockable rhythms,10–12 there have been limited studies describing if airway management influences these relationships. Overall, there is a paucity of studies investigating whether the approach to airway management should differ in shockable versus non-shockable rhythms. One large, robust observational study by Okubu et al. found that advanced airway management within 15 min of initiation of EMS CPR was associated with 1-month survival in the non-shockable rhythm group, whereas no survival benefit was seen in the shockable rhythm groups.6 The results of Okubo et al. differ from the results of the present study and this may be due to several contributing factors. First, the study population as well as EMS systems in Japan differ from the U.S. which may influence results. For example, the average age of the non-shockable rhythm group in the Okubo et al. study was 80 years-old in comparison to 66.5 for the PEA group and 62.3 for the asystole group in the present study.6 Second, sample size may also play a role. Okubu et al. included 27,957 individuals in the shockable rhythm group and 396,303 in the non-shockable group. In the non-shockable group, advanced airway management was associated with 1-month survival of 1.12 (95 % CI, 1.00–1.27) between 0 and 5 min, 1.34 (95 % CI, 1.25–1.44) between 5 and 10 min, 1.39 (95 % CI, 1.26–1.54) between 10 and 15 min, 1.20 (95 % CI, 0.99–1.45).6 This large sample size may have contributed to the finding of a small but statistically significant differences in outcomes.
The parent study from which this present study is derived identified improved outcomes with a strategy of initial airway management of LT vs ET.9 Further parsing of this result by initial rhythm, as done in this study, decreased our precision for each initial rhythm, impacting our ability to find subtle differences in outcome by airway strategy/initial rhythm and is likely underpowered in this regard.
Our work considered whether using a different airway method may be beneficial depending on initial rhythms in OHCA with the hypothesis that the value of ETI vs. SGA may vary based on the underlying pathophysiology of the arrest. Patients experiencing a PEA OHCA had better survival rates than patients with asystolic OHCA arrest in this study independent of an initial airway management strategy. However, these data do not support the concept that the optimal prehospital airway strategy varies by initial rhythm. Based on the results of the present study, consideration of the patient’s initial rhythm should not be a determining factor in choosing airway management with ETI or SGA. Medical directors and EMS systems may determine which OHCA arrest airway management strategy fits their respective system based on local issues such as EMS clinician training, experience level and available equipment.5
Limitations
This study has several limitations. The only SGA device investigated was the LT and so the results may not be generalizable to other commonly used devices such as the i-gel®. There was overall a low success rate of intubation in the parent trial (51 %) and significant crossover of airway device ultimately used to secure the airway between the ETI and LT groups. The time to first airway attempt was 2.7 min shorter in the LT group. Furthermore, the trial could not assess the impact of chest compression or ventilation quality on outcomes. There are also patient and arrest characteristic differences in the United States when compared to other countries, including age differences, higher rates of obesity and lower rates of bystander CPR; these limit the ability to compare our finding to previously published studies.2,13–15
In addition, sample size may have limited the ability to determine a significant difference in outcome by advanced airway particularly in non-shockable rhythms. While there was a small but significant difference in survival between the PEA and asystole groups, the interaction term did not suggest a benefit of ETI vs SGA. Future studies directly comparing advanced airway management strategies on outcomes of PEA and asystole may be helpful to clarify this issue.
Lastly, while adjustments were made to address known covariates, residual or unknown covariates may impact the results. Although this study focused on the pre-hospital setting, additional variation in outcomes may be attributed to differences between hospitals where patients ultimately received their care from.16
Conclusion
Prehospital advanced airway management strategy (ETI vs. LT) was not significantly associated with OHCA outcomes regardless of initial cardiac arrest rhythm.
Footnotes
Declaration of generative AI in scientific writing
The authors did not use a generative artificial intelligence (AI) tool or service to assist with preparation or editing of this work. The author (s) take full responsibility for the content of this publication.
CRediT authorship contribution statement
Kianna Eurick-Bering: Writing – review & editing, Writing – original draft, Project administration, Methodology, Investigation, Conceptualization. David A. Berger: Writing – review & editing, Methodology, Investigation. Robert Swor: Writing – review & editing, Methodology, Investigation, Conceptualization. Graham Nichol: Writing – original draft, Methodology, Investigation, Conceptualization. Ahamed Idris: Writing – review & editing, Methodology, Investigation, Conceptualization. Mohamud R. Dayac: Writing – review & editing, Methodology, Investigation, Conceptualization. Jestin Carlson: Writing – review & editing, Methodology, Investigation, Conceptualization. Henry E. Wang: Writing – review & editing, Visualization, Project administration, Methodology, Investigation, Formal analysis, Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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