Effect of a Strategy of a Supraglottic Airway Device vs Tracheal Intubation During Out-of-Hospital Cardiac Arrest on Functional Outcome: The AIRWAYS-2 Randomized Clinical Trial

Key Points

Question  Does an initial strategy of a supraglottic airway device for advanced airway management during nontraumatic out-of-hospital cardiac arrest result in a better functional outcome compared with tracheal intubation?

Findings  In this cluster randomized clinical trial that included 1523 paramedics and 9296 patients with out-of-hospital cardiac arrest, favorable functional outcome (modified Rankin Scale score in 0-3 range) at hospital discharge or after 30 days (if still hospitalized) occurred in 6.4% of patients in the supraglottic airway group vs 6.8% of patients in the tracheal intubation group, a difference that was not statistically significant.

Meaning  In this study, a strategy of using a supraglottic airway device for advanced airway management did not provide a superior functional outcome.

Importance  The optimal approach to airway management during out-of-hospital cardiac arrest is unknown.

Objective  To determine whether a supraglottic airway device (SGA) is superior to tracheal intubation (TI) as the initial advanced airway management strategy in adults with nontraumatic out-of-hospital cardiac arrest.

Design, Setting, and Participants  Multicenter, cluster randomized clinical trial of paramedics from 4 ambulance services in England responding to emergencies for approximately 21 million people. Patients aged 18 years or older who had a nontraumatic out-of-hospital cardiac arrest and were treated by a participating paramedic were enrolled automatically under a waiver of consent between June 2015 and August 2017; follow-up ended in February 2018.

Interventions  Paramedics were randomized 1:1 to use TI (764 paramedics) or SGA (759 paramedics) as their initial advanced airway management strategy.

Main Outcomes and Measures  The primary outcome was modified Rankin Scale score at hospital discharge or 30 days after out-of-hospital cardiac arrest, whichever occurred sooner. Modified Rankin Scale score was divided into 2 ranges: 0-3 (good outcome) or 4-6 (poor outcome; 6 = death). Secondary outcomes included ventilation success, regurgitation, and aspiration.

Results  A total of 9296 patients (4886 in the SGA group and 4410 in the TI group) were enrolled (median age, 73 years; 3373 were women [36.3%]), and the modified Rankin Scale score was known for 9289 patients. In the SGA group, 311 of 4882 patients (6.4%) had a good outcome (modified Rankin Scale score range, 0-3) vs 300 of 4407 patients (6.8%) in the TI group (adjusted risk difference [RD], −0.6% [95% CI, −1.6% to 0.4%]). Initial ventilation was successful in 4255 of 4868 patients (87.4%) in the SGA group compared with 3473 of 4397 patients (79.0%) in the TI group (adjusted RD, 8.3% [95% CI, 6.3% to 10.2%]). However, patients randomized to receive TI were less likely to receive advanced airway management (3419 of 4404 patients [77.6%] vs 4161 of 4883 patients [85.2%] in the SGA group). Two of the secondary outcomes (regurgitation and aspiration) were not significantly different between groups (regurgitation: 1268 of 4865 patients [26.1%] in the SGA group vs 1072 of 4372 patients [24.5%] in the TI group; adjusted RD, 1.4% [95% CI, −0.6% to 3.4%]; aspiration: 729 of 4824 patients [15.1%] vs 647 of 4337 patients [14.9%], respectively; adjusted RD, 0.1% [95% CI, −1.5% to 1.8%]).

Conclusions and Relevance  Among patients with out-of-hospital cardiac arrest, randomization to a strategy of advanced airway management with a supraglottic airway device compared with tracheal intubation did not result in a favorable functional outcome at 30 days.

Trial Registration  ISRCTN Identifier: 08256118

Out-of-hospital cardiac arrest is common, sudden, and often fatal. During 2014, emergency medical services (EMS) in England attempted resuscitation in almost 30 000 people; only 25% achieved a return of spontaneous circulation and 8% were discharged alive from the hospital.¹

Few advanced life support therapies have been shown to improve outcome following out-of-hospital cardiac arrest.² There is a lack of data from high-quality randomized clinical trials (RCTs), which are challenging to conduct in patients with out-of-hospital cardiac arrest. Consequently, many current clinical recommendations are based on observational studies and expert consensus.³

Optimal airway management during out-of-hospital cardiac arrest is a key area of uncertainty because there is very little high-quality research on which to base treatment recommendations.⁴ Options range from basic or minimal airway intervention to early advanced procedures that require training and expertise.

The advanced procedure of tracheal intubation has been considered a definitive airway management technique.⁵ However, large observational studies (including >100 000 patients) have consistently favored basic airway management (eg, bag-mask ventilation) over tracheal intubation.^6,7 The introduction of a supraglottic airway device offers an alternative advanced airway management technique during out-of-hospital cardiac arrest.

Insertion of a supraglottic airway device is simpler and faster than tracheal intubation,⁸ and proficiency requires less training and ongoing practice.⁹ Observational evidence has suggested a possible survival advantage for tracheal intubation compared with a supraglottic airway device.¹⁰ However, a large-scale RCT is required to identify the optimal approach to advanced airway management during out-of-hospital cardiac arrest.

The objective of this trial was to estimate the between-group difference in modified Rankin Scale score at hospital discharge or 30 days after out-of-hospital cardiac arrest for patients treated by paramedics randomized to use either a supraglottic airway device or tracheal intubation as their initial advanced airway management strategy.

The trial protocol and statistical analysis plan for this multicenter, cluster RCT appear in Supplement 1; the trial protocol has been published.¹¹ Paramedics were recruited from 4 large EMS provider organizations (ambulance services) in England, which respond to emergencies for approximately 21 million people (40% of England’s population). The trial population was adults who had a nontraumatic out-of-hospital cardiac arrest.

The patient inclusion criteria were (1) known or believed to be aged 18 years or older; (2) nontraumatic out-of-hospital cardiac arrest; (3) treated by a paramedic participating in the trial who was either the first or second paramedic to arrive at the patient’s side; and (4) resuscitation was commenced or continued by emergency medical services personnel.

The patient exclusion criteria were (1) detained by Her Majesty’s Prison Service; (2) previously recruited to the trial (determined retrospectively); (3) resuscitation deemed inappropriate (using guidelines from the Joint Royal Colleges Ambulance Liaison Committee¹²); (4) advanced airway already in place (inserted by another paramedic, physician, or nurse) when a paramedic participating in the trial arrived at the patient’s side; (5) known to be enrolled in another prehospital RCT; and (6) the patient’s mouth opened less than 2 cm.

Paramedics could not be blinded to their allocation and mechanisms were required to avoid the risk of differential recruitment by paramedics based on the patient’s perceived likely outcome. Therefore, every eligible patient treated by a participating paramedic was automatically enrolled in the study under a waiver of consent provided by the confidentiality advisory group (reference No. 14/CAG/1030).

Ethics review and approval was provided by the South Central–Oxford C research ethics committee (reference No. 14/SC/1219), which included a process of written informed consent for participating paramedics. A disadvantage of automatic enrollment was that enrolled patients might not be treated according to the study protocol if the enrolling paramedic could not recall the protocol details (an out-of-hospital cardiac arrest is a relatively rare event) or if the paramedic mistakenly deemed the patient to be ineligible.

Because out-of-hospital cardiac arrest requires immediate treatment, randomizing patients at the point of out-of-hospital cardiac arrest was considered impractical. Therefore, paramedics were randomized to use 1 of the 2 advanced airway management strategies for the eligible patients that they treated (Figure 1). This design created many clusters with a small average number of patients per paramedic that minimized the effect of intracluster correlation and lowered the risk of chance imbalances between groups.

Paramedics were randomized in a 1:1 ratio using a purpose-designed secure internet-based system. The computer-generated random sequence was done in advance using varying block sizes (range, 4-8) and stratified by EMS provider organization (4 levels), paramedic experience (2 levels), and distance from the paramedic’s base ambulance station to the usual destination hospital (2 levels).

The intervention was the insertion of a second-generation supraglottic airway device with a soft noninflatable cuff (i-gel; Intersurgical). Because of its speed and ease of insertion, this device has become the most commonly used supraglottic airway device during out-of-hospital cardiac arrest in England.^13,14 The current standard of care is tracheal intubation using direct laryngoscopy; video laryngoscopy is not used by paramedics in England.

A standard approach to airway management (from basic to advanced techniques) was agreed on by the participating ambulance services. This included the use of bag-mask ventilation and simple airway adjuncts prior to advanced airway management. Apart from the initial advanced airway management, care proceeded as usual for patients with out-of-hospital cardiac arrest enrolled in the trial. All other care was delivered according to standard international resuscitation guidelines.³

Paramedics received additional training in their allocated advanced airway management intervention immediately after randomization. Training comprised theoretical and simulation-based practice over 1 hour with a brief assessment to confirm competence. For tracheal intubation, a 2-person technique using an intubating bougie was recommended. End-tidal carbon dioxide monitoring was used to confirm correct device placement in all patients.

Protocol deviations could arise because paramedics have both strategies available to them. Usual practice follows a step-wise approach from simple to more advanced techniques, but paramedics have the clinical freedom to adapt airway management during out-of-hospital cardiac arrest to the patient’s anatomy, position, and perceived needs. The trial protocol specified 2 attempts using the allocated strategy before proceeding to the alternative; however, paramedics had discretion to deviate from the trial protocol on clinical grounds.

Allowing discretion was necessary to avoid a paramedic feeling obliged to undertake an intervention that he or she believed to be contrary to the patient’s best interests. This also was necessary to secure approval from the research ethics committee and professional support.

The primary outcome was modified Rankin Scale score at hospital discharge or at 30 days if the patient remained in the hospital. Patients were transported to and followed up at each hospital by assessors blinded to treatment group who collected the modified Rankin Scale score. The modified Rankin Scale score is used widely in out-of-hospital cardiac arrest research,^15,16 and is usually divided into 2 ranges: 0 to 3 (good outcome) or 4 to 6 (poor outcome to death).

The following secondary outcomes were collected for all eligible patients and all but the last 2 were reported by the paramedics: (1) initial ventilation success, which was defined as visible chest rise and was classified as “yes” when advanced airway management was not used; (2) regurgitation (stomach contents visible in the mouth or nose) or aspiration (stomach contents visible below the vocal cords or inside a correctly placed tracheal tube or airway channel of a supraglottic airway device) and each was classified as “no” when advanced airway management was not used; (3) any unintended loss of a previously established airway (patients with advanced airway management only); (4) sequence of airway interventions delivered (patients with advanced airway management only); (5) return of spontaneous circulation (patients with advanced airway management only; patients who died at the scene classified as “no” for return of spontaneous circulation at hospital admission); (6) airway management in place when return of spontaneous circulation was achieved or resuscitation was discontinued (patients with advanced airway management only); (7) chest compression fraction (in a subset of patients in 2 EMS provider organizations); and (8) time to death.

High-quality, continuous cardiopulmonary resuscitation (CPR) is associated with increased survival and improved function following out-of-hospital cardiac arrest; the concept of compression fraction has been developed to standardize its measurement.¹⁷ Therefore, compression fraction was measured and compared in a subset of patients treated by 2 ambulance services using the “CPR Card” (Laerdal), which is a small disposable device placed in the center of the patient’s chest during CPR. The device gives no feedback to the paramedic but records data that can be retrieved later.

Data on resource use to support a cost-effectiveness analysis and longer-term function also were collected. These data are not reported herein.

In a previous feasibility study, 9% of patients survived to hospital discharge.¹⁸ No data were available for the modified Rankin Scale score. However, death and poor functional outcome after out-of-hospital cardiac arrest are closely related because death is the most common outcome.¹⁶

An improvement of 2% in the proportion of patients achieving a good outcome (modified Rankin Scale score range, 0-3) was judged to be clinically important and consistent with the 2.4% difference observed in retrospective data¹⁹ between tracheal intubation and a supraglottic airway device for survival to hospital discharge. This meant that 9070 patients in total were needed to detect a difference of 8% vs 10% at the significance level of 5% with 90% power after allowing for clustering.¹¹

Analysis of the primary outcome and exploratory analyses of secondary outcomes were performed according to a prespecified statistical analysis plan, which was finalized before data lock and any comparative analysis, but after the end of recruitment due to staff changes within the statistical team. Some typographical errors were corrected in version 2 and some points were clarified, but no substantive changes were made. No comparative post hoc analyses were performed.

The primary analyses included all eligible patients with outcome data available except for the following secondary outcomes that only applied to those who received advanced airway management: (1) any unintended loss of a previously established airway; (2) return of spontaneous circulation during airway management; and (3) airway management in place when return of spontaneous circulation was achieved or resuscitation was discontinued. Chest compression fraction was only measured in a small subset of patients. Patients were grouped by the allocation of the first participating paramedic on the scene (main analyses). The analyses were adjusted for stratification factors as fixed effects.

For binary outcomes, mixed-effects logistic regression was used to estimate the odds ratios (ORs) for the primary analysis and paramedic was fitted as a random effect. Risk differences and risk ratios also were estimated using generalized linear regression and standard errors were calculated using a sandwich estimator to allow for clustering. The risk ratios are reported in Supplement 2.

For time-to-event outcomes, Cox proportional hazards regression was used. The proportionality assumption, which was checked using Schoenfeld residuals, was met.

Multiple imputation was not done because the level of missing data was only 7 patients (0.08%) for the primary outcome and less than 1.5% for all but 1 of the secondary outcomes, which had missing data for 6.4% of patients.

Two prespecified exploratory subgroup analyses were performed for the primary outcome: (1) out-of-hospital cardiac arrest with a likely cardiac cause that is witnessed and has an initial rhythm amenable to defibrillation (Utstein comparator group)²⁰ vs a noncomparator group and (2) out-of-hospital cardiac arrest witnessed by a paramedic vs not witnessed by a paramedic. The treatment effect in the subgroups was compared by testing for a paramedic randomization × subgroup variable interaction.

Three prespecified exploratory sensitivity analyses were performed for the primary outcome. The first extended the population to include patients treated by a participating paramedic but who were not resuscitated (ie, trial patients plus nonresuscitated patients). This was prompted by feedback from the data and safety monitoring committee on a preplanned closed interim analysis of half the sample.

The second and third sensitivity analyses were planned from the outset and were restricted to the cohort of patients who received advanced airway management. Comparisons were made as allocated and by the treatment received.

A 2-sided significance level of 5% was used. The 2 groups were compared using Wald tests. No adjustment was made for multiple testing; therefore, the secondary outcomes should be considered exploratory.²¹ All analyses were performed using Stata version 15.1 (StataCorp).

There were 1523 paramedics who were recruited and randomized. Of the 13 462 potentially eligible patients treated by the participating paramedics between June 2015 and August 2017, 4166 (31%) were excluded and 9296 (69%) were enrolled (median age, 73 years; 3373 were women [36.3%]; Figure 1 and Table 1).

Enrolled patients were transported to 95 hospitals and followed up to hospital discharge. Follow-up ended in February 2018. The randomization of paramedics was well balanced (759 to the supraglottic airway device group and 764 to the tracheal intubation group). There were 113 paramedics who withdrew after randomization (58 randomized to tracheal intubation and 55 randomized to the supraglottic airway device; additional information appears in the eText in Supplement 2).

There were more patients in the supraglottic airway device group (n = 4886) than in the tracheal intubation group (n = 4410). The proportion of patients with out-of-hospital cardiac arrest was similar in the 2 groups for attempted resuscitation (7007 of 13 587 patients [51.6%] in the supraglottic airway device group vs 6455 of 12 789 patients [50.5%] in the tracheal intubation group) and eligibility (4886 of 7006 patients [69.7%] in the supraglottic airway device group vs 4410 of 6454 [68.3%] in the tracheal intubation group).

The patient characteristics and cardiac arrest details were balanced between the groups (Table 1; eTables 1 and 2 in Supplement 2). Patients randomized to tracheal intubation were more likely to crossover to the supraglottic airway device as a result of a clinical decision made by the paramedic on scene (Figure 2; eTable 3 and eFigure 1 [contains further information regarding return of spontaneous circulation during or after advanced airway management] in Supplement 2).

The primary outcome was available for 9289 of 9296 patients (99.9%; Table 2). In the supraglottic airway device group, 311 of 4882 patients (6.4%) had a good outcome (modified Rankin Scale score range, 0-3) vs 300 of 4407 patients (6.8%) in the tracheal intubation group (adjusted OR, 0.92 [95% CI, 0.77 to 1.09]; adjusted risk difference [supraglottic airway device minus tracheal intubation], −0.6% [95% CI, −1.6% to 0.4%]; Figure 3 and eFigure 2 in Supplement 2).

Including patients treated by a participating paramedic who were not resuscitated did not change the conclusion for the primary outcome (311 of 11 462 patients [2.7%] in the supraglottic airway device vs 300 of 10 741 patients [2.8%] in the tracheal intubation group had a good outcome; adjusted OR, 0.96 [95% CI, 0.81 to 1.14]; risk difference, −0.2% [95% CI, −0.6% to 0.3%]; Figure 3 and eTable 4 in Supplement 2).

However, of the 7576 (81%) patients who received advanced airway management, more patients in the supraglottic airway device group had a good outcome (163 of 4158 patients [3.9%] vs 88 of 3418 patients [2.6%] in the tracheal intubation group; adjusted OR, 1.57 [95% CI, 1.18 to 2.07]; risk difference, 1.4% [95% CI, 0.5% to 2.2%]).

This effect also was observed in the analysis of patients grouped according to the first type of advanced airway management intervention received (193 of 4630 patients [4.2%] in the supraglottic airway device group vs 58 of 2838 patients [2.0%] in the tracheal intubation group; adjusted OR, 2.06 [95% CI, 1.51 to 2.81]; risk difference, 2.1% [95% CI, 1.2% to 2.9%]).

There was no interaction between randomization group and either subgroup (Figure 3; Utstein comparator group vs Utstein noncomparator group, P = .24; out-of-hospital cardiac arrest witnessed by a paramedic vs not witnessed by a paramedic, P = .24).

The secondary outcomes appear in Table 2 and in eTable 5 in Supplement 2. The supraglottic airway device treatment strategy was significantly more successful in achieving ventilation after up to 2 attempts (4255 of 4868 patients [87.4%] vs 3473 of 4397 patients [79.0%] with tracheal intubation; adjusted OR, 1.92 [95% CI, 1.66 to 2.22]; risk difference, 2.1% [95% CI, 1.2% to 2.9%]).

Two of the secondary outcomes (regurgitation and aspiration) were not significantly different between groups when all instances occurring before, during, or after advanced airway management were combined. Regurgitation occurred among 1268 of 4865 patients (26.1%) in the supraglottic airway device group compared with 1072 of 4372 patients (24.5%) in the tracheal intubation group (adjusted OR, 1.08 [95% CI, 0.96 to 1.20]; adjusted risk difference, 1.4% [95% CI, −0.6% to 3.4%]). Aspiration occurred among 729 of 4824 patients (15.1%) in the supraglottic airway device group compared with 647 of 4337 patients (14.9%) in the tracheal intubation group (adjusted OR, 1.01 [95% CI, 0.88 to 1.16]; adjusted risk difference, 0.1% [95% CI, −1.5% to 1.8%]).

The median time to death was not significantly different between the groups (67 minutes for the supraglottic airway device in 4871 patients vs 63 minutes for tracheal intubation in 4400 patients), and neither was the compression fraction in a very small sample of 66 patients (median of 86% [interquartile range, 81%-91%] in 34 patients for the supraglottic airway device vs median of 83% [interquartile range, 74%-89%] in 32 patients for tracheal intubation (P = .14; eTable 6 in Supplement 2).

In this pragmatic, multicenter, cluster RCT, no significant difference was found between tracheal intubation and the supraglottic airway device for the primary outcome of modified Rankin Scale score (range, 0-3; good outcome) at hospital discharge or 30 days after an out-of-hospital cardiac arrest for all trial patients.

Patients with a short duration of cardiac arrest and who receive bystander resuscitation, defibrillation, or both, are considerably more likely to survive and are also less likely to require advanced airway management.²² This problem of confounding by indication is an important limitation of many large observational studies that show an association between advanced airway management and poor outcome in out-of-hospital cardiac arrest.²³ This study found that 21.1% (360/1704) of patients who did not receive advanced airway management achieved a good outcome compared with 3.3% (251/7576) of patients who received advanced airway management.

Paramedics randomized to use tracheal intubation were less likely to use advanced airway management than paramedics randomized to use the supraglottic airway device. Tracheal intubation is a more complex skill than supraglottic airway device insertion and requires 2 practitioners, additional equipment, and good access to the patient’s airway²⁴; however, out-of-hospital cardiac arrest often occurs in locations where patient access is challenging.

Tracheal intubation has been associated with potential harms including unrecognized esophageal intubation, lengthy pauses in chest compressions, and overventilation.^25,26 No evidence of a difference in compression fraction was found in a small subsample of the enrolled patients, but the potential for harm associated with tracheal intubation persists.

At the outset, it was expected that most patients with a favorable outcome would not receive advanced airway management, and that some crossover would occur. For these reasons, 2 exploratory sensitivity analyses were prespecified only in patients who received advanced airway management, even though these analyses are susceptible to bias.²⁷

Patients who received advanced airway management were similar in the 2 groups (eTable 1 and eTable 2 in Supplement 2), and a strategy of using a supraglottic airway device first was associated with better outcomes whenever advanced airway management was undertaken by a trial paramedic (eTable 4); however, the between-group difference was less than the prespecified clinically important difference and less than the minimally important difference of approximately 3% reported by others.²⁸

The strategy of using a supraglottic airway device first also achieved initial ventilation success more often. Although regurgitation and aspiration occurred with similar frequency overall, regurgitation and aspiration during or after advanced airway management were significantly more common in the supraglottic airway device group. Conversely, patients in the tracheal intubation group were significantly more likely to regurgitate and aspirate before advanced airway management, possibly due to less frequent use of advanced techniques to secure the airway in this group and the increased time required for tracheal intubation compared with insertion of a supraglottic airway device.

A recent RCT of French and Belgian patients with out-of-hospital cardiac arrest that compared bag-mask ventilation with tracheal intubation delivered by physicians as part of an EMS team proved inconclusive.²⁹ To our knowledge, no RCT has compared bag-mask ventilation with a supraglottic airway device in patients with out-of-hospital cardiac arrest.

Reported rates of ventilation and tracheal intubation success have been higher in previous studies^29-31; however, these rates were based on selected populations and practitioners with greater training and experience, including physicians. The current study reflects both the reality of current paramedic practice in England, and the challenges of airway management in a patient group for which regurgitation and poor airway access are common.

Any unintended loss of a previously established airway occurred twice as frequently in the supraglottic airway device group than in the tracheal intubation group. There are some patients with cardiac arrest for whom effective ventilation cannot be achieved with basic airway management techniques or with a supraglottic airway device, and for whom tracheal intubation may be the only way of achieving effective ventilation. The exact role of different advanced airway management techniques in adults with out-of-hospital cardiac arrest, and the associated implications for skill acquisition and maintenance, remain to be determined.

This study has several limitations. First, the trial population included patients who did and did not receive advanced airway management, and the use of advanced airway management was greater among paramedics in the supraglottic airway device group compared with those in the tracheal intubation group, which could result in confounding by indication.³²

Second, there was an imbalance in the number of patients in the 2 groups, probably due to unequal distribution of a small number of paramedics who recruited considerably more patients than the average; however, it was not possible to stratify for this because these individuals could not be identified in advance.

Third, there was crossover between groups, which was inevitable on practical and ethical grounds.

Fourth, although other elements of care (eg, initial basic airway management and subsequent on-scene and in-hospital care, such as targeted temperature management and access to angiography) followed established guidelines, between-group differences in these factors could have influenced the findings.

Fifth, the participating paramedics were volunteers, and their airway skills may not be representative of those who chose not to participate in the study.

Sixth, the findings are applicable to use of the particular supraglottic airway device in countries with similar EMS provision to England where paramedics treat most patients with out-of-hospital cardiac arrest. The findings may not be applicable in countries with physician-led EMS provision or to another supraglottic airway device that may have different characteristics. However, the principles underpinning the insertion and function of all supraglottic airway devices are similar.

Among patients with out-of-hospital cardiac arrest, randomization to a strategy of advanced airway management with a supraglottic airway device compared with tracheal intubation did not result in a favorable functional outcome at 30 days.

Corresponding Author: Jonathan R. Benger, MD, Faculty of Health and Applied Sciences, University of the West of England, Glenside Campus, Bristol BS16 1DD, England (jonathan.benger@uwe.ac.uk).

Accepted for Publication: July 30, 2018.

Author Contributions: Drs Benger and Rogers had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Benger, Black, Brett, Nolan, Reeves, Robinson, South, Stokes, Thomas, Voss, Rogers.

Acquisition, analysis, or interpretation of data: Benger, Kirby, Brett, Clout, Lazaroo, Nolan, Reeves, Scott, Smartt, Stokes, Taylor, Thomas, Voss, Wordsworth, Rogers.

Drafting of the manuscript: Benger, Kirby, Lazaroo, Voss, Rogers.

Critical revision of the manuscript for important intellectual content: Benger, Black, Brett, Clout, Lazaroo, Nolan, Reeves, Robinson, Scott, Smartt, South, Stokes, Taylor, Thomas, Voss, Wordsworth, Rogers.

Statistical analysis: Lazaroo, Scott, Smartt, Rogers.

Obtained funding: Benger, Black, Reeves, Robinson, Voss, Wordsworth, Rogers.

Administrative, technical, or material support: Black, Clout, Nolan, Robinson, Taylor, Thomas, Voss, Rogers.

Supervision: Benger, Black, Brett, South, Voss, Wordsworth, Rogers.

Conflict of Interest Disclosures: The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Nolan reported being the editor-in-chief of Resuscitation for which he receives honoraria. Dr Reeves reported salary support from grants from the National Institute for Health Research. Dr Rogers reported salary support from a British Heart Foundation grant until March 2017. No other disclosures were reported.

Funding/Support: The trial was funded by the National Institute for Health Research (NIHR) Health Technology Assessment Programme (project No. 12/167/102), and supported by the NIHR Comprehensive Research Networks. The study was not funded by any commercial organization or equipment manufacturer. This study was designed and performed in collaboration with the Clinical Trials and Evaluation Unit, a UK Clinical Research Collaboration–registered clinical trials unit which, as part of the Bristol Trials Centre, is in receipt of NIHR clinical trials unit support funding.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: The views and opinions expressed in this report are those of the authors and do not necessarily reflect those of the Health Technology Assessment Programme, the NIHR, National Health Service, or the Department of Health and Social Care.

Additional Contributions: We acknowledge the following persons for their contributions: Megan Rhys, BSc (Hons) (South Western Ambulance Service NHS Foundation Trust, Exeter), the lead research paramedic in the feasibility study, supported paramedic engagement, and provided expertise when developing the protocol (no compensation was received); Rachel Brophy, MSc, Jenny Lamb, BA (Hons), and Abby Willcox, PhD (Clinical Trials and Evaluation Unit, Bristol Medical School, University of Bristol), assistant clinical trial coordinators and managed patient follow-up (no compensation was received); Adam Wallis, Tom Hill, MA, and Tony West, AAT (South Western Ambulance Service NHS Foundation Trust, Exeter), provided financial management (no compensation was received); Jonathan Green, MRes (South Western Ambulance Service NHS Foundation Trust, Exeter), Helen Hall, MCoP (East of England Ambulance Service NHS Trust, Melbourn), Richard Pilbery, MSc (Yorkshire Ambulance Service NHS Trust, Wakefield), and Gregory Adam Whitley, MSc (East Midlands Ambulance Service NHS Trust, Nottingham), research paramedics for each respective institution, delivered regional paramedic recruitment and training, patient screening, and data collection (funded by the NIHR grant); Theresa Foster, BSc (Hons) (East of England Ambulance Service NHS Trust, Melbourn), research manager and provided research support and governance (no compensation was received); Jane Shewan, MSc (Yorkshire Ambulance Service NHS Trust, Wakefield), head of research and provided research support and governance (no compensation was received); Anne Spaight, MA (East Midlands Ambulance Service NHS Trust, Nottingham), head of clinical governance, audit, and research for this institution and provided research support and governance (no compensation was received); Marcus Bailey, BSc (Hons) (East of England Ambulance Service NHS Trust, Melbourn), paramedic consultant for this institution and acted as ambulance service principal investigator (no compensation was received); Steven Dykes, MB ChB (Yorkshire Ambulance Service NHS Trust, Wakefield), deputy medical director for this institution and acted as ambulance service principal investigator (no compensation was received); A. Niroshan Siriwardena, PhD (East Midlands Ambulance Service NHS Trust, Nottingham), research lead for this institution and acted as ambulance service principal investigator (no compensation was received); Lisa Grimmer, BSc, and Katie Sweet, BSc (Hons) (University Hospitals Bristol NHS Foundation Trust, Bristol), and Rosalyn Squire, BSc (University Hospitals Plymouth NHS Trust, Plymouth), regional research nurses in southwestern region and coordinated and supported data collection for participating study hospitals (funded by the NIHR grant); Prematie Andreou, BSc (Hons) (University Hospitals of Leicester NHS Trust, Leicester), and Lucy Ryan, MNurSci (Nottingham University Hospitals NHS Trust, Nottingham), regional research nurses in East Midlands region and coordinated and supported data collection for participating study hospitals (funded by the NIHR grant); Sara Jones, BSc (Hons) (Cambridge University Hospitals NHS Foundation Trust, Cambridge), regional research nurse in eastern region and coordinated and supported data collection for participating study hospitals (funded by the NIHR grant); Helen Foot, BA (Hons) (Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield), regional research nurse in Yorkshire region and coordinated and supported data collection for participating study hospitals (funded by the NIHR grant); Simon Gates, PhD (University of Birmingham, Birmingham), trial steering committee chair and independent member, Charles Deakin, MD (University of Southampton, Southampton), Gavin D. Perkins, MD (University of Warwick, Coventry), and Jasmeet Soar, FRCA (Southmead Hospital, North Bristol NHS Trust, Bristol), independent members, and Keith Douglas and Margaret Douglas, patient representatives and independent members of the trial steering committee (each received reimbursement of travel expenses incurred during attendance at oversight meetings); Gordon Taylor, DPhil (University of Exeter Medical School, Exeter), data and safety monitoring committee chair and independent member, Richard Lyon, MD (NHS Lothian, Edinburgh), Andrew Newton, PhD (College of Paramedics, Bridgwater), Tom Quinn, MPhil (Kingston University and St George’s, University of London, London), and Helen Snooks, PhD (Swansea University, Swansea), independent members of the data and safety monitoring committee (each received reimbursement of travel expenses incurred during attendance at oversight meetings).