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Date: February 26th, 2019

Reference: Benger et al. 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. JAMA 2018

Guest Skeptic: Missy Carter, former City of Bremerton Firefighter/Paramedic, currently a physician assistant practicing in emergency medicine in the Seattle area and an adjunct faculty member with the Tacoma Community College paramedic program.

Case: EMS arrive to your emergency department with a 68-year-old man post cardiac arrest patient.  They had a difficult time getting a definitive airway pre-hospital. It required multiple attempts which caused several prolonged interruptions in CPR. After the patient is stabilized the medic asks you how he can improve his airway management skills during a cardiac arrest as it was difficult to intubate during compressions. What should you tell him?

Background: We have covered OHCA many times on the SGEM. Key to survival is high-quality CPR and early defibrillation. There is no evidence for a patient-oriented benefit with epinephrine (SGEM#238), other ACLS drugs (SGEM#64), pre-hospital therapeutic hypothermia (SGEM#54, SGEM#183), or mechanical CPR (SGEM#136). One issue we have not discussed is endotracheal intubation.

For many years endotracheal intubation has been the standard of care for airway management in out-of-hospital cardiac arrest (OHCA). Over recent years this practice has been questioned. Endotracheal intubation is a technical skill requiring optimal positioning, proficiency and a technical skill level which may be difficult to obtain in the pre-hospital cardiac arrest setting.

Clinical Question #1: Are superglottic airway devices non-inferior to endotracheal intubation in OHCA with regards to neurologic outcome?

Reference: Benger et al, 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. JAMA 2018

  • Population: Adults who had a non-traumatic OCHA.
    • Exclusions: Prisoners, resuscitation deemed inappropriate, advanced airway already in place, and patient’s mouth opened less than 2cm.
  • Intervention: The intervention was the insertion of a second-generation supraglottic airway (SGA) device with a soft non-inflatable cuff (i-gel; Intersurgical).
  • Comparison: Endotracheal tube intubation (ETI) with direct laryngoscopy
  • Outcomes:
    • Primary Outcome: Neurologic outcome at discharge or 30 days using the modified Rankin Scale (mRS score 0-3 = good outcome and mRS score 4-6 = bad outcome).
    • Secondary Outcomes: Initial ventilation success, which was defined as visualizing chest rise. 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 SGA device). Any unintended loss of a previously established airway. Sequence of airway interventions delivered. Return of spontaneous circulation (ROSC). Airway management in place when ROSC was achieved, or resuscitation was discontinued. Chest compression fraction. Time to death

Authors’ Conclusions: “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.”

Quality Checklist for Randomized Clinical Trials:

  1. The study population included or focused on those in the emergency department. No
  2. The patients were adequately randomized. Yes    
  3. The randomization process was concealed. No
  4. The patients were analyzed in the groups to which they were randomized. Yes
  5. The study patients were recruited consecutively (i.e. no selection bias). No
  6. The patients in both groups were similar with respect to prognostic factors. Yes
  7. All participants (patients, clinicians, outcome assessors) were unaware of group allocation.  No
  8. All groups were treated equally except for the intervention. Yes
  9. Follow-up was complete (i.e. at least 80% for both groups). Yes
  10. All patient-important outcomes were considered. Yes
  11. The treatment effect was large enough and precise enough to be clinically significant. Unsure

Key Results: They enrolled 9,296 patients with OHCA. The median age was 73 years and just over 1/3 (36.3%) were women.

Supraglottic airway was non-inferior to endotracheal intubation. 

  • Primary Outcome: mRS 0-3 was 6.4% SGA group vs. 6.8% ETI group. The adjusted risk difference [RD], −0.6% [95% CI, −1.6% to 0.4%])
  • Secondary Outcomes:
    • Two of the secondary outcomes (regurgitation and aspiration) were not significantly different between groups (regurgitation: 1,268 of 4,865 patients [26.1%] in the SGA group vs 1,072 of 4,372 patients [24.5%] in the ETI group; adjusted RD, 1.4% [95% CI, −0.6% to 3.4%]; aspiration: 729 of 4824 patients [15.1%] vs. 647 of 4,337 patients [14.9%], respectively; adjusted RD, 0.1% [95% CI, −1.5% to 1.8%]).
    • Initial ventilation was successful in 4,255 of 4,868 patients (87.4%) in the SGA group compared with 3473 of 4,397 patients (79.0%) in the ETI group (adjusted RD, 8.3% [95% CI, 6.3% to 10.2%]).
    • Patients randomized to receive ETI were less likely to receive advanced airway management (3,419 of 4,404 patients [77.6%] vs. 4,161 of 4,883 patients [85.2%] in the SGA group).

1) Cluster Randomization: Cluster randomization trials (CRT) have been around for a long time. Rather than randomizing the individual patients, it randomizes groups of patients to the intervention or control. There are strengths and weaknesses to any trial design. One strength is to avoid contamination between interventions when trial participants are being managed within the same setting. One weakness is that CRTs have decreasing returns in power and precision as cluster size increases. They attempted to mitigate this limitation by having a large number of clusters to increase accuracy of the results.

2) Cross-Over: Paramedics had the clinical freedom to adapt from assigned treatment groups. Only 81% of patients received an advanced airway, this was equal between groups. There was more crossover observed from the ETI to SGA group (18.6% vs 2.9%). Mitigating the problem of cross-over, they did an intention-to-treat (ITT) analysis.

3) Bias Against Endotracheal Intubation: There did seem to be a bias against obtaining an advanced in paramedics who were randomized to the ETI group. They were less likely to perform an advance (14.1% vs. 22.2%) compared to SGA group. This bias could have impacted the results

4) First Pass Success: Multiple prior studies have shown an association between increased intubation attempts and increased mortality. This trial showed a 69% success rate in the ETI group compared to an 89% success rate in the SGA group. Although this trial had a low is a low first pass ETI success rate (69%) compared to prior meta analyses (91%) it’s much higher than the 51% listed in the Wang et al trial.

5) Sensitivity and Subgroup Analyses for the Primary Outcome: The patients who received advanced airway management (81%) were grouped by the first type of advanced airway intervention received. That is accounting for crossover and excluding the patients who did not receive an advanced airway. SGA insertion as the first method showed better outcomes compared to the ETI (4.2 vs 2.0) which was statistically significant. However, these subgroup analyses should be viewed only as hypothesis generating.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: This trial provides a large data set suggesting that supraglottic devices are not inferior to endotracheal intubation. 

Clinical Question #2: Does the use of the LT supraglottic device have an effect on 72-hour survival when compared to endotracheal intubation in OHCA?

Reference: Wang et al. Effect of a Strategy of Initial Laryngeal Tube Insertionvs. Endotracheal Intubation on 72-Hour Survival in Adults With Out-of-Hospital Cardiac Arrest
A Randomized Clinical Trial. JAMA 2018

  • Population: Adult patients (>17 years of age) suffering a nontraumatic OHCA treated by EMS and requiring advanced airway management or anticipated ventilatory support
    • Exclusions: Pregnant women, prisoners, major facial trauma, major bleeding or exsanguination, patients with tracheostomy, LVAD, obvious asphyxia cardiac arrest and DNR
  • Intervention: Laryngeal tube (LT) insertion
  • Comparison: Endotracheal tube intubation (ETI)
  • Outcome:
  • Primary Outcome: 72-hour survival rates
  • Secondary Outcomes: Return of spontaneous circulation (ROSC), hospital survival and favorable neurologic status at discharge (modified Rankin Scale score of 0-3).

Authors’ Conclusions: “Among adults with OHCA, a strategy of initial LT insertion was associated with significantly greater 72-hour survival compared with a strategy of initial ETI. These findings suggest that LT insertion may be considered as an initial airway management strategy in patients with OHCA, but limitations of the pragmatic design, practice setting, and ETI performance characteristics suggest that further research is warranted.”

Quality Checklist for Randomized Clinical Trials:

  1. The study population included or focused on those in the emergency departments. No
  2. The patients were adequately randomized. Yes
  3. The randomization process was concealed. Yes
  4. The patients were analyzed in the groups to which they were randomized. Yes
  5. The study patients were recruited consecutively (i.e. no selection bias). Unsure
  6. The patients in both groups were similar with respect to prognostic factors. No
  7. All participants (patients, clinicians, outcome assessors) were unaware of group allocation. No
  8. All groups were treated equally except for the intervention. Yes 
  9. Follow-up was complete (i.e. at least 80% for both groups). Yes 
  10. All patient-important outcomes were considered. Yes
  11. The treatment effect was large enough and precise enough to be clinically significant. Unsure

Key Results: They recruited and analysed 3,004 patients and the median age of patients was 64 years with 39% women.

Greater survival in the LT group compared to the ETI group.

  •  Primary Outcome: 72-hour survival was 18.3% in the LT group vs. 15.4% in the ETI group (2.9% difference [95% CI 0.2% to 5.6%, p=0.04]).

1. First Pass Success: The initial LT and ETI success rates (excluding BVM) were 90.3% and 51.6% respectively. Patients with LT were much more likely to have first pass success over ETI. Multiple prior studies have shown increased mortality with increased intubation attempts. It’s possible that the low first pass success ETI rates seen in this trial could have skew that data towards LT.

2. Bag Valve Mask: The primary outcome showed a mortality benefit with LT. However, they included patients who had only a BVM (no LT or ETI). In the authors’ results section they list the data with the BVM group removed. In this as treated analysis, the 72-hour survival was not statistically different (16.0% LT vs. 13.5% ETI; P = .07).

3. Lack of Blinding: There was not blinding to interventions, allocation, crossover timings, and outcomes ascertainment. All of this could have biased the results.

4. Unbalanced Groups: Cluster randomization can lead to unbalanced baseline characteristics. One of the most powerful prognostic factors in survival of OHCA is the initial rhythm. Shockable rhythms were observed in 20% of patient in the LT group vs. 18% in the ETI group. When they did a post-hoc analysis and adjusted for age, sex, rhythm, response time, witness status and bystander chest compression the statistical difference in survival was gone.

5. Fragility Index: Looking at their primary outcome (72-hour survival) the fragility index of this study was 3. There were also four patients missing from the data set. This severely limits any strong conclusions that can be drawn from this trial.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We would change the conclusions to say that among adults with OHCA, LT insertion may or may not be considered as an initial airway management strategy.

SGEM Bottom Line: In adults with OHCA, key factors for survival with good neurological outcome are early defibrillation and high-quality CPR. Airway strategies do not seem to be as important.

Case Resolution: The patient goes on to have a poor neurologic outcome like most patients with OHCA.

Clinical Application: Using a supraglottic airway device is a reasonable management option in adult patients with OHCA. This could cognitively unload paramedics and allow them to concentrate on those things that have been demonstrated to improve patient-oriented outcomes like early defibrillation and high-quality CPR.

Missy Griffith

What Do I Tell the Medic? You tell the medic that we do not have good evidence on what is the best strategy for airway management in these cases. Inserting a supraglottic airway is easier, faster and more successful. However, it does not appear to result in better patient outcomes. Don’t get distract with the airway and focus on early defibrillation and high-quality CPR.

Keener Kontest: Last weeks’ winner was Matt Kennedy. He knew normal saline contains 9g per L of NaCl which is equal to 154mEq each of Na and Cl.

Listen to the SGEM podcast to hear this the new keener question. If you know the answer send an email to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

Other FOAMed:

• REBEL Cast Ep 59: AIRWAYS-2 – Supraglottic vs Tracheal Intubation in OHCA

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.