So far this week, I have covered 2 large trials looking at airway management strategies in out of hospital cardiac arrest. In both instances, outcomes were similar whatever strategy was employed. Maybe our choice of airway management doesn’t matter? Not so fast, we finish the series with a final RCT, and this time there is a winner.
The rest of the series:
Wang HE, Schmicker RH, Daya MR, et al. Effect of a Strategy of Initial Laryngeal Tube Insertion vs Endotracheal Intubation on 72-Hour Survival in Adults With Out-of-Hospital Cardiac Arrest: A Randomized Clinical Trial. JAMA. 2018; 320(8):769-778. PMID: 
This is a multicenter, cluster-crossover, open-label, randomized trial. Randomization occurred at the level of the EMS agency, with each agency crossing over between groups at 3-5 month intervals.
Patients: Adults (over 18 years) with non-traumatic out of hospital cardiac arrest requiring anticipated ventilatory support or advanced airway management.
- Patients were excluded if their initial care was provided by a different EMS service that was capable of providing advanced airway management.
Intervention: Initial airway management with laryngeal tube (“King LT”).
Comparison: Initial oral tracheal intubation.
- The protocol allowed for paralytics and videolaryngoscopy.
- If the initial attempt was unsuccessful, EMS could perform a rescue attempt with any technique.
Outcome: The primary outcome was overall survival at 72 hours.
A total of 3004 patients were included (out of 3840 screened).
For the primary outcome of survival at 72 hours, the laryngeal tube was better than endotracheal intubation (18.3% vs 15.4%, ARR 2.9%, 95% CI 0.2-5.6%, p=0.04).
- The laryngeal tube was also significantly better in:
- ROSC (27.9% vs 24.3%, ARR 3.6%, 95% CI 0.3-6.8%, p=0.03)
- Hospital survival (10.8% vs 8.1%, ARR 2.7%, 95% CI 0.6-4.8%; p=0.01)
- Favorable neurologic outcome at discharge (7.1% vs 5.0%, ARR 2.1%, 95% CI 0.3-3.8%, p=0.02).
- Per-protocol results were similar.
Compliance with the assigned group was 95.5% with the laryngeal tube and 90.7% with intubation.
Time from EMS arrival to start of airway management was shorter with laryngeal tube (9.8 vs 12.5 minutes).
12% of the cohort never had an advanced airway attempted. Reasons for BVM only management were: the patient regaining consciousness (29.3%), death prior to airway insertion attempts (14.2%), jaw clenching (trismus, 11.9%), adequate ventilation with BVM (9.9%), arrival at emergency department prior to airway insertion efforts (7.7%), and other (8.8%).
- There were more adverse events with intubation
- 3 or more attempts at airway (19% vs 5%)
- Unsuccessful initial airway (44% vs 12%)
- Unrecognized airway misplacement or dislodgement (1.8% vs 0.7%)
- Inadequate ventilation (1.8% vs 0.6%)
- Pneumothorax (7.0% vs 3.5%)
- Rib fractures (7.0% vs 3.3%)
- There were no differences in the adverse events that people are usually concerned about with laryngeal airways (oropharyngeal injuries, airway swelling, pneumonia or pneumonitis).
This is another important trial, but with significant limitations. Although I have a lot of sympathy for the difficulties of intubating in the prehospital environment, the numbers here are far from ideal. First pass success was only 56%. 20% of patients required 3 or more airway attempts, and they were completely unsuccessful in 9% of patients. Comparing a laryngeal mask to less than ideal intubation is not a fair comparison. (This also leads to questions about the reported adverse events. Were they caused by intubation, or just markers of poorly performed intubation?) That being said, the success numbers in AIRWAYS 2 were better, and patient outcomes still weren’t improved. (Benger 2018)
72 hour survival is not a great primary outcome. They are very upfront about the reason for this: this design requires a smaller sample size, and therefore saves money. In my mind, airway management in cardiac arrest is a lot less about getting the heart restarted (survival), and a lot more about ensuring oxygen delivery to the brain and therefore good neurologic outcomes. Therefore, I think airway studies really need to focus on neurologically intact survival.
Unlike the Jabre study, these were North American EMS agencies, so airway management was done by paramedics rather than physicians. Extrapolating results to different systems will remain an issue.
One problem with cluster randomized trials is that the number of clusters is often very small, increasing the chance of imbalance between the groups. (You wouldn’t do a RCT with just 13 patients, because there is a very high chance of baseline imbalance.) This trial somewhat accounts for that by doing crossovers, so that the imbalances between different EMS agencies should be balanced out because they will all be providing patients to both groups. However, the cross-overs were not perfectly randomized (they could wait for things like training), which reintroduces the possibility for imbalances between the groups, and if you look at Table 1, there are definitely some imbalances between the groups.
Ultimately, this trial leaves me with a bunch of questions. The laryngeal airway might be better than intubation in the prehospital environment, but is it better than basic airway maneuvers and BVM? Do these results apply once the patient has reached the emergency department? There are bound to be patients, despite these results, where early intubation is a good idea. Who are those patients?
In this trial, patients with out of hospital cardiac arrest had better outcomes with a laryngeal airway strategy than with an intubation strategy. Those results are consistent with prior research, but various methodological issues mean that the results are far from definitive.
Overall bottom line on airway management in cardiac arrest
For all the problems with these trials, their pragmatic design provides us with valuable information. Prehospital intubation does not improve outcomes in out of hospital cardiac arrest.
Might intubation be better in the hands of the world’s best intubator? Might there be patients for whom an endotracheal tube is better than an LMA? Sure. But these trials tell us that for most patients in most EMS systems, a BVM or SGA first strategy is at least as good as an intubation first strategy.
What we do with that information is the real question. Intubation comes with significant costs. It is a complex skill that requires lengthy training to perform well. There is a large cost associated with ensuring that prehospital personnel are capable of intubating. On the whole, this data doesn’t support that cost. However, these trials were pragmatic, with the option of crossing over to intubation if the clinical context required. Take away that option, and the outcomes might have been different. So, although I think that a SGA first approach is a great plan for most EMS agencies, it isn’t clear that we should stop training paramedics in intubation. (Another difficulty will be how to maintain intubation skills if the LMA strategy is used in most cases.)
Similarly, it isn’t clear how to apply these results in the emergency department. These trials all end at the moment that the patient arrives at the emergency department. At that point, airway management is left to the expertise of the clinician in charge. Therefore, I think emergency physicians still need to use their expertise when deciding the best airway strategy.
That being said, I am a big proponent of the supraglottic airway in the management of cardiac arrest. I think you could make an argument for BVM only (with waveform capnography to confirm breaths), but is so much more difficult that using a SGA that I am not sure why you would want to. The supraglottic airway is easy and highly successful. In cardiac arrest, there are more important things to accomplish than placing an endotracheal tube. I acknowledge that some patients may benefit from intubation. Clinical judgement can always overrule trial evidence. However, I think an SGA will be the best approach for the majority of patients.
Benger JR, Kirby K, Black S, 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; 320(8):779-791.