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Date: March 8, 2023
Reference: Smida et al. A Retrospective Nationwide Comparison of the iGel and King Laryngeal Tube Supraglottic Airways for Out-of-Hospital Cardiac Arrest Resuscitation. Prehospital Emergency Care 2023
Guest Skeptic: Dr. Chris Root is a third-year resident physician in the Department of Emergency Medicine at the University of New Mexico Health Sciences Center in Albuquerque, NM. He is also a flight physician with UNM’s air medical service, Lifeguard. He is a former New York City paramedic and this summer will be starting fellowship training in EMS medicine at UNM.
Case: A paramedic crew responds to a 54-year-old male in cardiac arrest at a private residence. A fire company is on scene providing high-quality cardiopulmonary resuscitation (CPR) and has defibrillated twice with an automated external defibrillator (AED). The fire-based crew has basic life support (BLS) airway supplies including the King Laryngeal Tube, the paramedic crew carries iGel supraglottic airways (SGAs) in addition to their intubation equipment. They plan to use a supraglottic airway as their initial airway strategy during the arrest, but they wonder if either of these two devices is superior.
Background: Airway management strategies for out of hospital cardiac arrest (OHCA) have been hotly debated since the dawn of CPR. Two large trials, PART by Wang et al and AIRWAYS-2 by Benger et al recently evaluated the King-LT and the iGel respectively as alternatives to endotracheal intubation (ETI) in cardiac arrest.
Given the difficulty associated with intra-arrest endotracheal intubation, use of supraglottic airways in the prehospital setting is becoming more common. This was discussed with paramedic and physician assistant (PA), Missy Carter when critically appraising the AIRWAYS-2 trial regarding the use of the iGel in OHCA on SGEM #247
Clinical Question: Which supraglottic airway is associated with better patient outcomes, the iGel or the King-LT in patients with an out-of-hospital cardiac arrest.
Reference: Smida et al. A Retrospective Nationwide Comparison of the iGel and King Laryngeal Tube Supraglottic Airways for Out-of-Hospital Cardiac Arrest Resuscitation. Prehospital Emergency Care 2023
- Population: Adult OHCA patients treated by EMS contained within the ESO database from 2018-2021 who received prehospital iGel or King-LT supraglottic airway insertion.
- Excluded: Patients who were less than 18 years of age, pregnant, had do not resuscitate or other physician orders for life sustaining treatment, achieved ROSC after bystander CPR only, or experienced OHCA due to trauma or hemorrhage were excluded from downstream analyses
- Exposure: iGel
- Comparison: King-LT
- Outcome:
- Primary Outcome: Survival to hospital discharge home
- Secondary Outcomes: First-pass success, return of spontaneous circulation (ROSC), prehospital rearrest, Intrarrest ETCO2 values
- Type of Study: Retrospective observational
Authors’ Conclusions: “In this dataset, use of the iGel during adult OHCA resuscitation was associated overall with better outcomes compared to use of the King-LT. Subgroup analyses suggested that use of the iGel was associated with greater odds of achieving the primary outcome than the King-LT when used as a rescue device but not when used as the primary airway management device.”
Quality Checklist for Observational Study:
- Did the study address a clearly focused issue? Yes
- Did the authors use an appropriate method to answer their question? Yes
- Was the cohort recruited in an acceptable way? Yes
- Was the exposure accurately measured to minimize bias? Unsure
- Was the outcome accurately measured to minimize bias? Unsure
- Have the authors identified all-important confounding factors? Unsure
- Was the follow up of subjects complete enough? No
- How precise are the results? Adequately Precise
- Do you believe the results? Yes
- Can the results be applied to the local population? Unsure
- Do the results of this study fit with other available evidence? Yes
- Funding of the Study: No external funding sources
Results: The assessed 286,192 OHCA cases for eligibility and were able to include 93,866 patients treated by 1,613 EMS agencies. iGels were inserted in 54,189 (58%) cases, and King- LTs were inserted in 39,677 (42%) cases. The average age of patients in this dataset was 63 years and 37% were female. Just over half (52%) of the 93,866 patients were transported to an emergency department. Of those transported to hospital (49,302), only 19% (9,456) had available disposition data. This means we have data on 10% of the original 93,866 patients. Among the 10% of patients that disposition data was available:
- 7% were discharged to home or self-care
- 84% died after arrival at a hospital
- 4% were discharged to hospice
- 3% were discharged to skilled nursing
- 7% were discharged to long-term acute care
Key Result: No statistical difference in discharge home between the two devices when a supraglottic airway was employed as the initial airway management strategy.
- Primary Outcome: Survival to hospital discharge home
- Overall: adjusted Odds Ratio (aOR) 1.36 [95% CI; 1.06 to 1.76]
- Primary Strategy: aOR 1.26 [95% CI;0.95 to 1.68]
- Rescue Strategy: aOR 2.16 [95% CI; 1.15 to 4.04])
- Secondary Outcomes: Use of the iGel was associated with higher first pass success with device placement, higher rates of prehospital ROSC, higher intra-arrest ETCO2 values, and lower rates of re-arrest.
1. Retrospective Data Set: This was a retrospective analysis. When retrospective data is used to answer clinical questions there is less ability to control for confounding factors than in a prospective study. The authors attempted to control for compounding factors through their propensity scoring however any retrospective study must be interpreted cautiously. These statistical tools cannot achieve the same rigor as a properly conducted randomized control trial.
2. Discharge Home: The authors utilized discharge home as their primary outcome. This is a pragmatic choice based on the available dataset. However, it is probably not the most patient-oriented outcome (POO). Having a good neurologic outcome is likely to be more important to patients than merely surviving with a severe disability. This dataset does not provide this important information.
3. ESO Data Collaborative: The dataset comes from a software vendor of over 2,000 EMS agencies in the US. That may sound like a lot but there are over 18,000 EMS agencies in the US (EMS World 2020). Only 1,600 of the agencies voluntarily submit their data for research purposes. This could create some selection bias. In addition, only 10% of the OHCA cases in the data set had data for the primary outcome of survival to hospital discharge home. This severely limits the strength of any conclusions from the available evidence.
They did provide some information on geographical region. However, there was no granularity on other factors such as urban vs rural setting or transport time to hospital.
The nature of the available dataset forced the authors to exclude any patients transferred to another hospital for continuing care form their analysis which may introduce a form of survival bias. The patients analyzed may have been more likely to recover completely without requiring transfer for subspecialty care.
4. Supraglottic Airways as Primary vs Rescue Device: The authors wanted to study the difference between the King-LT and the iGel as an initial airway management device and found that both devices were associated with similar rates of discharge home. Interestingly, the iGel was associated with higher rates of discharge home when it was employed as a rescue device after failed endotracheal intubation, however in this data set the King-LT was used as a rescue device almost twice as often (12.6% iGel vs 22.4% King-LT, p < 0.001).
5. ETCO2 Waves vs Numbers: The authors utilized recorded ETCO2 data in their sensitivity analysis to evaluate the ventilatory effectiveness of each device. The data available was in the form of discrete numbers charted by the clinicians or uploaded from the EMS monitor, not continuous waveform, and these values may have been influenced by factors like minute ventilation and device leak that are not clearly captured in numeric data alone.
UPDATE: March 11th, 2023
Tanner Smida
We are not perfect at the SGEM and do make mistakes sometimes. The lead author, Tanner Smida, reached out to us to clarify a few things and provide some additional background information after we posted the SGEM episode.
Tanner is an MD/PhD student studying at West Virginia University. He is currently in his second year of medical school and about to start his PhD in clinical and translational science. Tanner noticed some issues with our reporting of what we thought was the primary outcome.
Guest skeptic Chris Root thought perhaps he made a transcription error filling out the result section of the SGEM critical appraisal form for observational studies. It may have been me confusing the primary airway device used (iGel or King-LT) with the primary outcome.
When we were made aware of the issue we apologized to Tanner and invited him record a short update to the SGEM episode. He clarified the primary outcome was survival to hospital discharge home regardless of whether the supraglottic device was as the primary airway management strategy or as a rescue strategy following a failed intubation attempt. This means the primary outcome DID find superiority of the iGel over the King-LT with an adjusted Odds Ratio (aOR) 1.36 [95% CI; 1.06 to 1.76].
Tanner provided some background information about the peer review process. It was the peer reviewers who insisted on the subgroup analyses and that the results be included in their conclusions. If the supraglottic device was used as a primary airway management strategy there was no statistical difference between the two devices (aOR 1.26 [95% CI;0.95 to 1.68]). However, the rescue strategy did have a statistical difference favouring the iGel (aOR 2.16 [95% CI; 1.15 to 4.04]). This is what they think drove the overall result to show the iGel was associated with a greater odds ratio of the patient being discharged home after the OHCA.
This additional information helps explains why we were a bit confused and suggested the conclusions could be considered misleading. It was because of our misunderstanding that primary analysis of the primary outcome was not of the primary airway management strategy but rather a combination of both the primary strategy and the rescue strategy.
You can listen to the conversation with Tanner on the updated SGEM podcast. He does not think our error changes the SGEM bottom line. He agrees with our overall conclusions and appreciated us enhancing the reach of this groups work.
Again, we are sorry for the error and appreciate Tanner coming on the SGEM to help us better understand his research.
Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree with the authors’ conclusions.
SGEM Bottom Line: This is another study supporting that the airway is less important in adult OHCAs. We should focus more on high-quality CPR and early defibrillation for shockable rhythms and less on type of supraglottic airway device.
Case Resolution: The paramedic responsible for airway management elects to insert an iGel because this is the device they are most familiar with. The crew continues high quality CPR on scene and defibrillates the patient twice before he attains sustained ROSC. Serial 12-lead ECGs post ROSC do not demonstrate STEMI. The patient is transported to the nearest emergency department where he admitted to the Cardiac ICU. He later undergoes delayed cardiac catheterization (SGEM#344) which demonstrates no culprit lesions, he subsequently has an IACD implanted and is discharged home on hospital day four.
Dr. Chris Root
Clinical Application: The iGel and King-LT are both appropriate options for airway management in OHCA. The iGel may (may not) be the superior rescue device after failed ETI and it appears to be more likely to be successfully inserted on the first attempt.
What Do I Tell the Patient’s Family? We’re doing what we can to save your loved one. We are going to put something in his mouth to help him breath. The most important things we can do now are to continue high quality CPR. Then we will try to shock him out of the cardiac arrest. If that is successful, we will transfer him the closest hospital for more care.
Keener Kontest: Last weeks’ winner was Aman Hassan. He knew the anterior part of the nose with rich vascularization is called Littles Area or the Kiesselbach’s plexus.
Listen to the SGEM podcast to hear this weeks’ question. Send your answer to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.
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