Background
Supraglottic airways including the laryngeal tube (LT) enable rapid and effective ventilation in most cases [
1]. Contrarily, conventional bag-valve-mask (BVM) ventilation and endotracheal intubation may be difficult, especially when caregivers have little experience.
The promoted simplicity in handling makes the LT an attractive device for airway management during cardiopulmonary resuscitation (CPR), even for healthcare providers with only basic training [
2]. Success rates after short training on manikins were reported between 72% and 94% in emergency medical technicians (EMTs) [
1,
3‐
5]. Kurola et al. observed that the LT may enable rapid and effective airway control as compared to BVM when used by inexperienced personnel [
6]. The quick insertion of the LT may result in shorter hands-off intervals, increased chest compression fraction [
7] and may consequently improve chest compression quality [
8]. Muller et al. observed that mean tidal volume and mean minute volume were higher with LT ventilation than with BVM ventilation [
8]. Ventilation by LT may be particularly advantageous when anatomic conditions, e.g. facial hair, edentulism, facial dysmorphia and obesity, make BVM ventilation difficult or even impossible.
Application of the LT by trained EMTs during CPR has been legal in Austria since 2010. We aimed to investigate subjectively assessed ease of handling (LT insertion, tight seal) and efficacy of ventilation (chest rises visibly, no air leak) with LT as compared to BVM ventilation as performed by EMTs after pre-study training and during CPR in OHCA.
Discussion
EMTs preferred LT ventilation over BVM ventilation in the pre-study training, but on-site assessment regarding ease of handling and efficacy, frequency of complications and outcome showed no differences between the two methods. We prospectively studied ease of handling and efficacy of LT and BVM ventilation performed by EMTs during pre-study training. The standardized training program allowed comparison of LT and BVM airway management and ventilation in real life OHCA patients. However, data acquisition was prone to incomplete recording as compared to findings of previous experimental studies. As simulated conditions may substantially differ from real CPR situations, our prospective study design allowed subjective assessment of ventilation by EMTs after pre-study training and objective evaluation of ventilation by emergency physicians during real OHCA.
After training, 66.7% of EMTs in our study appraised LT ventilation as being highly efficient. This corresponds with findings made in other studies of LT ventilation administered by EMTs and nurses showing success rates between 72 and 94% [
1,
3‐
5,
11]. Although most EMTs in our study had only basic experience (fewer than ten LT insertions), they more often cited good ease of handling and fewer problems as compared to BVM. Roth et al. reported that LT ventilation in real CPR was more successful than BVM ventilation (93% vs. 30%) [
1]. In our study the attending emergency physicians confirmed efficient ventilation by EMTs in cases for LT (71.4%) as well as for BVM (58.5%;
p = 0.686). Presumably, the pre-study refresher in BVM ventilation may have had an impact on the frequency of efficient BVM ventilation.
After training, EMTs regarded LT ventilation as superior to BVM ventilation; only 13.9% of EMTs considered additional training with LT insertion and ventilation necessary. However, EMTs frequently reported difficulties with ventilation in both groups during pre-study training. Sunde et al. observed a high number of insertion-related problems with LT ventilation [
12]. The authors concluded that promising results in manikin studies may not be applicable to real-life CPR [
12]. We assume that high expectations for the LT may create a subjective reality. Perceptions of advantage and disadvantage may influence performance and efficacy beliefs in a competitive situation [
13]. Applied to our pre-study results this would mean that expectations of EMTs for the LT may eventually lead them to behave and achieve in ways that confirm their expectations.
In most patients on site, effective ventilation was provided within the first 10 min of OHCA. Within this interval airway management is not expected to substantially influence outcome. Iwami et al. reported that in patients with CA of presumed cardiac origin chest compression only (and defibrillation, if indicated) is superior to combined respiratory and cardiac resuscitation within the first 5 min of CPR [
14]. Maignan et al. compared 41 cases with intermittent chest compressions in the BVM group to 41 cases with continuous chest compressions in the LT group. Airway management with the LT was associated with a 27% increase in the chest compression fraction and significantly reduced hands-off intervals but survival to discharge did not differ significantly between the two groups [
7]. We doubt that increased chest compression fraction can be achieved with the comparatively low LT leak pressure. An estimated leak pressure of approximately 36 cm H
2O was reported for LT ventilation [
15]. Therefore, in our study intermittent chest compression and ventilation were continued at a ratio of 30:2 after LT insertion as we expected low LT leak pressure to interfere with continuous chest compression and simultaneous ventilation.
We encountered only one airway bleeding (blood stain on the device) and no case of aspiration in the LT group. However, factors associated with unsuccessful LT ventilation in the prehospital setting are numerous including incorrect placement of the tube in the trachea or in the pharynx, mucosa swelling of the tongue and throat and unrecognized airway obstruction [
7,
16,
17]. Incorrect LT placement may cause gastric inflation, regurgitation and massive pulmonary aspiration. Dengler et al. recommended that LTS should be used in all cases of emergency airway management [
16].
Tanabe et al. reported in a nation-wide study that prehospital use of supraglottic airway devices was associated with poorer neurological outcome as compared to tracheal intubation [
18]. Results from animal research indicate that carotid blood flow in the low-perfusion state during CPR is further diminished by pressure on the carotid arteries from inflated LT cuffs [
19].
The time may be nearing when BVM ventilation will lose its prominence as the standard ventilation technique during basic life support in favor of supraglottic airway devices [
20]. However, LT ventilation during cardiac arrest is not a strikingly simple solution. Currently, training in BVM ventilation remains paramount in EMT apprenticeship.
Limitations of our study arise from the fact that the study was conducted in a selected sample of OHCA patients collected from six different centers. The study design determined the enrollment of cases with OHCA, where one of 203 trained EMTs had started CPR and airway management before arrival of the emergency physician. This offers considerable risk of a selection bias as EMTs without training were not allowed to participate in the study, and whenever the emergency physician arrived first he initiated ALS airway management. As EMTs do not intubate OHCA patients in our county, we did not evaluate tracheal intubation by EMTs for efficacy and ease of handling. Of the EMTs 13.9% would have preferred additional training after the pre-study training. Procedural bias from anticipated pressure to perform might have induced some of the EMTs to not participate. Correlations between mode of ventilation and survival to discharge were not calculated as we do not know the various clinical aspects that might have influenced the outcome.
Acknowledgements
We thank everyone involved in the study, in particular the EMTs from EMS Tyrol (Rotes Kreuz Tirol gem. Rettungsdienst GmbH), the emergency physicians and the medical personnel from the emergency departments of Innsbruck Medical University Hospital, Hall State Hospital and Kufstein County Hospital.