Insertion Success of the Laryngeal Tube in Emergency Airway Management

Background. Emergency airway management (AM) is a priority when resuscitating critically ill or severely injured patients. The goal of this study was to determine the success rates of LT insertion during AM. Methods. Studies that included LT first-pass insertion (FPI) and overall-pass insertion (OPI) success by emergency medical services and in-hospital providers performing AM for emergency situations as well as for scheduled surgery published until July 2014 were searched systematically in Medline. Results. Data of 36 studies (n = 1,897) reported a LT FPI success by physicians of 82.5% with an OPI success of 93.6% (p < 0.001). A cumulative analysis of all 53 studies (n = 3,600) led to FPI and OPI success of 80.1% and 92.6% (p < 0.001), respectively. The results of 26 studies (n = 2,159) comparing the LT with the laryngeal mask airway (LMA) demonstrated a FPI success of 77.0 versus 78.7% (p = 0.36) and an OPI success of 92.2 versus 97.7% (p < 0.001). Conclusion. LT insertion failed in the first attempt in one out of five patients, with an overall failure rate in one out of 14 patients. When compared with the LT, the LMA had a cumulative 5.5% better OPI success rate.


Introduction
In critically ill or severely injured patients, efficacy of emergency airway management increased survival chances [1][2][3], independently of the setting in the emergency medical service, emergency departments, operating rooms, in-hospital resuscitation wards, or intensive care units [4,5]. While tracheal intubation is considered to be the gold standard for emergency airway management [6][7][8], even experienced laryngoscopists may fail to intubate resulting in significant morbidity and mortality [9][10][11]. Since supraglottic airway devices were described to be effective and simple to use, with a steep learning curve among providers [12][13][14], they were introduced into emergency airway management guidelines in the prehospital and in-hospital setting as first-line device as well as a backup strategy after failed intubation attempts [2,[15][16][17][18][19].
In 1999, the laryngeal tube was introduced to the market by VBM. In the meantime, the design has been modified several times. Currently, five versions are available, standard LT reuseable (LT), standard LT single-use (LT-D), LT with suction lumen reuseable (LTS II), LT with suction lumen single-use (LTS-D), and intubating LT, to place an endotracheal tube secondary through the lumen (iTLS D).
Although the laryngeal tube is now about 15 years in service [20], there is little data about efficacy (e.g., high success rates) in emergency airway management in the field and outside of expert centers, where more experience with this device may yield better results [13]. This may be of importance since providers need to be aware of their own and procedure-related limitations while employing the laryngeal tube and need to recognize them in a dynamic situation when a patient is threatened by hypoxia and hypercapnea [21]. More knowledge about success rates such as first-pass and 2 BioMed Research International overall-pass insertion success rates with the laryngeal tube compared with other supraglottic devices such as the laryngeal mask may also improve patient safety. While individual skills and experience may differ, it is important to know which device may score best behind the gold standard tracheal intubation.
The goal of this study was to summarize the existing evidence of first-pass and overall-pass insertion success rates of laryngeal tube insertions in the out-of-hospital and inhospital setting. Furthermore, we summarize the results of studies comparing the laryngeal tube with the laryngeal mask airway. Our hypothesis was that there would be no difference between devices being investigated.

Study Design.
This study is a meta-analysis and review of the literature and does not involve the use of human subjects or medical records and thus does not require ethics approval.

Search Strategy.
We searched Medline using the key words "laryngeal tube", "laryngeal tube suction", "first-pass success", "first attempt", and "overall success" as free-text terms and MeSH terms to identify relevant studies search strategy: [("first insertion" AND "success") OR ("insertion success") OR ("attempt" OR "attempts" AND "success") AND ("laryngeal tube" OR "laryngeal tube suction" OR "laryngeal tube suction-D" OR "LT" OR "LT-D" OR "LTS" OR ("LTSII") OR "LTS-D")]. We also hand-searched the references and bibliographies of the included and relevant articles and reviews. Citations were screened by all authors ( = 1,234), and those studies published upon 1999 meeting the predefined inclusion/exclusion criteria were then reviewed ( = 200). Relevant articles, as judged by all authors, were included for full review ( = 53). Disagreements were resolved through a consensus process with a third author. We did not search other databases such as Embase or Cochrane Central. As the rarely available studies were performed with the different modifications mentioned above (LT, LT-D, LTS II, and LTS-D), no observations of the single types were obtained, but all types were summarized as "LT."

Inclusion and Exclusion Criteria.
We considered studies in which emergency medical service personnel and inhospital and prehospital physicians, regardless of speciality background and level of training, performed airway management in a given setting (e.g., emergency medical services, emergency department, intensive care unit, airway management during scheduled surgery, and in-hospital resuscitation in wards) using the laryngeal tube. We excluded paediatric patients. Articles published in English and German were included. All case reports, case reviews, systematic reviews, letters to the editor, and animal as well as cadaver or mannequin studies were excluded.

Outcome Measures.
The primary outcome measures were the first-pass and overall-pass insertion success rates of laryngeal tube insertion. Secondary outcome measures were first-pass and overall-pass insertion success rates of laryngeal mask airway (as another often used supraglottic airway device) in studies comparing laryngeal tube and laryngeal mask airway. The criterion for "successful insertion" in the included studies was adequacy of ventilation observing the presence of end-tidal carbon dioxide waveforms, chest movement, and oxygen saturation.

Statistical
Analysis. The statistical analysis was performed with the statistical software package R (version 2.15.1). The results of first-pass and overall-pass insertion success rates of the included studies were summarized and reported in detail. Manual calculations of unadjusted effects estimates (odds ratio, OR) were performed, and the odd ratios were pooled. 95% confidence intervals (CI) for each study and over all studies were calculated. If the success rate was 100%, it was assumed that the lower confidence interval (CI) was reached and that the next attempt would fail. In those cases, the CI was marked in the results tables. We used a fixed effects model. Group comparisons of frequencies were performed using the Chi 2 test. For all randomized controlled trials, the odds ratio was calculated and presented with confidence intervals in a forest plot.

Results
This search identified 1,234 citations, of which 1034 were excluded ( Figure 1). We reviewed the full text of 200 studies, of which 53 studies met inclusion criteria.

Discussion
This study included 53 studies from 17 different countries with a pooled sample size of 3,600 patients, which is the largest summarized data set assessing laryngeal tube insertion success rates at the current time. Overall-pass insertion success rate employing the laryngeal tube was 92.6%, with the laryngeal mask insertion being significantly better at 97.7%. Our results were contrary to some findings in the literature from smaller meta-analysis, which found an overall success rate of the laryngeal tube insertions ( = 150) of 96.5% and of the laryngeal mask airway ( = 3,829) of 87.4% [74]. The different overall-pass insertion success rates of laryngeal tube insertion in comparison to laryngeal mask insertion may have the following reasons: first, anaesthetists are well trained in laryngeal mask airway usage in the operating room providing anaesthesia and airway management on a daily basis [14]; emergency airway management is then just an extrapolation of daily routine with this device. For the laryngeal tube, this remains a dilemma since this supraglottic airway device is usually not being routinely employed in the operating room at all [75], which subsequently may explain the low laryngeal tube first-pass insertion success rate (77.7%) and overall-pass insertion success rate (92.2%) in the     prehospital setting. Second, if a device is not being employed routinely in the operating room, anticipated success rates in an emergency airway management situation simply have to be worse compared to the daily routine device as a difficult situation has to be managed with an unacquainted device. Third, significant problems of laryngeal tube insertion have been reported, including incorrect positioning in prehospital and in-hospital settings, which may contribute to the phenomenon of inadvertent complications [21,76]. A prospective study reported a complication rate of 52% in 189 patients being managed with the laryngeal tube in the prehospital setting [76,77]: laryngeal tube-associated problems related to excessive cuff pressure, tongue swelling (39%), hypoxic cardiac arrest (2%), massive stomach distension with ventilation difficulty (11%), and bleeding from soft tissue of the upper airway (2%) [76,77]. A range of the previously mentioned complications were reported in the underlying studies. However, the reporting style of adverse events in those studies was unstructured and maybe incomplete. Therefore, those results have to be interpreted with caution, and a robust conclusion may not be drawn from those elective in-hospital studies.
Taken together, the laryngeal tube may not be as simple as anticipated, and lack of its daily usage in airway management including emergency cases may hamper success especially when hypoxic and hypercarbic patients need it the most [21].
The successful insertion of a supraglottic airway is important; however, this may not reflect successful ventilation with the given device during emergency conditions in all cases. Carlson et al. [78] described in a human unembalmed cadaver model that the required axial dislodgment force for a combitube required in this study is twice as much as for the endotracheal tube; and the laryngeal tube and the laryngeal mask airway dislodgment forces were similar to those of the endotracheal tube. Thereby, using secondgeneration supraglottic airway devices may optimize the seal and reduce the possibility of accidental dislodgement [76]. The current guidelines of the European Resuscitation Council [2] report rates of successful ventilation during cardiopulmonary resuscitation of 71-90% for the laryngeal mask airway in comparison to the combitube with 79-98% and no reported percentages for the laryngeal tube. However, cardiac arrest is only one of the prehospital emergencies requiring emergency airway management; other acute settings (e.g., trauma, respiratory insufficiency) need emergency airway management as well. The included studies in this review were not able to answer the question of which supraglottic airway Bein   is superior to another in means of successful ventilation in emergency circumstances. A meta-analysis and systematic review [79] assessing the survival rates of patients suffering from out-of-hospital cardiac arrest being managed with tracheal intubation versus supraglottic airway devices versus basic airway management suggested decreases in survival rates for out-of-hospital cardiac arrest victims treated by the EMS with advanced airway interventions. Unfortunately, this and other similar studies may fall prey to their design; namely, advanced airway management may simply trail ongoing resuscitation efforts. As such, a patient regaining spontaneous circulation quickly may simply not need tracheal intubation, while a patient undergoing prolonged resuscitation efforts with a slim survival chance is earmarked with advanced airway management. In this case, advanced airway management would simply be a surrogate parameter for bad outcome, but not the problem per se.

Limitations
This study has several limitations. First, the review pools existing evidence and is thus dependent on quality of reported data. Reviews of randomized controlled trials provide the strongest evidence, which only was the case in the studies comparing the laryngeal tube with the laryngeal mask airway, but not in studies investigating the laryngeal tube alone. Moreover, typical for advanced airway studies, the success rates are very high, and for the distributions these proportions may be much skewed towards the high end. Therefore, as the success proportions approach hundred percent, the variance of the study is squeezed towards zero, and, therefore, the study with the high success proportion may receive a disproportionately large weight when the inverse variance method such as fixed effects model is used. So, the pooled odds ratios of this might overestimate the effect [80]. Further, we excluded small case series and letters to the editor, which is a strength of our analysis; also, we excluded mannequin studies as this setting cannot be extrapolated directly to emergency airway management [81]. Also, the majority of data was extracted from studies with anaesthetists who are experienced in maintaining the airway, thus featuring a possible positive bias for success rates of the chosen airway device. In contrast, results from mixed providers including physicians and mostly paramedics performing laryngeal tube insertion revealed lower laryngeal tube insertion success rates, which further decreased when paramedics during training only inserted laryngeal tubes in the operating room, thus illustrating a learning curve. The different experience of the practitioners must be discussed; namely, some providers may have been much more skilled in using the laryngeal mask airway than the laryngeal tube and several of the comparative studies are thus a comparison of skill levels and not of devices per se. Dividing the comparative studies of the laryngeal tube and the laryngeal mask airway according to the performer level demonstrated that anaesthetists have a higher firstpass and overall-pass insertion success rate for both devices in comparison to nonanaesthetists and that first-pass and overall-pass insertion success rates of nonanaesthetists for the laryngeal tube are inferior to the laryngeal mask airway ( Table 2). These results suggest that there is a device and also a provider dependent influence on success rates. This analysis, however, is limited by the small number of patients in the studies of laryngeal tube insertion by nonanaesthetists ( = 82). Similar to a historic discussion about the combitube, airway device-related complications may be significantly more related to the training with airway devices than to the airway devices themselves [82]. Accordingly, it is possible that the full potential of the laryngeal tube has not been detected yet as teaching with it may remain insufficient and infrequent.

Conclusions
Laryngeal tube (including its newer modifications) insertion failed in the first attempt in one out of five patients, with an overall failure rate in one out of 14 patients. When compared with the laryngeal tube, the laryngeal mask airway had a cumulative 5.5% better overall-pass insertion success rate.