Introduction

Tracheal intubation is a standard procedure in anaesthesia and emergency medicine. Despite this, there is a persistent risk of encountering a difficult airway, whether expected or unexpected, which may lead to iatrogenic complications. Several organisations have produced protocols to manage such situations, including the 2022 guidelines from the American Society of Anesthesiologists (ASA) and the 2015 guidelines from the Difficult Airway Society (DAS) [1, 2].

Both guidelines advise using a second-generation Supraglottic Airway Device (SAD) as a rescue technique to ensure oxygenation and ventilation in airway emergencies. Once oxygenation is achieved, the SAD can facilitate tracheal intubation [3]. For improved safety and efficacy, tracheal intubation through SAD is preferably performed under bronchoscopic guidance. This technique enhances visualisation and can increase the likelihood of successful intubation [4–7].

The LMA Fastrach™ (Teleflex Incorporated; Wayne, PA, USA) represents the first commercially available intubating SAD. Engineered specifically to facilitate blind tracheal intubation, it serves as a crucial instrument for rapid airway management, particularly in emergencies [8].

Although the Fastrach™ intubating supraglottic airway device holds notable historical importance as a first-generation instrument, clinical practice has increasingly favoured the adoption of second-generation SADs. This shift is primarily ascribed to the numerous beneficial characteristics provided by these devices. Second-generation SADs are constructed to form a more secure seal in the airway, thereby reducing the likelihood of gastric content reaching the lungs [9]. Additionally, whereas the Fastrach™ employs a blind intubation technique, many second-generation supraglottic airway devices permit scope-guided visualisation of the glottis. This capability can facilitate more accurate intubation and may contribute to patient safety. Due to these advantages, use of the Fastrach™, the sole first-generation intubating laryngeal mask airway, has declined. Clinicians are increasingly opting for second-generation devices that better meet the demands of modern airway management [10].

I-gel^® (Intersurgical, Berkshire, UK) is the most widely studied second-generation SAD for blind tracheal intubation [11, 12]. Like the Fastrach™, it is a unique SAD that enables unassisted tracheal intubation [5, 13, 14]. However, the I-gel^® was subsequently developed with specific consideration for the growing application of flexible bronchoscopes [15]. Current research demonstrates that blind intubation utilising the Fastrach™ device achieves higher success rates than the I-gel^® [16]. However, when a flexible bronchoscope is utilised, I-gel^® demonstrates better first-pass success rates compared to Fastrach™ [17].

Since current literature and algorithms favour scope-assisted over blind intubation via SAD, more second-generation SADs have been developed for this purpose. The LMA Protector™ (Teleflex Medical Europe Ltd., Athlone, Ireland) is a more recently introduced pre-shaped second-generation SAD, offering the combined advantages of minimising the risk of gastric aspiration and the ability to function as a conduit for scope-assisted tracheal intubation [18]. Two randomised controlled trials (RCTs) have reported similar outcomes for fibreoptic-guided tracheal intubation using the I-gel^® and the Protector™ devices [6, 15], while, when an Aintree catheter is used, I-gel^® may offer some advantages [4], but there are limited additional data available in the literature.

The ability to perform tracheal intubation through a SAD can affect device selection for managing difficult airways. This clinical trial is designed to evaluate and compare three different SADs used as conduits for tracheal intubation. The study includes an examination of two techniques applied across three SADs.

Aim

Its objectives are to assess the effectiveness of blind intubation using the Fastrach™, a first-generation SAD, and to compare this approach with flexible scope-guided intubation using the I-gel^® and the Protector™, both classified as second-generation SADs.

Material and methods

Study design and setting

This was a prospective, three-arm, parallel-group, interventional, comparative, randomised controlled trial conducted at the University Hospital of Patras, Greece, from November 2021 to March 2023. The study followed the Declaration of Helsinki and met the requirements of the CONSORT 2025 statement [19]. Ethical approval was obtained from multiple entities. The Ethics Committee on Human Experimentation of the Faculty of Medicine at the University of Patras, chaired by Dr. Alexandra Lekkou, approved the study on 10 December 2019 (Approval no. 737/10-12-19). The Scientific Council of the Hospital, chaired by Prof. Markos Marangos, approved on 20 December 2019 (Approval no. 1143/20-12-19). Additionally, the Board of Directors of our Hospital, chaired by Dr. Panagoula Mammi, approved the study on 23 January 2020 (Approval no. 03/23-01-20). Written informed consent was obtained from all eligible patients before they participated in the study.

Participants

Inclusion criteria

Adult patients aged 18 years or older scheduled for elective procedures requiring general anaesthesia with tracheal intubation were considered eligible for inclusion in the study. All participants were required to meet the American Society of Anesthesiologists Physical Status (ASA-PS) classification I or II criteria [20]. All eligible patients underwent a comprehensive airway assessment during a pre-anaesthesia visit. This evaluation was performed by one of the investigators, who was a qualified anaesthesiologist.

Exclusion criteria

Exclusion criteria for the study included patients with contraindications to the insertion of a SAD or predicted difficulty of SAD insertion and patients who had contraindications to the use of neuromuscular blockade. Additionally, patients who required spontaneous breathing, indicated a need for awake intubation or surgical airway management, belonged to the obstetric population, were morbidly obese, or refused to provide written informed consent were also excluded from the trial.

Outcomes of the study

Primary outcome

The primary outcome of the study was the proportion of successful intubations performed via the SAD on the first attempt.

Secondary outcomes

Secondary outcomes included findings related to several key metrics about the utilisation of each SAD, such as 1) the rate of success of first pass, 2) ease of insertion of each SAD, 3) the oropharyngeal leak pressure (OLP), and 4) complications like the presence of blood staining following removal of the SAD and the occurrence of postoperative sore throat. In addition, 5) the SAD insertion and ventilation time (T1), 6) the carina visualisation time (T2), 7) the time for intubation and mechanical ventilation (TIMV), and 8) the total time from SAD insertion to intubation and mechanical ventilation (total) were considered as secondary outcomes.

Study intervention

Upon arrival in the operating room, standard monitoring protocols were implemented, and peripheral intravenous access was secured. Before preoxygenation, we confirmed that all necessary devices for the trial were available, including the rescue device and the video laryngoscope. Following this, the allocated SAD was revealed and prepared for use in accordance with the manufacturer’s recommendations.

The insertion technique for each SAD was performed by the same anaesthesiologist, who was skilled in airway management, in accordance with the manufacturer’s guidelines [21–23]. Proper placement of the SAD was verified through square wave capnography, capnometry readings exceeding 20 mm Hg, and auscultation confirming adequate breath sounds.

The protocol permitted up to three corrective manoeuvre attempts. According to DAS guidelines, the final attempt was advised to utilise either an alternative SAD or a different size of the same SAD [2]. The initial size of the selected SAD was determined collaboratively by the operator and research assistant in accordance with the manufacturer’s guidelines. Additionally, consideration of the patient’s airway history and unique characteristics could further inform the final selection to ensure optimal ventilation.

During the SAD insertion procedure, the assistant systematically documented several critical parameters: (1) the duration of each attempt until successful confirmation of mechanical ventilation, (2) the total number of attempts required, (3) the aggregate time for the procedure, including any corrective manoeuvres (T1), and (4) the degree of difficulty encountered during SAD insertion, classified as easy, moderate resistance, or severe resistance. The assessment of insertion difficulty was conducted in conjunction with the operator.

In both the I-gel^® and Protector™ groups, a flexible intubation video endoscope (Karl Storz 6.5 ´ 650 – the FIVE 6.5) was connected to a C-MAC^® HD Monitor 8403 ZX (Karl Storz) and used with a lubricated reinforced tracheal tube of either 6.5 mm or 7.0 mm internal diameter. The endoscope was introduced through the laryngeal lumen of the SAD and advanced toward the glottis. Once the glottic opening was visualised, the bronchoscope was inserted into the trachea until the carina was seen. The tracheal tube was then railroaded over the bronchoscope until its tip was positioned 3–4 cm above the carina. Following this, the cuff of the tracheal tube was inflated, and the bronchoscope was withdrawn.

The anaesthesia circuit was then attached, and proper tracheal tube positioning was verified by observing a square wave capnographic trace in conjunction with auscultation of bilateral breath sounds during manual ventilation of the patient. During these procedures, the research assistant documented the following parameters: (1) the time from bronchoscope insertion into the SAD until the carina was visible (T2), (2) the time from bronchoscope insertion into the SAD to successful tracheal intubation and ventilation (TIMV), (3) the number of attempts required, and (4) any difficulties encountered during the process.

In the Fastrach™ group, tracheal intubation was performed using the conventional technique for blind intubation as recommended by the manufacturer [21]. A reinforced tracheal tube (LMA Fastrach™ tracheal tube, Teleflex Medical Europe Ltd.) with an internal diameter of either 6.5 mm or 7.0 mm was utilised. The assistant recorded several key parameters during this process, including the time from tube insertion into the SAD until verification of intubation and mechanical ventilation (TIMV), the number of attempts made, and any necessary manoeuvres, such as the Chandy manoeuvre.

The total time required to complete the procedure, from SAD insertion to successful tracheal intubation (referred to as Total), was later calculated by the researchers in collaboration with the biostatistician.

The protocol specified termination criteria to be implemented under the following conditions: (1) occurrence of an unplanned adverse event during the procedure (such as SpO₂ dropping below 96%), (2) unsuccessful face-mask ventilation, (3) inability to insert the SAD or ventilate through it after three attempts, and (4) failure to intubate through the SAD after two attempts or after 120 s.

Randomisation, sample size, and statistical analysis

Participants were allocated at random to one of three SAD groups: Fastrach™, I-gel^®, or Protector™, with equal distribution. The assignments were made based on a computer-generated block randomisation list, which was accessible exclusively to the biostatistician. Allocation details were kept in sealed, numbered envelopes and were opened in the operating room before preoxygenation.

To ensure sufficient statistical power for the study, a sample size calculation was conducted before its commencement. This calculation employed the sample size estimation method for a two-tailed t-test, with the primary outcome being time for intubation and mechanical ventilation (TIMV). The assumptions for this calculation included two groups of patients using different SADs, degrees of freedom set at 1, a significance level (a) of 0.05, and a desired power of 90%. The effect size was estimated at 0.6, based on an anticipated 15% difference in TIMV between the I-gel^® and Protector™. Based on these parameters, we determined that a total of 120 patients would be required, with 60 patients in each group. Considering the inclusion of a third group for which TIMV would not be estimated, the total sample size needed increased to 180 patients. To account for potential erroneous assumptions and patient attrition, we decided to increase the estimated sample size by 25%, resulting in a target of 66 patients per group.

The normality of the data was evaluated employing both the Shapiro-Wilk and Kolmogorov-Smirnov tests. Comparative analyses of proportional and categorical variables were conducted using either the c² test or Fisher’s exact test, as appropriate. Group differences for variables with normal distributions were analysed using the t-test and ANOVA, applying the Bonferroni correction to adjust the significance level. For continuous data without a normal distribution, the Kruskal-Wallis test and Mann-Whitney U-test were used.

Group differences were presented as means with standard deviations (SD), medians with interquartile ranges (IQR 25-75), or as counts and percentages. Data analyses were conducted using SPSS statistical software for MAC (version 28.0; IBM, Armonk, NY, USA) and GraphPad Prism (version 10.4.1). Statistical significance was established at a two-tailed p-value of less than 0.05.

Results

A total of 198 patients were randomised from November 2021 to March 2023 (Figure 1). Following randomisation, 5 patients were excluded from the study: 1 declined to participate, 1 experienced an adverse event unrelated to the protocol, and 3 underwent direct tracheal intubation. Hence, a total of 193 patients were enrolled in the study and included in the analysis. No statistically significant differences were observed in patients’ baseline characteristics among the three devices (Table I). Detailed information regarding patients’ airway characteristics is provided in Table II.

Data on SAD insertion, intubation, efficacy, and associated complications are detailed in Table III and illustrated in Figures 2–4. The success rate of tracheal tube placement was comparable between I-gel^® and Protector™ (p = 0.66) but lower for Fastrach™, although no statistical significance was observed (Figure 2). Analysis of SAD first-pass success rates indicated no statistically significant differences among the three devices (p = 0.27; Figure 3 A). Notably, OLP was significantly higher with the Protector™ compared to the I-gel^® (p < 0.001; refer to Figure 3 B). Device insertion was more straightforward in the I-gel^® group compared to Protector™ (p = 0.01), while the requirement for device repositioning and additional manoeuvres did not differ significantly among the three SADs (p = 0.08 and p = 0.11, respectively).

Statistically significant differences were identified among the three SADs with respect to the interval from device insertion to ventilation (Figure 4 A), time to intubation (Figure 4 B), and overall total time required (Figure 4 C). Specifically, both Fastrach™ and Protector™ exhibited longer times from device introduction to ventilation compared to I-gel^® (p < 0.001 for both comparisons). Additionally, time to intubation (TIMV) was greater for I-gel^® than for Fastrach™ (p < 0.001), for I-gel^® compared to Protector™ (p = 0.03), and for Protector™ relative to Fastrach™ (p < 0.001). Total procedure time was extended in the Protector™ group compared to both Fastrach™ and I-gel^® (p < 0.001 for both), and in I-gel^® compared to Fastrach™ (p < 0.001).

Blood staining after removal of the device was more often observed in Protector™ compared to I-gel^® and Fastrach™ (p = 0.01), while sore throat incidence was similar among the devices.

Discussion

This study was designed to compare three supraglottic airway devices as conduits for tracheal intubation. The protocol included two second-generation devices (I-gel^®, Protector™) and one first-generation device (Fastrach™). Although there are several studies comparing either blind tracheal intubation [12, 16, 24] or bronchoscope-guided [5–8] via SADs, our trial is unique because it attempts to compare the gold standard blind technique with the more modern bronchoscopic-guided ones. The study found that Fastrach™ had shorter times for tracheal intubation and overall airway management compared to I-gel® and Protector™, which required more time due to additional steps and equipment such as a bronchoscope.

However, there was no statistically significant difference in intubation success rates among the three SADs (Fastrach™ 92.2%, I-gel^® 95.4%, Protector™ 96.9%).

Between the two second-generation SADs, I-gel^® had a longer intubation time compared to Protector™ (p = 0.03). While recent studies have not identified a statistically significant difference in intubation times between these devices, some have reported a clinical difference favouring Protector™, which is consistent with the present findings [4, 6, 15].

On the other hand, blind intubation using the Fastrach™ was faster compared to bronchoscope-guided intubation with the Protector™ and I-gel^® (p < 0.001). To our knowledge, in cases of an unanticipated difficult airway, the DAS algorithm (Plan B) recommends using a SAD to maintain oxygenation [2]. Although a second-generation device is recommended as the initial option in this scenario due to its superior safety profile, the algorithm specifies that the device should be changed if unsuccessful, with a maximum of three attempts permitted [24]. In this case, the use of the intubating laryngeal mask (Fastrach™) remains an option. Notably, as indicated in a recent systematic review, the first-generation Fastrach™ has not been surpassed by the new SADs for blind intubation concerning the first pass and overall success rate [19]. Moreover, considering that intubation through a SAD is recommended in Plan B when oxygenation is restored, the Fastrach™ provides the advantage of allowing intubation either blindly or with the assistance of a bronchoscope [25]. However, Fastrach™ was first developed for blind intubation – its characteristics (e.g. epiglottic elevating bar) require extra manipulations along with additional training to be used as a conduit for bronchoscope-guided intubation. Notably, a recent randomised trial compared the Protector™ to another second-generation SAD, the Blockbuster, used as a conduit for blind intubation. This revisits the discussion surrounding the effectiveness of the blind technique [26]. In this context, the results of our study could be particularly relevant in situations where a bronchoscope is not available or the operator lacks adequate training.

Moreover, regarding the clinical performance of all SADs, the I-gel^® was inserted more easily and required less time than the others (p < 0.001 for both comparisons) [27, 28]. This may be due to its design, which lacks an inflatable cuff. However, in terms of first-pass success rates, all devices demonstrated comparable outcomes, aligning with current literature [11, 18, 25]. Interestingly, unlike previous RCTs concerning the OLP, our trial observed a statistically significant superiority of the LMA Protector™ (p < 0.001) [4, 27, 29].

This finding is consistent with a recent network meta-analysis and systematic review that compared 17 types of SADs [9]. Additionally, in our study, we observed blood staining after the removal of the device more frequently in the LMA Protector™ group (p = 0.01), which also aligns with findings from previous studies [28, 29]. The incidence of sore throat was comparable among the different devices [25, 27]. However, it is important to recognise that the occurrence of a sore throat could be influenced by many other independent factors, such as the duration of the surgery [30]. Remarkably, a recent network meta-analysis examined clinicians’ SADs based on the incidence of postoperative sore throat as the primary outcome, along with blood staining, first-pass success rate, and OLP as secondary outcomes. This analysis ranked the I-gel^® as the only device among the top six SADs for all outcomes, despite its lower ranking concerning OLP [10].

Our study has certain limitations. Firstly, it was conducted at a single centre, but it involved a large sample size. Secondly, all patients enrolled were assessed to have normal airway anatomy, and those with potential difficulties in airway management were excluded. The study population was rigorously selected to omit individuals with morbid obesity, gastroesophageal reflux, or other known risk factors for aspiration. As a result, our techniques may yield different success rates and time prolongation in a more diverse population. Thirdly, although randomisation was implemented, the study was not double-blinded due to the inherent nature of airway management, which could potentially introduce observer bias.

Specifically, the attending anaesthesiologist, assistant, and nursing staff in the operating room were informed about the method used, while the postoperative outcome assessors and the statistician remained blinded to the group designations. Acknowledging these limitations is essential for accurately interpreting our findings. For future research, actionable steps include conducting multi-centre studies to enhance the diversity of the patient population and broadening inclusion criteria to include patients with a wider range of airway anatomies and risk factors. This approach can significantly improve the generalisability of our results.

Conclusions

In our study, the I-gel^® and LMA Protector™ demonstrated comparable performance when used as conduits for bronchoscope-guided intubation. Additionally, the I-gel^® was found to achieve ventilation faster and allowed for easier placement compared to the other devices, while the OLP was significantly higher in the Protector™ group. Interestingly, the Fastrach™ required a shorter time to achieve unassisted intubation. As a result, in a difficult airway scenario, the I-gel^® could be a reliable first-choice device for maintaining oxygenation, while both second-generation devices can effectively facilitate assisted intubation. However, when assisted intubation is not an option, the Fastrach™ should be readily available on all portable carts for difficult airway management because it offers a valid alternative intubation technique.

Funding

No external funding.

Ethical approval

Human subjects: Informed consent for treatment and open access publication was obtained or waived by all participants in this study. Ethics Committee on Human Experimentation of the Faculty of Medicine at the University of Patras issued approval, no. 737/10-12-19. Ethical approval was obtained from multiple entities. The Ethics Committee on Human Experimentation of the Faculty of Medicine at the University of Patras, chaired by Dr. Alexandra Lekkou, approved the study on 10 December 2019 (Approval no. 737/10-12-19). The Scientific Council of the Hospital (IRB), chaired by Prof. Markos Marangos, granted approval on 20 December 2019 (Approval no. 1143/20-12-19). Additionally, the Board of Directors of our Hospital, chaired by Dr. Panagoula Mammi, approved the study on 23 January 2020 (Approval no. 03/23-01- 20). Written informed consent was obtained from all eligible patients prior to their participation in the study.

Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organisation for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organisations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Conflict of interest

The authors declare no conflict of interest.

References