Multiple intubation attempts resulting in complications remain an important airway management problem [1, 2]. Standard tracheal intubation techniques using video laryngoscopy (VL) or direct laryngoscopy (DL) involve two steps; 1) glottic visualization and 2) tracheal access. Failure to intubate using standard DL or VL techniques is usually attributed to either difficult glottic visualization (most common in DL) or difficult tracheal access (most common in VL) [2-4].

Patients with risk factors for difficult intubation using standard DL or VL techniques may need advanced intubation techniques such as fiberoptic bronchoscopy (FOB), intubating supraglottic airways (SGA), lighted stylets or combined techniques (VL + dynamic stylet) [5]. The FOB helped overcome anatomic challenges by allowing both indirect visualization of the glottis and dynamic navigation around anatomic structures using a single device. In controlled studies of expertly trained providers, the FOB has a high rate of success [6]. However, these techniques require specific equipment, advanced training, and maintenance of specialized skills, potentially hindering safe airway management worldwide [1, 5, 7].

The combined technique is an advanced intubation technique that allows both indirect visualization of the glottis and dynamic navigation around anatomic structures using two separate pieces of equipment: 1) a VL for indirect visualization of the glottis and 2) a dynamic stylet for precise navigation of the trachea. Key features of dynamic stylets include an articulating tip for precision navigation and a flexible shaft that can conform to the entire serpentine pathway of the airway [8]. Recent studies of combined techniques have demonstrated high rates of success when managing anticipated and unanticipated difficult intubations [9-11].

The comparative performance of the combined techniques vs. FOB technique is unknown. We designed a study to compare effectiveness, speed, ease of performance, and oropharyngeal trauma between three advanced intubation techniques when used as a primary intubation approach in patients with anticipated difficult intubations. We formed a large database of perioperative medical records from a single academic anesthesiology department that consists of trainees, CRNAs, and anesthesiologists. The objective of this study was to compare combined techniques with awake and asleep FOB techniques. We hypnotized that combined techniques are associated with a higher first pass success rate, lower failure to intubate with the primary technique rate, faster “in-room to intubation time,” and higher ratings of “easy” and “atraumatic” intubations.

The cohort included 934 intubation procedures and 849 patients (some patients presented for multiple procedures during the time frame evaluated). All filtering criteria were applied to the data already. Patient characteristics for each of the groups compared are presented in Table 1.

Fig. (1). Data sorting flow and advanced intubation taxonomy. Advanced intubation technique primary groups compared. Combined technique subgroups compared.

Fig. (2). ‘In room to intubated time’ density curves for combined techniques as a group, FOB awake, and FOB and ‘In room to intubated time’ density curves for VL + FOB and VL + TCITM.

Fig. (3a). ‘In room to intubated time’ density curve for combined techniques as a group, FOB awake, and FOB asleep.

Fig. (3b). ‘In room to intubated time’ density curve for VL + TCITM, FOB awake, and FOB asleep.

Fig. (3c). ‘In room to intubated time’ density curve for FOB awake and FOB asleep.

Fig. (3d). ‘In room to intubated time’ density curve for VL + FOB and VL + TCITM.

Results of the comparison of the combined techniques vs., awake FOB, and asleep FOB are presented in Table 2. A subgroup analysis was performed within the combined techniques category, comparing VL + FOB with VL + TCI^TM. That data is presented in Tables 3 and 4. Results of “in room to intubation” time for different techniques are presented as destiny curves. (See Fig. 2a and Fig. 3b).

The combined techniques achieved the highest first-pass intubation success rate of (88.7%). This was significantly higher than awake FOB (74.2%, P<0.001). The combined technique also had the lowest rate of “failure to intubate with the primary technique” at (1.8%), compared to awake FOB (9.2%, P = 0.002). The combined techniques were rated as “easy” (72%) significantly more often than awake FOB (38.2%, P < 0.001). The combined techniques were found to have a significantly shorter “in room to intubated” time (13.0 min) than either awake FOB or asleep FOB (15.1 min and 21.2 min, P = 0.002).

Our study reveals important information about the combined techniques, awake FOB, and asleep FOB as primary approaches to anticipated difficult intubations. “Difficult” implies increased mental task load which can compromise operator performance, thereby increasing risk. [13, 15] “Difficult” also implies additional training for proficiency and maintenance of skills, which can limit the success of advanced intubation techniques.

Operating room time is an expensive and limited resource. Joseph et.al. studied “in room to intubation” time and found significant increases in time associated with awake FOB vs. asleep FOB [12]. Our study confirms this finding. “In room to intubated” times for the combined techniques have not been studied. Minutes spent setting up the operating room is precious time. Minutes spent in prolonged single attempts or multiple intubation attempts may cause harm. Further study of efficiency is important for patient safety and reducing operating room costs.

As all techniques (combined techniques, awake FOB, asleep FOB) utilize dynamic and precise tracheal access, this implies that differences in trauma may be influenced by the mode of glottic visualization and/or navigation. Trauma from ETT tip catching on the glottis is a well-known problem with FOB intubation. VL provides visualization and displacement of the glottis as the ETT tip enters; a FOB alone does not. Additionally, the combined techniques achieve visualization and dynamic tracheal access with physically separate pieces of equipment, mechanically uncoupling visualization from dynamic tracheal access. This allows dynamic tracheal access to be monitored in a stable (non-dynamic) and panoramic visual field. In FOB equipment, visualization, and dynamic tracheal access components are mechanically coupled. This means visualization remains dynamic and non-panoramic throughout tracheal access when a FOB is used alone. We speculate that the combined techniques’ separation of visualization and dynamic tracheal access into two distinct entities may contribute to easier and less traumatic intubations.

Subgroup analysis of dynamic stylets revealed significant differences. While the VL component (GlideScope® Laryngoscope with hyper-angulated blade) of the combined techniques studied did not vary, the type of dynamic stylet did (FOB vs. TCI^TM dynamic introducer). The TCI^TM is a novel dynamic stylet with a fully articulated tip and a flexible shaft. Tip articulation is controlled by a removable pistol grip handle allowing single-handed dynamic navigation of the trachea. (Fig. 3).

While both the FOB and TCI^TM are dynamic stylets, they differ in two ways; 1) the TCI^TM has no intrinsic visualization capacity while a FOB does, 2) the TCI^TM dynamic introducer can be operated with a single hand enabling the execution of a single operator combined technique.

The use of a TCI^TM dynamic introducer was rated by the operator as “easy” and “atraumatic” at a significantly higher rate than FOB used as a dynamic stylet. The combined technique using a TCI^TM dynamic introducer resulted in a higher first pass rate and a lower “failure to intubate with the primary technique” when compared to FOB as a dynamic stylet. We speculate that two factors may account for these differences: 1) single-view vs dual-view combined technique and 2) single-operator vs. dual-operator execution.

Table 5. Combined technique subgroup types.

Combined Technique Subgroup	Dual View / Dual Operator	Dual View / Dual Operator	Single View / Single Operator
Visualization component	Dual view (VL + FOB)	Single view (VL only)	Single view (VL only)
Tracheal access component	FOB as dynamic introducer	FOB as dynamic introducer	TCITM dynamic introducer
Operator component	Dual operator	Dual operator	Single operator

Both single-view and dual-view combined techniques are practiced at our institution. As the TCI^TM dynamic introducer has no intrinsic visualization capability, cases utilizing VL + TCI^TM are, by definition, a single-view combined technique. The combined technique using VL + FOB can be single-view (VL visualization) or dual-view (both VL and FOB visualization) [8, 11, 16]. In our database, the VL + FOB subgroup contains some dual view combined technique cases. We were unable to distinguish from airway notes between dual view and single view combined techniques for this subgroup. Both single-view and dual-view combined techniques have been reported and studied individually, however, these two subgroups have never been directly compared [9, 10]. Our data raises the possibility that a second FOB view may have an impact on the performance of the combined technique.

Furthermore, the combined techniques can be performed by a single operator or dual operator depending on the type of dynamic stylet used. (Table 5) [8], Single-operator procedures require less coordination and planning. The VL + TCI^TM allows for single or dual-operator use, while the VL + FOB requires additional assistance from a second provider. Coordination of the two operators and monitoring of the two fields of view may increase the mental task load in the primary operator and may affect performance [13, 15].

This study has limitations inherent to single-center, retrospective design. First, this study is not controlled for technique selection bias. Experience with a technique, availability of equipment, patient-specific physiology, and anatomical features can influence technique choice and outcomes. Second, this is a single-center study with providers of various skill levels. Caution is urged in generalizing these results. Third, Table 1 shows significant differences in potential difficult intubation risk factors between groups. These differences might influence the choice, difficulty, and outcomes of the different techniques studied. Fourth, this study includes only operating room intubations performed by anesthesia providers. Performance in other environments may vary. Fifth, recall bias is inherent as we are relying on provider documentation, which can be affected by providers inaccurately reporting the intubation. Despite these limitations, we believe this data provides new insights into the performance of different advanced intubation techniques in the natural workflow of a large teaching hospital’s surgical system.

The combined techniques may have advantages over the awake FOB and asleep FOB intubation approaches. It is a technique that could be considered a primary approach in anticipated difficult intubations. Prospective controlled trials should be designed and conducted to better understand the role of combined techniques as an advanced intubation technique.

Sean Runnels is the inventor of the TCI^TM dynamic introducer and holds shares in Cords LLC. He was not involved in data analysis or design in this study. He was involved in project management and manuscript preparation. No other authors have declared any competing interests. Presson and C Zhang (University of Utah, Dept of Statistics) handled all statistical evaluations including preparation, statistical methods, and preparation of results, (Tables 1, 2 and Fig. 3a-d).

This study was approved by the University of Utah Institutional Review Board #0096411.

No animals were used in this research. All procedures performed in studies involving human participants were in accordance with the ethical standards of institutional and/or research committee and with the 1975 Declaration of Helsinki, as revised in 2013.

As this is a retrospective chart review, the University of Utah IRB waived the need for individual patient consent for this study and publication.

STROBE guidelines were followed.

The datasets used and/or analyzed during the current study are available from the corresponding author [A.S] upon reasonable request.

None.