We compared DLT tracheal intubation with videolaryngoscopy with a thin video-blade to the conventional MacIntosh laryngoscopy. We found significantly prolonged intubation times and no significant difference in intubation success despite significantly better intubation conditions compared to conventional laryngoscopy. In addition, there was a significantly higher incidence of malpositioned double-lumen tubes in the videolaryngoscopy group. Our complex investigator blinded nasal endoscopic follow-up after DLT intubation showed significant differences in only five of the seventeen objectifiable parameters, e.g. a reduced incidence of vocal cord redness, vocal cord haematomas, vocal cord bleeding and hypopharynx haematoma in the videolaryngoscopic group. The dental follow-up showed no significant differences in DLT intubation-related injuries between the two groups. These results of reported intubation-related injuries from two trans-nasal endoscopic examinations after DLT intubation do not seem to have an impact on patient wellbeing, since none of the subjective symptoms like sore throat, dysphagia, cough and hoarseness differed between the two groups.
Prolonged intubation times for GVL videolaryngoscopy for DLT intubation were shown in previous studies (6, 16, 17). Prolonged intubation times inevitably have a greater risk of hypoxia and could be harmful to patients with pulmonary comorbidities. In a prior study by Russell et al. in 2012, anaesthetists found that GVL was more difficult to use than the MacIntosh laryngoscope and ETI took longer. In their study all DLT intubations were performed by less experienced novice anaesthetists (6), whereas in our study, all DLT intubations were performed by three consultants of anaesthesiology well experienced with DLT intubations in thoracic anaesthesia and GlideScope videolaryngoscopy. Nevertheless, we could also show prolonged intubation times with GVL. A limitation of our study was, that prior to present investigation our consultants had little experience using the Titanium single use blade GlideScope for DLT insertion.
In contrast to these findings are the results of a recent meta-analysis in 2018 from Liu et al., with a total of 14 studies showing no difference in intubation time. The meta-analysis included studies with various videolaryngoscopes like Airtraq, McGrath Series 5, McGrath MAC - not all of these provide hyperacute angled devices (8). Considering only the four studies using GlideScope® videolaryngoscopy of that meta-analysis, our results are consistent with three of these four studies (6, 7, 16, 17). Only Hsu et al. were able to show shorter intubation times with Glidescope videolaryngoscopy for DLT intubation.
The first attempt success rate reported here using GVL for DLT intubation was 85%. Our reported failure rate of 15% at the first attempt using GVL is similar to most of the results reported by other groups (6, 18, 19). We were also unable to show a 100% first pass success rate with GVL, like the group of Hsu et al. (7). In the study of Hsu et al., all DLT intubations were performed by two experienced anaesthetists, who had both performed over 300 intubations using DLT with GVL. In addition, the BURP manoeuvre was not required for successful DLT intubations with GVL (7).
The process of advancing the DLT past the vocal cords seems to be the main sticking point for using hyper-angulated videolaryngoscopy (6, 20). Our findings support that DLT tube delivery and advancement into the trachea is the most difficult step in the procedure using videolaryngoscopy with hyper-angulated non-channelled blades for DLT intubations which causes prolonged intubation times for GVL. This assumption is supported by our data. Our experienced anaesthetists needed a BURP manoeuvre in 32% of all DLT intubations with GVL and we reported significantly more malpositions of the DLT (in 47% of cases). Presumably caused by the rotation manoeuvre, which is needed for the advancement into the trachea, there is a higher incidence of main bronchus malposition of the DLT. Caused by the required bending of the DLT-tube for hyper-angulated blades, the tip of the DLT often hits the ceiling when trying to insert the tube into the trachea past the vocal cords. Usually, a BURP manoeuvre is first performed to adjust the trachea, positioning it more posterior and more in line. Second, a rotation manoeuvre could be necessary. Such a rotation manoeuvre was described by Bustamante and Hernandez (21, 22). Rotation manoeuvre more often results in the incorrect position of the DLT. Liu et al. concluded that the use of videolaryngoscopes, especially with a hyper-angulated blade for DLT intubation, complicates the already complicated DLT intubation technique through rotation manoeuvres (8). Our data support the thesis that these sequential rotation manoeuvres are probably the reason why videolaryngoscopy increases the incidence of mispositioning of DLT. We could not confirm our hypothesis that a thinner hyper-angulated blade provides better visibility and in consequence more space for a rotation manoeuvre and therefore a lower incidence of sore throat and hoarseness. Hsu et al. were able to show a lower incidence of sore throat and hoarseness (7). There are controversial results in the literature. Russell et al. were unable to identify any significant differences in their study (6). Due to the controversial results in the current literature and our results, the question remains whether the questionnaires used are sensitive enough to record differences in subjective symptoms.
In regard to the incidence of dental trauma, a study by Lee et al. (2011) comparing DL and VL showed that less force is exerted on the teeth of the upper jaw when using VL (23, 24). This is in accordance with the results of the current study situation (6, 17). Our dental follow up showed no significant differences in DLT intubation-related injuries. However, our study was not powered to detect that the incidence of dental trauma is different.
This study was randomised, but has some limitations. First, the operators were not blinded to the intubation device used; however, it is difficult to circumvent this problem when evaluating different intubation devices. Nevertheless, the patient and follow-up endoscopic examinations were anonymised and blinded. A second limitation might be that the operators were not equally experienced with both intubation devices. Videolaryngoscopy is used routinely in our department, but not for DLT intubation. Furthermore, the new GlideScope®-Titanium was used for the first time during this study in our hospital.
A further limitation of our study is the small number of patients with a supposed difficult airway (Mallampati 3 and 4, 13% in the DL group vs. 17% in the GVL group) and the low incidence of predicted difficult airways (CL 3 and 4, 3% in the DL group vs. 0% in the GVL group).
In addition, an appropriate rigid stylet for the DLT intubation with the GlideScope, like the GlideRite® Rigid Stylet, which is standardly used for the single lumen tube intubation, was not available at the start of the study (18). Instead, we used the original rigid GlideRite® stylet for the single-lumen endotracheal tube as a template to shape the inner stylet of the DLT. A technique like the one developed and described by Bussier et al. and Bustamante et al. was not mandatory for our anaesthetists (18, 21).
DLT intubation with the GlideScope®-Titanium might be improved if the users are given some additional training and use the adequate rigid stylet for DLT, which keeps its shape and is better adapted to the hyper-angulated blade of the GVL.
There are currently many different videolaryngoscopes with varying designs and quality available on the market. For these reasons, our study results should not be generalised, and further investigation into VL and DLT intubation is needed.