Discussion

 

 

In this clinical investigation, we evaluated the performance of the Lo Pro Adult GlideScope Video Laryngoscope (LGVL) in 442 adult patients with a wide range of conventional laryngoscopic views requiring orotracheal intubation for elective thyroid surgery as in our previous study with the Standard Adult GlideScope Video Laryngoscope (SGVL) including 334 patients (4). Unfortunately, we could not compare the SGVL (maximum blade thickness of 18 mm) with the LGVL (maximum blade thickness of 14 mm) because of breakage of the SGVL due to improper handling of the device. Laryngoscopy and tracheal intubation attempts with the SGVL were performed by formally instructed but novice operators; in the present study, the operators were experienced users of the SGVL. Therefore, comparisons of laryngeal views obtained, minor problems and difficulties, and the success and failure rates associated with laryngoscopy and tracheal intubation with both video laryngoscopes (VLs) should be evaluated only with restrictions.

 

In the present study, the operators were again very successful at visualizing the laryngeal aperture or at least the arytenoids when using the LGVL, despite the high incidence of conventional laryngoscopic views with visualization of only the epiglottis (grade 4) or just the soft palate (grade 5), intended by the study design. It should be noted that external laryngeal manipulation during laryngoscopy, not performed in both studies, might have improved the laryngeal views by at least one grade when optimum visualization of laryngeal structures not obtained. The laryngeal views obtained with both VLs were always comparable or superior to those provided by conventional laryngoscopy (CL). Both study designs provided only gentle lifting force on the blades at laryngoscopy; we suppose that the operators applied even less lifting force when using the VLs because they enabled a wide and panoramic view on the monitor early after proper insertion of the blades.

 

In patients with difficult CL (grade 4 or 5), the laryngeal views obtained with both VLs were always superior to those provided by CL; the worsest video laryngoscopic view with visualization of only the arytenoids was observed in 6 of 105 patients in the present study and in 4 of 76 patients in the previous study, respectively. In these patients, the success rates of video laryngoscopy-assisted tracheal intubation at the first attempt were 97 and 89 percent, respectively, with success of tracheal intubation after a maximum of two attempts in all patients as for the entire study populations. These favorable results should be taken into consideration when planning future equipment availability and updating formulated departmental strategies for difficult CL and tracheal intubation situations.

 

In the previous study with the SGLV, we observed minor problems and difficulties with blade insertion and oropharyngeal tracheal tube (TT) passsage in 2 and 6 percent, respectively; there were two primary failures of tracheal intubation due to failed oropharyngeal TT passage. In the present study with the LGVL, we encountered impeded oropharyngeal TT passage in only 2 percent; interestingly, there were no problems and difficulties with blade insertion. Based on these results, the new LGVL may be also suitable for patients with limited mouth opening but not less than 20 mm and/or restricted pharyngeal space; the lower profile of the LGVL made blade insertion easier and provided more space for oropharyngeal TT passage.

 

The oropharyngeal passage of the styletted TT is usually blind until the tip of the TT comes into view on the monitor; pharyngeal injuries may be the result of uncontrolled TT advancement (2). The corresponding author of this clinical investigation is also aware of a case with laceration of the soft palate experienced by a novice user of the LGVL (a staff anesthetist of our institution, without prior formal instruction in the technique) in a patient with unanticipated difficult CL. Multiple attempts to insert the TT into the oropharynx were required; probably, the stylet used in this patient protuded beyond the distal end of the TT. Because of bleeding, the surgical procedure planned had to be postponed. We therefore stress that the styletted TT should be introduced and advanced through the oral cavity with special caution.

 

We again used the Schroeder directional tracheal tube stylet (DS) to introduce and advance the TT. The shape of the TT is an important part of tracheal intubation with the both VLs and determines success or failure. Using TTs with prebended malleable stylets, the 60-degree curvature recommended by the manufacturer must often be increased. Inappropriate preshapening of the TT was the most frequent cause of difficulties with tracheal intubation in a study evaluating the SGVL on an airway model simulating easy and difficult CLs (5). In a recently published study in patients with normal airways, Jones and co-workers (6) found that a 90-degree angle provided the best results and should be the initial configuration of the styletted TT. Nevertheless, despite the routine use of the adjustable DS, we observed minor problems and difficulties with TT passage through the laryngeal aperture in 5 percent. Impeded TT advancement into a midtracheal position (encountered in 9 percent) might have been due to impingement of the TT on the anterior wall of the thyroid cartilage or the anterior trachea, but also due to tracheal deviation and/or compression by enlarged thyroid glands; complete withdrawal of the DS and rotation of the TT 90 degree or more to the right enabled TT passage into the proper position.  

 

In both studies, fogging of the camera system, usually encountered with optical systems of rigid fiberoptic laryngoscopes, was not evident. The camera system of the LGVL and also of the SGVL is resistent to fogging by warming-up the system slightly above normal body temperature within a short period of time, a special feature of both devices. Furthermore, secretions did not appear to interfere with the laryngeal view; excessive secretions in the hypopharynx, also a major problem with the use of rigid fiberoptic laryngoscopes, may obscure the view with both VLs but do not reduce the success rate of tracheal intubation as the video cameras are protected and remote from the tip of the blades.

 

Severe complaints and injuries associated with airway management (AM) were not observed; this may be due to vizualization of at least parts of the laryngeal aperture, except in 6 patients with visualization of only the arytenoids, during successful laryngoscopy and controlled TT advancement into a midtracheal position. In patients with difficult CL, conventional tracheal intubation, particulary after multiple attempts, may not provide these favorable results.

 

Although flexible bronchoscopes are essential in the management of difficult airways, they require different skills and an experienced assistance. Both VLs are easy to use and the obscured view by soft tissue is usually controlled by the operator due to the blade design. The LGVL together with the DS proved to be uniquely useful for routine and difficult laryngoscopy and tracheal intubation and may be superior compared to the SGVL.

 

 

References