In a large randomized clinical trial (3472 cases) conducted in urban academic centers, intubation with CP failed to show an advantage over intubation without CP in RSII in terms of preventing pulmonary aspiration [2]. However, the authors also mentioned that the results of the study may not be applied to emergency cases outside operating rooms where there are supposed to be more manpower and equipment, and patients probably has more adequate muscle relaxation for endotracheal intubation. Aspiration pneumonia is still a major concern to many anesthesiologists, so they will not hesitate to apply CP while intubating patients with risks of the complication [3].
As compared to DL, the video laryngoscopes during endotracheal intubation are associated with less neck manipulation, a better glottic view and a higher success rate of intubation in normal or difficult airways [15], but they don’t usually guarantee shorter intubation time [16, 17]. Moreover, like DL with a bulky blade, they are not usually chosen for patients presenting with limited mouth opening or fragile incisors. On the contrary, the CVS can be a tool of choice in such patients thanks to its slim stylet and video screen. The CVS has also been proved to provide faster endotracheal intubation than DL [10] and the Airway Scope (Pentax, Tokyo, Japan) in a simulated difficult airway [18]. Therefore, we assumed that the CVS is a preferable tool of intubation over laryngoscopic devices in intubation with CP.
Regarding the learning curve of the CVS, an inexperienced trainee can be proficient in using it after a few practices. Ten times of practice is sufficient for the inexperienced to learn the proper use of the CVS and after practicing on 20 patients, they are likely to accomplish intubation with the CVS at the first attempt in a mean intubation time less than 20 s [19]. As compared with the studies of intubation with the CVS without CP [10, 11], the median intubation time and success rate at the first attempt of intubation for CVS-V group in our study (50 cases) is 10.6 s [95% CI, 7.5 to 13.7] and 94%, 15 s [IQR, 12 to 19] and 89.9% in Yang et al’s study (200 cases) [10] and 9 s (mean) [SD, 4] seconds and 100% in Hsu et al’s study (30 cases) [11] (all the data calculated based on same definition of intubation time). Thus, CP does not appear to significantly affect the intubation time in CVS-V group in our study. When it comes to endotracheal intubation with CP, the intubation time in any of the three groups of our study is much shorter than that (78.8 s [SD, 41.2]) in the study by Hodgson et al. [12]. Therefore, with video assistance, the CVS-V as a video stylet is a handy device for endotracheal intubation with CP.
During intubation in CVS-L group, the application of CP may displace the larynx and cause difficulty for the operator to move the tube into the larynx, and under downward direction of the force the esophagus gets closer to anterior neck skin, so the false positive transillumination on the anterior neck tissue becomes more frequent. Nevertheless, the intubation still can be facilitated by checking the position of the tube on the video screen. Endotracheal intubation with the CVS-L may not be as straightforward as that with the CVS-V, but it can be accomplished sooner than that with a lightwand per se [12].
This study was conducted in simulated RSII while patients’ muscle power was not being monitored during anesthesia. Instead, we provided rocuronium 1.2 mg/Kg, which is proved by Magolian et al. to allow onset time (55 ± 14 s) [20]. The patients were intubated 1 min after injection of rocuronium and all the intubation conditions in the study were acceptable.
Thirty seconds was set as a cutoff point for the successful intubation time based on the research team’s experience and literature [7, 10, 11] where an intubation is usually completed in less than 30 s with either DL or the CVS. This study showed that the median time to successful intubation is within expected 30 s in all of the three groups.
There are three limitations in the study. Firstly, Lin did all the intubations in both CVS-V and DL group, so personal bias was possibly involved in the results. However, the results regarding our primary goals do not deviate from those in previous studies where the intubation using the CVS without CP [10, 11], so the personal bias should be minimal. Secondly, this was a randomized controlled study about how the CVS and DL perform in endotracheal intubation with CP, so ethically we need to conduct a study on patients whose airway conditions meet the indications to the use of the CVS and DL alike. Thirdly, the results revealed that the intubation time in CVS-V group was shorter than those in the other groups, but the intergroup difference was nonsignificant. It seems that the intergroup difference for intubation time is less than we expected and we should have had a larger sample size of patients to prove our hypothesis. Nevertheless, it is still worthwhile to further study how powerful the CVS-V can be in intubation in RSII when patients present with limited mouth opening or fragile incisors, which are two specific indications where an intubation stylet may be more advantageous over a laryngoscopic device.