The Evaluation of a Better Intubation Strategy When Only the Epiglottis Is Visible

A Randomized, Cross-over Mannequin Study

Tzu-Yao Hung; Li-Wei Lin; Yu-Hang Yeh; Yung-Cheng Su; Chieh-Hung Lin; Ten-Fang Yang


BMC Anesthesiol. 2019;19(8) 

In This Article


Levitan et al. found that for bend angles beyond 35°, straight-to-cuff ET can jeopardize the success rate of tracheal intubation and increase the difficulty of passing the ET.[4] However, among difficult airway, such as C-L III, larger angulations might confer some advantage. In our study, the straight-to-cuff and bend angles at 50° exhibited a trend of shorter intubation times and better success rates compared to bend angles at 35°, despite the method of holding the ET parts (97.92% versus 95.83%, 25.43 ± 14.17 versus 30.89 ± 26.05 s, p = 0.0859, 95% CI 0.97–1.61, respectively). Participants also felt that intubation was easier if a larger angulation was used (4.08 ± 2.18 versus 4.37 ± 2.20 cm). On the contrary, banana-shaped ET with larger angulations (longitudinal distance of 26 versus 28 cm) did not show any difference in the success rate, intubation time, or VAS score (equally 93.75%, 31.48 ± 28.21 versus 31.86 ± 27.21 s, 4.41 ± 2.21 versus 4.43 ± 2.02 cm, respectively). The banana shape might cross the visual axis twice if the tube axis is parallel to the visual axis. Thus, this method is believed to be unfavorable for intubation. Our results, however, showed no difference between the straight-to-cuff and banana-shaped tubes despite the effect of the bend angles and holding parts of the tube on success rate, intubation time, and subjective difficulty (96.88% versus 93.75%, 28.16 ± 21.10 versus 31.67 ± 27.60 s, 4.22 ± 2.19 versus 4.42 ± 2.11 cm, respectively).

By holding the top of the ET and flexing the elbow to the chest when the cuff passes the incisors, a larger torque is generated, which might be useful in managing a difficult airway. Compared to holding the middle part of the endotracheal tube, the tilting angle of the ET tip is larger during intubation when holding the top and starting up by the elbow instead of the wrist. However, no significant difference was found between holding the top or holding the middle of the ET on intubation success rates or VAS scores in spite of different bend angles and shapes (32.09 ± 28.04 versus 27.88 ± 20.66 s; 93.75% versus 96.88%; 4.40 ± 2.25 versus 4.23 ± 2.10 cm, respectively). The participants in our study were all inexperienced in holding the ET on the top before our study. Such a condition may lead to a higher failure rate. However, our study showed no evidence that the holding position improved the outcome of the management of the difficult airway.

When only the epiglottis is visible under laryngoscopy (C-L grade III), the ET passing between the vocal cord and trachea cannot be visualized directly and therefore, is considered a blind intubation. The success rate in the first attempt of intubations in C-L grade III was only 44.7% under direct laryngoscopy in one report in an ED setting.[5] When an intubation attempt fails, the practitioner usually will reposition the patient and focus on the left hand go deeper toward the vallecula or lift harder to obtain a better glottic view. However, we often neglect our right hand, which is directly lifting the epiglottis with stylets. This type of manoeuvre can improve the glottic view and allow the practitioner to focus only on the left hand. Nestling the tip of the endotracheal tube under the epiglottis and moving it along the anterior larynx leads to the tracheal inlet. Ueda et al. reported a case wherein lifting of the epiglottis with stylets helped improve the glottic view.[3] In our study, the success rate of intubation with stylet-assisted epiglottis lifting was 100% in contrast to without lifting (94.53%). Lifting of the epiglottis also decreased the mean duration of intubation more than without lifting (22.23 ± 11.20 versus 31.39 ± 25.86 s, respectively). In the survival analysis, lifting of the epiglottis was a strong factor in improving intubation (Figure 3, p < 0.0001). Additionally, lifting the epiglottis with stylets was not considered to be more difficult compared to not lifting the epiglottis (4.06 ± 2.16 cm versus 4.36 ± 2.16 cm, p = 0.137, 95% CI -0.80–0.11). Lifting of the epiglottis can accelerate intubation and improve the success rate in difficult intubations without increasing the level of difficulty.

Among the different conditions associated with C-L grade III in our study, holding the top of the endotracheal tube with a straight-to-cuff tube and a bend angle of 35° was considered to be the most difficult intubation performed, followed by holding the middle of the tube with the smaller curvature of the banana-shape (longitudinal distance = 28 cm). In contrast, holding the middle of the ET with the straight-to-cuff tube and a bend angle of 50° was the easiest. The VAS score was directly related to intubation time (odds ratio = 0.55), such that the higher the VAS scores, the longer the intubation duration will be.


First, this was a mannequin study. During the intubations, the participants were asked to avoid better glottic visualisation and continue intubating on a simulated C-L defined difficult airway. Such conditions are likely to not occur in the clinical setting. However, we recorded the entire intubation process on video clips and reviewed them with respect to the precise time intervals and C-L grades just before intubation. We found that the participants tended to lift the epiglottis unintentionally, particularly when they repeatedly failed to pass the ET. However, in simulating the clinical setting, prohibiting contact with the epiglottis would not be natural. Although the study was designed to investigate C-L grade III where only the epiglottis was visible, some of the glottic views, as reviewed by the video clips, were grade IIb (3.13%), in which the lower part of the vocal cord might be seen. The inexperience of the participants in 'holding the top' of the ET technique might have reduced the significance of the result in this group. Moreover, the study results were based on direct laryngoscopy on mannequin, further study need to be investigated for the video laryngoscopy and safety on real patients. Finally, this was a convenience sample and may be vulnerable to selection bias. But this study focused on experienced intubation performers that managing difficult airway in their daily practice and the technique of epiglottis lifting still significantly accelerated the intubation process despite their insufficient practice of this new technique.