We read with interest the recent study by Eum et al. [1], but do not feel it convincingly establishes the superiority of bougie over stylet use during hyperangulated videolaryngoscopy.

The results of the trial are statistically significant but also fragile. We calculated a fragility index of 1, indicating that just one patient allocated to the bougie group would have required a second attempt at tracheal intubation for the statistical significance of the primary outcome to be lost (p = 0.057) [2]. Furthermore, the difference in primary outcome in this single-centre trial of 166 patients derives from underperformance of the stylet group relative to the benchmark established in a recent multicentre trial of over 4000 cases [3]. While this study examined all patients independent of airway risk, its results were closely replicated in another small study looking specifically at expected difficult tracheal intubation [4]. In these studies, the first attempt success rates of hyperangulated videolaryngoscopy using a purpose-designed rigid curved stylet were 98.3% and 97%, respectively, compared with only 88% in the present study, limiting its external generalisability.

We echo the issues with stylet shape, already raised in other correspondence, that may have contributed to the poor performance in the stylet group. In addition, the major obstacle the authors identified to first attempt success in the stylet group, ‘hang up’ posterior to the arytenoid cartilages, suggests another potential contributor. The authors correctly note the tendency of bougies to sit posteriorly in the glottis. Conversely, an advantage of the stylet is the ability to keep the tracheal tube well anterior of the arytenoid cartilages, provided the correct technique is used.

During hyperangulated videolaryngoscopy, the styletted tracheal tube should ideally be introduced alongside the undersurface of the videolaryngoscope blade (Fig. 1a) so that it appears on the screen in the same horizontal plane as the glottis. It is important that the tracheal tube is adjacent to, rather than under, the laryngoscope blade to avoid impeding its subsequent manipulation. A small posterior tilt of the tracheal tube then allows it to be introduced between the vocal cords on a relatively shallow trajectory that deviates only slightly from the tracheal axis (Fig. 1a). This maintains its tip anterior to the arytenoid cartilages, avoiding ‘hang up’ above the glottis, and minimises impaction on the anterior wall of the trachea, allowing it to pass into the trachea once the stylet has been withdrawn.

If the stylet is introduced too posteriorly in the pharynx, so that it appears below the level of the glottis on the screen, the instinct of the operator is to redirect it upwards by performing an exaggerated posterior tilt (Fig. 1b). This causes the tracheal tube to approach the glottis at a much steeper trajectory, making it more likely to ‘hang up’ on the arytenoid cartilages or, if it clears these, impact on the anterior tracheal wall, impeding passage into the trachea. If posterior placement is instead corrected by lifting it vertically (‘Cooper manoeuvre’) (Fig. 1b) until its tip is level with the glottis, this returns it to the desired position (Fig. 1a), avoiding these issues.

We expect that, with appropriate training and equipment, stylets and bougies can be used equally effectively during hyperangulated videolaryngoscopy. However, we discourage use of a bougie without a stable curve. Although the study by Eum et al. shows that a straight bougie, bent to resemble the shape of the videolaryngoscope blade, can be used effectively for hyperangulated videolaryngoscopy, this technique may not be robust. The straight bougie will gradually unfurl towards its original shape, away from where the operator wishes to deliver the tracheal tube, the adverse impact of this being greater during more challenging and time-consuming tracheal intubation. Given bougies are available with a stable curve designed for use with a hyperangulated blade (e.g. Steerable Tracheal Intubation Guide, Lateral Medical, Woolloongabba, Australia), we advocate for use of only bougies with a stable curve in clinical practice and future research.

我们饶有兴趣地阅读了 Eum 等人最近的研究。 [ 1 ]，但并不认为它令人信服地证明了在超角度视频喉镜检查期间探条相对于探针使用的优越性。

试验结果具有统计学意义，但也很脆弱。我们计算出的脆性指数为 1，表明只有一名分配到探条组的患者需要第二次尝试气管插管，否则主要结果的统计显着性会丢失 (p = 0.057) [ 2 ]。此外，这项由 166 名患者参与的单中心试验中主要结果的差异源于探针组相对于最近一项针对 4000 多个病例的多中心试验中建立的基准的表现不佳 [ 3 ]。虽然这项研究对所有患者进行了独立的气道风险检查，但其结果在另一项专门针对预期困难气管插管的小型研究中得到了密切的重复[ 4 ]。在这些研究中，使用专门设计的刚性弯曲管心针进行超角度视频喉镜的首次尝试成功率分别为 98.3% 和 97%，而本研究中仅为 88%，限制了其外部推广性。

我们回应了在其他信件中已经提出的探针形状问题，这可能是导致探针组表现不佳的原因。此外，作者发现在管心针组中首次尝试成功的主要障碍是“挂在”杓状软骨后方，这表明了另一个潜在的因素。作者正确地注意到探条位于声门后方的趋势。相反，只要使用正确的技术，管心针的优点是能够将气管导管保持在杓状软骨前方。

在超角度视频喉镜检查过程中，理想情况下，应将带管芯的气管导管沿着视频喉镜刀片的下表面引入（图 1a），以便它在屏幕上与声门处于同一水平面。重要的是，气管导管位于喉镜刀片附近，而不是位于喉镜刀片下方，以避免妨碍其后续操作。然后，气管导管稍微向后倾斜，使其能够以相对较浅的轨迹引入声带之间，该轨迹仅稍微偏离气管轴（图1a）。这使其尖端保持在杓状软骨前方，避免“挂在”声门上方，并最大限度地减少对气管前壁的影响，从而在撤回管心针后使其能够进入气管。

如果管心针在咽部引入得太靠后，以致它出现在屏幕上声门水平以下，操作者的本能是通过执行夸张的后倾斜将其向上重定向（图 1b）。这导致气管导管以更陡峭的轨迹接近声门，使其更有可能“挂在”杓状软骨上，或者如果清除这些软骨，则会影响气管前壁，阻碍进入气管。如果通过垂直抬起（“库珀操作”）（图 1b）直到其尖端与声门齐平来纠正后置位置，则可以将其返回到所需位置（图 1a），从而避免这些问题。

我们期望，通过适当的培训和设备，在超角度视频喉镜检查期间可以同样有效地使用管心针和探条。然而，我们不鼓励使用没有稳定曲线的探条。尽管 Eum 等人的研究。表明弯曲成类似于视频喉镜刀片形状的直探条可以有效地用于超角度视频喉镜检查，但该技术可能并不稳健。直探条将逐渐展开至其原始形状，远离操作者希望输送气管导管的位置，在更具挑战性和耗时的气管插管期间，这种不利影响更大。鉴于探条具有稳定的曲线，设计用于超角度刀片（例如可操纵气管插管指南，Lateral Medical，Woolloongabba，澳大利亚），我们主张在临床实践和未来的研究中仅使用具有稳定曲线的探条。