In the recent study by Kriege et al. [1], comparing performance of the McGrath™ videolaryngoscope with direct laryngoscopy for rapid sequence intubation in the operating theatre, 94 of 500 patients (19%) in the direct laryngoscopy group had a Cormack and Lehane grade view ≥ 3.; however, study participants had an expected normal airway, direct laryngoscopy was performed under sufficient neuromuscular blockade and external laryngeal manipulations were allowed to improve laryngeal visualisation. Importantly, the incidence of difficult laryngoscopy was significantly higher in this study, compared with their previous work comparing the performance of the McGrath videolaryngoscope with direct laryngoscopy in elective patients with an anticipated normal airway [2]. As the two studies had almost identical research conditions, we are interested to know why there is an approximate 1.4-fold increase in the incidence of difficult laryngoscopy in their latest work.

Furthermore, in sample size evaluation, Kriege et al. state that the power calculation assumed first pass success rates of 97% and 92% for the McGrath and direct laryngoscopy groups, respectively. According to the two references cited by them in the power calculation [3, 4], we note that the reported first pass success rate with direct laryngoscopy was only 73.1–78.6%, rather than 92%. The EMMA trial by Kriege et al. comparing the performance of the McGrath videolaryngoscope with direct laryngoscopy in elective patients was completed in May 2019 [2], while this multicentre, randomised controlled trial comparing the two same devices for rapid sequence intubation in the operating theatre was initiated on 24 July 2021 (ClinicalTrials.gov: NCT04794764). It is unclear why Kriege et al. did not use the first-pass success rates of McGrath and direct laryngoscopy from their EMMA trial (94% vs. 71.6%) for sample size evaluation in this subsequent clinical trial comparing the same two devices. We are concerned that using an assumed first-pass success rate of 92% for direct laryngoscopy in this study will have overestimated the performance of direct laryngoscopy and resulted in an inappropriate estimation of a large sample size requiring 500 patients per group.

Finally, the actual difference in efficacy between the two studied devices greatly exceeds the assumed value in this study, that is, a 5% absolute between-group difference. Unlike other similar multicentre randomised controlled trials with large sample sizes [5, 6], the design of this study did not include an interim analysis. We believe that trial enrolment would have been stopped in advance by a data and safety monitoring board according to the prespecified stopping criteria if a pre-planned interim analysis had been performed.

在 Kriege 等人最近的研究中。 [ 1 ]，比较了McGrath™视频喉镜与直接喉镜在手术室快速顺序插管的性能，直接喉镜组的500名患者中有94名（19%）的Cormack和Lehane分级视图≥3。然而，研究参与者的气道正常，在充分的神经肌肉阻滞下进行直接喉镜检查，并允许进行外部喉部操作以改善喉部可视化。重要的是，与他们之前在预计气道正常的择期患者中比较 McGrath 视频喉镜与直接喉镜性能的研究相比，本研究中困难喉镜的发生率明显更高 [ 2 ]。由于这两项研究的研究条件几乎相同，我们有兴趣知道为什么在他们最新的研究中，困难喉镜检查的发生率增加了大约 1.4 倍。

此外，在样本量评估中，Kriege 等人。指出功率计算假设 McGrath 组和直接喉镜组的首次通过成功率分别为 97% 和 92%。根据他们在功效计算中引用的两篇参考文献[ 3, 4 ]，我们注意到报道的直接喉镜首次通过成功率仅为73.1-78.6%，而不是92%。 Kriege 等人的 EMMA 试验。比较 McGrath 视频喉镜与直接喉镜在择期患者中的性能于 2019 年 5 月完成 [ 2 ]，而这项比较两种相同设备在手术室快速顺序插管的多中心、随机对照试验于 2021 年 7 月 24 日启动（临床试验） .gov：NCT04794764）。目前还不清楚为什么 Kriege 等人。在比较相同的两种设备的后续临床试验中，没有使用来自 EMMA 试验的 McGrath 和直接喉镜检查的首次通过成功率（94% 与 71.6%）进行样本量评估。我们担心，在本研究中使用直接喉镜检查的首次通过成功率为 92% 的假设会高估直接喉镜检查的性能，并导致对每组需要 500 名患者的大样本量的不恰当估计。

最后，两种研究设备之间的实际功效差异大大超过了本研究中的假设值，即 5% 的绝对组间差异。与其他类似的大样本多中心随机对照试验不同[ 5, 6 ]，本研究的设计不包括中期分析。我们认为，如果进行了预先计划的中期分析，数据和安全监测委员会将根据预先指定的停止标准提前停止试验入组。