Comparing performance of stylets for orotracheal intubation by Glidescope videolaryngoscope

With great interest, we read the recent article by Sheta et al1 comparing performance of the Parker Flex-It stylet and GlideRite Rigid stylet for orotracheal intubation by Glidescope videolaryngoscope in patients with normal airways. They showed that the 2 stylets were equally effective for intubation when used by experienced operators, but the Parker Flex-It stylet was easier and less traumatic than the GlideRite Rigid stylet. Many things of this study were well done. The authors used a randomized, controlled design, which is a gold standard for comparing efficacy of different treatments. They chose well validated endpoints of intubation assessment: intubation time, ease of intubation, and success rate for the first attempt. They had attempted to control most of known factors affecting orotracheal intubation, such as patient’s upper airway anatomy, experience of the intubator, patient’s head and neck position, body mass index, depth of anesthesia, external laryngeal manipulation, blade size, tube size, and so forth.2 Furthermore, they openly discussed the limitations of their work. All of these are strengths in the study design. We congratulate the authors for conducting this clinically useful research, but we would like to ask some questions on their methodology and results. First, sample size calculation contributes to the quality of randomized, controlled trials due to its crucial to prevent type I and type II statistical errors. In this study, a power analysis was performed on the basis of intubation time data obtained from a pilot study on 10 patients using a GlideRite Rigid stylet in 5 cases and a Parker-Flex-It stylet in 5 cases. However, the authors did not provide the means and standard deviations of intubation times obtained when using the 2 stylets in the pilot study. Due to lack of these data, we were concerned that the author would have mistakenly related statistically significant outcomes with clinical relevance. Second, all study subjects were patients aged 18-50 years, with American Society of Anesthesiology physical status I or II, and body mass index of <35. Furthermore, preoxygenation was performed using 100% oxygen for 3 minutes via a facemask in all patients before induction of anesthesia. The mean intubation times in the 2 groups only were 34.6 to 36.4 sec. However, the mean lowest oxygen saturation (SaO2) during intubation attempts were 95.3 to 95.9%. We would like to know the SaO2 levels obtained after a 3-minute preoxygenation. According to the lung oxygen reserves provided by preoxygenation in healthy adult patients,3 it seems impossible that SaO2 rapidly decreases to 95% in a short apneic period of approximately 35 sec. Third, this study showed that intubation was significantly easier with a Parker-Flex-It stylet than with a GlideRite Rigid stylet. It is generally believed that orotracheal intubation by Glidescope videolaryngoscope involves 2 distinct challenges: delivering the tube to the glottis, and advancing the tube beyond the glottis and into the trachea.4 A limitation of this study design is no observation regarding causes of improved intubation performance by Glidescope videolaryngoscope when using a Parker-Flex-It stylet. Finally, the postoperative sore throat was regarded as a secondary variable comparing intubation performance of the 2 stylets. However, the authors did not specify the postoperative analgesic protocol. When the postoperative sore throat is used as a variable to evaluate the performance of the airway devices, standardization of postoperative analgesia should be a crucial component of study design. Also, the type and dose of analgesia and the timing of its administration in relation to the assessment of postoperative sore throat should have been described in the methods.5 In the absence of comparison of a postoperative analgesic protocol, the secondary outcome findings and their subsequent conclusions should be interpreted with caution, as they may have been determined using incomplete methodology.