The standard technique of the GlideScope (Verathon, Bothell, Washington, USA) tracheal intubation requires the operator to look away from the monitor in order to insert the endotracheal tube (ETT) into its initial position. This can result in injury to the pharynx as there is a ‘blind’ period before the ETT appears on the monitor and the upward forces exerted by the GlideScope blade stretch the tonsillar pillars, making them susceptible to injury. Reports of trauma as a result of GlideScope laryngoscopy have been cropping up in the literature.1,2
Several modified GlideScope tracheal intubation techniques have been described in which the ETT is inserted under direct vision before the GlideScope blade is introduced.1–3 This technique may decrease laryngoscopy time and allow the ETT to be continuously monitored and eliminating the need to look away from the screen.1 It thus has the potential to reduce the sympathetic response4,5 as well as reduce the risk of airway injury. The goal of this study was to examine the effect of a modified GlideScope technique on laryngoscopy time, haemodynamic response and postoperative airway morbidity.
Following trial registration (ClinicalTrials.gov Identifier: NCT01865643) and research ethics board approval (Protocol 13-0083-A, 6 May 2013, Mount Sinai Hospital REB, Toronto, Canada, Chair: Dr Ronald Heslegrave), 81 American Society of Anesthesiologists (ASA) physical status I and II patients, aged 18–65, undergoing elective surgery, who required tracheal intubation, were enrolled in the study. Patients were randomly assigned to either the standard or the modified GlideScope technique. In the standard tracheal intubation group, the GlideScope blade was inserted followed by insertion of the ETT. In the modified technique group, the ETT was inserted into the oropharynx to the right of the midline as deeply as possible under direct vision using tongue traction or jaw lift to achieve maximal exposure. This was followed by GlideScope laryngoscopy avoiding blind passage of the ETT.
An unblinded observer measured the procedure times. Heart rate (HR) and noninvasive blood pressure (BP) were recorded at 11 time points throughout the intubation. Difficulty of intubation was assessed by the intubation difficulty scale.6 Patients were assessed for airway trauma immediately following surgery and again 24 h later. The severity of postoperative sore throat hoarseness and painful swallowing were assessed on a 0 to 3 scale.4
A P value of less than 0.05 was considered statistically significant. Sample size was based on a previous study by the authors.4 To detect a 20% change (standard deviation = 25%) in HR or BP, 35 patients would be required in each group (power = 90%, P = 0.05). Group differences in haemodynamic outcome measures were assessed through a series of t tests and χ2 tests. Wilcoxon two sample tests were used in lieu of t tests for highly skewed measures and Fisher's exact test was used in lieu of χ2 tests for comparing categorical measures with sparsely populated categories. Changes in BP and HR over time across study groups were assessed through a series of mixed models.
Eighty patients completed the study. Groups were similar in terms of patient sex, age and BMI. Groups did not differ in terms of predictive signs for difficult laryngoscopy. Procedure times and intubation difficulty scale scores were not significantly different between the groups. Laryngoscopy time was shorter in the modified technique group but this difference did not reach statistical significance. Results are presented in Table 1. Haemodynamic values changed significantly over time within the groups, but not between the groups. The results of our study demonstrate that the modified GlideScope intubation technique is comparable to the standard technique in terms of procedure times, haemodynamic reaction and airway morbidity. A trend level effect was detected with a shorter laryngoscopy time in the modified technique but this should be interpreted with caution. The observed effect is, however, of a clinically meaningful magnitude (22.7s ± 8.6 versus 31.4s ± 19.7, P = 0.0589).
The modified technique has the advantage of allowing for the undivided attention of the operator during the ETT insertion. In our experience, when this technique is combined with manoeuvres that increase airway exposure such as jaw lift or tongue traction, the ETT can be inserted under direct vision deeply enough to bypass the potentially dangerous ‘blind spot’. Rarely, when the ETT does not reach the required depth, it will show up on the monitor during the initial insertion of the blade. The ETT can then be advanced simultaneously with the blade under direct visual control. Moulding the shape of the tube to match the curvature of the blade rather than a hockey stick shape will facilitate this technique. Our experience with novice operators shows that they find the modified technique easier to handle and master.
Major airway trauma is uncommon and our sample size was not adequate to compare these techniques from this aspect; therefore, despite the theoretical benefits, we cannot comment on the possible advantages of the modified technique for avoiding major airway trauma without a larger study. Also, a better study design would have used each patient as his own control; however, a double intubation could not be ethically justified. Our study did demonstrate that the modified technique is comparable to the standard technique in all aspects while having the potential advantage of reduced risk of airway trauma and possibly a shorter laryngoscopy time. Future larger studies are needed to further explore the advantages of this technique in reducing major airway trauma, as well as its advantages for inexperienced operators and its haemodynamic effects when monitored with more precise means. Similarly, studies examining the efficacy of the modified technique for managing difficult airways, especially those involving a limited oropharyngeal space, are required to explore the potential benefits of the modified technique.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: the study was supported by the Department of Anaesthesia, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada.
Conflicts of interest: none.
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