This single centre balanced parallel-group randomized clinical trial took place at University Hospital in London, Ontario, Canada from March to November 2009, and it involved patients having surgery in most surgical disciplines. The trial was registered at ClinicalTrials.gov (NCT00884754) before enrolment of the first patient in the trial. After obtaining local research ethics board approval, patients aged 18 yr and older and scheduled for elective surgery requiring orotracheal intubation were invited to participate. Exclusion criteria included a known or suspected difficult airway (determined by the attending anesthesiologist on physical examination), requirement for rapid sequence induction, or a contraindication to GVL use (determined by the attending anesthesiologist). Anesthesiology trainees were eligible as operators if they had performed ten or fewer GVL-assisted intubations. Written informed consent was obtained from all patients and operators.
The null hypothesis was that there would be no difference between the stylets in terms of time to intubation. The GRS was used according to the manufacturer’s instructions (Fig. 1), and tracheal intubation for the control group was performed according to the standard local practice. First, an ETT was loaded with forward camber4 onto a malleable stylet, 14 French Rusch Flexi-Slip™ (Teleflex Medical, Bannockburn, IL, USA), and a 90° angle was formed 8 cm from the distal end of the ETT; there was no other ETT angulation (Fig. 2).
Patient demographics and airway assessment11 were recorded preoperatively, and the ETT size was chosen prior to patient randomization. As each patient entered the operating room, group allocation was carried out by opening a sealed opaque envelope containing a computer-generated random code specifying the group assignment (the randomization sequence was generated using the ralloc program in Stata 11.0 for Mac OS X [StataCorp LP, College Station, TX, USA] with two blocks of 30 patients each created to ensure an equal number of patients randomly assigned to each group). One of the study investigators prepared an ETT with each of the stylets according to the study protocol. This investigator concealed the assigned ETT with a towel and concealed the remaining ETT in another towel to be used if the operator was unsuccessful with the allocated stylet. This investigator then had no further involvement with that patient’s clinical care or outcome assessment. To avoid any potential bias during induction, GVL laryngoscopy, or glottic view scoring, each ETT was concealed so that the GVL operator remained blinded until after the GVL laryngoscopy had been completed.4
Induction and maintenance of anesthesia were not standardized, but pre-oxygenation was mandated to an end-tidal oxygen concentration of ≥ 80%, and all patients were paralyzed with rocuronium. After induction, the patient’s lungs were ventilated with a volatile anesthetic agent in 100% oxygen until the operator deemed it appropriate to begin intubation. A minimum delay of 90 sec was utilized for onset of paralysis.
The operator performed laryngoscopy with the GVL (size five) and graded the glottic view using the classification described by Cormack & Lehane.12 The ETT was then revealed, unblinding the operator, and the patient’s trachea was intubated with the ETT and assigned stylet. If necessary, operators were permitted to use external laryngeal manipulation in order to improve the glottic view or to facilitate intubation. If the operator removed the GVL blade or ETT from the patient’s mouth, this was counted as an additional attempt at intubation.
The primary outcome was the time to intubation as measured by a blinded observer. The time to intubation was defined from the moment the GVL blade first passed the patient’s teeth to the moment end-tidal CO2 of at least 30 mmHg was present on the anesthesia monitor. As soon as the timer started, the blinded observer turned so that only the anesthesia monitor was visible. At no point did the observer see the allocated stylet. If the novice operator took > 150 sec or more than two tries to perform the intubation, it was deemed a failure, and the airway was subsequently managed using any technique deemed appropriate by the attending anesthesiologist (the patients were analyzed in the group to which they were randomized regardless of the stylet or modality used for successful intubation). Failed intubations were included in the analysis (recorded as a time to intubation of 150 sec). Ventilation between attempts was permitted if necessary. Pre-specified secondary outcomes for each group included ease of intubation (scored by the operator immediately after laryngoscopy on a five-point ordinal scale), number of attempts, glottic grade, and use of external laryngeal manipulation. The time to intubation was not divulged to the operator until after the data collection sheet had been completed.
The sample size calculation was based on parametric analysis, although non-parametric analysis was planned for the outcomes in the study.13 A between-group difference of 15 sec in time to intubation was considered clinically significant. The standard deviation of the time to intubation —estimated to be approximately 20 sec— was based on a previous study in a group of both experienced and inexperienced operators.4 Standard Type I and Type II error rates were used (α = 0.05, β = 0.20). The calculated sample size was 28 patients per group, but a total sample size of 60 patients was selected in order to maintain statistical power in case of patient drop out or missing data.
Due to an anticipated right-skewed distribution, both time to intubation and ease of intubation were assessed using a non-parametric method (the Mann-Whitney test). Categorical data were analyzed with Pearson’s Chi square test. Data are shown as median and IQR unless otherwise noted. No corrections for multiple comparisons were made.14 Data were analyzed using Stata version 11.0 for Mac OS X. Results were considered statistically significant when P < 0.05.