Assessment of Truflex™ articulating stylet versus conventional rigid Portex™ stylet as an intubation guide with the D-blade of C-Mac™ videolaryngoscope during elective tracheal intubation: study protocol for a randomized controlled trial
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A variety of videolaryngoscopes with angulated blade have been recently introduced into clinical practice. They provide an indirect view of the glottic structures in normal and challenging clinical settings. Despite the very good visualization of the laryngeal structures by these devices, the insertion and advancement of the endotracheal tube may be prolonged and occasionally fail as it does not conform to the enhanced angulation of the blade. To overcome this handicap, it is recommended to use a pre-shaped, styleted tracheal tube during intubation. Unfortunately, these malleable rigid stylets permit only a fixed shape to the advancing endotracheal tube. This may necessitate withdrawal of endotracheal tube-stylet assembly for reshaping, before undertaking a new attempt. This may cause soft tissue injury and hemodynamic disturbance.
This single-blinded randomized clinical trial aims to overcome these handicaps using a novel method of dynamically changing the shape of the advancing endotracheal tube by Truflex™ articulating stylet as per need during D-blade C-Mac™ videolaryngoscopy.
One hundred and fifty four patients between 18 and 60 years of age belonging to either sex undergoing tracheal intubation under uniform general anesthetic technique will be randomly divided into Portex™ malleable stylet group and Truflex™ articulating stylet group. The primary efficacy variable of success/failure between the two groups will be analyzed using the chi square test. For comparison of intubation times and the Intubation Difficulty Score, ANOVA will be used. Primary efficacy endpoint results will be successful or failed tracheal intubation in the first attempt, total intubation time and the intubation difficulty score. Secondary efficacy endpoints will be overall user satisfaction graded from 1 to 10 (1 = very poor, 10 = excellent), Cormack and Lehane’s grading, glotticoscopy time and ETT negotiation time and total number of intubation attempts. Result of safety endpoints will include dental and airway trauma, hemodynamic disturbances, arrhythmias or cardiac arrest.
Current Controlled Trials ISRCTN57679531; Date of registration 12/02/2013
KeywordsVideolaryngoscope Tracheal intubation Truflex stylet
- ADA score
Anticipated difficult airway score
Analysis of variance
Ear nose and throat
Intubation difficulty scale
Picture capture device
Portex™ intubation stylet
Truflex™ articulating stylet.
Despite several advantages offered by the videolaryngoscopes, their major handicap is their enhanced anterior angulation of the blades, such as that of the Glide-Scope™ (Verathon Medical, Bothell WA, USA), the McGrath series 5 (Aircraft Medical, Edinburgh, UK), and the TruView™ PCD devices (Truphatek International Limited, Netanya, Israel), which makes viewing of the laryngeal structure easier [1, 2], but negotiation of the endotracheal tube (ETT) towards the glottis difficult, and at times a failure [7, 8]. This is attributed to the fact that the tip of the ETT has to pass around the steep angle of the videolaryngoscope blade to site with the larynx. An un-styleted ETT is unable to do this as its inherent radius of curvature of nearly 14 cm  cannot align with the acute radius of curvature of the D-blade of the C-Mac™ or other videolaryngoscopes, which is 7 to 8 cm (Figure 1b). This may result in a longer intubation time . It is recommended that a pre-shaped, styleted tube be used during endotracheal intubation with a videolaryngoscope to overcome this problem . The Glide-Scope™ and TruView™ PCD have their own pre-shaped dedicated rigid stylets, which do not permit reshaping. Unfortunately, the pre-shaping of the ETT with a stylet may not always suit an individual patient’s need . In such a patient, if the stylet permits, such as the malleable Portex™ intubation stylet (PIS) (Smiths Medical ASD, Inc. Norwell, MA, USA], the ETT-stylet assembly has to be taken out and re-shaped before making another attempt at tracheal intubation. This may delay endotracheal intubation with a potential increased hemodynamic response and soft-tissue trauma [13, 14].
Anticipated difficult airway (ADA) score *
Class III to IV
Thyromental distance, cm
6.0 to 6.5
Head and neck movement, degrees
Body mass index, kg/m 2
Inter-incisor gap, cm
4.0 to 5.0
Primary efficacy endpoints will be successful or failed tracheal intubation in the first attempt, total intubation time and the intubation difficulty score. An attempt will be counted if the laryngoscope or the ETT needs to be removed for re-oxygenation (drop in oxygen saturation by 5%) or for reshaping of the ETT. The total intubation time will be the sum of the glotticoscopy time (from introduction of the videolaryngoscope blade between the teeth to the best laryngeal view) and the ETT negotiation time (from receiving the styleted ETT in laryngoscopist’s hand to passage of the black line just beyond the vocal cord). Secondary efficacy endpoints will be overall user satisfaction graded from 1 to 10 (1 = very poor, 10 = excellent), Cormack and Lehane’s grading, glotticoscopy time and ETT negotiation time and total number of intubation attempts with a maximum of three attempts, after which an alternative technique will be used. Safety endpoints assessed will be dental and airway trauma (present or absent), hemodynamic disturbances (blood pressure and pulse rate would be recorded before intubation, 1 minute and 5 minutes post-intubation; ≥20% change from the baseline value will be considered clinically important), arrhythmias (absent or present; type if present), or cardiac arrest.
For sample size assessment, a pilot study of 60 patients was conducted in which we observed that successful intubation could be achieved in the first attempt in 100% (30/30) of patients in group B (TAS) but was achieved in 90% (27/30) of group A (PIS). To detect a similar difference between the success of intubation (100 versus 90%) with a statistical power of 80% and 95% confidence interval and equal distribution of patients in both the groups, a total sample size of 154 was estimated for the present study using the open source browser-based calculator OpenEpi . However, in light of the stratification used for randomization the final sample size of 158 shall be used with equal distribution. All statistical evaluations will be made at a significance level of 0.05 (two-sided). A two-sided, 95% confidence interval will be calculated for the mean difference between the treatment groups. The data will be analyzed on an intention-to-treat basis. No imputations will be used for any missing data. The primary efficacy variable of success/failure between the two groups will be analyzed using the chi square/Fisher’s exact test, whichever will be applicable. Binary logistic regression will also be used on the whole dataset to identify predictors of success/failure of intubation. For evaluation of intubation times and the intubation difficulty score, analysis of variance (ANOVA) will be used for comparison between both treatment groups. The intubation difficulty scale (IDS) will also be transformed into an ordinal variable (0, 0 to 5, >5) and multinomial logistic regression will be used to evaluate for possible predictors of a difficult intubation.
The last decade has seen the emergence of videolaryngoscopes that enable us to visualize the laryngeal structures on a high-resolution video screen. These new aids provide a superior view of the laryngeal structures in normal conditions, and in a plethora of pathological and challenging conditions. However, the negotiation of the ETT into the trachea may still be a challenge despite using a malleable rigid stylet to pre-shape the ETT. In such situations, if the pre-shaping has not been optimal, the ETT-rigid stylet assembly needs to be taken out of the oropharynx for re-adjustment of its shape before making another attempt at tracheal intubation.
To overcome the limitation of a malleable rigid stylet, Schroeder’s directional stylet has been used to guide the ETT towards the glottis while using the D-blade of the C-Mac™ videolaryngoscope . However, Schroeder’s directional stylet has two limitations. First, its length is not sufficient, especially for the armored ETT to be fully mounted over it, and second, it helps to change the shape of the premounted ETT into a C shape rather than a curvature at its distal end where it is actually needed. In contrast, the TAS has sufficient length and its shape can be molded at its distal end to the need of laryngoscopy and tracheal intubation.
TAS is a newly introduced device that has an easily controllable flexible tip using a lever that allows an upward movement of 30 to 60° at its distal 3 cm. The ETT is premounted over a well-lubricated TAS and a stopper at the proximal end of TAS helps to hold the ETT in position (Figure 4b). The TAS permits dynamic shaping of the curvature of the distal end of the premounted ETT by an angle as per need during videolaryngoscopy.
In conclusion, in this clinical trial, we are evaluating the efficacy of TAS in aiding tracheal intubation using the D-Blade of the C-Mac™ videolaryngoscope, using a randomized and single-blinded design. The success of the trial will significantly improve the application of this relatively new method of tracheal intubation.
The first participants were included on 3 March 2013. There were 11 patients recruited at the time this paper was submitted.
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