A comparative study of Airtraq® and McCoy laryngoscopes for endotracheal intubation in adult patients with simulated difficult airway using a rigid cervical collar in elective surgeries under general anaesthesia

Background and Aims: Objective of intubation in patients with suspected neck injuries is sufficient laryngeal exposure with minimal cervical spine movement. Cervical collars reduce movements of spine but result in difficult laryngoscopy. Airtraq, an indirect optic-laryngoscope allows high quality viewing of vocal cords with minimal neck movement without alignment of oropharyngolaryngeal axis. McCoy is a modification of standard laryngoscope with flexible tip. This study intends to compare efficacy of Airtraq and McCoy laryngoscopes for endotracheal intubation in adult patients undergoing elective surgeries with simulated neck immobilisation using rigid cervical collar.


Introduction
Successful direct laryngoscopy and intubation depends on aligning oro-pharyngo-laryngeal axes which is achieved by 'sniffing position' with flexion at lower cervical spine and extension at atlantooccipital joint. 1 In cervical spine immobility, direct laryngoscopy is restricted and there is difficulty in getting a good glottic view. The main objective is to obtain a good glottic view with minimal cervical spine movement. Hence, the process of laryngoscopy and intubation is performed by stabilizing the neck. This is done by rigid collar, forehead tape or manual-in-line stabilisation (MILS). 2 Rigid cervical collar reduces mouth opening along with neck movement and leads to difficult laryngoscopy with conventional laryngoscopes. 3 Difficult Airway Society guidelines have recognized the role of videolaryngoscopes in difficult airway and recommend that all anaesthetists be skilled in use of videolaryngoscopes. 4 Airtraq® (Prodol Ltd., Vizcaya, Spain) is a disposable battery-operated indirect videolaryngoscope that allows high-quality viewing of vocal cords without requiring a straight line of sight from outside to the glottis. 5 (Figure 1,2)  It has a unique curvature in blade that gives adequate visual access to glottis without alignment of the oro-pharyngo-laryngeal axes with minimal neck movement.
The blade of the Airtraq® consists of two side-byside channels. One acts as a conduit through which endotracheal tube (ETT), suction catheter or bougie can be passed, whereas the other channel contains a series of lenses, prisms, and mirrors that transfers the image from illuminated tip to a proximal viewfinder. 6 McCoy TM laryngoscope (Penlon Ltd, Abingdon, UK), is a modification of Macintosh laryngoscope blades. These blades have a flexible distal tip activated by a lever that lies adjacent to handle. The curved levering tip blade is used by placing the tip in the vallecula. If glottic visualisation is poor, lever can be depressed, activating distal tip upward. 7 There are very few studies comparing efficacy of these two laryngoscopes in the setting of neck immobilisation. Statistical analysis was performed using SPSS version 21. Continuous data presented as mean±SD using the independent t-test, ordinal data as median (for comparing IDS and Cormack-Lehane grading) compared using Mann-Whitney U testwith interquartile range (IQR), and categorical data are presented as frequency and proportions. Categorical data were compared using Chi-square test. Significance level for all analyses was p value <0.05.

Results
Total of 60 patients were enrolled. There were no exclusions after enrolment. Demographic data and airway assessment data are given in Table 1.    Airway trauma was found in both groups though it was less with Airtraq (p-value =0.3) Airtraq causing trauma was restricted to minimal oral bleeding. Trauma cause is probably because of the novelty of the scope when compared to McCoy laryngsocope. 11 There was no failure to intubate in either group. No other airway related complications were noted.

Discussion
Patients with cervical spine injury requiring intubation is a common scenario seen in critical care units and operation theatres. New or exacerbation of pre-existing spinal injury is possible during intubation. Hence, cervical spine must be protected by stabilizing neck either by MILS or rigid cervical collar. Incidence of poor view on laryngoscopy is very high in patients immobilised in a collar, tape and sandbags orMILS. 12 A rigid cervical collar again reduces mouth opening significantly and this was the main factor contributing to increased difficulty of laryngoscopy. Though flexible fibreoptic bronchoscope is considered gold standard technique in such situations, non-availability in rural areas, long learning curve and lack of expertise are its disadvantages. immobilisation with collar. 14 Arslan et al, evaluated effectiveness of Airtraq and C Trach™ in patients with simulated cervical spine injury after application of rigid cervical collar. 15 Wetsch WA et al compared various video laryngoscopes with conventional Macintosh laryngoscope. It was found intubation time was least with Macintosh laryngoscope, closely followed by Airtraq. 16 Hence Airtraq was concluded to be a cheaper and superior alternative to other video laryngoscopes Although we faced no failure of intubation in either group, failure to intubate using Airtraq has been seen. 2,13 It was mostly due to difficulty in positioning blade's tip posterior to epiglottis. Channelled videolaryngoscopes perform better and extension of channel to tip of scope improves success rate.
There were a few limitations in our study. It is impossible to blind anaesthesiologist to devices being used. Certain variables like glottic view grading and lift force required are subjective. The results may differ in hands of less experienced users.

Conclusion
Airtraq laryngoscope improves ease of intubation and reduces intubation time significantly in patients with immobilised cervical neck when compared to McCoy laryngoscope. It can thus be an ideal and cheap alternative in patients with cervical trauma requiring laryngoscopy and intubation.