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

Introduction and Aims: Laryngoscopy in patients with suspected neck injuries has one goal: sufficient laryngeal exposure with least cervical spine movement. This is achieved by either Manual In-line Stabilisation (MILS), a forehead tape or rigid cervical collars. Cervical collars reduce movements of spine and also mouth opening leading to difficult direct laryngoscopy. This is due to difficulty in aligning the oropharyngo-laryngeal axes. The laryngoscope giving best glottic view with least cervical spine movement in the shortest time would be most ideal. We intend to compare Airtraq, McCoy and Macintosh laryngoscopes in terms of intubation time and Cormack-Lehane glottic view in patients undergoing elective surgeries with simulated neck immobilization using rigid cervical collar. Materials and Methods: Following approval from Institutional Ethical Committee, 90 consenting patients, aged 18-65years were assigned into three groups by random sampling (Serially numbered Opaque Sealed Envelope), namely Group A (Airtraq), M (McCoy) or C (Macintosh). Intubation time, Intubation difficulty scale (IDS) and Modified Cormack-Lehane grading were noted. Results: Mean intubation time was 27.2sec(± 6.47), 40.2sec (± 12.36) and 33.10sec (± 23.05) for Airtraq, McCoy and Macintosh respectively(p-value 0.00 7). IDS values were 0,3 and 2 respectively(P< 0.0001). Cormack Lehane glottic view was 2 for Macintosh and McCoy and 1 for Airtraq, respectively (P< 0.0001). Conclusion: Airtraq improves ease of intubation significantly when compared to McCoy and Macintosh blade with shorter intubation time and IDS Score, in patients with simulated difficult airway using neck


Introduction
Expertise in airway management is a lifeline for anaesthesiologist with patients presenting for anaesthesia. Maintaining a patent airway is essential for adequate oxygenation and ventilation, and failure to do so can be life threatening. 1 Respiratory events are the most common anaesthetic related injuries. Three main causes of respiratory related injuries are inadequate ventilation, esophageal intubation and difficult tracheal intubation. 2 It is a challenge to intubate patients in whom cervical spine movement is restricted. Here, use of direct laryngoscopy is restricted as it requires adequate neck extension for alignment of oro-pharyngo-laryngeal axes. Intubation must be performed using cervical spine immobilization to prevent exacerbation of spinal cord injury, by rigid collar forehead tape or manual-in-line stabilization (MILS). 3 Reduced mouth opening with no neck extension is a disadvantage when using rigid cervical collars. 4 It has been seen that the mouth opening reduces to almost half after https://doi.org/10.18231/j.ijca.2020.012 2394-4781/© 2020 Innovative Publication, All rights reserved. 64 application of a rigid cervical collar and the neck extension in all patients is reduced to less than 35 degrees thus simulating a difficult airway. 5 Video-laryngoscopy and optic intubation are preferred in such airways. Difficult Airway Society has included videolaryngoscopes as a part of difficult airway cart. 6 Macintosh is the most popular laryngoscope worldwide. Tongue of blade has a curve that extends to the tip. 7 Macintosh blade requires alignment of oro-pharyngolaryngeal axes and adequate neck extension which gives poor glottic view in cervical spine immobilization. 8,9 Airtraq ® (Prodo Ltd., Vizcaya, Spain) is a disposable battery-operated laryngoscope with unique blade curvature(90 degrees) that allows good glottic view without requiring alignment of oro-pahryngo-laryngeal axes. 10 Blade of Airtraq ® consists of two side-by-side channels. (Figure 1) One channel is a conduit through which endotracheal tube (ETT), bougie or suction catheter can be passed, and other channel contains a series of lenses and mirrors that transfers image from illuminated tip to a proximal viewfinder. 11 McCoy T M laryngoscope (Penlon), is a modification of standard curved laryngoscope blades. These blades have a hinged distal tip activated by a lever. Curved levering tip blade is used by placing the tip in the vallecula and activating it by pressing the lever. 12 There is not much literature on the utility of Airtraq ® in Indian population, with a simulated difficult airway. We intend to study the efficacy of Airtraq, Macintosh and McCoy laryngoscopes for endotracheal intubation undergoing elective surgeries under general anaesthesia with simulated difficult airway using a rigid cervical collar, this an investigational method of the research with primary objective of to comparing intubation time and secondary objective of to comparing Cormack -Lehane grading and IDS.

Materials and Methods
Following approval from Institutional Ethical Committee, informed consent taken from 90 American Society of Anaesthesiologists Physical Status (ASA PS) Class I-II patients, aged 18-65years undergoing elective surgery selected by an observer not conducting laryngoscopy and were randomly allocated into three groups by Simple random sampling (SNOSE:Serially numbered Opaque Sealed Envelope), into Group A(Airtraq ® ) , Group M(McCoy) or Group C (Macintosh).
Patients with anticipated difficult airway, pregnant patients, patients with cervical spine disease and obese patients with Body Mass Index (BMI) >30kg/m 2 were excluded.
Group A: Intubation with Airtraq ® preloaded with an endotracheal tube (ETT; 7.5mm internal diameter [ID] for women and 8.5 IDmm for men) and Group M: McCoy laryngoscope with styletted ETT of appropriate size.
Group C: Macintosh Laryngoscope with styletted ETT of appropriate size.
There were no confounders or effect modifications in the study .
Patients were evaluated and Tab. Alprazolam 0.5mg and Tab.Ranitidine 150mg per oral given on previous day. On day of surgery Intravenous(IV) access with 18G cannula was secured. In operation theatre ECG, Non Invasive Blood Pressure(NIBP) and Pulse oximeter were attached, and baseline parameters recorded All patients were premedicated with Inj.Ondansetron 0.15mg/kg and Inj.Fentanyl 1.5mcg/kg. Following preoxygenation patients induced with Inj.Propofol 2mg/kg. After confirmation of mask ventilation, Inj.Vecuronium 0.1mg/kg was given for neuromuscular blockade. Rigid Philadelphia Cervical Collar (Tracheostomy Philadelphia Collar; Philadelphia Cervical Collar Co., Thorofare, NJ, USA) of appropriate size was positioned around neck but not fixed. After adequate neuromuscular blockade, collar was fixed. Laryngoscopy was done by experienced anaesthesiologist. Intubation was done with appropriate size ETT. Closed circuit was connected to Dräger Fabius ® Plus workstation and ventilation confirmed by capnography. Collar was removed after intubation.
Potential bias was reduced by using the same anaesthesiologist for all the intubations with all three laryngocopes.
Time taken for intubation was considered as the primary end point and additional endpoints include, the number of intubation attempts and the number of optimization maneuvers required (use of a bougie, external laryngeal pressure, second assistant) to aid tracheal intubation, and the Cormack and Lehane grade at laryngoscopy.In event of failed intubation rigid cervical collar was removed, and patient intubated with Macintosh laryngoscope.

Definitions
1. Experienced anaesthesiologist is defined as one, who has done at least 25 laryngoscopies with all three laryngoscopes 2. Time required for intubation, defined as time from insertion of blade between teeth to successful intubation and confirmation with capnography. 13 3. Intubation difficulty score (IDS) described by Adnet et al as described 14    Continuous data are presented as mean±SD, ordinal data as median with interquartile range (IQR), and categorical data are presented as frequency and proportions. Categorical data were compared between three groups Chisquare test. Significance level for all analyses was P <0.05.

Results
Total of 90 patients were enrolled. There were no exclusions after the enrollment. Demographic data are as follows. (Table 5) Intubation time in Group A was 27.22sec (6.47) as compared to 40.2sec (12.36)  (p value =0.98404). (Tables 6 and 7) Cormack Lehane grading was significantly better with Airtraq scope with 27 patients having grade I view. In McCoy group only 10 patients had Grade I view whereas 19 patients had grade II view.
Macintosh group18 patients had grade II view and 4 patients had grade III view. Alignment of oro-pharyngo-laryngeal axes were poor with minimal neck extension while using Macintosh  (Table 7) Laryngeal pressure required is more in McCoy and Macintosh laryngoscope. Lifting force used in minimal in Airtraq. 11 Airway trauma was found in all groups though it was less with Airtraq with 4 when compared to McCoy with 8 and 5 in Macintosh group. Airtraq ® causing trauma was restricted to minimal oral bleeding when compared to McCoy. 16 Flexible tip of McCoy may injure uvula or surrounding structures if it gets entrapped into hinge of the tip.
One patient in Macintosh group could not be intubated with collar who was eventually intubated as per protocol.
No other airway complications noted.

Discussion
Patients with cervical spine injury requiring intubation is not unusual in the hospital. Quadriplegia has occurred  0(0%) 0(0%) 0(0%) -Failed intubations (% of group) 0(0%) 0(0%) 1(3.3%) - in association with airway management in cervical-spine injured patient whose neck was not immobilized. 17 Hence these patients must be stabilized either by MILS or rigid collar. MILS and rigid collars reduce segmental angular rotation and distraction, therefore protects from further injury. 18 Rigid collar reduces mouth opening significantly and this leads to increased difficulty of laryngoscopy in this form of cervical spine immobilization. Rigid collar also lifts and tips the larynx anteriorly. Fibreoptic is gold standard in such situations. Non-availability in rural areas, long learning curve and lack of expertise are disadvantages. 19 Airtraq, novel indirect-laryngoscope with prism system unlike no other laryngoscope, is a good cheap alternative.
Airtraq has been proven to be superior than other conventional laryngoscopes in normal airway 20,21 as well as in difficult conditions in mannequins and in patients with simulated difficult airway. [20][21][22][23] Hosalli et al, found that IDS scores were significantly better with Airtraq when compared to McCoy and Macintosh laryngoscopes. But when comparing Macintosh and McCoy group, IDS score was better with McCoy, but statistically insignificant. Cormack Lehane view was better statistically with Airtraq consistent to our results. 24 Tolon MA et al compared Macintosh and Airtraq laryngoscopes in patients with cervical spine immobilisation (confirmed by using C-arm) and found higher intubation times and IDS scores with Macintosh compared to Airtraq. 25 Koh et al. reported higher success rate of intubation with Airtraq in patients with cervical immobilization with collar. 26 Arslan et al. evaluated effectiveness of the Airtraq and C Trach TM in lean patients with simulated cervical spine injury after application of rigid cervical collar. 27 Wetsch WA et al, compared various videolaryngoscopes with conventional Macintosh laryngoscope. It was found that intubation time was least with conventional Macintosh laryngoscope, closely followed by Airtraq. Video-laryngoscopes required significantly more time to secure airway. 28 Hence, Airtraq was concluded to be a better alternative to other video -laryngoscopes.
Although we faced no failure of intubation with Airtraq, it has been quoted in a few studies. 3,20 Failure to intubate using video laryngoscopes despite a good glottic view is known. Channelled video-laryngoscopes perform better in these cases and extension of channel to tip of scope further improves success rate. Channel doesn't extend to the tip in Airtraq and this can cause a difficulty.
Limitations were that anaesthesiogist was not blinded to devices used, Measurements used like glottic-view grading, lifting force applied are subjective. IDS score utility when used with indirect laryngoscopes is less clear.
Results may differ in hands of less experienced users as this study is conducted by anaesthesiolist experienced in using all three devices.

Conclusion
Airtraq laryngoscope reduces intubation time significantly when compared to McCoy and Macintosh laryngoscopes in patients with an immobilised neck using a rigid cervical collar. It also improves ease of intubation with better glottic view and is a cheaper alternative to various other videolaryngoscopes.
It can be an ideal laryngoscope in patients with cervical neck injuries requiring intubation.

Source of funding
None.

Conflict of interest
None.