A prospective, longitudinal, comparative study was conducted at Surgery and Gynaecology operation theatres of Calcutta National Medical College and Hospital, Kolkata, West Bengal, India during January 2017 to July 2018 after obtaining the approval from the Institutional Ethics Committee (CNMC/3 dated 18/11/2016).

With 5% margin of error and a 95% confidence interval considering a sample proportion of 50% and expecting a 10% dropout, the sample size was calculated around n=90 which was rounded-up to 100 patients.

Inclusion criteria: Patients between 21 to 50 years of either sex with ASA physical status I-II and Mallampati score I-II that were scheduled to undergo elective surgery of expected duration of 60 to 120 minutes, requiring general anaesthesia with endotracheal intubation were included in the study.

Exclusion criteria: Patients with Body Mass Index (BMI) >35 kg/m², pregnant females, with previous neck surgery, with unstable C-spine, in whom difficult intubation was anticipated, need rapid sequence intubation and having risk of pulmonary aspiration were excluded.

Following screening based on inclusion/exclusion criteria, the selected patients were further divided by odd and even sequence into group V (VL) and group M (McCoy laryngoscope) with (n=50) each, respectively. All the study participants underwent routine preoperative check-up including thorough airway examination and documentation. On the night prior to the operation all the patients received Tab. Alprazolam 0.5 mg, Tab Metoclopramide 5 mg and Tab. Ranitidine 150 mg.

In the operation room, after establishing Intravenous (IV) access, all necessary monitoring devices such as Non-Invasive Blood Pressure (NIBP), pulse oximeter, Electrocardiography (ECG) leads were attached and the baseline parameters were recorded. A pre induction reading of pulse, systolic, diastolic, mean arterial BP and SpO₂ was recorded five minutes before induction. Preoxygenation with 100% oxygen for three minutes was done in each of the patients.

All patients were given Inj. Midazolam 1-2 mg, Inj. Fentanyl 2 mcg/kg and then induction was started with Inj Propofol 2 mg/kg body weight. Inj. Lidocaine 2%, 2 mL, was administered intravenously just before to prevent pain associated with the propofol administration. On loss of verbal contact, bag mask check ventilation was done. Neuromuscular paralysis was done with Inj. Vecuronium bromide 0.1 mg/kg body wt. Before laryngoscopy, patients head was placed in the neutral position on the operating table. A trained person applied MILS by applying varying amount of force while holding the both mastoid processes and side of the neck in an effort to counteract the force of laryngoscopy, thus preventing flexion/extension or rotational movement of the head and neck.

Laryngoscopy was performed by a single trained anaesthetist throughout the whole study period. Time required for laryngoscopy and intubation was documented by separate anaesthetist, not involved in the study. The view of the glottis was graded using a modified classification reported by Cormack and Lehane where grade 1 denotes most of glottis (with or without the epiglottis) is visible and grade 4 signifies worst situation i.e., no glottis is visible, and the larynx (such as the epiglottis) cannot be located [11]. Laryngoscopy was defined as difficult when the view of the glottis was either grade 3 or grade 4. An attempt was made to improve the glottis view by the application of External Laryngeal Maneuver (ELM). If difficult laryngoscopy persisted even after ELM, then tracheal intubation was attempted using bougie or stylet guidance. In case of failure of first attempt only one extra attempt, up to 2 minutes (starting from insertion of the second blade), was allowed for tracheal intubation. If tracheal intubation failed after these two attempts, the study was terminated, MILS was released and the airway was managed as a routine clinical practice. Following tracheal intubation the lungs were mechanically ventilated throughout the whole procedure and anaesthesia was maintained with sevoflurane (1.25-1.75%) and nitrous oxide-oxygen mixture in a 2:1 ratio.

Any other medications or maneuver apart from those intended to be used in this study were strictly restricted during the vital 5 minutes data collection period after tracheal intubation. Pulse rate, systolic and diastolic BP were recorded at baseline i.e., baseline, pre intubation, 1 and 5 minutes after intubation respectively. Any dental or soft tissue injury of the oral cavity during laryngoscopy procedure was noted.

The results of the observations thus obtained in each group of patients were tabulated, compiled in Microsoft excel 2007 and statistically analysed using Statistical Package for the Social Sciences (SPSS) statistics version 23.0. Qualitative data (sex, ASA physical status, Mallampati classification, Cormack and Lehane glottis view grade, number of laryngoscopic attempts, number of optimisation maneuver required etc.,) were compared between the groups with Chi-square test (χ²) and Fisher-exact test and quantitative data (age, BMI, inter-incisor distance, thyromental distance, duration of laryngoscopy and intubation etc.,) were compared between groups with Mann-Whitney U test. Haemodynamic parameters within groups at different time intervals were compared with general linear model and repeated test. A p-value <0.05 was considered statistically significant and <0.01 was considered as highly significant. The 95% confidence interval for the mean difference between the two devices was calculated.

All the study participants, (n=100) of the two groups were comparable with respect to their demographic profile, baseline parameters and were statistically insignificant [Table/Fig-1]. The entire participants were analysed at the end of the study without any follow-up loss.

Most of the study participants were female (65%) and majority of them were between 40-50 years of age group [Table/Fig-2]. The success on first attempt of laryngoscopy were found to be statistically significant more (p=0.014) in case of video assisted group as compared to the other group and thus second attempt to do so required significantly less [Table/Fig-3]. The time taken to do the procedure of laryngoscopy required significantly lesser time (p<0.001) in the group V as compared to group M. The duration of intubation was observed to be significantly less (p<0.001) in group V and the blood stain on laryngoscope was also found to be much lesser in group V as compared to the other group. Incidence of procedural dental injury was absent in group V while there were 4 such patients in group M [Table/Fig-3]. Soft tissue injuries were just lesser in group V (p<0.03) as compared to group M. Optimisation maneuver was required in 50% of the group M patients as compared to 10% of group V was again statistically significant (p<0.001).

[Table/Fig-4] exhibits that group V patients were graded 1 as per Cormack and Lehane view in 76% cases with no grade 3 and 4 occurrence as compared to group M, which was statistically highly significant (p=0.002).

There were significant (p<0.01) changes in pulse rate, systolic BP and diastolic BP in group M as compared to group V owing to the greater mean duration of intubation [Table/Fig-5].

To reduce the difficulty of tracheal intubation in patients of limited cervical spine mobility, a variety of techniques has been developed including McCoy levering blade laryngoscope and VLs with highly curved blades like King Vision^®, Pentax Airwayscope, McGrath MAC, Airtraq etc., and intubating Laryngeal Mask Airway (LMA) like CTrach^®. McCoy laryngoscope has traditionally been used in patients with restricted neck movement. Recent studies have demonstrated that VL with highly curved channeled blade poses several advantages over conventional laryngoscopes [6,12]. In addition, the VL also appears to cause less cervical spine movements during tracheal intubation when compared with the Macintosh or McCoy laryngoscopes. The present study was designed to evaluate the relative efficacies of these novel devices in tracheal intubation in patients with simulated restricted neck mobility undergoing general anaesthesia.

Although the first attempt success rate was 96% for KVVL and 80% for McCoy laryngoscope [Table/Fig-3], Aziz MF et al., and Shravanalakshmi D et al., studied that success rate of tracheal intubation in patients with cervical spine immobilisation with KVVL were 100% with first attempt success rate of 93.3% and second attempt 6.7% [6,13]. In the current study, it was found that the overall success rate of laryngoscopy and intubation by video laryngoscopy in the setting of simulated restricted neck mobility was 100%, significantly higher from the McCoy laryngoscopy group (77%). Regarding the glottic view (Cormack and Lehane scores), it was observed that group V had more grade 1 Cormack and Lehane glottis view, shorter duration of laryngoscope and intubation less requirement of ELM leading to less haemodynamic stimulation than the group M. It can be concluded that this equipment provides a view of the glottis without much necessity to align the oral, pharyngeal, and tracheal axis.

Study conducted by Shravanalakshmi D et al., found that VLs provided better visualisation despite immobilisation of cervical spine and Ng I et al., conducted a randomised controlled trial and found that Mc Grath, a highly curved VL produced more grade 1 glottic view than C-MAC, a conventionally curved blade [13,14].

The authors also observed better glottic view with KVVL. It was observed that the duration of successful laryngoscopy and intubation were significantly longer in group M compared to group V, whereas Shravanalakshmi D et al., found that duration of intubation in seconds was significantly faster with conventional C-MAC VL (23.3±4.7) compared to King Vision (24.9±7.2) [13]. Group M, in this study, required a greater number of optimisations maneuvers (50%) to facilitate tracheal intubation while it was very less (10%) in case of KVVL [Table/Fig-3].

The incidence of tooth breakage and airway laceration was found with McCoy laryngoscope [Table/Fig-3]. In the study by Ng I et al., they found a total seven minor oropharyngeal mucosal injuries as a result of the intubation, six from using the McGrath VL and one from the C-MAC VL of the 65 patients in each group [14].

Unlike the findings of the study by Ng I et al., where incidences of dental injury were only 8% with Mcintosh laryngoscope against 0% with video laryngoscope with minor oesophageal injury [14], this study also demonstrated 8% dental injury with McCoy and 0% with video laryngoscope. In another study done by Malik MA et al., [15] where it was as high as 30% incidence of appearance of blood over Mcintosh laryngoscope was observed in contrast revealed much lesser such incidences [15]. There was no incidence of oesophageal intubation in both the group. Arterial haemoglobin Oxygen Saturations (SpO₂) were well maintained in both the groups.

The study was conducted in a single institute on a limited number of selected patients with specific operative indications excluding challenging cases involving paediatrics or restricted neck mobility patients. Levels of catecholamines like adrenaline, noradrenaline regulating the haemodynamic status and its variability with procedures like laryngoscopy was not assessed during this study.

Patients having simulated cervical spine immobilisation, undergoing elective abdominal surgery under general anaesthesia with tracheal intubation, KVVL appears to possess more advantages over the McCoy laryngoscope in respect to easy of viewing glottis, reduced duration of laryngoscopy and intubation, lesser complications and haemodynamic instability. To attain external validity, accurate and acceptable findings, a multicentric study incorporating large sample size may help in substantiate the current observation.