Laryngoscopy and endotracheal intubation are amongst the most important procedures for the anaesthesiologists performing airway management during routine as well as emergency general anaesthesia in the operating rooms.

A Macintosh type direct laryngoscope is most routinely used for direct laryngoscopy (DL) under direct vision to perform endotracheal intubation in ‘sniffing’ position which is classically described as optimal position of head and neck for this purpose as it allows closer alignment of the pharyngeal and laryngeal axes with oral axis to provide a better line of vision for DL.^1,2 ‘Sniffing’ position is achieved by flexing the neck over the chest and extending the head at atlanto-occipital (AO) joint with the help of pillows, head rings or towels under the head. However, there are conflicting reports on this issue which proclaim that these axes can never be perfectly aligned and provide no significant advantage during DL and tracheal intubation.³

One of the latest additions to the series of laryngoscopes is video laryngoscope which is used almost in the same manner as Macintosh type direct laryngoscope. Videolaryngoscopy (VL) provides the view of the glottis by utilizing a digital video camera located at the point of angulation of the blade to generate a view of the glottis in a separate small colour LCD monitor. Such video laryngoscopes have been found to be useful for tracheal intubations in various clinical situations related to normal as well as difficult airways.⁴

In a situation during induction of anaesthesia when a patient is in ‘‘sniffing’ position’ and the initial attempt at DL proves difficult or fails, VL is used as a rescue method if the videolaryngoscope is available. While proceeding for VL, most anaesthesiologists are habitual of keeping the patient in the same position of head and neck as DL without any alteration. A suboptimal position for DL as well as VL can result in a wasted attempt for intubation and further repeated attempts can result in poor outcomes including death.¹

Poor laryngoscopic visualizations and difficult/failed intubations with DL have prompted the anaesthesiologists to try many modified positions of head & neck for achieving better laryngoscopic views and successful intubations. Some of these include changing the pillow height⁵, utilizing ramped position⁶, using maximum head extension or no head extension⁶, head-elevated-laryngoscopy position⁶ and back-up position⁶ etc. Various pillow heights from 3.0 cm to 13.5 cm have been tried in ‘‘sniffing’ position’ by various authors but no clear-cut established universal consensus on this subject has been reached and very conflicting recommendations about pillow heights for DL have surfaced viz., 4.0, 4.5, 5.0, 7.0, 9.0 and even 10.0 cm. ^7,8,9Credibly in the present day context when video-laryngoscopes are being more frequently and successfully used for difficult laryngoscopy and tracheal intubation as a rescue tool, VL is now being suggested by several authors to be accepted as first choice method for all intubations.¹⁰ Despite recognising the utility of VL, still there are no reports recommending any specific head and neck position for best glottic views for tracheal intubation with video-laryngoscopes.

Most recently, a secondary indicator i.e., horizontal alignment of external auditory meatus (EAM) and supra-sternal notch (SN) which is not directly related to airway configuration, has also been suggested to allow closer alignment of pharyngeal, laryngeal axes and oral axis to provide a better line of vision for DL and has been recommended as a satisfactory endpoint for getting optimal head and neck position for laryngoscopy in obese as well as non-obese patients, irrespective of degree of head elevation.¹¹ However, there is no study which mentions the change in angle of EAM-SN line in comparison to the horizontal axis in different head and neck positions for VL.

In view of the fact that optimal positioning of head & neck has been well accepted as an essential requirement for laryngoscopy¹² and intuitively, there are discordant results about the utility of ‘sniffing’ position and a clear-cut pillow height for better laryngeal exposure with DL⁷ and moreover, role of  ‘sniffing’ position is ambiguous while performing VL, in view of no need to align three anatomical axes to obtain a direct view of glottis during VL and literature is still devoid of any studies which recommend any specific positioning of head and neck for video laryngoscopy, the present study was planned to assess using video-laryngoscope, the effects of different head and neck positions, namely, flat without head elevation and with pillow heights of 4, 6 and 8 cm for head elevation on the Percentage of Glottic Opening (POGO) score,¹³ modified Cormack and Lehane (MCL) grade,¹⁴ ease of insertion of videolaryngoscope, need of optimization manoeuvres for facilitating ease of intubation, intubation difficulty score (IDS), time to successful intubation, number of Intubation attempts, failure to intubate and angle of EAM-SN line in comparison to the horizontal axis and to recommend the most optimal pillow height for best outcomes with VL.

Lacunae in the existing knowledge

Extensive search of literature revealed that there is no study which suggests or recommends any specific head & neck position for best glottic views and easy intubation while using videolaryngoscope and which also compares the effect of using different pillow heights on glottic view, easiness in insertion of blade of videolaryngoscope, ease of intubation, intubation difficulty score, time to successful intubation, number of Intubation attempts, failure to intubate and change in the angle of ‘EAM-SN line with horizontal’ with different pillow heights in adult patients. Though literature is full of various head and neck positions used for DL,¹⁵ the ideal head & neck position for VL has not been recommended till date, hence the present study.