The sniffing position (SP) has been traditionally been considered the optimal head position for direct laryngoscopy (DL).  In this position, the neck must be flexed on the chest, typically by elevating the head with a cushion under the occiput and extending the head on the atlanto-occipital joint. However, the degree of head raise required to achieve an optimal cervical spine flexion is not clear. It has been suggested that a horizontal alignment of the external auditory meatus - sternal notch line produces a better alignment of the airway axes. It was postulated that this alignment may provide a better laryngoscopic view and ease of intubation.

After approval from institutional review board, this prospective, randomized, cross-over study titled “Compare evaluation of laryngoscopy positions in adults attained by conventional 7cm head raise with that attained by horizontal alignment of external auditory meatus - sternal notch line” was conducted. 100 ASA I-III for elective surgery participated in this study. They were divided into two groups: S & H, with 50 patients each.

Patient was premedicated with i.v. fentanyl 2 microgram/kg 5min before induction. After preoxygenation with 100% O₂ for 3min, anaesthesia was induced with i.v. propofol 2mg/kg. Ability to mask ventilate was checked. Muscle relaxation was achieved using i.v.vecuronium 0.1mg/kg. The patient was ventilated via facemask with 2% isoflurane in oxygen for three minutes before attempting laryngoscopy in either group.

 In one group (Group-H), patients were positioned such that external auditory meatus and sternal notch (AM-S line) were in same horizontal line during first laryngoscopy. The second laryngoscopy was performed with patient head placed on 7cm pillow. Thereafter, patient was intubated in second position. In the other group (Group-S), laryngoscopy was performed first with head placed on 7cm pillow while second laryngoscopy was performed with AM-S line horizontal alignment and patient intubated in second position.  Modified Cormack Lehane grading of laryngeal view in both the head positions were compared, along with ease of intubation (Intubation difficulty score) and the time to intubate between the two groups. The time to intubate was from the introduction of laryngoscopy blade into the mouth till the appearance of square wave capnograph trace.

Results: All the patients who participated in the study were demographically matched for age, weight and gender between the two groups: S and H. There was no statistical difference in any of demographic parameters.

All the patients had laryngoscopic view evaluated with both the positions i.e. AM-S alignment and with a 7cm head raise. One patient had AM-S line alignment at 7cm; hence laryngoscopy was performed only once followed by intubation.

During CL grading with AM-S alignment, 40% patients had CL grade I, while only 30% patients had CL grade I with 7cm head raise. In 7cm head raise position, 40% patients had CL IIa and CL IIb was present in 21% patients. When compared to AM-S line alignment, CL IIa was present in 36% patients while CL IIb was present in 15% patients. For CL IIIa, results were almost similar for AM-S group and 7cm head raise group having 9% and 8% incidence respectively. Interestingly, CL grade IIIb was not encountered during laryngoscopic grading in AM-S alignment but one patient (1%) had CL IIIb during laryngoscopy with 7 cm head raise. There was statistically significant difference between CL grades for two positions. For MMPC- I & II, CL grades improved with AM-S alignment (p<0.05) but not for MMPC-III.

Al-Jadidi et al used a single infusion bag with a head ring placed in it for finding optimal sniffing position. We found that their infusion bag assembly was unstable during intubation and also indentation would occur when patients head was placed on it. We devised an innovative inflatable pillow made using two pressure infusion bags connected using a three way to single inflation bulb. This assembly was then placed between two firm surfaces (wooden base and stiff plastic sheet on top) and then encased in a cover. This prevented the indentation of the pillow by the patient’s head which changes the height of head raise. This assembly allowed the head raise to be adjusted between 3cm to 10cm by progressive inflation. The degree of head raise was recorded by a scale fixed to the base of this pillow and the height could be recorded in cm with a least count of 1mm. The inflation bulb could be controlled easily. Using two pressure bags side by side provided stability and allowed a uniform height of the pillow.

The mean IDS for group-S was less than that for group-H, being 1.18±1.69 and 2±1.59 (p<0.05) respectively. The time to intubate in AM-S line alignment position was   17.33±4.52 sec while that with 7cm pillow was 18.44±4.64 sec (p<0.05). Significantly lesser amount of lifting force was required for laryngoscopy in AM-S line alignment position (p<0.05

The mean head raise required for AM-S alignment in this study 4.920±1.460 cms. Sinha et al in their study found that 4.5cm pillow provided best laryngeal view, compared to 9 & 13.5cm pillow. However in contrast Park et al found best possible laryngeal view with 9cm pillow. Schmitt and Mang  suggested that elevation of the head and neck beyond the sniffing position may improve visualization of the glottic structures in case of difficult laryngoscopy, leading to better intubation performance. Levitan et al in their cadaveric study also found POGO scores to improve with increasing head elevation. Likely explanation is that our study and that done by Sinha et al were conducted in Asian population while the latter mention studies were conducted on population of western countries, who have larger body proportions, thus likely to have longer neck length compared to Asians and hence require a greater head raise.

From the results of present study we conclude that External Auditory Meatus-Sternal notch alignment (AM-S alignment) provides better laryngeal view as compared to conventional sniffing position with 7cm head raise. We also conclude that AM-S alignment provides better intubating conditions, and requires lesser time to intubate as compared to a conventional 7cm head raise. The size of pillow used for head raise should be individualised. The horizontal alignment of auditory meatus - sternal notch line can be used as an end point for attaining proper laryngoscopic position. An average pillow height of 4.920±1.460 cm conforms more closely to a proper laryngoscopy position as compared to a 7cm pillow in Indian patients.