Comparative evaluation of laryngoscopy position in adults attained by conventional 7cm head raise and that attained by horizontal alignment of external auditory meatus-sternal notch line

Thesniffing position (SP) has been traditionally been considered the optimal headposition for direct laryngoscopy (DL).  Inthis position, the neck must be flexed on the chest, typically by elevating thehead with a cushion under the occiput and extending the head on theatlanto-occipital joint.However, the degree of head raise requiredto achieve an optimal cervical spine flexion is not clear. It has beensuggested that a horizontal alignment of the external auditory meatus - sternalnotch line produces a better alignment of the airway axes. It was postulatedthat this alignment may provide a better laryngoscopic view and ease ofintubation.

Afterapproval from institutional review board, this prospective, randomized,cross-over study titled “Compare evaluationof laryngoscopy positions in adults attained by conventional 7cm head raisewith that attained by horizontal alignment of external auditory meatus -sternal notch line†was conducted. 100 ASA I-III for elective surgeryparticipated in this study. They were divided into two groups: S & H, with50 patients each.

Patientwas premedicated with i.v. fentanyl 2 microgram/kg 5min before induction. Afterpreoxygenation with 100% O2 for 3min, anaesthesia was induced withi.v. propofol 2mg/kg. Ability to mask ventilate was checked. Muscle relaxationwas achieved using i.v.vecuronium 0.1mg/kg. The patient was ventilated viafacemask with 2% isoflurane in oxygen for three minutes before attemptinglaryngoscopy in either group.

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

Results***:***All the patients who participated in the study were demographically matched forage, weight and gender between the two groups: S and H. There was nostatistical difference in any of demographic parameters.

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

DuringCL 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 IIaand CL IIb was present in 21% patients. Whencompared to AM-S line alignment, CL IIa was present in 36% patients while CLIIb was present in 15% patients. For CL IIIa, results were almost similar forAM-S group and 7cm head raise group having 9% and 8% incidence respectively.Interestingly, CL grade IIIbwas not encountered duringlaryngoscopic grading in AM-S alignment but one patient (1%) had CL IIIb duringlaryngoscopy with 7 cm head raise. There was statistically significantdifference between CL grades for two positions. For MMPC- I & II, CL gradesimproved with AM-S alignment (p<0.05) but not for MMPC-III.

Al-Jadidiet al used a single infusion bag with a head ring placed in it forfinding optimal sniffing position. We found that their infusion bag assemblywas unstable during intubation and also indentation would occur when patientshead was placed on it. We devised an innovative inflatable pillow made usingtwo pressure infusion bags connected using a three way to single inflationbulb. This assembly was then placed between two firm surfaces (wooden base andstiff plastic sheet on top) and then encased in a cover. This prevented theindentation of the pillow by the patient’s head which changes the height ofhead raise. This assembly allowed the head raise to be adjusted between 3cm to10cm by progressive inflation. The degree of head raise was recorded by a scalefixed to the base of this pillow and the height could be recorded in cm with aleast count of 1mm. The inflation bulb could be controlled easily. Using twopressure bags side by side provided stability and allowed a uniform height ofthe pillow.

Themean 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 positionwas   17.33±4.52 sec while that with 7cmpillow was 18.44±4.64 sec (p<0.05). Significantly lesser amount of liftingforce was required for laryngoscopy in AM-S line alignment position (p<0.05

Themean 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 laryngealview, compared to 9 & 13.5cm pillow. However in contrast Park et al foundbest possible laryngeal view with 9cm pillow. Schmitt and Mang suggested that elevation of the head and neckbeyond the sniffing position may improve visualization of the glotticstructures in case of difficult laryngoscopy, leading to better intubationperformance. Levitan et al in their cadaveric study also found POGO scores toimprove with increasing head elevation. Likely explanation is that our studyand that done by Sinha et al were conducted in Asian population while thelatter mention studies were conducted on population of western countries, whohave larger body proportions, thus likely to have longer neck length comparedto Asians and hence require a greater head raise.

Fromthe results of present study we conclude that External Auditory Meatus-Sternalnotch alignment (AM-S alignment) provides better laryngeal view as compared toconventional sniffing position with 7cm head raise. We also conclude that AM-Salignment provides better intubating conditions, and requires lesser time tointubate as compared to a conventional 7cm head raise. The size of pillow usedfor head raise should be individualised. The horizontal alignment of auditorymeatus - sternal notch line can be used as an end point for attaining properlaryngoscopic position. An average pillow height of 4.920±1.460 cm conformsmore closely to a proper laryngoscopy position as compared to a 7cm pillow inIndian patients.