Establishment of clear glottic visualization is of great significance for successful tracheal intubation. The aim of direct laryngoscopy is to visualize the vocal cords through the anatomically curved, oropharyngolaryngeal space. When laryngoscopy is difficult with the curved blade, use of a straight type may help to achieve adequate laryngeal visualization.

There have been few studies of correlation between the operating table height and the quality of laryngeal view during direct laryngoscopic intubation. It has been suggested. A study done using Macintosh laryngoscope blade validated that higher operating tables, with the patient’s forehead at either xiphoid process or nipple level of the anaesthetist can provide better laryngeal views during tracheal intubation, however, the patient’s head and neck posture during laryngoscopy was neither controlled nor monitored. There is no study comparing the laryngeal views obtained at different table heights using a straight blade laryngoscope.

In this study, we compared the laryngeal views obtained using Miller and Macintosh blades at three different table heights by keeping a fixed head position. Additionally we also compared the degree of head extension achieved during the use of the two laryngoscope blades at the three different operating table heights.

METHODS:

A randomized controlled study was undertaken to evaluate and compare the laryngeal view obtained with the use of  Miller and Macintosh blade at operating table height with the patient’s forehead at three different levels i.e. anaesthetist’s umbilicus, xiphoid process and nipples. The degree of head extension achieved with the two laryngoscope blades at the three above mentioned positions of the operating table height was also measured. 105 ASA I/II patients of either sex, between the age group of 18-65 years, with no anticipated difficulty in laryngoscopy and intubation who were scheduled to undergo elective surgery under general anaesthesia were enrolled in the study. Patients were randomized to one of the three predetermined operating table while using the same 7cm incompressible pillow below the occiput. Randomization was also done for the blade first used for laryngoscopy. The quantitative variables were expressed as mean±SD and compared using Mann-Whitney test while qualitative variables were expressed as percentages and compared using Chi-Square / Fisher’s exact test.

Results:

With the use of Miller blade, CL grade of 1 was obtained in 9.5% of the study population. Among the patients with operating table height at nipple level with Miller blade, 25.7% were found to have CL grade 1, 2.9% at umbilicus and 0% at xiphoid process. Using Pearson Chi square test, the p value was found to be .002. This difference was found to be statistically significant. 10.5% patients had CL grade 3 with Miller blade. 14.3% of the patients at level of umbilicus, 11.4% at xiphoid and 5.7 % at nipple level exhibited CL grade 3. None of the patients in any of the study groups were found to have CL grade 4.

With the use of Macintosh blade, CL grade of 1 was obtained in 33.3% of the study population. Among the patients with operating table height at the umbilicus with Macintosh blade, 42.9% were found to have CL grade 1, 37.1% at Nipple and 20% at xiphoid process. Using Pearson Chi square test the p-vale was found to be .264. The difference was not found to be statistically significant. Only 2 (1.9%) patients were found to have CL grade 3, 1 at Nipple level and 1 at xiphoid.

Comparison of percentage distribution of CL grades with the use of Miller and Macintosh at different operating table heights, Macintosh laryngoscope blade provided a higher percentage of CL grade 1 across all table heights.

On assessing the secondary parameter, mean angle of head extension of 7.102Ëš was found with Macintosh blade and 7.899Ëš with Miller blade. With the use of Macintosh blade, Mean head extension was compared at the three table heights. Using Kruskal-Wallis test, the p-value was found to be 0.062 which was statistically non-significant.

Using Kruskal-Wallis test for mean head extension with the use of Miller blade, the p-value was found to be 0.011. The difference in the mean degree of head extension found at different table heights with Miller Blade was found to be statistically significant.

Comparing the different operating table heights, best laryngeal views were obtained at the level of anaesthesiologist’s nipple with CL grade 1 found in 31.43% of the laryngoscopies followed by umbilicus (22.86%) and the minimum of 10% found at the Xiphoid level. However assessment of the degree of head extension revealed that laryngoscopy was possible with the least head extension at the level of umbilicus with mean head extension of 6.5145˚ followed by 7.892˚ at xiphoid level. Maximum head extension was found at nipple level with a mean head extension of 8.1015˚