Forces Applied by The Laryngoscope Blade onto The Base of The Tongue and their relation with Postoperative Sore Throat

The forces applied by the laryngoscope blade onto the base of the tongue have been measured indirectly by some investigators. The relation between these forces and postoperative sore throat has not been studied previously. The aim of this study was to directly measure the forces applied by the tip of the laryngoscope blade onto the base of the tongue and its relation to incidence and severity of sore throat.
One hundred patients, 18-65 years old, all candidates for abdominal or lower limb operations under general anesthesia were selected. Maximum and mean force, laryngoscopic time and force-time product were measured using a modified macintosh laryngoscope blade during laryngoscopy. The occurrence and severity of postoperative sore throat were determined after operation using visual analogue scale. Data were analyzed statistically using t-test and Spearman's correlation coefficient.
The laryngoscopic time was 10.57 ± 1.66 seconds, the maximum force was 61.56 ± 8.07 N, the mean force and force - time product were 38.29 ± 6.74 N and 404.72 ± 71.24 N.S. respectively. There was a positive correlation between sore throat intensity, its maximum intensity maximum and mean forces.
This study showed that these forces were higher than those of previous reports. Instant forces applied by the laryngoscope blade may be a more important factor than duration of applied forces regarding the severity of postoperative sore throat.