Analysis of forces applied during microlaryngoscopy: a descriptive study

Microlaryngoscopic interventions are part of daily clinical routine in modern laryngology. In most cases, fulcrum-based laryngoscopy is performed, where endolaryngeal structures are exposed by laryngoscopes of different sizes and kinds. Aim of our study was to describe forces appearing during microlaryngoscopy (MLX) as well as parameters influencing easiness of exposure and given gender differences. Starting from May 2006, 100 consecutive patients scheduled for microlaryngoscopy underwent study procedures. While performing microlaryngoscopy under general anaesthesia by using a device after Kleinsasser, force measurements were obtained with a tension spring balance attached to the laryngoscope holder (F _chest). By using the law of the lever and given distances, we calculated dimensions of occurring forces on upper teeth (F _teeth) and base of the tongue (F _tongue). Mean force (F _chest) obtained by measurement with the spring balance in our study cohort was 4.4 kg (43.2 N). Whereas the force exerted on the teeth/toothless upper jaw is 4.4-fold F _chest, the force exerted on base of the tongue (F _tongue) is the sum of both forces (F _teeth + F _chest). Thus, the mean force exerted on teeth is 19.4 kg (∼190 N), force exerted on base of the tongue is 23.8 kg (233.5 N). Status of teeth was described as an independent variable and correlated with both easiness of exposure of the operational field, as well with occurring forces. We could not identify gender differences of either kind. Jet anaesthesia did not influence pressure loads or easiness of exposure.