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A3159
October 15, 2018
10/15/2018 3:30:00 PM - 10/15/2018 5:30:00 PM
Room North, Hall D, Area C
Safe Stylet Use During Tracheal Intubation: A Mathematical Analysis and In Vitro Experimental Study
Masakazu Kotoda, M.D., Takeshi Oguchi, M.D.,Ph.D., Kazuha Mitsui, M.D., Sohei Hishiyama, M.D., Kenta Ueda, M.D., Akiko Kawakami, M.D., Takashi Matsukawa, M.D.,Ph.D.
University of Yamanashi, Chuo, Japan
Disclosures: M. Kotoda: None. T. Oguchi: None. K. Mitsui: None. S. Hishiyama: None. K. Ueda: None. A. Kawakami: None. T. Matsukawa: None.
Background Intubating stylets have been widely used to facilitate tracheal intubation. Although stylets provide better maneuverability for the tracheal tube, styletted tubes can cause laryngeal complications. During intubation, the stylet should be extracted along a course that does not generate excessive force on the vocal cords. However, the proper method of stylet removal has not been discussed in the literature. In addition, although the force applied on the vocal cords is a critical factor in vocal cord injuries, the relationship between this force and stylet use has not been investigated. In the first half of this study, we explored how the stylet should be extracted to avoid vocal cord injuries using a mathematical model and analysis. In the second half of this study, the relationship between the force applied on the vocal cords and stylet use was investigated via simulated tracheal intubation.

Methods This study consists of a modeling analysis and an in vitro experiment. The modeling analysis shown in Figure 1 used a geometrical model of tracheal intubation. The ideal position of the stylet during removal to minimize the force applied on the vocal cords was calculated using mathematical software. Both arcuate-shaped and hockey stick-shaped stylets with various bending angles (15, 30, 60, and 75°) were considered. In the in vitro experiment, simulated tracheal intubation was performed using a training manikin. The upward and downward force applied on the vocal cords and the stylet extraction force were measured using force meters. Regular and reinforced tubes arcuate-shaped and hockey stick-shaped stylets with various bending angles were tested.

Results The ideal positions of the stylet end determined by the mathematical analysis are shown in Figure 2. The stylet should be diagonally extracted with an appropriate angle rather than in a straight direction toward the direction of the stylet end. Stylets with larger bending angles required greater extraction angles. After the bent part of the stylet reaches the teeth, the extracting direction should be changed. While the change was small and the overall position was nearly arcuate with use of stylets with smaller bending angles, a drastic change of the extraction direction was required with use of stylets with larger bending angles. In simulated tracheal intubation, as shown in Figure 3, the extraction force and the force applied on the vocal cords significantly increased as the bending angle increased. Compared to the hockey stick-shaped stylet, the arcuate-shaped stylet resulted in smaller forces.

Conclusions Stylets with larger bending angles used a more complicated course during removal, resulting in greater force on the vocal cords. The present results indicate the potential risk of vocal cord injury when using a hockey stick-shaped stylet with large bending angles.

Figure 1
Figure 2
Figure 3

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