氣道處理長久以來都是臨床醫療一個非常重要的議題。大部分的醫療從業人員都須學習基本的呼吸道處理原則。在眾多方法中，氣管插管是最安全有效的氣道處理方式。目前臨床上有許多工具可被應用於氣管插管，其中以傳統硬式Macintosh喉頭鏡最常被使用。但由於傳統硬式喉頭鏡有結構上的限制，使得在臨床上無論插管者有無經驗皆很難避免以牙齒當支點旋轉施力。臨床統計結果發現，由困難插管所導致的併發症中以牙齒傷害最常發生，機率高達12.1%，也是麻醉醫師最主要的醫療糾紛來源。至今，氣管插管所造成的牙齒傷害仍然是臨床上經常面對的問題。
近年來，一款新型阻力回饋型喉頭鏡，其設計透過其傳動機構與前端前端可抬式翹頭葉片，可以增加挑管效率並有效降低牙齒傷害的風險。本研究目的為透過有限元素分析比較傳統硬式喉頭鏡與新型阻力回饋型喉頭鏡的挑管效果。
在插管模型建立方面，本研究採用逆向工程軟體來重建假體上呼吸道模型與喉頭鏡3D電腦模型。假體上呼吸道透過電腦斷層掃瞄CT影像來重建，喉頭鏡則按照實體模型尺寸以電腦軟體等比例繪製而成。插管模型為假體上呼吸道結合喉頭鏡的組合件並且依挑管方式總共分三個組別，組別一:傳統硬式喉頭鏡結合上呼吸道施以平行握把軸向位移；組別二:傳統硬式喉頭鏡結合上呼吸道並以牙齒當支點在喉頭鏡上施以位移；組別三:阻力回饋型喉頭鏡結合上呼吸道施以平行握把軸向位移加上翹頭抬升位移。在喉頭鏡位移量測實驗中，本研究在喉頭鏡握把上貼上標籤並以相機連拍來記錄喉頭鏡在假體中的挑管過程，在拍攝的相片結果中由喉頭鏡握把上的標籤相對位置變化可換算出其實際位移量。將以上三組別匯入ANSYS做有限元素分析，在施力條件上給予上述喉頭鏡握把上標籤所量測到的位移。
實驗結果發現，組別一與組別二的會厭位移量分別為15.55和23.05(mm)，且組別二的牙齒受力為40.68(N)，這結果顯示出以牙齒當支點並旋轉施力的方式的確可以產生較好的挑管效果，但卻會對牙齒造成傷害。此外，在舌頭受力比較方面，組別一與組別二在舌頭受力上分別為24.62和34.42(N)，其結果顯示出以牙齒當支點的施力方式因為喉頭鏡葉片與舌頭表面積的接觸範圍較小，所以在舌頭上產生比組別一稍微大的力量。另外本研究亦透過ANSYS模擬出RFL在翹頭抬升的最大位移量為19.25(mm)，雖然組別三的模擬目前還未得到一個非常完整的結果，但是藉由RFL在挑管時的作動方式可得知，其整體位移為一平行軸向握把位移加上翹頭可抬升高度(19.25mm)。由此推斷，組別三的挑管效果(會厭位移)優於組別一。
本研究利用科學方法，透過有限元素模擬解析各種參數並且提出數據，說明RFL將會優於傳統硬氏喉頭鏡，希望能對未來產品開發有莫大的幫助。此外，生物力學插管模型可以提供完整模型給往後的研究使用。

Airway management is an important issue in clinical practice. Most health care providers are required to learn the basic principles of airway management. Tracheal intubation (TI) has been considered the safest and most effective technique related to airway management. A variety of instruments are currently used to conduct TI, and the conventional Macintosh laryngoscope (CML) is the most commonly used tool. However, due to limitations in the structure of the CML, it is difficult to use intubators to perform laryngoscopy without using the teeth as a fulcrum to lift the larynx. According to previous studies, it has been found that dental trauma, with a incidence of 12.1%, is the most common complication occurring during difficult TI, which also makes up the majority of malpractice claims against anesthesiologists. Therefore, dental trauma resulting from TI remains a common problem for intubators in clinical practice.
A novel developed resistance feedback laryngoscope (RFL) with a resistance feedback mechanism and a distal levering tip is designed to increase the efficiency of direct laryngoscopy and reduce the risk of dental trauma.
The purpose of this study is to compare the CML with this novel RFL during laryngoscopy by constructing a simulation intubation model to use for finite element analysis.
The intubation model, including a manikin upper airway structure and two laryngoscope 3D structures, was constructed using reversed engineering. First, the structure of the manikin upper airway was constructed according to CT images of the head and neck using Mimics computer software and SolidWorks, and the structures of the two laryngoscopes were drawn according to the sizes of the CML and RFL using SolidWorks computer software. Then, the intubation model was developed through assembling the upper airway of the manikin and construction of laryngoscope 3D models. According to the laryngoscopy techniques and the choice of laryngoscopes, three models were conducted for analysis: (1) Model 1 using the CML to perform laryngoscopy with a parallel displacement along the axis of the laryngoscope handle; (2) Model 2 using the CML to perform laryngoscopy with a rotation displacement at a center point of the contacted teeth; (3) Model 3 using the RFL to perform laryngoscopy with a combined displacement involving paralleling the handle and levering the blade tip.
Experimental measurements of actual displacements of the laryngoscopes used during direct laryngoscopy were performed to determine the values of laryngoscope movement in the three intubation models. First, several markers were set up on the handle of the laryngoscopes. Second, the procedure for direct laryngoscopy was continually recorded by a camera. Third, the values of the laryngoscope movements were determined through the displacement of the markers during direct laryngoscopy. Finally, the measured values of displacement were imported into the intubations models as loading conditions for finite element analysis.
The results of this study showed that the epiglottis displacement in both Model 1 and Model 2 were 15.55 mm and 23.05 mm, respectively. The force occurring on the teeth in Model 2 was 40.68 N. This result indicated that although applying a force with the teeth as a fulcrum to lift the larynx can provide better epiglottis displacement as compared to applying a parallel force on the handle during laryngoscopy, it may harm the teeth. The reaction force of the tongue in Models 1 and 2 were 24.62 N and 34.42 N, respectively, which was due to the small contact area on the tongue in Model 2. In addition, in this study, the blade tip during the use of the RFL was simulated using ANSYS, with a maximum elevation displacement of 19.25(mm). Although the simulation for Model 3 has yet to get very complete results, as a result of the RFL motion during laryngoscopy, the overall displacement is axial displacement parallel to the handle coupled with elevation of the blade tip. By inference, epiglottis displacement is more significant in Model 3 than in Model 1 during laryngoscopy.
In this study, scientific methods are used to resolve various parameters with finite element simulations; then, the data are used to explain why RFL may be superior to the conventional Macintosh laryngoscope. It hoped this research will contribute to product development. In addition, this biomechanical intubation model can provide a complete model for use in future studies.

References
1. Murphy, C. and D.T. Wong, Airway management and oxygenation in obese patients. Can J Anaesth, 2013.
2. Owen, H. and I. Waddell-Smith, Dental trauma associated with anaesthesia. Anaesth Intensive Care, 2000. 28(2): p. 133-45.
3. Hong, J.S., et al., Three-dimensional analysis of pharyngeal airway volume in adults with anterior position of the mandible. Am J Orthod Dentofacial Orthop, 2011. 140(4): p. e161-9.
4. Jackson, A.M., et al., Effects of various anesthetic agents on laryngeal motion during laryngoscopy in normal dogs. Vet Surg, 2004. 33(2): p. 102-6.
5. McCoy, E.P. and R.K. Mirakhur, The levering laryngoscope. Anaesthesia, 1993. 48(6): p. 516-9.
6. McCoy, E.P., R.K. Mirakhur, and B.V. McCloskey, A comparison of the stress response to laryngoscopy. The Macintosh versus the McCoy blade. Anaesthesia, 1995. 50(11): p. 943-6.
7. Hirsch, N.P., G.B. Smith, and P.O. Hirsch, Alfred Kirstein. Pioneer of direct laryngoscopy. Anaesthesia, 1986. 41(1): p. 42-5.
8. Katz, S.H. and J.L. Falk, Misplaced endotracheal tubes by paramedics in an urban emergency medical services system. Ann Emerg Med, 2001. 37(1): p. 32-7.
9. Adnet, F., et al., A survey of tracheal intubation difficulty in the operating room: a prospective observational study. Acta Anaesthesiol Scand, 2001. 45(3): p. 327-32.
10. American Society of Anesthesiologists Task Force on Chronic Pain, M., A. American Society of Regional, and M. Pain, Practice guidelines for chronic pain management: an updated report by the American Society of Anesthesiologists Task Force on Chronic Pain Management and the American Society of Regional Anesthesia and Pain Medicine. Anesthesiology, 2010. 112(4): p. 810-33.
11. Biboulet, P., et al., Fatal and non fatal cardiac arrests related to anesthesia. Can J Anaesth, 2001. 48(4): p. 326-32.
12. Cormack, R.S. and J. Lehane, Difficult tracheal intubation in obstetrics. Anaesthesia, 1984. 39(11): p. 1105-11.
13. Tiret, L., et al., Complications associated with anaesthesia--a prospective survey in France. Can Anaesth Soc J, 1986. 33(3 Pt 1): p. 336-44.
14. von Goedecke, A., et al., Field airway management disasters. Anesth Analg, 2007. 104(3): p. 481-3.
15. Rosenberg, M.B., Anesthesia-induced dental injury. Int Anesthesiol Clin, 1989. 27(2): p. 120-5.
16. Warner, M.E., et al., Perianesthetic dental injuries: frequency, outcomes, and risk factors. Anesthesiology, 1999. 90(5): p. 1302-5.
17. Holzer, J.F., Analysis of anesthetic mishaps. Current concepts in risk management. Int Anesthesiol Clin, 1984. 22(2): p. 91-116.
18. Bucx, M.J., et al., Does experience influence the forces exerted on maxillary incisors during laryngoscopy? A manikin study using the Macintosh laryngoscope. Can J Anaesth, 1995. 42(2): p. 144-9.
19. Wilson, M.E., et al., Predicting difficult intubation. Br J Anaesth, 1988. 61(2): p. 211-6.
20. Rodrigues, M.A., D. Gillies, and P. Charters, A biomechanical model of the upper airways for simulating laryngoscopy. Comput Methods Biomech Biomed Engin, 2001. 4(2): p. 127-48.
21. McIntyre, J.W., Laryngoscope design and the difficult adult tracheal intubation. Can J Anaesth, 1989. 36(1): p. 94-8.