Direct laryngoscopy is a procedure which allows for the visualization of the glottis during the process of endotracheal intubation (placement of the endotracheal tube into the trachea). The primary device used for this procedure is called the laryngoscope. The laryngoscope consists of a handle and a blade. During insertion of the blade, the curvature of the tongue is followed and the tip of the blade is inserted into the vallecula. In the vallecula resides the hyoepiglottic ligament, which connects the anterior surface of the epiglottis and the body of the hyoid bone. Different types of laryngoscopes exist, with the two most frequently used being the Macintosh and the Miller laryngoscope. The two laryngoscopes differ in the shape of the blade, one being curved (mac) and the other one straight (miller). During laryngoscopy with the Macintosh laryngoscope, the tip of the blade is used to push on the hyoepiglottic ligament, which lifts the epiglottis up and allows for exposure of glottis. In this procedure, the forces exerted on tissues can be significant (up to 50 N) and there can be complications as a result of the forces exerted on the soft tissues of the oropharynx and larynx. These complications can be esophageal intubation, hypoxia, and nerve damage. Furthermore, difficult intubations result in increased intubation time and a higher number of intubation attempts. The most common hurdle is the inability to successfully complete the endotracheal intubation. One of the reasons why the endotracheal intubation may not be successful is the inability to visualize the glottic opening. The level of intubation difficulty is based on the extent of the view of the glottis obtained during intubation and is classified into four grade views. A new type of laryngoscope blade, which looks like the Macintosh blade, but adds features that would allow to mitigate the aforementioned factors, was designed. The primary goal of the design was to provide a mechanism which could deliver a more anterior direct laryngoscopy view and allow for an enhanced lift of the epiglottis. This would be accomplished by adding a feature which would compress the body of the tongue and also lift the tip of the epiglottis more than the conventional Macintosh blade. The new design, unlike current blades, consists of three blade segments—one fixed and two movable. The fixed blade segment is the largest, with one end fixed to the laryngoscope handle and the other hinged to the first movable segment. The first movable segment is the second largest segment of the blade, and at one end is hinged to the fixed segment and at the other it is hinged to the third segment. The middle segment is designed to compress the tongue and push it out of the way to improve vocal cord visualization. The third (smallest) segment is the blade tip which is hinged at one end to the middle second segment. This is used to enter the vallecula and push against the hyoepiglottic ligament to lift the epiglottis. The design is purely mechanical with no electrical or electronic components. A prototype was built and tested on manikins by anesthesiologists to primarily assess the change in the grade view of intubation by the flexible design. To evaluate the efficacy of the blade, a poor intubation grade view was forced and then without applying any incremental lifting forces, the mechanism was engaged to produce a final grade view. A qualitative pressure distribution was mapped for each attempt, and was compared to that obtained by a Macintosh blade. The improvement in the view with the flexible design was significant (p=0.000038). The pressures applied on the manikin airway by the flexible laryngoscope was less than that applied by the Macintosh laryngoscope to successfully intubate. The design of the flexible laryngoscope allowed for an improvement in the grade view of intubation and reduced the lifting forces applied on the airway. The built device proved that a flexible design can assist in difficult intubations.
University of Minnesota M.S.M.E. thesis. August 2016. Major: Mechanical Engineering. Advisor: Arthur Erdman. 1 computer file (PDF); x, 115 pages.
Redesign Of The Standard Macintosh Laryngoscope To Improve Glottic Visualization During Endotracheal Intubation.
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