Tracheal tube forces on the posterior larynx: index of laryngeal loading

Most tracheal tubes sold today are arcuate in shape while the human airway is S-shaped. In situ, the tubes exert different forces on the posterior larynx, depending on their stiffness. Laryngeal damage after prolonged intubation is recognized as the result of these forces. The authors tested 8 types of size 8.0 tracheal tubes to determine the magnitude of laryngeal loading in a model approximating the geometry of the human airway. The force each tube exerted on the posterior larynx was measured in conditions simulating both, immediately after intubation and after prolonged intubation of 24 h. The force was converted into an integer number, an index of laryngeal loading, that can be used to compare various types of tracheal tubes. The airway model and test procedure can be utilized by manufactures, designers, and others to provide valuable information on tracheal tube performance and to develop improved tracheal tubes in the future. The results indicate that the polyvinylchloride tubes (PVC) and the silicone rubber tubes had the lowest index of laryngeal loading after long-term conditioning and would be preferable for prolonged intubation. The red rubber tube had the highest index of laryngeal loading after long-term conditioning, yet its stiffness would facilitate intubation.