FINITE-ELEMENT DETERMINATION OF THE FORCES EXERTED BY ENDOTRACHEAL-TUBES ON THE UPPER AIRWAYS

Accidents occurring during intubations often originate in the mechanic al interaction between the tube and the upper airways. A review of the se accidents, including their possible complications, shows that they are mainly due to the forces exerted by the tube on the anatomical str uctures during the long intubation periods. The structural design of c urrently available tubes is presented, and the viscoelastic properties of the constituent PVC materials are analysed. It is shown how the lo ng-term viscoelastic behaviour of the polymer can be assessed from acc elerated relaxation tests in uniaxial tension at temperatures higher t han the body temperature and how the variation in the relaxation modul us can be modelled through a simple constitutive equation with a minim um number of parameters. From these data, the mechanical interaction o f the tubes with the trachea are computed by means of the finite eleme nt method. The relative efficiency of different types of endotracheal tubes is thus discussed and operational criteria are eventually define d for the choice of tubes in clinical situations. (C) 1996 Elsevier Sc ience Limited.