The effects on mucus transport of different grades of tracheal injury produced experimentally by an intubation tube were studied in 26 pigs. Two of them were not intubated and served as controls, while the rest were anaesthetized and either intubated or tracheostomized, or both, and ventilated for approximately 4.5 h. They were then killed and the trachea and larynx were immediately removed and placed in a specially designed chamber at 37 degrees C and 85% relative humidity. Cardio-green dye was deposited caudally in the trachea as a mucus marker. The mucus transport was observed macroscopically and the ultrastructure of the tracheal wall at the region of mucus arrest was studied by light microscopy and scanning and transmission electron microscopy. In non-intubated pigs the mucus was transported to the posterior larynx. The ciliated epithelium was usually intact along the pathway where cardio-green-stained mucus had travelled. In pigs which had been intubated and/or tracheostomized, mucus transport stopped completely at different levels of the trachea. The damage to the ciliated epithelium varied; in some animals there was almost none at all and in others there was a patchy loss of a large proportion of the cilia, or complete lack of cilia. Lesions which also included epithelial cells were often seen. Tracheal injury due either to a cuffed endotracheal tube or to a tracheostomy tube, with destruction of epithelium and cilia, causes a barrier to mucus transport, leading to arrest and accumulation of mucus further down in the airway. We were unable, however, to demonstrate a direct correlation between grade of damage and tendency to mucus arrest.
The shape of the standard endotracheal tube does not conform to the anatomy of the airway and this nonconformity is probably the most injurious factor of tracheal intubation. In order to measure the tube recoil deformation pressure at different points of the airway, it is necessary to know the exact shape of the airway. The contours of the airway were studied from lateral radiographs in patients lying supine on the operating table, with the neck in the normal, extended and flexed position. A computer programme calculated the anterior and posterior contours of the airway as mean values of the original contours on the radiographs as well as of seven selected anatomical points. The mean configuration of the airway in non-intubated individuals was then presented in a standard coordinate system. The "ideal" shape of the airway was subsequently designed in accordance with our results, and this shape can be used clinically as a standard for comparison in cases with suspected pathological configurations.
In a group of 100 patients intubated with standard polyvinyl chloride (PVC) endotracheal tubes, 26 spontaneously complained of airway discomfort postoperatively. A further 55 patients complained of airway discomfort upon direct questioning. In a comparison group of 100 patients intubated with PVC orotracheal tubes shaped to conform with the anatomy of the airway, the corresponding figures were 14 and 21. Laryngoscopy before and 5 days after intubation revealed that among patients intubated with standard tubes there was a significantly higher frequency of mucosal lesions at the cricoid plate and at the posterior commissure of the larynx, but lesions at the medial side of the arytenoids occurred to approximately the same extent in the two groups.
Two groups of patients intubated for long periods were examined post mortem. In Group A (22 patients) the mean duration of intubation was 4.0 days and in Group B (19 patients) 5.7 days. The mean for the two groups was 4.8 days. In Group A a conventional endotracheal tube was used, and in Group B an anatomically shaped tube. Both tubes had cuffs of the intermediate-volume, low-pressure type. The larynx and trachea, from the epiglottis to the bifurcation, were removed in one piece at autopsy and the inner surface was photographed. The photographs were magnified and from these the size and estimated depth of any lesions were recorded. In the arytenoid and tracheal regions no significant difference was found between the two groups. In the cricoid region, on the other hand, the outcome was significantly more favourable following use of the anatomically shaped tube.
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