Articles: intubation.
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Delayed onset of obstruction in the Oxford endotracheal tube during anaesthesia is described in five patients. The effects of intra-cuff voluem and pressure on the wall of the tube were investigated and discussed with special refernce to the ffects of body heat and repeated use on the consistency of the tube. It is concluded that inward collapse of the tube wall is caused by a combination of factors, namely: frequent use, softening of the tube wall by body heat, the gradual increasing of intra-cuff volume and pressure by diffusion of nitrous oxide into the cuff, replacing a damaged cuff by a new one and heat sterilization. Deflation and re-inflation of the cuff to minimal occlusive volume at hourly intervals is suggested as a precautionary measure in the prevention of inward collapse of the tube wall.
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Changes of volume and pressure due to N2O-diffusion into PVC and Latex cuffs of endotracheal tubes were measured. Endotracheal tubes with a small-volume cuff (Magill and Portex) and one type of a large-volume, low-pressure cuff (Lanz) were examined. Within 48 h significant changes of volume and pressure were registered at different starting volumes and different N2O-concentrations. ⋯ In the large-volume cuffs of the Lanz tube there were increases of volume and pressure; the measured pressures where however, in a clinical unimportant range. These changes are caused by N2O-diffusion into the cuff, slowed N2-diffusion out of the cuff, prestretching of the cuff membrane by the starting volume and further stretching by N2O diffusing into the cuff. These measurements are of practical clinical significance: This high-pressures due to starting volume and N2O-diffusion in small-volume cuffs explains the higher rate of trauma to the trachea, even after short term intubation, in contrast to the extremely low pressures in large-volume, low-pressure cuffs.