Faulty construction of a reinforced latex endotracheal tube.

SUMMARY This paper describes a fault in the cuff of a reinforced latex endotracheal tube, where the cuff splits into layers. On attempting to deflate the cuff, the pilot balloon subsides but not the cuff itself. The cause of this fault is examined, and, by implication, steps to eliminate it during manufacture suggested. It would appear that not all such available latex endotracheal tubes are potentially liable to this fault. Reinforced endotracheal tubes have been used in various forms in anaesthesia for many years. At an early stage one such design consisted of a woven silk mesh embedded in gum-elastic. Since then various attempts have been made to incorporate a reinforcing helix of metal, and later nylon, in the wall of a latex tube. In the last few years such tubes have achieved a high degree of reliability. Still more recently attempts have been made to add an inflatable cuff to these tubes. Results have been uneven, varying from manufacturer to manufacturer. Figure 1 shows a common fault arising in tubes apparently from a single manufacturer. When deflation is attempted the pilot balloon subsides, but on extubation it would appear that the main cuff is still inflated. Closer examination reveals that the cuff wall is in two layers (fig. 2). When the cuff is inflated air blows up the inner cuff, passes around the end of this and inflates also the covering layer of latex. On deflation the inner cuff subsides, leaving air trapped between it and the covering layer of latex. There is no external or proximal indication that this inflation is present. We consider this fault a dangerous one and it appears sometimes after use on only a few occasions. Tube A (fig. 1) also shows the additional fault of distal extension of the cuff due to the separation of the layers of latex. These faults appear to arise as follows: Such a tube is built up by repeated dippings of the helix in latex. It would appear that after a few dippings 128 FIG. 1 Showing examples of failure of the main cuff to deflate ; the pilot balloons have subsided. Tube A also shows distal extension of the cuff due to separation of the layers of latex. 129 FIG. 2 Unbonded inner layer of cuff. the pilot tube is applied and over its distal end a balloon sleeve is placed to form the basis of the …