DESIGN AND DEVELOPMENT OF ULTRATHIN-WALLED, NONKINKING ENDOTRACHEAL-TUBES OF A NEW NO-PRESSURE LARYNGEAL SEAL DESIGN - A PRELIMINARY-REPORT

Background: Endotracheal tubes (ETTs) of conventional design and manuf acture greatly increase the air-flow resistance of the upper airways. This increase in upper-airway resistance can lead to a significant inc rease in the work of breathing and may necessitate the use of assisted mechanical ventilation. Current ETTs are relatively stiff and contrib ute greatly to patient discomfort. The inflatable cuffs now mounted on to the ETTs function well in short-term use but impart significant mor bidity when used over longer periods. These issues were addressed by t he designing of a low-resistance ETT. Methods: Using new techniques, w e developed ultrathin-walled, wire reinforced ETTs of conventional con figuration and ETTs the oropharyngeal-section diameter of which was a few millimeters larger than the diameter of the tracheal section. The wall thickness was a constant 0.20 mm. The wire reinforcement was stai nless steel flat wire or superelastic nickel-titanium alloy. The super elastic nickel-titanium alloy reinforcement made those ETTs crush-proo f; after forceful manual compression, recovery was complete. To obtain a seal with the upper airways, we first shaped a short section of the oropharyngeal section of the ETT from round to oval (or egg-shaped) t o conform better to the larynx. We then attached to this segment numer ous soft, pliable, 0.025-0.075-mm-thick rings of polyurethane to occlu de voids for potential air leaks from within the larynx.Results: In vi tro pressure-flow studies showed a decrease by as much as four- or fiv efold in air-flow resistance in the adult ETT range, effectively incre asing the internal diameter by 2.3-3.7 mm, compared with conventional ETTs of the same outside diameter. In vivo studies for 24 h in sheep s howed no air leaks at airway pressures to 30 cmH(2)O and minimal leak at greater pressures. The gross appearance of the trachea was normal. Conclusions: Although the new tubes appear to offer advantages to thos e currently used, testing in humans is required to assess the clinical utility of the tube-cuff design.