Comparison of physical and flow characteristics of "streamline" and "normal" cuffed tracheal tubes

A comparative study was undertaken of the physical and flow characteristics of "streamline" cuffed tracheal tubes (SCT; Medishield) and "normal" cuffed tracheal tubes (NCT) of sizes 6.0, 6.5, and 9.0 mm. The embedding of the pilot tube within the wall of SCT imparts a D-shaped lumen which is more marked in 6.0- and 6.5-mm tubes. As a result, there is a 15% reduction in the lumen of a 6.5-mm SCT. All sizes of SCT studied had a smaller outer diameter compared with the corresponding sizes of NCT and thus occupied less space in the trachea. In sizes 6.0 and 6.5 mm, the SCT was found to have distinct disadvantages, such as increased resistance to ventilation of up to twice that of NCT, and turbulent flow even at a minute volume of 5 litre min-1. SCT, size 9.0 mm, however offered marginally less resistance compared with NCT of the same size.