Using infrared thermography, the changes in the surface temperatures of the tracheal tube between the tip and 15 cm from the proximal end are measured following dipping into 60°C water for 3 minutes. Infrared thermographs show the changes in the surface temperature after 5 minutes of the Mallinckrodt Nasal RAE Tube (a) and the Portex North Polar Preformed Tube (b) after withdrawing the tube from 60°C water. Color bars represent the temperature scale ranging from 20 to 60°C.

Dots indicate the mean surface temperature between the tip and 15 cm from the distal end measured by infrared thermography (n = 5). Each polygonal line shows the sequential values of the surface temperatures of the tubes at 30-second intervals for 5 minutes after withdrawing the tube from 45 or 60°C water. (a) Mallinckrodt Nasal RAE Endotracheal Tube; (b) Ivory PVC Portex North Polar Preformed Endotracheal Tube.

The pressure force for a 1-mm reduction of the minor axis of the tracheal tube was used as the index of hardness of the tube. Blue circles and orange circles indicate Mallinckrodt Nasal RAE Endotracheal Tube and Ivory PVC Portex North Polar Preformed Endotracheal Tube, respectively. Dots and error bars indicate the means and SDs. n = 5; ** p < 0.01 versus hardness at 25°C (Bonferroni's Multiple Comparison Test).