Laser Resistance of Endotracheal Tubes II: ObservedTemperature Rise and Theoretical Explanation

An infrared camera was used to measure the temperature rise which takes place in endotracheal tubes exposed to a 20 W CO2 laser beam. It was seen that a metallic tube was heated up within 1 s to temperatures of 200-300°C which was very destructive to the PVC conduits inside the tube. A compound tube, on the other hand, reached temperatures of only 60°C at its inner surface after an exposure of 20 s. The experimental results can be explained by a physical model which uses the heat conduction and the heat capacities of both tubes. Whereas heat conduction in the metal tube is isotropic, heat conduction in the compound tube is anisotropic with a high conductivity along the outer surface and a low conductivity to the inside. This anisotropy and the cooling mechanism in the compound tube due to vaporising water are the reason for the high laser resistance of the tube.