Laser resistance of endotracheal tubes II: Observed temperature rise and theoretical explanation

An infrared camera was used to measure the temperature rise which takes pla ce in endotracheal tubes exposed to a 20 W CO2 laser beam. It was seen that a metallic tube was heated up within is to temperatures of 200-300 degrees C which was very destructive to the PVC conduits inside the tube. A compou nd tube, on the other hand, reached temperatures of only 60 degrees C at it s 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 c apacities of both tubes. Whereas heat conduction in the metal tube is isotr opic, heat conduction in the compound tube is anisotropic with a high condu ctivity 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.