<title>Endotracheal tubes: model calculation for heat distribution in the Rusch Lasertubus and a metallic tube</title>

Abstract

ABSTRACT In earlier experiments it was shown that the laser resistance of a composite tube (RUsch,Lasertubus) is high enough to withstand power densities of up to 106 W/cm2 for exposuretimes up to 120 seconds, while the metallic tube (Laser-F1ex, Mallinckrodt) got destroyedwithin some seconds at several 1000 W/cm2. The reason for the high laser resistance of thecomposite tube was explained by a cooling mechanism due to vaporisation water stored in themoistened foam which covers the outside of this tube. This model was checked by measuringthe laser induced temperatures of the tubes by an IR camera and compare these results withmodel calculation carried out by the method offinite elements.Key words: Laser Safety, Laser Surgery, Endotracheal Tubes, FE Calculations 1 IIITRODUCTION Endotracheal tubes are used for the supply of the patient with oxygen and narcotic gases during surgery in the upper aerodigestive tract. Since many of the tumours in this area areresected by laser beams and an accidentally hit of the laser beam onto the tube can not beexcluded, endotracheal tubes have to be sufficiently laser resistant. Laser induced ignition ofendotracheal tubes is seen as the most serious accidence in the field oflaser surgery.Laser powers of several watts focused to power densities of several thousand W/cm2 areharmfW to unprotected polymer tubes and simply shielded constructions. Even material withhigh melting points like stainless steel (Laser-Flex', Mallinckrodt, Glens Falls, Inc. USA)are destroyed in several seconds as has been found in earlier experiments [1 , 2]. The highestand for medical application absolutely sufficient laser resistant was observed at a compositetube (Lasertubus, RUsch, Waiblingen, Germany) which is build by a tube of ivory colouredrubber, surrounded by an ondulated silver foil, which itself is covered by a white moistenedpolyacetate foam (Merocel' foam). This tube withstood all experiments of laser exposurewith power densities up to 106 W/cm2 and exposure times up to 120 seconds. This high laser