Helium Retards Endotracheal Tube Fires from Carbon Dioxide Lasers

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Abstract
Polyvinyl chloride (PVC) endotracheal tube segments were exposed to a 5.0-W CO2 laser beam in the presence of different fractions of O2 and either He or N. Time from onset of exposure until ignition was recorded, and mean time to ignition (MTI) was calculated after 10 exposures with the same gas mixture. A 2nd series was done with 40% O2 in either N or He and a laser intensity of 7.5, 10.0 or 12.5 W; a 3rd with 40% O2; 60% He and 2% halothane and a 10.0-W laser beam and a 4th with 40% O2 and 60% He and a 10.0-W laser beam directed at the radioopaque BaSO3 stripe on the tube. With 5.0-W and 20% O2 in either N or He segments did not ignite. With concentrations of O2 > 20% in N, segments ignited sooner than with comparable concentrations in He: MTIHe = 55.6 s and MTIN2 = 27.6 s in 40% O2 (P < 0.05). He (60%) remained protective at laser intensities up to 10.0 W (MTIHe = 42.6 s vs. MTIN2 = 14.3 s) (P < 0.05). At 12.5 W, MTIHe = 11.5 s and MTIN2 = 11.3 s. Two per cent halothane in 4% O2 and 60% He reduced MTIHe to 25.3 s compared with 42.3 s without halothane. With the laser directed at the Ba stripe, MTIHe was 7.2 s and MTIN2 1.1 s. Adding He in concentrations .gtoreq. 60% to anesthetic gases delays laser-induced PVC endotracheal tube fires, if laser intensity is .ltoreq. 10.0 W and laser bursts are .ltoreq. 10 s. The BaSO3 stripe should be avoided when using this technique.

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