Background: Tracheal tube fire is a well recognized complication of airway laser procedures. The use of helium in the anesthetic gas mixture delays the ignition time of polyvinyl chloride tracheal tubes when a carbon dioxide laser is used. The effects of helium gas mixtures on potassium titanyl phosphate (KTP) laser-induced tracheal tube ignition have not been studied.
Methods: One hundred forty unmarked polyvinyl chloride tracheal tube segments were exposed to KTP or carbon dioxide laser beams. Each tube segment was suspended in a burn chamber with varying mixtures of oxygen in either nitrogen or helium. The gas mixtures were 21%, 30%, and 40% O2 in N2 or 30% and 40% O2 in helium. Fourteen tube segments were tested for each gas mixture. The ignition time was recorded for each segment. The laser beam was turned off at 60 s if ignition did not occur.
Results: At 30% O2/N2, mean ignition time with the carbon dioxide laser was 41.3 +/- 10.8 s (mean + standard deviation), whereas at 30% O2/He, the mean ignition time was 60 +/- 0 s. Increasing the oxygen concentration to 40% significantly shortened the ignition time with both helium and nitrogen for the carbon dioxide laser. With the KTP laser, ignition time varied greatly at any oxygen concentration. At 30% O2/He, median ignition time with the KTP laser was 6.9 s (mean time 15.6 +/- 19.5 s), whereas at 30% O2/He, median time was 8.6 s, (mean time 9.9 +/- 5.33 s). No statistically significant differences were found for the ignition times in the KTP laser groups.
Conclusions: Using helium instead of nitrogen with oxygen delays unmarked polyvinyl chloride tracheal tube ignition time when the tube segments are exposed to a carbon dioxide laser beam as compared to a KTP laser. The different laser wavelengths and penetration properties may produce this difference. The helium protocol previously described has been proven safe only with the carbon dioxide laser and should be tested with other laser types before being used clinically with these lasers.
(C) 1994 American Society of Anesthesiologists, Inc.