Positive end-expiratory pressure lowers the risk of laser-induced polyvinylchloride tracheal-tube fires

The possibility of ignition of polyvinylchloride (PVC) tracheal tubes by a CO2 laser is of concern in patients undergoing CO2 laser surgery of the airway. The authors analyzed the ignition of PVC tracheal tubes by a CO2 laser beam to determine what variables were involved, and then designed a study to determine how they affect the incidence of such fires.

For the analysis, PVC tracheal tubes were enclosed in a clear plexiglass enclosure and a laser beam was focused on the tubes. The enclosure contained one of three different gas combinations. A high-speed camera photographed the tubes during the analysis and showed that tracheal tube perforation always preceded ignition in all three gas combinations. These results led to the hypothesis that intraluminal gauge pressure (IGP) may be an important variable, because it would affect the flow of O2 across the perforation. This hypothesis was tested by aiming a CO2 laser beam at PVC tracheal tubes and varying IGP in 0.25-cm H2O increments, from 0.25 to 28 cm H2O, while nitrogen or helium containing O2 at 40, 50, or 60% flowed through the tubes. To simulate the clinical effect of IGP on PVC tracheal tube ignition, we used a mechanical lung model connected to an anesthesia breathing circuit with a standing bellows ventilator in which 60% He and 40% O2 flowed through a PVC tracheal tube. Laser beam exposure was started at three different times during the respiratory cycle: at the start of inspiration, at the end of inspiration, or at the end of expiration. Also, for each condition, trials were made at baseline circuit pressure (2.5 cm H2O) and at 5.0 cm H2O by the addition of 2.5 cm H2O positive end-expiratory pressure (PEEP) applied to the circuit.

The incidence of tracheal tube ignition decreased as IGP increased. The IGP at which ignition did not occur (which increased as O2 concentration increased) did not differ between N2 and He at 40% O2, but was twice as high with N2 as with He at O2 of 50% and 60%. Fires never occurred when PEEP was added to the system and, when PEEP was not added, always started during the last 2 s of end expiration (when airway pressure is lowest), regardless of when the laser beam was activated.

It is recommended that, in addition to other safety practices, PEEP be added to the breathing circuit during CO2 laser operations on the airway in which PVC tracheal tubes or laser-resistant tracheal tubes with PVC components are used.