[Ignition and burning of biological tissue under simulated CO2-laser surgery conditions]. / Entflammungs- und Brandverhalten von biologischem Gewebe bei In-vitro-Bestrahlung mit dem CO2-Laser.

BACKGROUND: Laser surgery in endoscopy has greatly enhanced the surgical armamentarium for treating various laryngeal and hypopharyngeal disorders, but harbours a risk of tissue ignition and inflammation of surgical and anaesthetic instrumentation. However, even if non-inflammable material is used, there is still a residual fire hazard from endogenous tissue that may develop an ignitable aerosol (so-called laser smog) as an effect of laser irradiation. The aim of this study was to investigate how tissue carbonisation and vaporisation contributes to the risk of airway fire. METHODS: For the simulation of gas accumulation in the hypopharynx and larynx following the European standard ISO-11990, a cylindrical steel chamber with an open and a closed end has been used to simulate the operative setting. Pork meat chunks with a tissue composition similar to the larynx and hypopharynx such as fat, muscle, cartilage and bone were introduced into this chamber. Ventilation was achieved through jet ventilation with disposable, non-inflammable laser jet catheters. The tissue was then repeatedly exposed to a laser beam in super-pulse mode (pulse rate 250 Hz) with various intensities and exposure lengths at an impact angle of 75 degrees. The laser intensity was varied from 2 to 15 W. The type, duration, intensity and incidence of tissue ignition were recorded and analysed. RESULTS: The degree of tissue ignition correlated with laser intensity. Low laser intensity caused spark formation whereas high intensity resulted in sustained tissue fire. The type of tissue had an impact on ignition intensity thereby showing lower ignition thresholds and higher ignition susceptibility in fat-containing tissue compared to muscle. The most important factor for occurrence of tissue ignition was the chamber oxygen concentration which displayed an inverse correlation with the time until tissue ignition. Oxygen concentrations of 35% led to tissue ignition in 42 s, 40% oxygen in 20 s. Oxygen concentrations higher than 60% resulted in immediate tissue ignition. CONCLUSIONS: Despite the use of non-inflammable materials in endoscopic laser surgery of the upper airway and hypopharynx, the risk of tissue ignition remains due to the inflammable laser smog which is easily ignited in an oxygen-rich environment. Hence to minimise this risk, we recommend using oxygen concentrations lower than 40%, low laser intensities (<6 W) and limiting continuous laser activation to periods shorter than 10 s.

[Laser-resistance of a new jet ventilation catheter (LaserJet) under simulated clinical conditions]. / Verhalten des neuen LaserJet((R))-Katheters bei CO(2)-Laser-Anwendung unter simulierten klinischen Bedingungen.

BACKGROUND: Laser surgery within the airway is often performed with the patient under general anaesthesia and with infraglottic jet ventilation via a specially designed catheter which should not be inflammable. We investigated the laser-resistance of a recently introduced jet ventilation catheter (LaserJet) made of polytetrafluoroethylene. METHODS: For the simulation of gas accumulation in the hypopharynx a cylindric steel chamber with an open and a closed end was used to simulate the operative setting according to the European standard ISO-11990. In a series of 12 tests the disposable laser jet catheter was attached to the proximal end of the oxygen supply tubing, and the distal end was introduced 10 cm into the steel chamber. The catheter was repeatedly exposed to the beam of a CO(2)-laser device with energies varying from 2-15 W and with an impact angle of 75 degrees. The changes in the catheter were assessed with and without an oxygen flow of 6 l/min. Time of exposure varied from 1 to 10 s. Size and nature of the changes in the catheter were documented. RESULTS: We found damage to the catheter that occurred in the following order: simple (front wall) and double perforation (front and back wall), smoke emission as evidence for pyrolysis, discolouration, deformation and rupture. The extent of damage to the catheter shaft under direct laser beam exposition was dependent on the laser intensity. When there was no oxygen flow, a beam of 2 W needed 40 s to perforate the catheter shaft, while with an oxygen flow of 6 l/min, a laser intensity of 4 W needed 20 s to cause perforation. Rupture of the catheter occurred in less than 10 s with a laser intensity of 8 W or more. CONCLUSIONS: We could demonstrate that the LaserJet catheter is not inflammable and also does not sustain fire. However, it is not laser-resistant as to maintaining its texture and shape while under direct exposure to a continuous laser beam, as applied under clinical conditions. Polytetrafluoroethylene deforms and melts at temperatures above 327 degrees C which is usually exceeded by the CO(2)-laser.