Editor's Note: This article is an abbreviated version of a guide prepared by ASTM Subcommittee F29.02.10. Reprints of the original document are available from APSF. Address correspondence to APSF in Park Ridge, IL. by The ASTM Subcommittee F29.02.10: Annette G. Pashayan, M.D., Gerald Wolf, M.D. Allan Gottschalk, M.D., Tom Keon, M.D., Jay Crowley, B.S., M.E., Albert De Richmond, M.S., P.E., and Robert Virag, B.S., M.S. 

Dr. Pashayan is Associate Professor of Anesthesiology and Neurosurgery, University of Florida College of Medicine. Dr. Wolf is Professor of Clinical Anesthesiology, State University of New York. Dr. Gottschalk is Assistant Professor of Anesthesiology, University of Pennsylvania. Dr. Keon is Associate Professor of Anesthesiology, Children's Hospital of Philadelphia. Mr. Crowley is Systems Engineer, U. S. Food and Drug Administration. Mr. De Richmond is Senior Project Engineer, Emergency Codes and Regulations Institute, and Mr. Virag of Director of Research and Development, Mallinckrodt. 

Lasers provide a source of intense energy that can ignite flammable material, such as tracheal tubes, catheters, sponges, or latex gloves, in the operative field. 

Risk of fire is particularly enhanced in oxygen (02) and nitrous oxide (N20) enriched atmospheres. At the present time, we have no means of abolishing the risk of an airway fire during laser use. But there are available methods of airway management that reduce the risk of fire during operations in which a laser is used. Each method has its own risks and benefits. This guide summarizes current methods and informs clinicians of each method's applications, advantages, and disadvantages. No significance should be associated with order in which these practices are presented herein. This guide serves to assist the anesthesiologist and airway surgeon in their joint decision regarding selection of the most appropriate method for the individual patient and the wavelength of the laser to be used. This guide does not prescribe any one method of airway management. Decisions regarding practice methods can only be made by clinicians who have knowledge of the practice options as well as the needs of the individual patient. 

Non-intubation Technique 
These methods of ventilation do not use a tracheal tube. All non-intubation techniques have the following advantages: (1) there is no flammable material in the airway so that the risk of fire is minimized; (2) the method provides excellent visibility of the surgical field; (3) the potential trauma to the airway that a tracheal tube might cause is avoided. 

Spontaneous Breathing Techniques 
With the patient breathing spontaneously, an oxygen-enriched gas with or without potent inhalation anesthetic is insulated through a side port of the operating laryngoscope, a metal hook, or a catheter.' The anesthetic may be supplemented with intravenous agents and/or regional anesthesia to the airway. Disadvantages: Adequacy of ventilation cannot be assessed with capnography or spirometry. Pulmonary aspiration of gastric contents, surgical debris, and/or laser plume as well as inadvertent laser bum to the trachea are a risk since no tracheal tube is present. Ventilation cannot be assisted or controlled. Depth of anesthesia may fluctuate, and the patient may move. Insufflation techniques make scavenging anesthetic gases difficult. The risk of fire is increased if a flammable catheter is used as the insulation device. 

Apneic Techniques 
The patient s lungs are ventilated with a mask, through a tracheal tube, or via a bronchoscope using an oxygen-enriched gas, with or without potent inhalation anesthetic. The anesthetic may be supplemented with intravenous agents, muscle relaxants, and/or regional anesthesia to the airway. During ventilation, the laser is not used. Ventilation is then temporarily discontinued, and the mask or tracheal tube is removed. During apnea, 02 may be insulated while laser resection is performed with no flammable materials in the airway. After a period of time, laser resection is discontinued and ventilation is resumed. Periods of ventilation alternate with periods of laser resection/apnea. Disadvantages: Hypoventilation is a risk which may go undetected since capnography and spirometry are not applicable during apnea. Pulmonary aspiration of gastric contents, surgical debris, and/or laser plume as well as inadvertent laser bum to the trachea are a risk since no tracheal tube is present. 

Jet Ventilation Technique 
A metal needle or similar device is mounted in the operating laryngoscope and attached to a jet injector. The surgeon directs a high-velocity jet of 02 into the airway lurnen either above or below the glottis. The lungs are thereby ventilated with 02 and entrained room air.' Anesthesia is provided by intravenous agents supplemented by muscle relaxants. Disadvantages: Hypoventilation can be a problem with this technique due to any of the following: obstructive airway lesions, decreased pulmonary compliance (e.g., bronchospasm, obesity, or chronic obstructive pulmonary disease), and/or inability of the surgeon to direct the jet correctly. Adequacy of ventilation cannot be assessed by spirometry or capnography. The inspired 02 concentration cannot be controlled or monitored. Pulmonary aspiration of gastric contents, surgical debris, and/or laser plume, as well as inadvertent laser bum to the trachea, are a risk since no tracheal tube is present. Misdirection of the jet may cause gastric distention or barotrauma including pneumothorax and pneumomediastinum. With this technique, it is difficult to administer inhalation anesthetics. 

Intubation Techniques 
With intubation techniques, ventilation can be monitored and controlled, and both inhalation and intravenous agents can be administered. However, an 'ideal tracheal tube,' which does not ignite and yet has all of the characteristics of conventional tracheal tubes specified in ASTM F1242 (standard specification for cuffed and uncuffed tracheal tubes), does not exist. Therefore, this guide will now describe current intubation practices and how they affect the risk of airway fire. 

Conventional Tubes 
Conventional tubes may consist of polyvinyl chloride (PVC), red rubber, or silicone rubber. Polyvinyl chloride tracheal tubes are highly combustible when used in an oxidizing atmosphere. In certain well-controlled conditions, PVC does not ignite when in contact with the laser,(3) and FVC tracheal tubes have been used without causing fires when all conditions are met.(4) However, these conditions may be difficult to maintain in a clinical setting. Manufacturers discourage the use of unprotected PVC tracheal tubes in airway operations in which a laser is used. Presently available studies indicate that red rubber and silicone rubber tubes combust more readily than PVC tubes in air.(5) However, red rubber is more resistant to puncture and ignition by C02 laser energy than is PVC.(6) PVC tubes, if ignited, soften and deform. Silicone tubes, if ignited, become a brittle ash that crumbles easily and can separate and lead to retention of segments within the airway or be aspirated. In contrast, red rubber tubes, if ignited, tend to maintain their structural integrity. Each of the conventional tube materials has its own advantages and disadvantages for use with lasers (see Table 1). Advantages: Conventional tracheal tubes do not reflect laser light and so avoid injury to non-targeted tissue. These tubes and attached components are provided in sterile, preassembled, ready-to-use form and are intended for single use. These tubes do not retain and transfer heat to adjacent tissues, and meet standard specifications for cuffed and uncuffed tracheal tubes as outlined in ASTM F1242. Polyvinyl chloride tubes are transparent and so condensation of airway vapor and evidence of combustion can be seen within the lumens. Disadvantages: Tracheal tubes made of conventional materials readily ignite and maintain combustion in the presence of oxidizing atmospheres. In the event of such a fire, the tube integrity may be compromised, allowing components to be retained within the tracheobronchial tree. Conventional tubes can produce products of combustion which are toxic to human tissue.(7) 

Conventional Tubes with Protection 
Flammable materials such as PVC, red rubber, and silicone can be wrapped with metallic tape, metallic backed surgical sponges, or other materials to shield the flammable material from laser contact. Advantages: Metallic wrapping may prevent the laser beam from igniting the tube yet still allow use of a conventional tracheal tube. A metallic backed surgical sponge has been designed specifically for use in airway laser operations. Disadvantages: Metallic tapes may reflect the laser beam onto nontargeted tissues. The user must apply the tape smoothly and
continuously so as to prevent rough edges, which may abrade mucosa, and to prevent gaps, which expose the tube to the laser beam. The tape may cause the tube to kink. The metal backed sponge preparation diffuses beam reflection but adds considerable thickness to the tube; the sponge must be kept wet to avoid thermal injury, tissue abrasion, and fire. If the tape or wrap is dislodged, it may occlude the airway. &-cause tubes cannot be wrapped at or below the cuff, this area remains exposed and vulnerable to laser energy. The adhesive backing or surface coating of some tapes can be ignited by laser beams. Not all metallic tapes can protect all types of tubes from all types of lasers at every power setting. (8,9,10) Metallic wrapping does not necessarily confer an advantage when the site of operation is distal to the tube and/or the laser beam is delivered through the lumen of the tube. Sterility is difficult to maintain when tubes are prepared in this manner. Presently available metallic tapes have not been specifically designed for medical use. Therefore laser protection of tracheal tubes, other than that specified in certain products, is not the responsibility of the manufacturer of the product. 

Ready-to-use, Laser-resistant Tubes 
These are commercially available products designed for use during operations on the upper airway in which a laser is used. Many of these products have flammable components that can ignite if manufacturers' warnings, precautions, and directions for use are not followed. 
Aluminum and silicone rubber spiral with a silicone covering and a self-inflating foam sponge cuff (Fome-Cuf, Bivona, Inc., Gary IN). This item is intended for use with carbon dioxide (CO2) laser. Advantages: A traumatic external surface with a nonflammable inner surface. The cuff tends to maintain a seal despite penetration by the laser. Disadvantages: Flammable external surface and cuff. It may be difficult and time consuming to deflate the cuff if the cuff or inflation tube is damaged. 
Airtight stainless steel corrugated spiral with a PVC Murphy eye tip and double cuffs (Laser Flex. Mallinckrodt, St. Louis. MO). An uncuffed version is available for pediatric use. This item is intended for use with C02 or potassium titanyl phosphate (KTP) lasers. Advantages: Metal components are noninflammable. The tube maintains its shape during intubation and is kink resistant. The proximal cuff serves as a shield for the distal tracheal cuff. Disadvantages: Although metal may reflect the laser onto non-targeted tissues and result in damage, the matte finish and convexity of this product reduce this potential. The cuffed model contains materials which are flammable and requires that the cuff be inflated with saline to decrease the risk of ignition. Metal tubes are thick walled. The double cuff takes more time to inflate and deflate than a single cuff. Metal may transfer heat to adjacent tissue and other materials. 
Silicone rubber tube covered with an aluminum-filled silicone layer (Laser-Shield. Xomed. Inc.. Jacksonville. FL). This item, intended for use with the C02 laser, is no longer manufactured but may still be present in hospital inventory. Advantages: General characteristics similar to unwrapped conventional tracheal tubes (se above). Disadvantages: Can be ignited by lasers in the presence of room air and is difficult to extinguish once ignited. 
Silicone rubber tube wrapped with aluminum and wrapped over with teflon (no adhesive is used in this process) (Laser-Shield 11. Xomed. Inc., Jacksonville, FL). This item has replaced the original Laser-Shield. Methylene blue is contained in the pilot balloon. This item is intended for use with CO2 and KTP lasers. Advantages: The wrapping may prevent the laser beam from igniting the tube yet still allow use of a pliable tracheal tube. The Teflon coating is smoother and less traumatic than most manually wrapped tubes. The methylene blue in the pilot balloon will mix with normal saline and provide a marker of cuff perforation. An additional advantage of this product over tubes wrapped by the practitioner is that it is preassembled and quality checked by the manufacturer. Disadvantages: If the tape is dislodged it can occlude the airway. Tubes cannot be wrapped on or below the cuff, so this area remains exposed and vulnerable to laser energy. These tubes confer no advantage when the site of operation is distal to the tube and/or the laser beam is delivered through the lumen of the tube. Combustion and pyrolysis of Teflon yields toxic fluorinated by-products. 
Silicone rubber tube uniformly impregnated with ceramic particles (LaserShielding Tube, Phycon, Fuji Systems, Tokyo, JAPAN). Intended for use with Nd:YAG and C02 lasers. Advantages: General characteristics similar to unwrapped conventional tracheal tubes (see above). The cuff is thicker on the machine side to provide somewhat better resistance to laser puncture than most cuffs. Disadvantages: Can be ignited or punctured by laser energy. (11) 
Metal Tracheal Tubes (12). A flexible, non-airtight, interlocked metal spiral tube with a standard 15-mm tracheal tube adapter attached, these tubes are no longer manufactured but since they are reusable, they may still be in use. A polyvinyl chloride (PVC) or latex cuff may be attached by the user. Advantages: Under these conditions, metal is nonflammable. Disadvantages: These metal tubes are technically difficult to place in the airway and have joints through which airway gas can leak. Applying a cuff to the tube adds flammable material to the system. Metal may reflect the laser energy to nontargeted tissues and result in damage. The corrugated outer surface of metal tubes may injure mucosa. Metal tubes are thick walled. Metal may transfer heat to adjacent tissues and other material. 

Additional Protective Measures 

The following additional measures should be taken to help reduce the risk of fire: 

Limitation of oxidizers. The FiO2 should be limited to the lowest concentration necessary to maintain acceptable arterial 02 saturation. The balance of the fresh gas flow should be nitrogen and/or helium (3) potent nonflammable inhalation agents may be added as clinically indicated. Nitrous oxide should not be used. (3,6) 
Limitation of power density. The laser output should be limited to the lowest clinically acceptable power density and pulse duration. 
Saline-filled cuffs. Filling tracheal tube cuffs with saline serves as a protection against fire should the laser beam strike the cuff. However, the addition of fluid to the cuff system may prolong the process of cuff deflation. Methylene blue or other biocompatible and highly visible dye may be added to the saline to help detect cuff perforation. 
Saline-soaked pledgets. In order to provide some protection for the cuff, saline-soaked pledgets should be applied to reduce the likelihood of laser hit. The pledgets must be layered sufficiently and placed carefully to reduce the possibility of penetration. Pledgets, if not kept wet, may ignite. Nonmetallic strings attached to the pledgets can be severed and ignited by the laser. Care must be taken to retrieve 0 pledgets at the end of the operation. 
Other. Nonreflective operating platforms and other tissue-protective devices should be used whenever possible. 

Since the only way to totally avoid a laser fire is to avoid use of the laser, practitioners must be prepared for such an event. Management of airway fires will be the subject of a future newsletter. 
References 

1. Johan TG, Reichert TJ. An insulation device for anesthesia during subglottic carbon dioxide laser microsurgery in children. Anesth Analg 63:368-370,1984. 
2. Ruder CD, Raphael NL, Abramson AL, Oliverio RM. Anesthesia for carbon dioxide laser microsurgery of the larynx. Otolaryngol Head Neck Surg 89:732-737,1981. 
3. Pashayan AG, Gravenstein JS, Helium retards endotracheal fires from carbon dioxide lasers. Anesthesiology 62:274-277,1985. 
4. Pashayan AG, Gravenstein IS, Cassisi NJ, McLaughlin G. The helium protocol for laryngotracheal operation with C02 laser: a retrospective review of 523 cases. Anesthesiology 68:801-804,1988. 
5. Wolf GL, Simpson JI. Flammability of endotracheal tubes in oxygen and nitrous oxide enriched atmosphere. Anesthesiology 67-.236-239,1987. 
6. Ossoff RH. Laser safety in otolaryngology head and neck surgery: anesthetic and educational considerations for laryngeal surgery. Laryngoscope (suppl 48) 99: I26,1989. 
7. Ossoff RH, Duncavage JA, Eisenman T'S, Kartan MS. Comparison of tracheal damage from laser-ignited endotracheal tube fires. Ann Otol Rhinol Laryngol 92:333-336, 1983. 
8. Sosis M. Evaluation of five metallic tapes for protection of endotracheal tubes during C02 laser surgery. Anesth Analg 68:392-393,1989. 
9. Sosis K Dillon F. What is the safest fog tape for endotracheal tube protection during Nd:YAG laser surgery? A comparative study. Anesthesiology 72:553-555, 1990. 
10. ECRI: Laser resistant endotracheal tubes and wraps. Health Dev 19:112-139,1990. 
11. ECRI: Laser resistant tracheal tubes, Health Dev 21:4-13,1992.
12. Norton ML, de Vos P. New endotracheal tube for laser surgery of the larynx. Ann Otol Rhinol Laryngol 87:554-557,1978. 
13. Oxygen index of flammability: minimum concentration to support candle like combustion of plastics. Oxygen index, ASTM test D2W (08.02).

Michael Walsh, MD, Armin Schubert, MD, and Sawsan AlHaddad, MD. Am J Anesthesiol. 1997;24:189-193.

We tested the ability of a lidocaine jelly and saline mixture injected into the cuff of the endotracheal tube to seal small carbon dioxide (CO2)-laser-induced cuff leaks without increasing the risk of combustion. In part 1, 8 groups of microlaryngeal endotracheal tube (ML-ETT) cuffs were exposed to the CO2 laser with a spot size of 0.8 mm, at various power settings (10 to 40 W) and ambient fraction of inspired oxygen (FiO2) (0.3 to 1.0) for up to 60 seconds. The cuffs were filled with saline, air, or a 1:2 mixture of 2% lidocaine jelly and saline. In part 2, baseline ventilation values were established using a model of positive pressure ventilation. The lidocaine jelly and saline mixture was injected into the laser-perforated cuffs of 24 ML-ETTs, and ventilation was reestablished. Wasted ventilation (extrapolated baseline minus total treatment) at 30 minutes and minute ventilation every 5 minutes were recorded. Cuff perforation occurred in less than 1 second in all groups. None of the saline or jelly plus saline cuffs ignited, even at FiO2 = 0.86 and 40 W. AR air-filled cuffs ignited in 6.24 +/- 2.48 seconds (mean +/- SD); 14 of 24 perforated ML-ETTs maintained adequate ventilation (>86% of control) at all measured intervals. Wasted ventilation was 10.8% +/- 9.5% (mean +/- SD) of extrapolated total ventilation in those tubes effecting a seal. A 2% lidocaine jelly plus saline mixture injected into laser-perforated ML-ETT cuffs effectively seals small leaks while preventing combustion. In a significant number of cases, exchange of the ML-ETT may be delayed or unnecessary.

It has been estimated that only one in ten to one in one hundred operating room fires is reported. The exact incidence is therefore unknown. By "guesstimate," there are probably between one hundred and two hundred operating room fires in the United States per year, as gleaned from FDA reports and ECRI investigations. Approximately 20% of those reported fires result in serious patient injury. The one or two deaths per year are usually secondary to airway fire. Most operating room fires are associated with an oxygen enriched atmosphere which may also include nitrous oxide.

At the ASA Annual Meeting in Dallas in October, there was a Panel presentation entitled "Fire in the Operating Room! Still a Problem" moderated by Gerald L. Wolf, M.D. from SUNY, Brooklyn. Panelists included Carol Hirshman, M.D. from the College of Physicians and Surgeons of Columbia University, George W. Sidebotham, Ph.D., from the Albert Nerken School of Engineering of  The Cooper Union for the Advancement of Science and Art, Frederick W. Williams, Ph.D., Director, Navy Technology Center for Safety and Survivability of the Naval Research Laboratory and Daniel E. Supkis, Jr., M.D., from the Division of Anesthesiology and Critical Care of the MD Anderson Cancer Center, Houston.

Dr. Hirshman discussed various reported operating room fire events published in the medical literature and lay press. She reinforced that these are no longer flammable anesthetic agent fires since halogenation of hydrocarbon anesthetics has made modern anesthetics nonflammable. Included in her discussion were examples of surgical drape fires ignited by the electrosurgical unit in the oxygen enriched atmosphere common to operating rooms, particularly in the area of the head and neck. Also discussed were cases of surgical drape fires ignited by lasers.

Endotracheal tube fires, the most lethal, were also presented in detail. These included electrosurgical ignition of the endotracheal tube in an oxygen- enriched atmosphere during tracheostomy and tonsillectomy. The polyvinyl chloride tube ignition during tracheostomy occurs when the electrosurgical unit is used to incise the pretracheal fascia and trachea, or during cauterization of trachea edge bleeders at the tracheal incision site. Laser ignition of endotracheal tubes during laryngeal surgery was discussed, including ignition of  "laser resistant" endotracheal tubes. A report of a laser igniting a surgeon's glove during jet ventilation was mentioned. Intestinal gas fires and explosions, ignited by an electrosurgical unit or laser were also outlined as significant, potentially lethal, problems.

Prof. Sidebotham reviewed some aspects of combustion science particularly related to the operating room environment. He discussed the three legs of the fire triangle which are required for a fire: the oxidizer, the ignition source, and the fuel. A fire cannot occur if one of these components is absent. A fire may occur if all the physical and chemical factors are present. Air, compressed air, oxygen and nitrous oxide are the oxidizers in the typical operating room. There are many ignition sources, including especially the electrosurgical unit and laser. Potential fuels commonly present include surgical drapes, endotracheal tubes, and alcohol-based prep solutions. A fire is possible when the three legs are present in "appropriate" (combustible) chemical and physical configurations.

Endotracheal tube fires are typically composed of an intraluminal flame traveling along the inner surface of the tube toward the flow of oxidizer and a secondary flame anchored at the downstream end of the tube. The heat from the intraluminal flame vaporizes volatile combustible products from the downstream tube wall that become the fuel for the secondary flame that can shoot out the internal end of an endotracheal tube like a blowtorch, causing massive airway damage.

Dr. Williams reviewed the U.S. Navy's approach to fire safety. Two categories of fire safety were discussed, the passive and active approaches. The passive approach implies minimizing the chance of and damage from a fire by careful assessment and adjustment/regulation of the available fuel load. Decisions, for example: choice of a mattress, are made by balancing comfort and the contribution of the mattress to the total fuel load present in a given environment. Another passive approach is the creation of flame-spread barriers. The active approach refers to the actual method of fire extinguishment. With the phasing out of halon as a fire extinguishing agent because of its environmental impact, other fire extinguishing techniques have been explored. The most promising technique is water droplet delivery to the flaming fuel. Required droplet size is less than 100 microns. The effect of the water droplets is based on expansion to water vapor at the flame origin site thereby diluting available oxygen to the flame below that is required for a sustained flame. The flame is also cooled by the uptake of heat of vaporization of the water droplets.

Dr. Supkis reviewed anesthetic considerations intended to reduce the operating room fire hazard. He discussed the appropriate use of oxygen pointing out the need to consider its concomitant increased fire risk.

The pulse oximeter provides us with a means to assess the need for supplemental oxygen and allows us to withhold supplementation in potentially dangerous situations when it is not really indicated in order to minimize the fire risk. He discussed the appropriate use of the electrosurgical unit, including the increased risk during head and neck procedures during which an oxygen enriched atmosphere is common. He also recommended "holstering" the electrosurgical unit when not in active use to help prevent accidental activation causing ignition. During tracheostomy the use of sharp dissection to enter the trachea is encouraged to avoid ignition of the underlying endotracheal tube in the oxygen and nitrous oxide enriched anesthetic atmosphere. The placement of the laser in "standby" mode when not in active use is mandatory for reasons similar to those for holstering the cautery wand.

For surgery of the upper airway involving a laser, a laser-resistant tube should be utilized, the FiO2 should be kept to 30% or below, and as limited as possible an amount of power should be utilized by the laser. For surgery involving the lower airway, mainly trachea, there are currently no laser resistant tracheal tubes. Therefore, there should be no flammable material below the tip of the laser fibers. FiO2 should be limited to 30% or less without the use of nitrous oxide. If an airway fire is suspected, stop ventilation and immediately disconnect the breathing tube Y-piece from the endotracheal tube adaptor, and in the same motion remove the endotracheal tube and any other airway adjunct from the airway. Then, resume ventilation via bag/mask and re-intubate the patient. Perform rigid and/or flexible bronchoscopy to assess airway damage. Draw blood for carboxy hemoglobin determination to access the amount of smoke the patient has inhaled during the airway fire.

Fires can occur in and around the patient. The use of organic solvents can serve as accelerants to help ignite the draping system. The drapes can be easily ignited by the electrosurgical unit, hot wire cautery and laser devices. It must be remembered that supplemental oxygen supplied to the patient can migrate through the draping system and be trapped between the layers of drapes rendering the draping system layers extremely flammable. Care must be taken in using any source of ignition around the draping system where supplemental oxygen is being employed.

Intestinal gas fire and explosion can occur when ignited by the electrosurgical unit or laser. Sufficient oxygen to support combustion of hydrogen and/or methane is normally not present in intestinal gas. However, the administration of nitrous oxide and its subsequent diffusion into the intestinal lumen can create a flammable premixed fuel/oxygen mixture. The chance of such an explosion/fire is reduced if nitrous oxide is avoided.