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.
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.
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.
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.
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 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.
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.
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