Question: “What are the safest endotracheal tubes for use during ND-YAG and C02 laser treatment of the upper airway?”
Answer: This question, like many apparently simple questions, must receive a hedged answer with caveats. Although the American National Standards Institute has addressed this issue’, its directives are rather general and some confusion exists now about choices.
The primary concern in using lasers in the aerodigestive tract is fire (6): not primarily of the tissues, which because of their water content provide a large heat sink and a relatively noncombustible substrate, but of the endotracheal tube. The localized fire caused by the laser beam striking combustible material may initiate a blowtorch-like combustion that can rage down the tracheal tube, sustained by the oxidizers oxygen and nitrous oxide, and devastate the respiratory tract with severe bums (5).
Efforts at preventing laser-induced combustion in the aerodigestive tract consist of:
1) Reducing the concentration of oxygen and nitrous oxide in the inspired gas and the ambient gas surrounding flammable materials (20)
2) Reducing the flammability of endotracheal tubes placed in the path of the laser (7,8,ll,l8)
3) Keeping energy levels and firing times as short as practicable.
Since lasers remove tissue by heating cellular water and thus bursting cells with the steam generated, combustion is not necessary for the beneficial effects of laser surgery. Tissue combustion (and consequent smoke) can be decreased by using concentrations of oxygen approaching that of room air, if such low concentrations are appropriate for the patient under anesthesia (frequently not the case). In addition, the use of helium instead of nitrous oxide as a dilutent increases the time required for ignition of some tracheal tubes by as much as 100% due to the increased thermal diffusivity of the gas mixture (18).
One approach to preventing ignition of the endotrachial tube by the laser is not have one in place when the laser is Firing. This can be accomplished by spontaneous ventilation with insulation, jet venturi ventilation via special attachments to the suspension laryngoscope (9,10,15,16,21,22)or by successive periods of hyperventilation with an endotracheal tube separated by apneic laser intervals with the tube removed.
Two basic types of endotracheal tubes for laser surgery are still acceptable for use (in spite of strong statements in the literature condemning one and praising the other): non-flammable metal tubes and tubes of potentially flammable materials that have been rendered resistant to ignition by some means. A variety of metal tubes have been proposed;2,12 with two exceptions 16, all are uncuffed. They have a relatively small internal/external diameter ratio, thus restricting their use in pediatric patients. ‘mere is some degree of reflection of the laser off the tube to adjacent tissues, there may be heating of the tube with resultant thermal injury, and cleaning is problematic because of the crevices inherent in their spiral construction. Nevertheless, some institutions live with these problems, preferring the impossibility of ignition.
Several papers have discussed both ignition and flammability of endotracheal tubes (1) in atmospheres of varying concentrations of oxygen and/or nitrous oxide, (2) with varying power of the lasers, (3) with different wavelengths of lasers, and (4) with different combinations of tube materials and provide schemes. lotion, the tendency of a tube to begin to bum, is divided into two categories: external ignition, which occurs when sufficient thermal energy is transferred from the laser to the tube material, and internal ignition, which happens when the laser penetrates the tube material and combustion is supported by the respiratory gases. Flammability refers to the ability of the tube material to support combustion continuously once ignition has occurred. Ignitability and flammability of tube materials do not necessarily correlate with one another.
Tube materials vary considerably in their ignitiability and flammability, and research data are hard to compare without standardization of ambient atmosphere inside and outside the tube, laser type, power, pulse duration and repetitions, or maximum continuous application of the laser to the tube. Certain common factors emerge from the literature, however. Some authors have suggested that tubes made of polyvinyl chloride should not be used with lasers in the aerodigestive tract (11, 17, 18) because of their susceptibility to easy penetration by both C02 and Nd-YAG lasers and their subsequent internal ignition. Tubes of silicone tend to be resistant to lower laser energies, but when they do bum they leave silica ash in the respiratory tract, a fact of unknown significance (5,13,20). The, is a special-material “laser shield” tube. Although initial reports with lower power lasers were promising (8), it appears to fall apart with violent ignition and flammability at high laser energies, arguably higher than clinically likely (18). In the event of an incorrect power setting, however, the initial impulse might prove dangerous for the patient.
The red-rubber tube has the disadvantage of a high-pressure low-volume latex cuff, is relatively susceptible to ignition, but is resistant to continuous combustion (7,11,18,20). Aside from generating quantities of black smoke, the tube tends to hang together because the hole created by the laser tends not to extend, and a blowtorch-like flammability is not such a problem, particularly at lower 02 and N20 concentrations. Finally, these tubes can be protected dependably from ignition with reflective aluminum or copper tape (18)
Use of metallic tapes has a checkered past, since not all tapes are created equal. Earlier studies failed to show protection, but they used inferior tapes compared to those used in later studies. Sosis et al. (18) found the 3M #425 tape (3M Corp., Minneapolis, MN) offered the best protection against ND-YAG laser followed by I mm thick copper foil (Venture Tape Corp., Rockland, MA). These tapes were also protective against the C02 laser at high outputs. Other tapes tested offered varying degrees of protection or no protection. Controversy still exists about whether to wrap the tubes in a continuous spiral from cuff to connector or to use an overlap wrapping of a single larger piece laid longitudinally against the tube. In either case, the possibility of shredding, kinking, tissue damage including epistaxis and tape delamination with exposure to the laser must be considered. Also, reflections may contribute to unwanted tissue damage in non-diseased areas. In addition, protection of all printed areas, and the barium stripe, if present, from exposure to the laser helps minimize laser penetration due to energy absorption by the markings.
Tubes can be protected as far as they can be wrapped. They are vulnerable at the cuff and the distal unprotected tube tip. Protection of the tracheal tube cuff is problematic, since the wall is so thin, and a leak of respiratory gases caused by a ruptured cuff may accelerate ignition by an external hit of the laser on tube or tissues. Many use saline to inflate the cuff, since the water acts as a heat sink, and any holes caused by the laser immediately spray saline over the area, protecting against combustion. Deflating the cuff for extubation in case of a fire in the tube shaft may be much slower, however. Others use saline-soaked cotton pledgets or patties, whose strings, unless made of wire, are flammable, too. The pledgets may dry out and be ignited, also.
In summary, intelligent choice of an appropriate endotracheal tube for laser surgery involves planning: (1) Whether a tube needs to be present during Laser impulses; (2) A cuffed versus uncuffed tube; (3) Whether a metallic or nonmetallic tube will be used; (4) How a nonmetallic tube will be protected, both shaft and cuff; (5) What cumbustion-supporting gas concentrations will be necessary in the tube during laser therapy; and (6) Confirming that the wavelength of laser used really is safe for the tube planned (if the combination of tube and laser is new, it is prudent to conduct on-site tests before clinical use).
Answer by Reynolds J. Saunders, M.D., Staff Anesthesiologist and Co-Chairman, Quality Assurance Committee, Cedars -Sinai Medical Center, Los Angles.
1. American National Standards Institute Z 1 36.3 (1987): American national standard for the safe use of lasei3 in health care facilities.
2. Bradley IP. flexible metal endotracheal tubes for ENT laser surgery [letter] Anaesth Intensive Care 1987; 15:248-9.
3. Brightwell AP. A complication of the use of the laser in ENT surgery. J. Laryngol Otol 1983;97: 671-2.
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17. Sosis M. Polyvinylchloride endotracheal tubes are hazardous for C02 laser surgery [letter] Anesthesiology 1988;69:801-2.
18. Sosis M. Evaluation of five metallic tapes for protection of endotracheal tubes during C02 laser surgery. Anesth Analg 1989; 68:392-3.
19. Thode SA. Laryngo-tracheal laser surgery and general anesthesia. Lasers Surgery Mod 1986;6:369-72.
20. Waif GL; Simpson 11. Flammability of endotracheal tubes in oxygen and nitrous oxide enriched atmosphere Anesthesiology 1987;67:236-9.
2 1. Woo P; Strong MS. Venturi jet ventilation through the metal endo-tracheal tube: a nonflammable system. Ann Otol Rhinol Laryngol 1983;92:405-7.
22. Woo P; Vaughan CW. A safe, nonflammable, all metal, cuffless endotracheal Venturi ventilation system for use in laser surgery. Otolaryngol Head Neck Surgery 1983;91:497-501.