The history and development of lasers parallels our understanding of electromagnetic radiation, ions, molecules, and atoms. In 1900, Max Planck revised his earlier work on radiation and the absorption of light and heat by a black body (i.e., a perfect absorber).⁴⁰ He proposed that electromagnetic energy could be emitted only in quantized form. In this process, called the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from short-wavelength electromagnetic radiation, such as visible or ultraviolet light. In 1905, Albert Einstein described how the photoelectric effect was caused by absorption of quanta of light (i.e., photons) and explained that the energy of these quanta was directly related to the frequency of the radiation absorbed. From these observations, Einstein developed his ideas on quantum mechanics, and in 1917, he developed the quantum theory of radiation,^41,⁴² in which he discussed the interactions of atoms, ions, molecules, photons, and electromagnetic radiation. According to the quantum theory of radiation, electrons, atoms, molecules, and photons interact with electromagnetic radiation of quantum units by absorption, spontaneous emission, and stimulated emission.⁴³

In 1954, Charles Townes described the first amplification and generation of electromagnetic waves by stimulated emission by using microwaves, which he called microwave amplification by the stimulated emission of radiation (MASER). In 1960, Theodore Maiman produced light amplification by the stimulated emission of radiation (LASER) using a ruby crystal and red light. Throughout the 1960s and 1970s, many substrates and ions were tried as the laser medium. Some, such as the carbon dioxide (CO₂) laser, were successfully developed, found to be useful in medical practice, and are still used.⁴⁴

B Physics

An atom consists of a nucleus around which electrons orbit in discreet shells. These shells, or orbits, have specific energy levels associated with them. Electrons in the stable ground state occupy the lowest orbit, which is closest to the nucleus and has the lowest energy level. Electrons can move from one orbit to a higher-level orbit by absorbing energy, or they can move from a higher-level orbit to a lower level by emitting energy. The energy absorbed or emitted is exactly equal to the difference between the orbital energy levels, and it can take the form of a photon, which is the elementary particle of light and a quantum of electromagnetic energy.

In absorption, an electron is boosted to a higher energy level by absorption of the energy of a colliding photon. The natural state for matter is to be at the lowest energy level. An electron in a higher orbit will spontaneously drop back to the lowest-energy orbit possible and emit energy as a photon, which is exactly equal to the photon required to take the electron to the higher orbit. This process, known as spontaneous emission, occurs in a random manner that results in incoherent light.

In 1917, Einstein postulated that if a photon released from an excited atom collided with another atom already in the excited state, the second atom would release two photons with the same wavelength, phase, and direction (i.e., identical photons). If these two photons stimulated more excited atoms, more identical photons would be released. Einstein called this process stimulated emission of radiation, and it is the basic principle of laser physics (Fig. 40-2).⁴⁵

Figure 40-2 The processes of absorption, spontaneous emission, and stimulated emission are necessary for a laser to operate. Top: In an excited state (i.e., electron in a higher-energy orbit), the electron is unstable and reemits this energy (i.e., spontaneous emission). Middle: A photon or light packet with energy (hν) or another power source can provide the energy necessary to raise the energy level of electrons from the ground state to an excited state (i.e., absorption). Bottom: A photon of the appropriate energy impinging on an electron in the excited state causes the release of a second photon of the same energy (i.e., stimulated emission). The latter photon travels in the same direction and is in phase with the first photon.

The energy of a photon is proportional to the frequency of light and is described by the following equation:

where

e = quantum energy

h = Planck’s constant

λ = wavelength

All lasers consist of a laser medium (e.g., CO₂, argon) contained in an optical cavity between two mirrors, one totally reflecting and one partially reflecting mirror. An external energy source continuously excites or pumps the laser medium, causing many of the atoms to reach a higher energy level (Fig. 40-3). When more than one half of the atoms are in an excited state, a population inversion has taken place. In this state, spontaneous emission occurs in every direction, but photons emitted in the direction of the optical cavity strike the mirror and are reflected back, striking excited atoms, and resulting in stimulated emission. This process repeats itself at an increasing rate with each passage of the photons reflected off the mirrors through the laser medium, generating a huge number of identical photons that all have the same wavelength, phase, and direction. The partially reflecting mirror lets a small amount of this energy escape through the aperture, creating the laser beam.

Figure 40-3 Laser apparatus. A power source (yellow box) stimulates the lasing medium (inside the cylinder within the gray box). The spontaneous emission of photons from electrons in the excited state stimulates the emission of more photons. The parallel mirrors (circles at the ends of the gray box) reflect the photons traveling along the axis of the laser, amplifying the intensity of the radiation. This results in a coherent monochromatic laser beam emerging from the partially reflective mirror (red arrow).

Laser light may be in the invisible infrared, visible, or ultraviolet part of the electromagnetic radiation spectrum. It is monochromatic, with all the photons having the same wavelength, and collimated, allowing the beam to be intense and unidirectional, with no divergence, preventing spread as the light moves farther away. The laser light is coherent spatially and temporally, with all the photons in phase, and it has high energy density.

C Laser Parameters

The operator can select three parameters to alter the effectiveness of the laser on tissue by adjusting the exposure time, spot size, and power.

D Laser-Tissue Interaction

When a laser interacts with tissues, the energy can be reflected, absorbed, conducted as heat, or scattered. The extent to which these processes occur depends on the type of laser used and the tissue with which it interacts. Laser wavelengths depend on the medium, and the degree of absorption depends on the target tissue components. The CO₂ laser (10,600-nm wavelength) is particularly well absorbed by water, whereas the neodymium : yttrium-aluminum-garnet (Nd : YAG) laser (1064-nm wavelength) is absorbed less by water and creates more energy scatter. The argon laser (488- and 514-nm wavelengths) and potassium titanyl phosphate (KTP) laser (532-nm wavelength) are in the visible spectrum, and their energies are absorbed well by pigments such as melanin and hemoglobin. For the most commonly used lasers in medicine, absorption of laser energy excites the atoms within tissues, which produces heat (Fig. 40-4).

Figure 40-4 The surface of an orange after a CO₂ laser strike shows charring and carbon debris deposited at around 350° C. The words Benumof and Hagberg can be seen.

The CO₂ laser heats the water within cells, and as the temperature rises to about 65° C, proteins denature and thermal necrosis occurs. As the heating continues and the temperature reaches 100° C, the water within the cell boils and produces water vapor; this leads to an explosive vaporization, and the cell explodes. The tissue surface in contact with the CO₂ laser disintegrates and undergoes charring, with carbon debris deposited at about 350° C. There is little damage to the underlying structures. Surrounding the charred area is a zone of thermal necrosis, and around this is an area of thermal conductivity and repair.⁴⁸

E Laser Classification

The American National Standards Institute (ANSI Z136 report on safe use of lasers) and the International Standard International Electrotechnical Commission (IEC 60825 report on the safety of laser products) define four classes of laser according to their power and wavelength:

Class 1. These lasers are considered safe, with no risk when viewed by the naked eye. Class 1M denotes that the beam is potentially hazardous if it is viewed with an optical instrument, such as a microscope.

Class 2. These lasers emit low-power visible radiation in the range of 400 to 700 nm. An aversion reaction or blink reflex limits exposure to less than 0.25 seconds and provides protection from equipment such as a laser pointer. Class 2M devices are the same as class 2, but they may be hazardous if viewed with an optical instrument.

Class 3. A class 3R laser is considered safe with restricted beam viewing, and if the maximum permissible exposure is exceeded, the risk of injury is low. Class 3B lasers are hazardous if the eye is exposed directly, and protective eyewear is required if direct viewing of a laser beam may occur. A key switch and safety interlock must be present on all class 3B lasers.

Class 4. Most medical lasers belong in this class and pose dangers to the eye, skin, and combustible material. They are a fire risk and produce air contaminants and plumes. All class 3B and class 4 lasers must be operated by trained, authorized personnel and be equipped with a key switch and a safety interlock.

F Types of Laser

Lasers are named according to their medium, which can be a gas, solid, liquid, or semiconductor. Many types of lasers exist, and their clinical application depends on their wavelength, tissue absorptive characteristics, cost, ease of use, and safety. Lasers have differences in their emitted wavelength, output power, mode of operation (i.e., pulsed or continuous mode), and application (i.e., contact or noncontact). For laser airway surgery, the CO₂, argon, Nd : YAG, KTP, and diode lasers are the most commonly used (Table 40-1).

TABLE 40-1 Characteristics of Commonly Used Medical Lasers

1 Carbon Dioxide Laser

The CO₂ laser has been used for many otolaryngology and head and neck surgical procedures and in gynecologic surgery for the treatment of intraepithelial neoplasms, condylomata acuminata, and other lesions. It is the most commonly used laser for airway surgery and is particularly suited to laryngeal and head and neck surgical procedures (Fig. 40-5).

Figure 40-5 The CO₂ laser (AcuPulse, Lumenis, Yokneam, Israel) has an articulating arm for attachment to a surgical microscope or handheld device. The coaxial helium-neon, low-intensity laser can be seen as a continuous, visible red light.

This laser uses CO₂ mixed with nitrogen and helium as its medium. The nitrogen is used to aid in energy transfer to the upper excitation level of the CO₂ molecule. The CO₂ laser emits invisible infrared light at a wavelength of 10,600 nm in the infrared range of the electromagnetic spectrum, and the light cannot be seen by the human eye. To allow the CO₂ laser to be seen, a second, coaxial helium-neon (He-Ne) laser is incorporated into the CO₂ laser and acts as a pointer. The low-intensity (0.8-mW) He-Ne laser has a wavelength of 6328 nm, which is within the visible part of the electromagnetic spectrum, and the light is red. As soon as the CO₂ laser is switched on, this visible red light is seen continuously and independently of the status of the CO₂ laser. The He-Ne laser must be aligned with the CO₂ laser in the coaxial arrangement, and the alignment must be checked before use. If the coaxial arrangement is not aligned, the CO₂ laser and the He-Ne beam will strike different areas, resulting in destruction of healthy tissue or increasing the risk of an airway fire.

The CO₂ laser is preferred for laryngeal lesions. It is used for the treatment of benign laryngeal pathology, such as nodules, polyps, papillomas, granulomas, Reinke’s edema, webs, hemangiomas, subglottic stenosis, and arytenoidectomy, and for phonosurgical procedures. CO₂ lasers allow precise cutting and shallow penetration of tissues. These qualities are imperative for removal of lesions situated in the supraglottic or immediate subglottic regions. It can be used for leukoplakia on the vocal cord and within the oral cavity. Transoral laser procedures use a CO₂ laser to excise and debulk tumors within the oral cavity and from the vocal cord itself. Many early vocal cord tumors are treated with excision by a CO₂ laser.

The CO₂ laser can be used in a continuous, pulsed, or superpulsed mode. The superpulsed mode reduces the exposure time to a few nanoseconds while delivering high energies of 400 to 500 W with each peak (Fig. 40-6). The rest time between each peak allows the tissues to cool and reduces thermal injury to adjacent tissues.

Figure 40-6 CO₂ laser parameters include continuous, pulsed, and superpulsed modes.

The CO₂ laser can be attached to an operating microscope or a handheld device so it can be used for intraoral procedures such as palatal surgery. CO₂ laser energy is highly absorbed by water, and because water is the primary component of most biologic tissue, CO₂ laser energy is highly absorbed by most tissues. It is readily absorbed by the first 200 µm of biologic materials, independent of tissue pigmentation.

The CO₂ laser has advantages that make it an effective surgical tool. Its use with an operating microscope allows the surgeon to precisely destroy targets approximately 2 mm in diameter under binocular vision. This degree of precision may be impossible to achieve with conventional cautery. During CO₂ laser surgery, the surgical field is usually bloodless because of the laser’s considerable hemostatic action. Vessels up to 0.5 mm in diameter usually can be sectioned without bleeding.⁴⁹ The CO₂ laser has been used successfully to excise vascular lesions, even in patients with a bleeding diathesis.⁵⁰ The use of more traditional surgical tools, such as cautery, usually results in considerable postoperative edema. Edema does not usually occur after using the CO₂ laser because of the sharp line of tissue destruction, with virtually no injury to surrounding tissue. Ninety percent of the laser’s energy is absorbed within 0.03 mm.⁵¹ There is no manipulation of tissues because laser treatment is usually a noncontact technique. Microscopic examination of tissue after CO₂ laser surgery reveals a discrete line of destruction, with preservation of capillaries and normal features of adjacent tissues. The preservation of adjacent tissues is thought to account for the rapid healing, minimal scarring, and reduced pain often observed after CO₂ laser surgery.⁴⁹

The CO₂ laser is a safe and extremely useful surgical modality in the airways and the digestive tract.⁵² It is best suited for widening benign tracheal stenoses and for removal of granulation tissues.⁵³

2 Flexible-Fiber Carbon Dioxide Laser

A drawback of CO₂ lasers is that they are fixed to a line-of-site delivery mechanism and cannot be transmitted through ordinary fiberoptic bundles, which limits their use to areas accessible by a straight approach. Flexible-fiber CO₂ lasers (Omniguide, Cambridge, MA; Fiberlase CO₂ Fiber, Lumenis, CA) have been developed for use in airway procedures, including base of tongue tumors, laryngeal tumors, tracheal tumors, laryngeal papillomas, tracheal stenosis, and laryngeal lesions.⁵⁴^–⁵⁹

Flexible-fiber CO₂ lasers have a photonic band gap mirror lining, which guides light through a hollow core. The mirror lining reflects the CO₂ laser energy along the hollow core to the distal tip. The hollow core also delivers a cooling flow of inert gas, usually helium, that helps to prevent the fiber from overheating, clears the surgical field of blood, minimizes tissue heating, and ensures the hollow core is clear. The flexible laser fiber can be passed through a rigid bronchoscope or flexible bronchoscope or can be used with a handpiece.

The anesthesiologist should be aware of the risk of a gas emboli, and this possibility should be monitored. Pressurized gas exiting the fiber tip during the laser procedure may cause gas emboli, and the fiber tip should not be brought into direct contact with blood vessels or vascular tissues. Pressurized gas exiting the fiber tip during the laser procedure may cause separation of submucosal flaps or mild emphysema under superficial layers of tissue, and the CO₂ fibers should not be used for lesions below the carina. The flexible CO₂ laser allows access to areas inaccessible by traditional line-of-sight CO₂ lasers, including the nasal cavity, oral cavity, tongue base, larynx, subglottis, and trachea up to the carina.

3 Potassium Titanyl Phosphate Laser

The KTP laser is strongly absorbed by hemoglobin and melanin, and it is used for otolaryngologic lesions, vascular diseases, and hemorrhages.⁶⁰ The KTP laser has been used to treat several skin conditions, including port wine stains, hemangioma, telangiectasia, spider nevi, and red scars of the skin (Fig. 40-7).

Figure 40-7 Potassium titanyl phosphate (KTP) laser (AuraXP, American Medical Systems, Minnetonka, MN). The flexible fiber is coiled in front of the laser.

The KTP laser is generated by passing the light of a rapidly pulsed Nd : YAG laser through a potassium titanyl phosphate crystal, which doubles the frequency and halves the wavelength to 532 nm, producing a beam in the bright green visible spectrum that has a tissue penetration of 0.5 to 2 mm.⁶⁰ The radiation is able to pass through a flexible fiberoptic bundle and is used in a pulsed mode. It is used in vascular lesions within the airway, and because it can be transmitted through clear substances and can pass through a flexible fiberoptic fiber, it can be used in areas where a direct line-of-site laser cannot. The KTP laser has been used for laryngotracheal stenosis, laryngeal paralysis, and choanal atresia. The convenience of fiber delivery, concomitant telescopic control, and low-grade edematous reaction were the main advantages over the CO₂ laser. Healing time was longer for the KTP laser than for the CO₂ laser.

4 Argon Laser

The argon laser contains argon gas and produces a visible blue-green beam with wavelengths of 488 nm and 514 nm, which are absorbed selectively by hemoglobin, melanin, and other pigments that lie under the retina. The beam is readily transmitted down a fiberoptic bundle, allowing endobronchial surgery (Fig. 40-8).

Figure 40-8 HGM Elite argon laser (HGM Medical Laser Systems, Salt Lake City, UT) has a flexible fiberoptic bundle protected by a red lead.

Applications of the argon laser include ophthalmologic surgery, especially for retinal and anterior chamber procedures. Because the laser passes readily through fluid inside the eye without damage, it is used in the treatment of retinal vascular lesions, including diabetic retinopathy, retinal detachment, glaucoma, and macular degeneration. Its applications in dermatologic and plastic surgery include the removal of port wine stains, hemangiomas, and tattoos because of the laser’s absorption by hemoglobin and other pigments. Because the tissue penetration is 0.5 to 2 mm, it is useful for superficial coagulation of capillary vessels. Port wine stains are lightened without scarring after treatment with the argon laser.⁵⁰ To vaporize tissues, the power density is increased to produce a small focal spot; this allows argon laser stapedotomy. The argon laser has been used in infants to remove obstructive endobronchial lesions due to traumatic suction catheter injuries by passing argon laser fibers through the suction port of the fiberoptic bronchoscope (FOB) and targeting the obstructive endobronchial lesion with the argon laser beam.

5 Neodymium : Yttrium-Aluminum-Garnet Laser

The Nd : YAG laser has been used for photocoagulation and deep thermal necrosis in the treatment of gastrointestinal bleeding and obstructing bronchial lesions. The Nd : YAG laser uses a clear, solid, crystalline medium that emits radiation in the infrared region of the electromagnetic spectrum; the radiation has a wavelength of 1060 nm and is invisible (see Table 40-1). Conventional fiberoptic bundles readily transmit Nd : YAG laser radiation at high power, which is applied in a continuous or pulsed mode. The radiation is more readily absorbed by dark tissue. Blue or black pigmentation enhances Nd : YAG absorption, whereas pale colors enhance its penetration.^61,⁶² Nd : YAG radiation penetrates tissues to a depth of 2 to 6 mm and provides good homeostasis for blood vessels up to 0.5 cm in diameter. However, the depth of penetration is less predictable than that of the CO₂ laser. The power density below the tissue surface depends on the color of the surface, which makes laser penetration more difficult with the Nd : YAG laser than with the CO₂ laser.

The Nd : YAG laser is recommended for lesions distal to the larynx and for bulky, vascular endobronchial neoplasms. The advantage of the Nd : YAG laser is that the radiation can be transmitted through fiberoptic bundles. Excision of lesions that are located distal to the larynx is complicated because it is difficult to reach the tumor with the laser beam. In these situations, the Nd : YAG laser is preferred because it can be used with a rigid bronchoscope or an FOB.⁶² Nd : YAG lasers are less precise in cutting, penetrate the tissue deeper, and have improved photocoagulation and superior hemostasis compared with other lasers.

Dumon and coworkers,⁶³ reporting a large series of cases, recommended the use of rigid rather than flexible bronchoscopy for treating obstructive pulmonary lesions by means of endoscopic Nd : YAG laser surgery. Brutinel and associates reported difficulty ventilating and oxygenating patients’ lungs through an endotracheal tube (ETT) during Nd : YAG surgery with an indwelling FOB in place.⁶⁴ Casey and colleagues reported combustion of the FOB and ETT in a patient undergoing Nd : YAG laser airway surgery.⁶⁵ The use of a rigid bronchoscope for the treatment of obstructing pulmonary lesions facilitates the removal of tissue and the treatment of complications.⁶⁶ Power levels less than 50 W given in short pulsations decrease the chances of impingement on vital underlying structures.⁶⁶ McDougall and Cortese reported two patients who died during Nd : YAG laser endoscopic treatment of airway obstructions using very high power.⁶⁷ At high power, the penetration of tissues by the Nd : YAG laser cannot be readily controlled, and perforation of a large blood vessel is possible.

6 Ruby Laser

The ruby laser uses a solid medium of a crystal aluminum oxide (i.e., sapphire) containing chromium ions. It emits visible red radiation at a wavelength of 695 nm (see Table 40-1). The ruby laser is used only in the pulse mode. The radiation is not readily absorbed by water but is significantly absorbed by pigments such as melanin and hemoglobin. The ruby laser can easily penetrate the anterior structures of the eye. It is used to photocoagulate vascular and pigmented retinal lesions. Use of this laser has decreased with the availability of newer types, and the ruby laser is not commonly used for laser airway surgery.

7 Diode Laser

The diode laser is another addition to a growing array of tools for laser surgery. This laser is effective for treatment of hyperplastic inferior nasal turbinates and provides good hemostasis and a sufficient reduction of tumors in otolaryngology practice.⁶⁰ The continuous-wave, semiconductor diode laser emits radiation at wavelengths of 810 and 940 nm in the near-infrared spectrum. The radiation is delivered by a flexible fiber coupled with an aiming beam. The diode laser penetrates tissue to a depth of 1 to 3 mm, and it is suitable for vascular lesions. It is used to remove and debulk airway pathology, including tumors throughout the airway.

8 Other Lasers

Other lasers may have krypton, gold, copper, xenon, erbium : YAG, or holmium : YAG as their medium, but none is used for laser airway surgery.

III Laser Hazards

General laser hazards exist for any type of surgery being done with a laser. Hazards include eye, skin, and drape damage; laser plumes; gas embolism; and misdirected laser beams.

Airway laser hazards exist when a surgeon is using a laser within the airway. The greatest danger is an airway fire. Fires require three components known as the fire triad: a fuel source, an oxidant source, and an ignition source.

A General Laser Hazards

1 Eye Damage

Lasers can easily damage the eyes by direct or indirect exposure, causing serious corneal and retinal injuries that may be irreversible. Eye protection is essential for anyone within the operating room, including the patient, auxiliary staff, nursing staff, surgeon, and anesthesiologist (Fig. 40-9). General precautions for the patient include taping the eyes closed and avoiding the use of petroleum-based eye lubricants. Further protection includes saline-soaked eye pads, protective eye glasses, or metal eye goggles, depending on the wavelength and type of laser used.

Figure 40-9 In the selection of laser glasses, notice the protection offered by the sides of the glasses, which wrap around the eye.

All laser glasses should be labeled clearly with the optical density value, the wavelengths against which protection is afforded, and maximum radiant exposure, or irradiance, to which the eyewear can be exposed (Figs. 40-10 and 40-11).⁶⁸ The correct protective eye glasses must be used for the type of laser used for the procedure; failure to do so provides no protection for the eyes. In hospitals where only one type of laser is in use, this is less of a problem, but care must be taken in hospitals with many types of lasers and protective eye goggles.

Figure 40-10 Eyes must be protected from laser energy. Laser glasses are labeled with the optical density value, the wavelengths against which protection is afforded, and maximum radiant exposure or irradiance to which eyewear is exposed.

Figure 40-11 The correct protective eye glasses must be used with any given laser. The optical density value, the wavelengths against which protection is afforded, and maximum radiant exposure or irradiance to which eyewear is exposed are part of the design of laser glasses.

For CO₂ lasers, the damage to the eye is limited to the cornea because its radiation is largely absorbed by water, and the cornea is more than 75% water.^61,⁶⁹ There is no risk to the retina. For airway use, the patient’s eyes should be taped, protective saline-soaked eye pads placed, and surgical drapes applied and covered with another layer of saline-soaked swabs placed over the drapes. For the operating room staff, CO₂ laser–protective eyeglasses should be worn. Contact lenses protect only the area covered and provide inadequate protection. Regular conventional eyeglasses can protect against the CO₂ laser beam if the beam has been directed or reflected straight onto the eyeglass; however, if the beam is reflected accidentally into the side of the eyeglasses, damage to the eye can occur. When working with CO_2, lasers, all operating room staff should use eyeglasses that wrap around the eye, protecting from CO₂ laser entry from the side. The surgeon does not need to use CO₂ laser protective eyeglasses when working with the operating microscope because the optics of the microscope provide protection⁷⁰; however, if the surgeon uses the CO₂ laser with a handpiece, the surgeon must also wear protective eyeglasses.

For Nd : YAG lasers, unprotected eyes may absorb and focus laser light at the ocular fundus, resulting in irreparable damage. Radiation from the KTP and other lasers such as the Nd : YAG can penetrate the cornea and lens of the eye, resulting in severe retinal damage. The endoscopist is at greatest risk because of the Nd : YAG laser’s potential for backscatter.⁶² The patient and all operating room staff should wear protective eyeglasses. Filters that absorb the Nd : YAG wavelength of 1.06 µm can be placed into rigid and flexible bronchoscopes. If the fibers break during laser surgery, the beam may be deflected to anywhere in the operating room.

For KTP and argon lasers, all operating room personnel require protective amber-colored eyeglasses, and for laser procedures on the face, metal goggles are used (Fig. 40-12). For rigid and flexible endoscopes and operating microscopes, filters that absorb the KTP wavelength can be introduced.

Figure 40-12 Metallic goggles are used during laser procedures on surface skin.

2 Skin and Drape Damage

Laser burns to the skin can occur, and the face or exposed areas should be protected with wet towels and drapes. For laser airway procedures involving a suspension laryngoscope, all of the area around the surgical laryngoscope and face should be completely covered with wet towels, which must be kept wet throughout the procedure. Care should be taken, particularly around the draping of the proximal portion of the surgical laryngoscope, to ensure that the lips and nose are fully protected because this region is more likely to be struck by a reflected laser beam from the proximal rim of the surgical laryngoscope (Fig. 40-13).

Figure 40-13 Care should be taken to ensure complete coverage of the face and area around the surgical laryngoscope with wet towels. A CO₂ laser is attached to the operating microscope by an articulating arm.

Preparation solution should not contain alcohol. Oxygen saturation monitors are a standard of care and should be used because detection of cyanosis is difficult with the patient’s face covered. Disposable surgical drapes are a potential fire hazard. They are treated with flame-retardant chemicals and are water resistant, but all types of surgical drapes are potentially flammable. Many cases of drapes catching fire have been reported. When the drapes catch fire, it is difficult to extinguish because the drapes are water resistant, and the water rolls off them. A CO₂ fire extinguisher should be available. Drapes, once ignited, go up in flames immediately, causing the operating room to be inundated with smoke and making it difficult for everyone to see and breathe.⁷¹^–⁷³ It is important to keep the towels moist, or they can become flammable.

3 Laser Plume

The plume of smoke produced by vaporization of tissues in electrocautery or laser surgery may be hazardous. The smoke contains fine particles (mean size, 0.31 µm; range, 0.1 to 0.8 µm) that can be efficiently transported and deposited in the alveoli.⁷⁴ In rat lungs, the deposition of laser plume particles could produce interstitial pneumonia, bronchiolitis, a reduction in mucociliary clearance, inflammation, and emphysema.^75,⁷⁶ The laser’s smoke plume acting as a vector for viruses is a controversial idea. Viral DNA has been detected in plumes from condylomas and skin warts but not from laryngeal papillomas.⁷⁷^–⁸⁰ CO₂ lasers seem to produce the most smoke from vaporization of tissue. Operating room personnel can be protected by using an efficient smoke evacuator at the surgical site (Fig. 40-14).^81,⁸² Ordinary operating room masks can filter particles no smaller than 3.0 µm. Laser masks that are more efficient should be used to protect the operating room personnel from plume particles.

Figure 40-14 The AtmoSafe smoke evacuator (Atmos Medical Limited, Hampshire, United Kingdom) holds a metal coin by its suction.

4 Gas Embolism

Gas embolism has been reported with Nd : YAG laser resection of tracheal and bronchial tumors, and it may be a risk factor for flexible-fiber CO₂ lasers introduced into the bronchial tree.^83,⁸⁴ Gas embolism has been reported in laparoscopic surgery that used Nd : YAG laser probes that required a gas cooling system.^85,⁸⁶

5 Misdirected Laser and Laser Protocol

A misdirected laser may result from equipment failure or an inadequate knowledge of that equipment. Safety protocols should be in place to prevent this problem. Burn (discussed earlier) can occur even with an unfocused laser.

The intensity of the laser and the potential for tissue damage and combustion with a misdirected beam necessitates that strict safety precautions are followed. Hospitals should have a laser safety officer or advisor, access to laser technicians, a laser register, and adequate staff training.

Lasers should always be set to the standby mode, except when they are ready to fire, to prevent inadvertent actuation. They should be used in the pulsed (shuttered) mode rather than the continuous mode whenever possible to limit the energy delivered by the laser and to allow the area being lasered to cool between firings. The laser radiation should never be allowed to strike highly polished or mirror-like surfaces. Most instrumentation for use with lasers has a dull or matte finish, and blackened instruments are widely used. This is important because reflection of the coherent laser beam may not disperse it, and injury to the patient or operating room personnel is possible, even from a reflected laser beam. Any instruments that become hot as a result of laser radiation may cause burns.^68,⁸⁷ Tracheal laceration, tooth damage, injury to soft tissue, and cutaneous burns to operating room personnel have been described during laser surgery.⁸⁸

The Nd : YAG and argon lasers can penetrate glass, and any windows in the operating room should have an opaque covering to prevent penetration by laser radiation. A warning sign should be placed on the operating room door so that anyone entering is informed that the laser is in use (Figs. 40-15 and 40-16). To prevent personnel inadvertently entering the operating room during laser surgery, the doors may be automatically locked when the operating room is in laser mode (Fig. 40-17). Extra goggles should be available for personnel entering the operating room.

Figure 40-15 The sign warns personnel entering the operating room that a KTP laser is being used.

Figure 40-16 A warning sign should be placed on the operating room door to prevent personnel from inadvertently entering during laser surgery.

Figure 40-17 Interlock control system in the operating room prevents entry during laser use. When these systems are engaged, operating room doors are locked automatically.

B Airway Laser Hazards

The high energy of the laser and its potential for combustion can cause an airway fire when the surgical field is near to the airway (Fig. 40-18). When a laser strikes the unprotected external surface of a tracheal tube during laser airway surgery, the surface starts to disintegrate and can catch fire. If the fire is not recognized and the laser continues to be applied, it can produce a hole in the tracheal tube and expose the burning surface to the oxidant-rich gas within the anesthesia system. At this stage, an explosive blowtorch-like fire may occur and rapidly spread in a distal and proximal manner. Any airway fire is a life-threatening complication, but the blowtorch fire is especially feared (Fig. 40-19).

Figure 40-18 An airway fire results when a laser strikes the polyvinyl chloride endotracheal tube.

Figure 40-19 Continued laser application can produce a hole in the tracheal tube and expose the burning surface to the oxidant-rich gas within the anesthesia system, producing a blowtorch airway fire.

If the cuff of an ETT is punctured, the oxidant-rich gas within the circuit becomes exposed to the external surface of the ETT, and the risk of an airway fire, including a blowtorch fire, is increased significantly. Examination of an ETT after a blowtorch laser fire reveals total or near-total destruction of the ETT, with molten material, smoke, and other particulate material spreading out from the distal end of the tube (Figs. 40-20 and 40-21).

Figure 40-20 Smoke, molten material, and other particulate material spread out after an airway fire.

Figure 40-21 A laser striking the polyvinyl chloride endotracheal tube (ETT) created an airway fire. A, Smoke emerges from the outer shaft of the ETT after a continuous laser strike. B, The outer surface glows orange. C, After perforation into the inner aspect of the ETT in the presence of 100% oxygen flow, flames emerge from the puncture site and distal ETT. D, After the fire is extinguished, damage to ETT and material spreading out from its distal end can be seen.

It is thought that operating room fires are under-reported and that there are probably 100 to 200 operating room fires in the United States per year. Of the reported fires, 20% result in serious injury to the patient. One or two deaths per year are caused by airway fires.⁸⁹

Many options are available for anesthesia management during airway laser surgery. Selection of the ventilation method and type of laser depends on the nature and location of the lesion, the condition of the patient, and the availability of equipment and expertise. Different anesthesia management techniques have been described in the treatment of recurrent respiratory papillomatosis using the CO₂ laser.⁹⁰ In a 1995 survey, 92% of otolaryngologists preferred using a CO₂ laser for removal of recurrent respiratory papillomas. However, there is no consensus with respect to anesthesia management. About 46% preferred using a laser-safe ETT, 26% favored using jet ventilation, 16% preferred an apneic technique, and 12% preferred spontaneous ventilation.⁹¹ Other options include awake with topical anesthesia, general anesthesia through an ETT, rigid bronchoscopy with general anesthesia, and general anesthesia by a laryngeal mask airway (LMA). The possibility of complete airway collapse or an inability to ventilate must be taken into consideration when deciding on spontaneous or positive-pressure ventilation.

When general anesthesia for laser airway surgery is conducted without an ETT, special techniques are used. They include Venturi jet ventilation, intermittent apneic technique, LMA, and insufflation, which are discussed later in this chapter.

If ventilation through an ETT is proposed, prevention of an ETT fire or explosion requires the use of special techniques and appropriate ETTs. Surveys of otolaryngologists active in this type of surgery concerning the complications of CO₂ laser laryngeal surgery have found ETT fires or explosions to be the most common major complication.^52,⁹² Historically, the estimated incidence of airway fires was between 0.4% and 0.57% of the patients undergoing laser airway surgery.³⁹ The one or two deaths per year are caused by airway fires. As reported by Cozine and colleagues, patients have died because of combustion of an ETT during CO₂ laser surgery.⁹³

1 Fuel Source

Fires require three components (i.e., fire triad): a fuel source, an oxidant source, and an ignition source. Fuel source includes flammable material, such as ETTs, gauze, sponges, drapes, volatile anesthetics, masks, nasal cannulas, suction catheters, gloves, gowns, endoscopes, and any material that may burn in the presence of an oxidant-rich atmosphere. The only exception is stainless steel.

2 Oxidant Source

An oxidant-rich atmosphere exists within closed breathing circuits when high concentrations of oxygen or nitrous oxide are present, and this increases the chances of an airway fire. An oxidant-rich atmosphere also can occur under drapes or masks and can increase the likelihood of a fire.

3 Ignition Source

Any high-energy source has the potential to ignite a fire. During laser airway surgery, the laser is the ignition source. Other ignition sources include electrocautery devices, fiberoptic cables, light cables, defibrillator pads, heated probes, and drills. The influence of special equipment and anesthesia on airway fires is discussed later in this chapter.

IV Preventing Airway Fires

The risk of an airway fire during laser airway surgery depends on the many factors that affect the three components of the fire triad. The first component is the fuel source, and the most common fuel source is the ETT. Attempts have been made to reduce the risks of a fire by protecting the tube shaft by covering it with metal foil, protecting the tube shaft by covering it with laser-protective coatings, adding saline to the tube cuff, and developing specially manufactured laser tubes suitable for laser airway surgery.

The second component is the oxidant source. An understanding of the effect of anesthetic gases on tracheal tube flammability is required, as well as an appreciation of the flammability limits of potent inhaled anesthetics.

The third component is the ignition source. The different types of lasers, power settings, modes of operation, exposure times, and spot sizes have been discussed. Most of these parameters depend on the type and site of surgery undertaken, but the anesthesiologist should understand the factors that increase the risk of an airway fire.

A Fuel Source Considerations

1 Use of Metallic Foil Tapes to Protect Endotracheal Tubes

Metal foil tape wrapped around a standard ETT that is used during laser surgery in adults is of historical interest, but it is not commonly used for laser airway surgery. Foil tapes were first suggested as a simple, inexpensive means of protecting the shafts of combustible ETTs from laser beams by Strong and Jako in 1972.⁴⁹ Their use during laser surgery was described during the 1970s and 1980s,⁹⁴^–⁹⁷ when specially manufactured laser-resistant ETTs were not available or performed poorly.

Metallic foil tapes provide protection only from the direct impact of the laser beam. Indirect combustion caused by sparks or heat from gaseous or tube combustion is still possible because the ETTs used typically were combustible and usually had an enriched concentration of oxygen flowing through them. Problems with the use of metallic foil tape have included obstruction of the airway when the tape came loose from a wrapped ETT ^98,⁹⁹ and aluminum foil tape becoming trapped in the trachea after laser airway supraglottoplasty.¹⁰⁰

No metallic foil tapes are manufactured for medical applications, and the U.S. Food and Drug Administration has not sanctioned their use. The physician who wraps an ETT with metal foil tape incurs some product liability risk as a noncertified “manufacturer” if injury occurs.¹⁰¹ One manufacturer, when questioned, cautioned against the use of its aluminum tape for medical purposes.¹⁰²

Wrapping the metal foil tape in a spiral, overlapping manner should cover the shaft from the cuff to the most proximal region possible and should include the pilot tube. Poor wrapping may cause some areas of the shaft to be unprotected, and bending of the tube may expose unprotected areas. Foil-wrapped tubes may loose flexibility, and their foil edge surface may traumatize. The type of metallic tape used to protect combustible ETTs is important.¹⁰²

The possibility of changes in the composition of any metallic foil tape requires every batch of tape to be evaluated for its incendiary characteristics before use.⁹⁵ Metal foil tape wrapped around a standard ETT is not recommended for laser airway surgery.

2 Laser-Guard Protective Coating

The Merocel Laser-Guard (Medtronic Xomed Corp, Mystic, CT) ETT protective coating is no longer available in many parts of the world and is largely of historical interest. It can be regarded as an advance from the use of metallic foil tape to cover a combustible tracheal tube, but its use has been replaced by specially manufactured tracheal tubes for laser airway surgery. The Merocel Laser-Guard consisted of a rectangular sheet of embossed silver foil covered with a thin, absorbent Merocel sponge layer on one side and adhesive on the other.

3 Prevention of Endotracheal Tube Cuff Fires with Saline

During laser airway surgery, the ETT cuff is particularly vulnerable to a laser strike. The high-volume, low-pressure cuff is thin and relatively large because the tube size chosen is undersized to provide the best exposure of the larynx for the surgeon.

The laser beam is aligned along the axis of an operating laryngoscope, which is along the same axis as the ETT but is almost perpendicular to the cuff, which expands away from the tracheal tube until it reaches the tracheal wall. Because undersized ETTs are used, the cuff size is large, and the area exposed to a laser strike is greater than for a larger ETT. A laser strike of the cuff can result in an airway fire at the cuff or lead to a leak of anesthetic gases from within the circuit and expose the outer part of the tracheal tube to an oxidant-rich environment, increasing the chance of a shaft- or cuff-related airway fire or blowtorch fire.

During the 1970s and 1980s, attempts were made to improve the laser-resistant properties of the shaft of combustible ETTs. In 1982, LeJeune and colleagues suggested that filling ETT cuffs with saline could protect them from the CO₂ laser, because a laser strike on the cuff results in a jet of water that acts as a “built-in fire extinguisher” (Fig. 40-22).¹⁰³ The saline also can act as a heat sink. Sosis and Dillon compared air-filled and saline-filled cuffs, and they found the saline-filled cuffs,¹⁰⁴ although perforated by the laser beam as rapidly as air-filled cuffs, were significantly slower to deflate, allowing more time before reaching the point at which airway pressure could no longer be maintained. Saline-filled cuffs prevented ETT ignition by the CO₂ laser set to 40 W (Table 40-2) in a statistically significant number of cases compared with the control group of air-filled cuffs, and saline filling of ETT cuffs was recommended for laser airway surgery. A small amount of dye, such as methylene blue, should be added to the saline so that laser-induced ETT cuff perforation becomes obvious to the surgeon, who can immediately terminate operation of the laser. Further protection of the ETT cuffs can be obtained by placing moistened pledgets above them and keeping the pledgets moist throughout the procedure.¹⁰⁵

Figure 40-22 A, The endotracheal tube cuff is filled with saline and methylene blue dye. B, Perforation of the saline-filled cuff results in jets of water.

TABLE 40-2 Incidence of Endotracheal Tube Combustion with Air- and Saline-Filled Cuffs with the Carbon Dioxide Laser Set to 40 W

Cuff Type	Number of Cases	Combustion (%)
Air	5	100*
Saline	5	20*

^* P < 0.05, Mann-Whitney U test.

From Sosis MB, Dillon FX: Saline-filled cuffs help prevent laser-induced polyvinylchloride endotracheal tube fires. Anesth Analg 72:187, 1991.

4 Special Endotracheal Tubes for Laser Airway Surgery

Beginning in the 1970s, laser surgery of the airway became increasingly popular, and as the dangers of an airway fire became clearer, many attempts were made to reduce this risk. Two strategies were used to reduce the risk. The first involved the anesthesiologist using a standard combustible ETT and covering it in some form of protective coating. Early attempts involved protection of the shaft by metal foil and then specially designed protective coatings. The second approach involved manufacturers producing tracheal tubes that had laser-resistant properties. Some of the early manufactured laser tubes were not particularly effective, but they were thought to allow any type of laser use, and subsequently, a number of airway fires were reported. It is useful to discriminate between laser-proof and laser-resistant devices.

Laser proof implies that irrespective of the oxidant environment and the power of the laser, the ETT cannot catch fire. With a laser-proof ETT, a continuous laser strike with extremely high power in a 100% oxygen environment does not produce a fire of the tube. Only one laser-proof tracheal tube (Norton) has been designed, and it is discussed later.¹⁰⁶

All other manufactured ETTs for laser airway surgery are only laser resistant. Laser-resistant tubes provide some degree of protection against a laser strike, but these tubes vary in their materials, protective coating, relative size, and number of cuffs used. Any laser-resistant tube can result in an airway fire or blowtorch fire (Fig. 40-23) if it is used outside of its limits, such as a laser strike on an unprotected area between the tube shaft distal and the cuff, at the unprotected proximal part of the shaft, or at the cuff itself. The anesthesiologist should appreciate the maximum power settings for which a laser-resistant tube has been tested, the range within which ignition does not occur, and the effect the oxidant environment has on the laser resistance characteristics. All laser-resistant tubes are not laser proof, and they must not be used outside of their limits.

Figure 40-23 Laser-induced fire damage to endotracheal tubes (ETTs). Left to right, the first three are standard nonlaser polyvinyl chloride ETTs, and all three have been damaged by an airway fire. The two ETTs on the right are designed for laser use. Both tubes have sustained fire damage in their unprotected areas distal to the cuff by high-energy, sustained CO₂ laser strikes to the ETTs with 100% oxygen passing through them.

a Norton Laser Endotracheal Tube

The Norton ETT (V. Mueller, Baxter Healthcare Corp., Niles, IL), first described in 1978 by Norton and De Vos, was the only laser-proof tracheal tube produced (Fig. 40-24).¹⁰⁶ It was constructed from interlocking, spiral-wound, stainless steel parts. It is no longer manufactured. Because it was made of steel, it was extremely resistant to multiple uses and autoclaving, and it may still exist in some hospitals.

Figure 40-24 A and B, In the selection of Norton laser tubes, notice the absence of a cuff and ribbed exterior.

The Norton ETT had a matte or sand-blasted finish, rather thick walls, and a ribbed exterior. It came in three sizes: 4.0-, 4.8-, and 6.4-mm internal diameter (ID) (Table 40-3).¹⁰⁷ The matte finish diffused reflected laser beams.¹⁰⁶ A 4.8-mm-ID Norton ETT has a wall thickness of 1.4 mm. The thick wall of this ETT is considered a disadvantage because the tube can obscure the surgeon’s view more than an ETT with the same ID but with thinner walls—an important consideration during laser airway surgery. This ETT’s large size and stiffness may make surgical exposure and laryngoscope positioning difficult, and it can make passage through the glottis traumatic. It is usually necessary to use a stylet to introduce the Norton ETT.

TABLE 40-3 Internal Diameter, External Diameter, and Wall Thickness for the Norton Laser Endotracheal Tube

The Norton tube had no cuff, but a separate latex cuff was available and could be attached to it. If an external cuff was added to the device, it was no longer laser proof because the cuff and pilot tube could act as a fuel source for an airway fire. The separate latex cuff is no longer manufactured, and because they degraded over time, they are not commonly found.

Alternatively, the pharynx may be packed with wet gauze, sponges, or packs to seal the system to allow positive-pressure ventilation of the lungs, but this introduces a potential fuel source and can cause an airway fire, particularly if they are allowed to dry out. Even if ventilation of the patient’s lungs is not compromised by leakage, the presence of anesthetic gases in the oropharynx increases the possibility of combustion in the surgical field and increases operating room pollution.

The relatively small diameter and ridged internal surface produce turbulent airflow and an increased resistance to airflow. Woo and Strong suggested Venturi ventilation through the Norton tube in an attempt to overcome the ventilation issues of increased resistance,¹⁰⁸ airflow, and air leaks.

b Xomed Laser-Shield I Endotracheal Tube

The Xomed Laser-Shield I ETT (Xomed-Treace, Jacksonville, FL) is no longer manufactured and is of historical interest only. The silicon rubber tube was coated with a silicon elastomer to which metallic particles had been added, and it was designed to be used only with a CO₂ laser. Several airway fires were reported with its use.¹⁰⁹^–¹¹² It is a useful reminder of the limitations of a laser-resistant ETT and the dangers of using a device outside of its intended range.

c Bivona Laser Endotracheal Tube

The Bivona (Gary, IN) laser ETT is no longer available in many parts of the world and is mainly of historical interest. It was designed to limit the effect of cuff perforation by a laser strike, because the polyurethane foam cuff with its silicone envelope maintained the cuff seal even when penetrated. The Bivona laser ETT was designed to be used only with a CO₂ laser. Blowtorch airway fires were reported with this tube.¹¹²

d Xomed Laser-Shield II Endotracheal Tube

The Xomed Laser-Shield II ETT (Xomed Surgical Products, Jacksonville, FL) has a laser-resistant overwrap of aluminum foil tape and a Teflon cover. The proximal and distal ends of the silicon elastomer shaft and cuff are not protected and therefore are not laser resistant (Fig. 40-25). The metallic tape provides protection against laser impact. The Teflon tape gives the tube a smooth surface to minimize mucosal injury from tube manipulation. No adhesives are used because adhesives with metallic tape increase the risk of an ETT fire.⁹⁸ Dry methylene blue dye has been placed in the cuff inflation valve to enable detection of a cuff rupture. The Xomed Laser-Shield II comes packaged with neurosurgical cottonoid, which is used wet to protect the distal shaft and cuff for an added margin of safety.