A History

Laser is an acronym for light amplification by the stimulated emission of radiation. Photons are released in a very narrow, intense, high-energy beam as a result of a stimulated emission.

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

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:

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).

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

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.

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.

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

A Fuel Source Considerations

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.

Figure 40-25 Xomed Laser-Shield II endotracheal tube (Xomed Surgical Products, Jacksonville, FL). A, The proximal and distal ends of the silicon elastomer shaft and cuff are not protected. B, The laser-resistant aluminum foil tape can be seen proximal to the cuff. C and D, An airway fire occurred in the distal, unprotected area after a sustained, high-power CO₂ laser strike in 100% oxygen.

Dillon and associates evaluated the combustibility of the Xomed Laser-Shield II ETT and compared it with 3M’s no. 425 aluminum foil–wrapped, combustible, polyvinyl chloride (PVC) ETTs used with a CO₂ laser and an Nd : YAG laser.¹¹³ Exposure of the bare silicon rubber shaft of the Laser Shield-II ETT to CO₂ laser radiation resulted in combustion in 2.1 ± 0.7 seconds; Nd : YAG laser radiation–induced combustion occurred at 3.3 ± 4.5 seconds (P = 0.05). The silicon rubber burned with a bright flame and disintegrated. It was difficult to extinguish. Dillon and colleagues concluded that the foil-wrapped shaft of the Laser Shield-II ETT provided adequate protection against high-power, continuous-mode Nd : YAG and CO₂ laser radiation.¹¹³

Ossoff and colleagues also studied the Laser-Shield II for combustibility with CO₂ and KTP lasers. They evaluated the Laser-Shield II dry, with blood, with a blood/K-Y jelly mixture, and with K-Y jelly alone on the ETT. Each tube was clamped, and 100% oxygen was delivered at 3 L/min through it. All trials were performed with 3 minutes of continuous output. The maximum power output was 40 W for the CO₂ laser and 15 W for the KTP laser. These settings far exceed the clinical settings used. With the KTP laser (13.5 to 15 W), no fires were observed, regardless of surface penetration. For the CO₂ laser, no fires were observed at 40 W for 3 minutes on continuous mode with the dry ETT. Blood or KY-jelly, or both, decreased the resistance of the ETT to CO₂ laser radiation. For the tube with blood alone, 25 W was the highest power that the tubes withstood without ignition. For the K-Y jelly/blood mixture, the maximum power was reduced to 19 W. With K-Y jelly alone, no fire occurred at the maximum power setting of 40 W.¹¹⁴

The Xomed Laser-Shield II ETT offers the potential advantage of an adhesive-free foil wrapping for ETT protection. Silicon, however, disintegrates during combustion, whereas rubber and PVC tend to retain their integrity. The Teflon overwrap around the foil raises questions because pyrolysis of Teflon may liberate toxic fumes that can cause polymer fume fever.

Medtronic Xomed recommends only the Xomed Laser-Shield II for all surgical procedures involving the use of CO₂ or KTP lasers in a normal-pulsed or continuous mode of noncontact delivery. It is contraindicated for use with any Nd : YAG laser, argon laser, or any laser other than the CO₂ or KTP. When the laser beam hits the Laser-Shield II Teflon, the reflective aluminum wrapping may be exposed, and it is possible for the beam to be reflected into the patient’s tissue. The sizes of Xomed Laser-Shield II ETTs are given in Table 40-4.

TABLE 40-4 Internal Diameter, External Diameter, and Wall Thickness for the Xomed Laser-Shield II Endotracheal Tube

Internal Diameter (mm)	External Diameter (mm)	Wall Thickness (mm)*
4.0	6.6	1.3
4.5	7.3	1.4
5.0	8.0	1.5
5.5	8.6	1.55
6.0	9.0	1.5
6.5	10.0	1.75
7.0	10.5	1.75
7.5	11.0	1.75
8.0	11.5	1.75

^* Calculated.

Courtesy of Xomed-Surgical Products, Jacksonville, FL.

e Mallinckrodt Laser-Flex Endotracheal Tube

Mallinckrodt (Glens Falls, NY) Laser-Flex ETTs have corrugated stainless steel shafts. They are designed as a single-use item, and the manufacturer states that this type of ETT should be used only with the CO₂ and KTP lasers. The adult version of this ETT incorporates two PVC cuffs. The manufacturer suggests that the distal cuff can be used if the laser damages the proximal one. The adult tube’s distal end, including its Murphy eye and the proximal 15-mm connector, is constructed from combustible PVC (Fig. 40-26). The Laser-Flex cuffs are inflated by means of two 1-mm-diameter PVC pilot tubes that are located on the inside of the ETT. An Nd : YAG or other laser fiber should never be inserted through this tube. Heyman and colleagues found that prolonged laser impingement on the shaft of a Mallinckrodt Laser-Flex ETT could prevent cuff deflation, and they stressed the importance of aspirating the saline from the cuff in a slow, gentle manner.¹¹⁵

Figure 40-26 A and B, The Mallinckrodt Laser-Flex endotracheal tube (Covidien, Hazelwood, MO) has a corrugated stainless steel shaft and double cuff filled with saline. C and D, An airway fire occurred in the distal, unprotected area after a sustained, high-power CO₂ laser strike in 100% oxygen.

The adult sizes of Mallinckrodt Laser-Flex ETTs available with the double-cuff system are 4.5-, 5.0-, 5.5-, and 6.0-mm ID. Three pediatric sizes (3.0-, 3.5-, and 4.0-mm ID) of uncuffed Mallinckrodt Laser-Flex ETTs are also available. They are all stainless steel, except for a PVC 15-mm adapter. They are not equipped with Murphy eyes (Table 40-5).

TABLE 40-5 Internal Diameter, External Diameter, and Wall Thickness for the Mallinckrodt Laser-Flex Endotracheal Tube

Unlike the all-stainless-steel Norton ETT, the Mallinckrodt Laser-Flex ETT has an airtight shaft. However, the walls of both types of tubes are somewhat rough. In their product information for the uncuffed pediatric tubes, Mallinckrodt states, “Due to the spiral design of the tube, the airflow resistance for a given size will be approximately equal to a PVC tube, which is 0.5 mm smaller.” They add, “Due to the bore size of the tube, patients should be monitored closely to guard against overinflation of the respiratory system and a build-up of expiratory gases.”¹¹⁶

Sosis and coworkers studied the resistance to CO₂ laser radiation of size 4.5-mm-ID Mallinckrodt Laser-Flex ETTs.¹¹⁷ The tubes were positioned horizontally on a stainless steel tabletop covered with a wet towel. An oxygen flow of 5 L/min passed through the tubes as a Sharplan (Tel Aviv, Israel) model 734 CO₂ laser was aimed at an ETT’s shaft. A laser power setting of 35 W was used with a beam diameter of 0.6 mm. This resulted in a power density of 13,400 W/cm². The laser, set to the continuous mode of operation, was activated for 90 seconds or until combustion occurred. Blowtorch combustion occurred in one of five Laser-Flex ETTs studied. However, when human blood was applied to the shafts of four 4.5-mm-ID Mallinckrodt Laser-Flex ETTs, blowtorch combustion occurred in all cases.

In another study, Sosis and Dillon noted that there is less danger of a reflected laser beam causing damage when the Mallinckrodt Laser-Flex ETT is used compared with foil-wrapped ETTs.¹¹⁸ In an evaluation of the Laser-Flex ETT with the Nd : YAG laser, Sosis found that the shaft of the Laser-Flex ETT could be ignited in all cases by the Nd : YAG laser when operated at high power.⁹⁷ Clinical Laser Monthly reported the occurrence of an airway fire during a case in which a Mallinckrodt Laser-Flex ETT was used during a laser excision of vocal cord polyps.¹¹⁹ They stated that the patient had minor burns. They reported that, at the time of the fire, the cuffs of the ETT were not inflated with saline as recommended by the manufacturer.

f Sheridan Laser-Trach Endotracheal Tube

The Sheridan (Argyle, NY) Laser-Trach ETT is a single-use, red rubber tube that has a spiral-wrapped, nonflammable, embossed copper foil from cuff to the proximal end of the tube. The copper foil is covered by an outer, absorbent fabric. The company recommends saturating the outer layer with sterilized isotonic saline before use, and it must remain saturated during the procedure, because a laser strike on a dry outer coating of fabric will produce a fire.

The outer covering reduces heat buildup and must be vaporized before the copper foil is reached. The Sheridan Laser-Trach is recommended only for use with CO₂ and KTP lasers. The outer fabric coating adds additional size to any given internal diameter and these tubes are therefore relatively large compared to other laser-resistant tracheal tubes.

Sosis and associates compared 6.0-mm-ID Sheridan Laser-Trach ETTs with plain (bare) Rüsch red rubber ETTs of the same internal diameter.¹²⁰ Five liters per minute of oxygen flowed through the tubes being studied. The tubes were subjected to continuous radiation at 40 W from a Sharplan CO₂ laser or 40 W of continuous output from a Laserphotonics (Orlando, FL) Nd : YAG laser. The Nd : YAG laser radiation was propagated by a 600-µm fiber bundle. Each type of laser was directed perpendicular to the ETT being studied. The laser’s output was continued until a blowtorch fire occurred or 50 seconds elapsed. No ignition occurred after 60 seconds of CO₂ laser fire to the shafts of eight Sheridan Laser-Trach ETTs tested. However, blowtorch ignition of all eight bare rubber ETTs tested occurred after 0.87 ± 21 (mean ± SD) seconds of CO₂ laser fire. Nd : YAG laser contact with the Sheridan copper and fabric-covered rubber ETTs resulted in perforation and blowtorch ignition in all tubes tested after 18.79 ± 7.83 seconds. This was significantly (P < 0.05) longer than the 5.45 ± 4.75 seconds required for blowtorch ignition of all eight plain red rubber ETTs tested with the Nd : YAG laser.

It was concluded that under the conditions of the study, the Sheridan Laser-Trach ETT was resistant to CO₂ laser radiation. It is not recommended for use with the Nd : YAG laser. Table 40-6 lists the sizes of the Sheridan Laser-Trach ETTs available.

TABLE 40-6 Internal Diameter, External Diameter, and Wall Thickness for the Sheridan Laser-Trach Endotracheal Tube

Internal Diameter (mm)	External Diameter (mm)	Wall Thickness*
4.0	8.2	2.10
5.0	9.5	2.25
6.0	10.6	2.30

^* Calculated.

Courtesy of Sheridan Catheters, Argyle, NY.

g Lasertubus Endotracheal Tubes

Lasertubus (Rüsch, Duluth, GA) is a laser-resistant ETT with a shaft made of soft white rubber and a laser guard approximately 17 cm long, consisting of a Merocel sponge and silver foil with a double cuff. A cuff within a cuff arrangement exists and the sponge surface should be soaked to reduce the risk of an airway fire in a manner similar to that for the Sheridan Laser-Trach. According to the manufacturer, the Lasertubus offers resistance to all types of medical lasers, such as argon, Nd : YAG, and CO₂, with wavelengths ranging from 488 to 1060 nm. Sosis and colleagues evaluated the Rüsch Lasertubus in vitro.¹²¹

Jacobs and colleagues reported crimping of the Lasertubus, resulting in hypoxemia in a patient.¹²² After placement of the Lasertubus, the surgeon extended the patient’s head and neck and within 30 seconds, peak inspiratory pressures increased, oxygen saturation decreased, and no end-tidal CO₂ was evident. Immediate direct laryngoscopy confirmed that the ETT was correctly placed. On inspection, no kinks or obvious obstruction was seen. Ultimately, the laser tube was removed and the patient reintubated with a PVC ETT. The patient’s oxygen saturations returned to 100%. On inspection of the Lasertubus, the tube had crimped under the tape. Although this was a small defect not obvious to cursory inspection, it resulted in complete obstruction to airflow. The investigators then experimented by bending unused laser tubes and found that a weakness within the wall of the tube remained, predisposing to crimping with minimal force and producing complete obstruction to airflow.¹²²

B Oxidant Source Considerations

C American Society of Anesthesiologists Practice Advisory for the Prevention and Management of Operating Room Fires

In 2008, a report by the American Society of Anesthesiologists (ASA) Task Force on operating room fires published a practice advisory for the prevention and management of operating room fires.¹ Practice advisories are systematically developed reports that are intended to assist decision making in areas of patient care.¹ They are based on scientific literature, expert opinion, clinical feasibility data, open forum commentary, and consensus surveys. They are not intended as standards, guidelines, or absolute requirements and can be adopted, modified, or rejected according to clinical needs and constraints.¹ This practice advisory looked at operating room fires, surgical fires, airway fires, and high-risk procedures.

The practice advisory defined an operating room fire as a fire that occurred on or near patients who are under anesthesia care and included surgical fires, airway fires, and fires within the airway circuit. A surgical fire was defined as a fire that occurred on or in a patient. An airway fire was a special type of surgical fire that occurred in a patient’s airway and that may or may not include fire in the attached breathing circuit.¹ A procedure was designated as high risk when an ignition source came close to an oxidizer-enriched atmosphere (e.g., tracheostomy, laryngeal surgery).

The task force developed the advisory by a seven-step process that involved consensus on the criteria for evidence; systematic review of originally published, peer-reviewed studies; expert opinions of consultants asked to participate in surveys on the effectiveness of various strategies for fire prevention, detection, and management and comment on a draft of the advisory; comments of active members of the ASA on the advisory; open forum discussions at a major national meeting; survey of consultants on the feasibility of implementing the advisory; and all available information that was used to build consensus within the task force to formulate the advisory statements

The ASA Task Force’s primary findings commented on education, operating room fire drills, preparation for every case, and prevention and management of operating room fires. The anesthesiologist should collaborate with all members of the procedure team throughout the procedure to minimize the presence of an oxidizer-enriched atmosphere in proximity to an ignition source.¹

For all procedures, surgical drapes should be configured to minimize the accumulation of oxidizers (i.e., oxygen and nitrous oxide) under the drapes and to keep them from flowing into the surgical site. Flammable skin prepping solutions should be dry before draping. Gauze and sponges should be moistened before use near an ignition source.¹

For high-risk procedures, the anesthesiologist should notify the surgeon whenever there is a potential for an ignition source to be in proximity to an oxidizer-enriched atmosphere or when there is an increase in oxidizer concentration at the surgical site. Any reduction in supplied oxygen to the patient should be assessed by monitoring pulse oximetry and, if feasible, inspired, exhaled, and delivered oxygen concentrations.¹

For laser procedures, a laser-resistant ETT should be used. The laser-resistant ETT used should be chosen to be resistant to the laser used for the procedure (e.g., CO₂, Nd : YAG, argon, erbium : YAG, KTP). The ETT cuff of the laser tube should be filled with saline and colored with an indicator dye such as methylene blue.¹

Before activating a laser, the surgeon should give the anesthesiologist adequate notice that the laser is about to be activated.¹ The anesthesiologist should reduce the delivered oxygen concentration to the minimum required to avoid hypoxia, stop the use of nitrous oxide, and wait a few minutes after reducing the oxidizer-enriched atmosphere before approving activation of the laser.¹

For cases involving an ignition source and surgery inside the airway, cuffed tracheal tubes should be used when clinically appropriate.¹ The anesthesiologist should advise the surgeon against entering the trachea with an ignition source (e.g., electrosurgery unit).

Before activating an ignition source inside the airway, the surgeon should give the anesthesiologist adequate notice that the ignition source is about to be activated. The anesthesiologist should reduce the delivered oxygen concentration to the minimum required to avoid hypoxia, stop the use of nitrous oxide, and wait a few minutes after reducing the oxidizer-enriched atmosphere before approving the activation of the ignition source.¹ In some cases (e.g., surgery in the oropharynx), scavenging with suction may be used to reduce oxidizer enrichment in the operative field.¹

For a fire in the airway or breathing circuit, remove the ETT as fast as possible, stop the flow of all airway gases, remove all flammable and burning materials from the airway, and pour saline or water into the patient’s airway.¹ If the airway or breathing circuit fire is extinguished, reestablish ventilation by mask, avoiding supplemental oxygen and nitrous oxide, if possible. Extinguish and examine the ETT to assess whether fragments were left in the airway. Consider bronchoscopy (preferably rigid) to look for ETT fragments, assess the injury, and remove residual debris. Assess the patient’s status and devise a plan for ongoing care.¹

D Management of an Airway Fire

Many factors must be considered when an airway fire occurs. All operating room personnel must be prepared for the possibility of an airway fire during laser endoscopic surgery. If an airway fire occurs, sterile isotonic saline or water should be immediately available in a 30- or 60-mL syringe. Another laser and PVC ETT should be available. A plan of action should be rehearsed by operating room personnel so that rapid action can be taken if a fire occurs.

Schramm and colleagues discussed immediate management of an airway fire.¹³² The management protocol calls for immediate removal of the ETT.¹³² Sosis wrote a laser airway fire protocol in which certain steps should be taken simultaneously by the anesthesiologist and surgeon (Box 40-1).¹³³ In the event of an airway fire, the protocol calls for immediate cessation of ventilation and turning off of all anesthetic gases, especially oxygen, by disconnecting the hose from the common gas outlet, detaching the ETT from the anesthetic circuit, or clamping the ETT or turning off the flow meters. At the same time, the flames should be extinguished with a sterile saline or water solution. Presuming an easy airway, the protocol calls for the ETT to be removed immediately because it no longer provides an airway and may be on fire. After the ETT has been removed and the fire completely extinguished, the patient’s lungs should be ventilated with 100% oxygen by bag and mask.

Chee and Benumof described “a patient scheduled for an elective tracheostomy whose airway evaluation revealed an in situ 8-mm-ID PVC ETT, swollen lips, an edematous tongue protruding out of the mouth and an oropharynx filled with secretions.”¹³⁴ General anesthesia was induced with 300 mg of intravenous propofol and maintained with 0.4% inspired isoflurane (Forane) and a 35% oxygen-air mixture. The vital signs remained stable. Electrocautery was used for coagulation by the surgeons. The patient was administered 100% oxygen immediately before insertion of the tracheostomy tube. Suddenly, the surgeons reported a blue flame shooting up vertically from the patient’s neck. The breathing circuit was disconnected immediately from the ETT, and 20 mL of 0.9% saline was flushed in the ETT. The fire was extinguished promptly. The ETT was not removed because the ability to reintubate was uncertain. Despite a leak around the perforated cuff, the seal was sufficient to generate a peak inspiratory pressure of 20 cm H₂O. Meanwhile, the surgeons were able to insert a tracheostomy tube into the trachea. Fiberoptic bronchoscopy was performed in the operating room and postoperatively revealed generalized upper airway edema consistent with prolonged intubation, no distal airway burn injury, and minimal burn injury to the proximal aspect of the tracheostomy site. The patient experienced no sequelae from the airway fire.

Each patient before laser surgery must be evaluated for risk of possible difficult intubation. If the patient is difficult to intubate or potentially a high risk for difficult intubation and an airway fire occurs, the patient will still be difficult to intubate. In these circumstances, the risk of removing the ETT and not being able to reestablish an airway outweighs the risk of leaving the tube in after the airway fire is extinguished. Van Der Spek and coworkers suggested that if the patient is not easy to intubate,¹³⁵ a long stylet can be passed through the existing tube before removing it to facilitate the passage of a new one. Chee and Benomuf also suggested that the ETT can serve as a conduit for a tube exchanger.¹³⁴ For reintubation, an airway exchange catheter is placed through the ETT with the assistance of a laryngoscope, if possible, to facilitate the passage of a new ETT over the airway exchange catheter. To minimize the risk of failing to pass an ETT over the airway exchange catheter, the operator can use a relatively small ETT over a relatively large airway exchange catheter. The airway exchange catheter allows ventilation, which allows time for an alternative reintubation strategy, such as a surgical airway or FOB.¹³⁶

After the airway is reestablished, the extent of the airway damage should be assessed. Foreign bodies (e.g., pieces of tube, metal foil, pledgets) should be removed. This may entail fiberoptic bronchoscopy through an ETT or rigid bronchoscopy. Careful clinical judgment must be used to decide whether to extubate. Extensive burns should be managed with controlled ventilation of the lungs through an ETT or tracheostomy. The use of antibiotic and steroids should be considered if burns are severe. All inhaled gasses should be humidified.

A Laryngeal Mask Airway

The LMA was first described in 1983.¹³⁷ It is used in routine anesthetic practice and for management of the difficult airway.¹¹⁹ The LMA and reinforced flexible laryngeal mask airway (fLMA) have been used for awake and anesthetized patients undergoing fiberoptic bronchoscopy for diagnostic and airway evaluation.^138,139 It has also been used for laser pharyngoplasty.¹⁴⁰ Carinal obstruction was managed using a combination of Nd : YAG laser therapy through a FOB inserted through an LMA and subsequent Nd : YAG through an FOB with a rigid bronchoscope.¹⁴¹ Other reports described the use of a LMA and high-frequency jet ventilation for resection in tracheal surgery.¹⁴²

The LMA and fLMA are constructed from silicon rubber that contains silica filler, which provides high-temperature resistance and some flame-retardation ability. The same material has been used to manufacture laser-resistant ETTs.¹³⁷ Pennant and colleagues did a limited study of the incendiary characteristics of the LMA and fLMA, suggesting that they are resistant to CO₂ lasers at power densities below 1.25 to 2.35 × 10³ W/cm², but 1.2 × 10⁴ W/cm² produced immediate ignition.¹⁴³ Brimacombe looked at the incendiary characteristics of the LMA and fLMA with the CO₂ laser and compared them with two standard PVC ETTs: Mallinckrodt reinforced armored tube and Mallinckrodt RAE tube. Continuous firing led to light smoke production and penetration of the tube in 20 to 30 seconds. Both PVC tubes were penetrated in 0.5 to 2 seconds, and ignition occurred at 2 to 6 seconds with 100% O₂ and 2 to 8 seconds with an O₂-N₂O mixture.¹⁴⁴

At intermediate power density (4.7 × 10³ W/cm²), LMA and fLMA were penetrated at 0.5 to 2 seconds and ignited in 2 to 5 seconds with 100% O₂ and an O₂-N₂O mixture. At the highest power setting (9.8 ×10³ W/cm²), all four (i.e., LMA, fLMA, and two PVC ETTs) ignited in 0.05 to 0.1 seconds with 100% O₂. The LMA and fLMA are more resistant to CO₂ laser fire than standard PVC tubing. The CO₂ laser at power densities below 2.35 × 10³ W/cm² appears to be safe with use of the LMA and fLMA.

Pandit and colleagues showed that at laser outputs and distances of the KTP fiber tip from the fLMA normally encountered in clinical practice, the fLMA was not penetrated or ignited.¹⁴⁵ Keller and associates looked at the standard LMA (silicon based) and fLMA (silicon based with metal wire) and at a disposable LMA (PVC based) and intubating LMA (silicon and steel based) and PVC-based ETTs using KTP and Nd : YAG lasers at two power densities used commonly in airway surgery (570 and 1140 W/cm²).¹⁴⁶ Each airway device was fixed to a table in room air and attached to a closed-circuit breathing system with 30% oxygen in air delivered at 3 L/min. The laser was fired at the same distance of 3 mm. They also evaluated the marked and unmarked parts of the airway device and the unmarked device after application of 0.1 mL of unclotted fresh human blood. They evaluated the cuff with air or undiluted methylene blue dye.

There was no ignition of any airway device. The impact sites of the silicon-based LMA for both lasers revealed a layer of silica ash just like that found by Pandit and colleagues. The silicon-based tubes were less easily penetrated than the PVC-based tubes, except for the intubating LMA, which flared sooner than with the KTP laser at both densities. The disposable LMA cuff was more resistant to penetration than the silicon LMA cuff or PVC ETT. The cuffs filled with air were penetrated more rapidly than those with methylene blue.⁹⁹

Pandit and Keller and their colleagues showed that the cuff was more vulnerable to a laser strike with the CO₂ and KTP lasers, especially when filled with air. Pandit filled the cuff with saline, and Keller filled the cuff with nondilute methylene blue, and both found increased resistance to the laser strike. The disadvantage of using saline in the cuff is that the manufacturers recommend filling the cuff only with air. It has been reported that if not all the saline is withdrawn from the cuff after use in the standard reusable LMA, the cuff may rupture during autoclaving.^147,148 Coorey and colleagues reported a technique in which they were able to empty the saline-inflated LMA reliably by a syringe without the plunger with the cuff held above the syringe to facilitate gravitational drainage. The cuff was then manually squeezed. The LMA with the syringe barrel attached was placed in a warming cupboard at 60° C for 12 hours. They found that filling the LMA cuff with saline was a viable option for laser airway surgery.¹⁴⁹

The other option is the disposable LMA, for which filling the cuff with saline is not a concern because it is used only one time. The only concern is that the disposable LMA shaft is more easily penetrated than the silicon-based LMA, but the disposable LMA cuff was more resistant to penetration than the silicon-based LMA or PVC ETT cuffs. When filled with methylene blue dye and with the Nd : YAG laser power density at 570 W/cm², none of the cuffs was affected after 30 seconds.¹⁴⁶

B Management of Anesthesia

Operations on the airway are unique in that the surgeon and anesthesiologist are working in the same area. This can be challenging, and the anesthesiologist has to allow the surgeon adequate exposure to any lesions within the airway and at the same time oxygenate the patient, remove CO₂, maintain anesthesia, prevent soiling of the tracheobronchial tree, and maintain safe conditions and prevent an airway fire.

An ideal laser airway technique would be simple to use; provide complete control of the airway with no risk of aspiration; control ventilation with adequate oxygenation and CO₂ removal; provide smooth induction and maintenance of anesthesia, provide a clear and motionless surgical field that is free of secretions; not impose time restrictions on the surgeon; not be associated with the risk of airway fire or cardiovascular instability; allow safe emergence with no coughing, bucking, breath holding or laryngospasm; produce a pain-free, comfortable, alert patient at the end of the operation; and be laser proof.

The ideal technique does not exist, and some of these ideal conditions conflict. The presence of a cuffed ETT provides control of the airway and prevents aspiration but may obscure a glottic lesion and is not laser safe. A cuffed laser tube provides some protection against laser-induced airway fires but has a greater external-to-internal diameter ratio and may obscure laryngeal lesions. Jet ventilation techniques require specialist equipment and knowledge and an understanding of their limitations, and they do not protect the airway from soiling.

Safe laser airway surgery requires an understanding of the airway pathology, its location within the airway, the type of laser used, the surgical requirements, and the patient’s comorbidities. It is essential that careful communication and cooperation between anesthesiologist and surgeon takes place before, during, and after any procedure.

During laser airway surgery, Rontal and colleagues used a video monitor during all laser endoscopic procedures so that the entire operating room team could observe the procedure.¹⁵⁰ The use of a video monitor to observe the impact of the laser beam on tissues in shared airway procedures is used by many surgical units and allows the operating room nurses to anticipate the surgeons’ needs and the anesthesiologist to communicate better, adjust the anesthesia accordingly, and act quickly if there is an airway fire (Fig. 40-31). Without a video monitor, only the surgeon can see the surgical site and the impact of the laser beam; vital seconds may be lost before the team recognizes an airway fire is happening, but it would have been obvious on a monitor screen. The presence of a video monitor has no disadvantage, but its absence may be detrimental, and some units regard it as a standard requirement for shared laser airway surgery.

Figure 40-31 Video monitor allows all operating room staff to observe the procedure.

A Laser Tube

Closed systems are familiar to all anesthesiologists and involve the placement of a laser tube. The different types of laser tubes and their relative laser-resistant properties have been discussed. Placement of laser tubes is routine, although care should be taken to prevent traumatizing the laryngeal lesion as the laser tube is passed through the glottis and into the trachea. After the laser tube is in position and the cuff inflated, there is protection of the lower airway from blood and secretions. Routine control of the airway and ventilation are established, and because the system is closed, there is little danger of pollution of oxygen or volatile agents unless the cuff is compromised. It is important to appreciate immediately any cuff compromise due to a laser strike because it causes oxygen and volatile agent leaks around the laser tube, increasing the fire risk. All laser tubes have a greater outer diameter for any given internal diameter because of their laser-resistant coverings, and this may limit surgical access and visualization of laryngeal lesions. Because the surgeon requires adequate exposure, small laser tubes usually are placed, which can lead to higher inflation pressures.

B Spontaneous Ventilation and Insufflation Techniques

Open systems can be used during anesthesia for laser procedures on the vocal cords, and spontaneous ventilation techniques have been used in adults and in children. Spontaneous ventilation techniques with insufflation are particularly suitable for infants and children in whom it is not possible to pass a tube past a lesion or when a laser tube obscures the lesion.

Spontaneous ventilation and insufflation techniques are useful in the removal of foreign bodies, evaluation of airway dynamics (e.g., tracheomalacia), and laser airway surgery. The technique requires a spontaneously breathing patient and provides a clear view of an unobstructed glottis. Insufflation of anesthetic gases and agents can be achieved by several routes: a small catheter introduced into the nasopharynx and placed immediately above the laryngeal opening; a tracheal tube cut short and placed through the nasopharynx, emerging just beyond the soft palate; a nasopharyngeal airway; and the side arm or channel of a laryngoscope or bronchoscope.

The absence of any fuel source (e.g., tube) within the airway makes this a laser-safe procedure for laryngeal lesions. However, great care must be taken to prevent the catheter or nasopharyngeal airway from getting very close to or entering the larynx. This would provide a fuel source that could easily cause an airway fire if struck by a laser beam. If the catheter is inadvertently inserted too far, it may enter the esophagus, causing marked gastric distention and possible regurgitation.

Inhalational induction may be commenced with sevoflurane in 100% oxygen. At a suitable depth of anesthesia, as assessed by clinical observations of the rate and depth of respiration, pupil size, eye reflexes, blood pressure, and heart rate changes, laryngoscopy is undertaken and topical lidocaine administered above, below, and at the level of the vocal cords. One hundred percent oxygen is administered by face mask with spontaneous ventilation and anesthesia continued with inhalational (insufflation) or an intravenous route (propofol infusion). At a suitable depth of anesthesia assessed by clinical observations, the surgeon undertakes rigid laryngoscopy or bronchoscopy.

Movements of the vocal cords are usually minimal with a spontaneously breathing technique, provided an adequate level of anesthesia is maintained. If the depth of anesthesia is too light, the vocal cords may move, the patient may cough, or laryngospasm may occur. If the depth of anesthesia is too great, the patient may become apneic with cardiovascular instability. Careful observation throughout the procedure, observing movements, respiratory rate and depth, cardiovascular stability, and unobstructed breathing, is vital, with the concentration of the volatile anesthetic adjusted accordingly. The insufflation technique requires close cooperation between the anesthesiologist and the surgeon.

The limitations of spontaneous ventilation or insufflation techniques include the lack of control over ventilation and the potential for airway soiling. Operating room pollution due to insufflation of volatile agents is also an issue and requires high-intensity suction catheters near the mouth (see Fig. 40-14). Insufflation techniques may not be suitable for large, soft, floppy lesions, particularly in the supraglottis or glottis, which may obstruct the airway after the onset of general anesthesia with spontaneous ventilation.

Rita and associates used the CO₂ laser successfully to excise subglottic stenosis in infants,¹⁶⁵ avoiding a tracheostomy, and reported that ETTs of any size in this group make surgery in infants difficult or impossible because the operative field is obstructed. They reported that in some infants with subglottic stenosis, even a 2.5-mm-ID ETT, was difficult to pass through the stenotic area. Rita and associates concluded that although the insufflation technique is potentially hazardous,¹⁶⁵ if it is done correctly, it provides an appropriate anesthetic technique for surgery on the larynx of infants.¹⁶⁶ They reported good results with this technique over the course of many years.

C Intermittent Apneic Technique

Weisberger and Miner described the use of an intermittent apneic technique for laser laryngeal surgery in the resection of juvenile papillomatosis of the larynx without the use of an ETT.¹⁶⁷ The investigators stated that a clear, unobstructed view of the airway and complete immobility of the surgical field were essential for the surgeon during these cases (see Fig. 40-30). During a 2-year period, 51 procedures were performed by the investigators on nine patients who had juvenile laryngeal papillomatosis. Their average age was 10.5 years (range, 3.5 to 37 years). After induction of general anesthesia, the patients were paralyzed with atracurium or vecuronium and anesthesia maintained with halothane or enflurane in 100% oxygen. The patients’ tracheas were intubated with small-caliber ETTs wrapped with foil tape. In cases of extensive papillomatosis, resection was started with the ETT in situ while the patients’ lungs were ventilated with 40% oxygen. Otherwise, the ETTs were removed and the surgery started. The surgery was interrupted when the oxygen saturation decreased. The patients’ tracheas were then reintubated, and they were hyperventilated with 100% oxygen. This resulted in a rapid rise in the oxygen saturation so that repeated extubations and surgery could continue. The median number of apneic episodes required for each procedure was two, with a range of one to five. The duration of apneic episodes was 2.6 minutes, with a range of 1 to 4.5 minutes. A suspension laryngoscope and microscope, which provided excellent visualization of the larynx, were used in these cases so that endotracheal intubation could be readily accomplished without moving the laryngoscope. The apneic technique removes all the flammable material from the larynx during laser actuation and is thought to decrease greatly the possibility of an airway fire. Weisberger and Miner stated that the apneic period should be shortened for small children because of their decreased functional residual capacity.¹⁶⁷ The technique is contraindicated in patients in whom visualization of the larynx is difficult.

D Jet Ventilation Techniques

Jet ventilation techniques are suitable for ventilation during laser surgery of most adult vocal cord lesions. The main limitation for their use is the experience of the anesthesiologist and the absence of suitable equipment. Jet ventilation techniques involve the intermittent administration of high-pressure jets of air, oxygen, or oxygen-air mixtures that entrain room air and lower the delivered pressures. The risk of life-threatening barotrauma is the most serious complication, and it occurs when entrainment of room air is absent. This results in the delivery of very high driving pressures, leading to pneumomediastinum, pneumothorax, and surgical emphysema.^168–170

In 1967, Sanders first described a jet ventilation technique using a 16-gauge, high-pressure source (jet) placed down the side arm of a rigid open bronchoscope.¹⁷¹ Sanders used intermittent manual ventilation with a rate of 8 L/min and a driving pressure of 700 torr to entrain room air and showed the technique could maintain supranormal oxygen pressure and prevent a rise in the CO₂ partial pressure. Since 1967, modifications to Sanders’ original jet ventilation technique have been made for endoscopic airway surgery. These modifications include frequency of ventilation (i.e., low-frequency, high-frequency, or superimposed frequency jet ventilation) and the site at which the jet emerges in the airway (i.e., supraglottic, subglottic, or transtracheal).

The frequency of ventilation and the location of the jet cannula should be selected according to the degree of airway obstruction and the location of the lesion. Specially designed catheters, laryngoscopes, bronchoscopes, and ventilators are available for the clinician to choose from. Many techniques have been described, claiming different advantages over the other methods.

There is no clear consensus about the ideal ventilation modes or the laser techniques. Selection must be done on the basis of a thorough understanding of the pathophysiology of airway obstruction and individual experience with use of these devices. Hunsaker introduced a laser-safe subglottic monojet ventilation tube.^109,172

High jet pressure increases the risk of subcutaneous emphysema related to facial plane dissection in the neck, especially when there is disruption of the mucous membrane during surgery. If mucosal disruption is noticed, the jetting catheter should be positioned away from the mucosal opening because pressure drops rapidly with the distance from the jetting orifice. Because there is no ETT to protect the airway, vomitus, blood, smoke, or debris and seeding of papillomas down the tracheobronchial tree can occur. There is a possibility of polluting the operating room with infectious agents or the anesthetic gases. Mucosal dehydration and inspissated secretions can result from dry jetting gases. End-tidal CO₂ cannot be easily measured. Volatile agents cannot be used, and scavenging of gases is required.

1 Site of Jet Delivery

a Supraglottic Jet Ventilation

Supraglottic jet ventilation describes a technique in which the jet of gas emerges in the supraglottis by attachment of a jetting needle to the rigid surgical suspension laryngoscope. High- or low-frequency ventilation can be used. Supraglottic jet ventilation techniques allow a clear, unobstructed view for the surgeon with no risk of a laser airway fire. However, if the surgeon places surgical swabs into the operating field, there is a risk of an airway fire with the swab acting as a fuel source.

Supraglottic techniques have limitations: misalignment of the suspension laryngoscope to the glottic inlet, which results in poor ventilation and the risk of gastric distention with entrained air; blood, smoke, and debris blown into the distal trachea; considerable vibration and movement of the vocal cords, which may require ventilation to be stopped whilst operating; inability to monitor end-tidal CO₂ concentration; and risk of barotrauma with pneumomediastinum, pneumothorax, and subcutaneous emphysema.

b Subglottic Jet Ventilation

Subglottic jet ventilation involves placing a small (2 to 3 mm external diameter) catheter or specifically designed tubes (e.g., Benjet, Hunsaker, Acutronic, Carl Reiner) through the glottis and into the trachea, which allows delivery of a jet of gas directly into the trachea (Fig. 40-32). This means a fuel source is present within the airway, and care must be taken during laser airway surgery. Many of the subglottic catheters that are commercially available have some laser-resistant properties, but if their tolerance is exceeded, the catheters can degrade and fracture. If after a fracture of the catheter and after a laser strike, jet ventilation is resumed, the distal fragment may be forced into the distal airways. Some catheters (e.g., Hunsaker) have metal wires within the catheter to reduce the chances of this distal fragmentation.

Figure 40-32 Hunsaker Mon-Jet catheter (Xomed, Jacksonville, FL) and Acutronic subglottic catheter for jet ventilation (Acutronic Medical Systems, Hirzel, Switzerland). The green basket of the Hunsaker catheter reduces catheter tip movement within the trachea.

Subglottic jet ventilation is more efficient than supraglottic jet ventilation and results in reduced driving pressures, minimal vocal cord movements, a good surgical field, and no time constraints for the surgeon in the placement of the rigid laryngoscope. The main disadvantage is the potential for a laser-induced airway fire due to the presence of a potential fuel source within the airway and a greater risk of barotrauma than in supraglottic jet techniques (Fig. 40-33).

Figure 40-33 A, Hunsaker Mon-Jet catheter after it sustained a high-power CO₂ laser strike in 100% oxygen. B, The internal stainless steel wire prevented fragmentation.

c Transtracheal Jet Ventilation

Elective transtracheal catheter placement under local anesthesia in individuals with significant airway pathology or under general anesthesia for elective laryngeal surgery has been described.¹⁷³ Transtracheal jet techniques carry the greatest risks of barotrauma. Other potential problems include blockage, kinking, infection, bleeding, and failure to site the catheter. None of the commercially available transtracheal catheters is specifically designed for laser use, and transtracheal jet ventilation techniques for endoscopic laser surgery of the larynx require a careful evaluation of the potential risks and benefits.

2 Jet Ventilation Frequency

a Low-Frequency Jet Ventilation

Low-frequency ventilation typically describes ventilatory rates of less than 60 breaths/min (1 Hz), and in practice, most low-frequency ventilation is accomplished by a manual Sanders-type device at rates of 15 to 25 breaths/min. With sufficient driving pressures, this leads to near-normal tidal volumes, visible chest inflation, and passive chest deflation. A metal jet needle or cannula is positioned inside a laryngoscope or a rigid bronchoscope and is connected to a source of oxygen. To prevent barotrauma, a reducing valve and a pressure regulator should be in line so that the oxygen pressure is limited to 50 psi for adults. In children, extreme caution should be used. The anesthesiologist should start with much lower values and gradually increase the pressure while observing the chest movements. Holding down the handheld lever controls the duration and frequency of the jet of oxygen. The actual delivered tidal volume, concentration of oxygen, and inspiratory pressures depend on the amount of air entrainment by the jet, length of the cannula and its alignment to the trachea, size of the laryngoscope, and lung compliance. These factors are hard to measure in a clinical situation with any great precision and at best are estimates. Adequate ventilation is accomplished in most patients who are anesthetized and given muscle relaxants.

The minimal possible pressure that can provide adequate ventilation should be used. The Venturi jet must be kept in perfect alignment with the trachea to achieve streaming of the flow into the lungs. Anesthesiologists should be watchful after any readjustment of the operating laryngoscope to which the jet is clamped, which may impair ventilation of the lungs. Oxygen saturation must be constantly monitored and chest movement continually observed.

During supraglottic jet ventilation, there is considerable movement of the laryngeal structures, and the timing of each breath can be coordinated with the surgeon operating the laser. Even small movements are magnified under the operating microscope. This movement is much less of an issue with subglottic jet ventilation. Intravenous agents, such as propofol infusions, are used to maintain anesthesia. Short-acting muscle relaxants are used to prevent movements of the patient that can be dangerous during a laser operation. Gastric distention with possible regurgitation may occur with a misaligned cannula,¹⁷⁴ and a nasogastric tube may be required. Adequate fluids are given intraoperatively, and gases may be humidified in the postoperative period to prevent mucosal drying.

Jet ventilation is helpful in many situations in which a laser is not used. Intermittent jet ventilation has been applied through the instrument channel of the flexible FOB to expand atelectatic lungs and through the Hunsaker jet ventilation tube for one-lung ventilation for lobectomy.¹⁷⁵ However, extreme care should be taken to avoid pulmonary barotrauma.

b High-Frequency Jet Ventilation

During high-frequency jet ventilation (HFJV), small tidal volumes are delivered at a rate of 60 to 150 cycles per minute from a high-pressure source (5 to 50 psi), with inspiration taking 20% to 40% of each cycle. This is an effective ventilation method that provides adequate gas exchange. This method has been used in rigid bronchoscopy. Hautmann and colleagues described a technique of delivering HFJV through a noncompliant insufflation catheter.¹⁷⁶ The catheter can be threaded through the sidearm of the bronchoscope and positioned in the trachea or in the main stem bronchus. Medici and coworkers used an insufflation catheter with a side hole in the contralateral main stem to deliver high-frequency positive-pressure ventilation during endobronchial surgery using an Nd : YAG laser.¹⁷⁷ HFJV catheters can be placed transtracheally; however, in a prospective multicenter study, the rate of subcutaneous emphysema was 8.4%.¹⁷⁸

An advantage of HFJV is that it provides excellent views and access to the surgical site. Catheters are small and obstruct the surgical field less than larger conventional ETTs. To-and-fro movements of the major airways that are invariably present during normal respiratory excursions are not present. Because a small tidal volume is used, there is less movement of the larynx, trachea, and lungs. This greatly facilitates the precise operation of the laser beam.

Although the reported incidence of pulmonary barotrauma in HFJV is low, it can lead to serious complications. Pulmonary barotrauma can result from high driving gas pressures and air trapping. Ventilators should initially be set at the lowest possible driving pressures and increased incrementally while carefully observing chest movements. There is a potential risk of barotrauma if the air pressures are not monitored. In addition to an injector catheter, Unzueta and associates used a second identical catheter placed 7 cm distal to the injector site to measure airway pressure continually.¹⁴⁶ Continuous monitoring of end-expired CO₂ and O₂ by conventional methods is difficult to interpret because of fast respiratory rates and high gas flow rates. However, there is a well-defined relationship between arterial CO₂ concentrations and end-tidal CO₂ concentration when expiratory gas is obtained by sidestream sampling during jet ventilation.¹⁷⁹ Observation of chest wall movements and blood gas analysis are reliable methods for assessing the adequacy of ventilation. Klein and coworkers suggested the use of a double-lumen jet catheter for respiratory monitoring.¹⁶⁸

Air trapping and stacking of breaths are inherent problems in high-frequency ventilation because of short expiratory times.¹⁸⁰ In airways distal to the obstruction, injurious excess pressure can easily build up. Obstruction to gas outflow can easily occur because of the tumor and because of the presence of surgical instruments, bleeding, and mucosal edema. Light anesthesia or inadequate muscle relaxation can cause laryngospasm, closing the glottis and further obstructing the airflow. To prevent barotrauma, it is essential to ensure that there is adequate outflow.

c Combined Frequency Jet Ventilation

Oxygenation and CO₂ elimination may be improved by using low-frequency and high-frequency ventilation in combination (Fig. 40-34). In this method using combined (superimposed) frequencies of ventilation, the location of the gas inflow in the airway seems to influence the efficiency of jet ventilation. Supraglottic, combined-frequency ventilation seem to be superior to subglottic, monofrequent jet ventilation in providing an unobstructed view and access to glottis.¹⁸¹ With intratracheal jet ventilation, aspiration and air entrapment are virtually absent. There is no clear advantage of one ventilation technique over the other.¹⁸² In a study of 37 adult patients, supraglottic, combined-frequency ventilation was more efficient than subglottic, low-frequency or subglottic, combined-frequency ventilation.¹⁸¹ However, in a bench model of laryngotracheal stenosis, supraglottic HFJV was associated with significantly larger end-expiratory pressures and peak inspiratory pressures.¹⁸³ Two risks are built in because of the location of the jet cannula: aspiration at the supraglottic location and barotrauma at the subglottic location.

Figure 40-34 The combined-frequency jet ventilation monitor (Carl Reiner, Vienna, Austria) allows observation of the inspired oxygen concentration, measurement of end-tidal CO₂, and scrutiny of three- and four-lumen catheters. It has a laser-safe mode.

High-frequency ventilation should be reserved for patients with severe airway obstruction or severe pulmonary dysfunction. Most cases do well with a variety of simpler techniques that are well established. They include ventilation with a laser-resistant tube or microlaryngoscopy tube, supraglottic jet ventilation with a jet needle, and subglottic jet ventilation with a catheter.¹⁸⁴

There is no perfect mode of ventilation that suits all clinical conditions. Complications have been associated with various ventilation techniques in laser resections (Table 40-9). Table 40-10 suggests a general approach that is used in the pediatric population.

TABLE 40-9 Complications Associated with Jet Ventilation of the Lungs

Ventilation Related (n)*	Ventilation Unrelated (n)*
Major
Pneumothorax (9)	None
Hypoxemia during anesthesia (6)
Mediastinal air (2)
Tension pneumothorax (1)
Minor
Carbon dioxide retention during anesthesia (3)	Prolonged mask support (10)
Subcutaneous emphysema (2)	Prolonged endotracheal intubation (5)
Gastric dilation (2)	Laryngospasm (5)
Airway bleeding (2)	Prolonged sleep or paralysis (2)
Recall of procedure (1)

^* Data from 15,701 patients were analyzed.

Adapted from Cozine K, Stone JG, Shulman S, Flaster ER: Ventilatory complications of carbon dioxide laser laryngeal surgery. J Clin Anesth 3:20, 1991.

TABLE 40-10 Techniques for Pediatric Laser Bronchoscopy

A Rigid Ventilating Bronchoscopy

Although the rigid bronchoscope is an old instrument, it continues to play a major role in newer therapies for access to the airway.¹⁹³ Rigid bronchoscopy is the standard technique for anesthesia management during laser resection of severely obstructing tracheal masses.¹⁹⁴ The main advantage of the rigid bronchoscope is complete control of the airway. The bronchoscope ultimately functions as a rigid ETT. The area and clarity of the view of the surgical field with rigid scopes are superior to those with flexible scopes. However, the view is limited to the trachea, carina, and the main bronchi. Subglottic lesions can be visualized through a rigid bronchoscope. Compared with flexible bronchoscopes, rigid bronchoscopes have large-diameter instrument side channels. A variety of baskets, forceps, and grabbers that are used for a wide range of therapeutic procedures can pass easily through these wide channels. In the event of significant bleeding or tenacious secretions, the telescope can be withdrawn and suction catheters passed directly down the bronchoscope while maintaining oxygenation and control of the airway.

The rigid bronchoscope has a side port that can be attached to any conventional anesthesia delivery system. It substitutes for the ETT during the procedure. A removable eyepiece allows surgical interventions when open and control of ventilation when in place. Usually, there is a variable leak around the scope, which can be compensated for by increasing the fresh gas flow.

The rigid bronchoscope provides an excellent view of the larynx, similar to the view provided by the direct laryngoscope. Ventilation can be provided through the rigid bronchoscope. Eliminating the ETT improves the access to the surgical field and reduces the risk of airway fire. With experience, rigid bronchoscopy is simple to use, is low cost, and is relatively safe when the proper precautions are observed.

Rigid bronchoscopy can be invaluable and life-saving in cases of severe obstruction because the bronchoscope can be pushed past the obstruction.^141,195 It is unsurpassed in evaluation, control, and therapeutic manipulation of the tracheobronchial tree.¹⁹⁶ A retrospective review of 300 patients over a 12-year period concluded that the use of rigid bronchoscopy offers certain advantages in ventilation during general anesthesia. Rigid therapeutic bronchoscopic intervention is increasingly accepted to treat patients with central airway obstruction. Laser resection is applicable when the obstruction is caused by malignant exophytic tracheobronchial lesions, benign granulation tissue, or tracheobronchial stenosis with scar tissue formation.¹⁹⁰ In one study, rigid bronchoscopy was preferred for proximal lesions and FOB used for distal lesions. Often, the rigid and flexible bronchoscopes were used together to maximum advantage.¹⁹⁷

Drawbacks of rigid bronchoscopy include increased secretions and finite access to the distal airways and upper lobes. Conditions such as ankylosis of the jaw or rigid cervical spine, which make direct visualization of the larynx difficult, may preclude the use of a rigid bronchoscope. General anesthesia is often necessary for rigid bronchoscopy, whereas flexible bronchoscopy can be performed with sedation and topical anesthesia. Patients do not tolerate pressure on the soft tissues, and significant neck extensions are painful.¹⁹⁸

B Flexible Bronchoscopy

Flexible bronchoscopy is used to reach lesions in distal airways. Flexible fiberoptic scopes are more suited for procedures under sedation and local anesthesia.¹⁶¹ Flexible bronchoscopes are built with bundles of optical fibers or a camera at the distal end. The fibers deliver light to the tip and transmit pixels. An image is constituted when all the pixels are reassembled. However, the image formed is not as good as the view from direct laryngoscopy. It is possible to visualize the entire airway because the tip of the bronchoscope can be flexed through an arc of 220 degrees. There is usually a working channel, which can be used for suction and for passing instruments. In adults, 5.5- to 6.0-mm flexible bronchoscopes are used, and in children, 3.6- and 2.2-mm scopes are popular. The disadvantage of the smaller scopes is that there is no instrument channel or, if present, it is too narrow. As technologic improvements occur in the design of smaller instruments and improved forceps, the therapeutic and diagnostic role of flexible bronchoscopes will become more prevalent in clinical practice.¹⁹⁹