Учебники / Otolaryngology - Basic Science and Clinical Review

It was quickly recognized that the unique properties of laser energy would allow it to be harnessed for use as an ideal surgical tool, providing unparalleled user control for bloodless, inherently sterile tissue incision and ablation. Furthermore, the ability to deliver the beam to previously inaccessible regions of the body with precision, often at some distance, and the ability to incise muscle without electrical stimulation have contributed to its widespread use in surgery.

Laser photocoagulation of retinal vessels was performed by the mid-1960s, only a few years after its initial discovery as a laboratory instrument. In 1965, the carbon dioxide (CO2) laser was developed, and 3 years later an optical articulating arm was introduced that allowed precise delivery of the beam to the upper airway. Use of the laser in ophthalmology and otolaryngology quickly spread to other medical fields, along with a several-fold increase in site-specific applications throughout medicine. Fueled by a rapidly growing industry for medical applications, laser technology advanced with the introduction of a plethora of new lasers—argon, potassium titanyl phosphate (KTP/532), CO2, neodymium:yttrium-aluminum-garnet (Nd:YAG), erbium:YAG,holmium:YAG,thulium-holmium-chromium (THC):YAG, Q-switched YAG, Q-switched ruby, candela, alexandrite, excimer, gold vapor, copper vapor, mercury vapor, pulsed dye, tunable dye, holmium, diode, free electron lasers, and others—each with unique properties best suited for specific applications. Novel delivery systems (optical fibers, wave guides, contact tips) and new beam distribution technology (swift lase, silk touch, ultra pulse, flash scan, etc.) have evolved to improve controlled surface tissue ablation (e.g., laser skin resurfacing and epilation) and permit minimally invasive endoscopic application. Specialized laser instrumentation has also evolved to improve smoke evacuation and visibility and to protect adjacent nontarget structures.The use of laser light in conjunction with photosensitizing agents promises to become a major primary and adjunctive treatment for accessible superficial epithelial tumors.

In the last decade, the use of laser technology has permeated the ambulatory surgery environment and more recently has become a standard piece of equipment in the office setting. Solid-state lasers have become diminutive in size, facilitating portability and creating a small office “footprint.” The hemostatic properties of the laser are especially advantageous in upper aerodigestive tract surgery, which in the past, required endotracheal intubation to protect the airway from bleeding and obstruction. “Bloodless” surgery in this region of the head and neck can now be performed safely on an awake patient in an ambulatory setting.

With the popularization of laser-assisted office-based procedures such as laser-assisted uvulopalatoplasty (LAUP), laser-assisted intranasal surgery (LAST), laser-assisted endoscopic laryngeal surgery (LAELS), laser-assisted myringotomy (CTOLAM), and laser-assisted skin resurfacing and epilation, the number of physicians using laser technology and the number of procedures performed are expected to dramatically increase.

LASER PHYSICS AND

TISSUE INTERACTION

A detailed discussion of laser biophysics is beyond the scope of this chapter, and the reader should consult other texts for greater technical depth.The word laser stands for light amplification by stimulated emission of radiation. The generation of laser energy involves two principles of quantum mechanics and atomic theory first postulated by Albert Einstein: spontaneous emission and stimulated emission. Electrons, which orbit the nucleus of an atom, exist in a low energy or ground state. An external energy source will excite atoms within the lasing medium and force electrons from the ground level to a higher energy orbit. This quickly decays back to its ground energy state, spontaneously emitting a discrete amount of light energy called a photon. Stimulated emission is said to occur when an atom, already in an excited state, absorbs an additional photon of energy from the same type of atom and quickly decays back to the ground state. When this occurs, two photons of energy with identical wavelengths and phase are emitted. The atoms of a laser exist within the lasing medium (which may be any of three states of matter) encased within an optical, resonant chamber with parallel, inward-facing end mirrors. On one end of the chamber, the mirror is partially reflective, which permits the energy to escape from the aperture of the laser tube.

To begin the process of laser emission, an external source of energy, or “pump,” is first used to excite the atoms of the lasing medium.This may be in the form of a flash lamp, electric arc, or another laser, as in the case of theYAG laser.The internal energy created by spontaneous emissions contributes to a cascade of stimulated emissions when incident to other atoms within the lasing medium, thus creating a form of energy amplification. Energy released within the laser tube travels in random directions and may be reflected between the two end mirrors, further amplifying the process (Fig. 14-1). When more than one half of the atoms are in the excited state than in the ground state, a population inversion is said to occur, and laser energy is emitted.

Figure 14-1 A laser resonator tube,with a partially reflective end mirror, allowing escape of laser energy from the aperture after the lasing medium has undergone stimulation by the pump energy source and an atomic population inversion is said to have occurred.

The energy released from the end of the laser tube has unique properties that distinguish it from ordinary light, which is disorganized or scattered in all directions from its source and composed of many wavelengths. Incident, reflected, and emitted light waves traveling back and forth between the mirrors of the laser chamber will eventually resonate in phase-producing coherent light (all waves in phase) (Figs. 14-2 A,B). The energy is monochromatic (one wavelength) based on the content of the lasing medium. Laser energy may be in the visible light spectrum, as in the case of the argon laser, or invisible, as produced from the CO2 gas laser. Light that escapes from the aperture through the partially reflective end mirror will also become collimated, so that all light waves travel parallel to the source.With the aid of a lens, the parallel light from a laser can be focused down to the

TABLE 14-1 ABSORPTIVE HEATING BY LASER ENERGY

smallest possible spot size, a diffraction-limited spot. White light from a tungsten filament will focus to an inverted image of the filament but never to as small a spot. These properties (coherence, monochromicity, and collimation) allow the energy to be optically focused down to a small spot with little beam divergence or attenuation, creating a very intense beam of energy. The monochromicity allows selective absorption of the energy by different components of the tissue and is an important feature that permits photodynamic therapy, as described later.

These unique properties of laser energy allow it to be concentrated into a small target area from a distance and its biological effect controlled by varying the energy density and rate of delivery of the beam.The mechanisms of laser–tissue interaction involve photochemical, photothermal, and photomechanical/acoustic effects. The ultimate biological response is a complex summation of these effects on cellular and subcellular tissue components, the postsurgical inflammatory response, and long-term healing.The immediate biological response to a specific energy density will cause a physical effect, which ranges from warming and blanching to complete vaporization (see Table 14–1). The spread of thermal

A

Figure 14–2 (A) Disorganized or incoherent light waves from an incandescent lightbulb. Here, waves are emitted in all directions at random, out of phase, with mixed, broad-spectrum wavelengths. (B) An illustration of organized or coherent light waves from a laser tube.

B

Here, the light waves are shown in phase with each other, all of the same wavelength, and parallel or collimated.The phase matching of the light generated by the laser further intensifies the energy emitted at the end of the tube.

Figure 14-3 Four types of laser light–tissue interactions. Both scattering and absorption will generate heat, which ultimately achieves tissue vaporization and denaturation.Transmission is essential when the target area is deep to the surface.

energy through the tissue depends on the depth of laser penetration, the tissue’s thermal conductivity, and the dynamic heat sink effect of the local microcirculation over the time of application.The depth of tissue effect also depends on the way in which the specific wavelength of energy is reflected, transmitted, absorbed, or scattered at the tissue interface, which in turn is dependent on specific tissue composition (e.g., pigmentation, water content, and vascularity)(Fig. 14-3). Reflection prevents penetration and creates safety concerns. Scatter will limit beam penetration and promote thermal spread. Transmission is critical when the target area is not located at the tissue surface (first-strike zone). For example, the ability of laser energy to transmit through the cornea, lens, and vitreous-filled eye chamber to reach the retina is essential for its ophthalmologic application. Scatter will limit beam penetration and promote thermal spread.

THE LASER AS A SURGICAL TOOL

The specific wavelength of laser energy will determine both its precision as a scalpel and its hemostatic properties.When used as a scalpel, the laser relies on its ability to cut tissue precisely with little thermal spread and tissue injury. In this case, laser energy must be intense, sharply focused, and absorbed almost entirely at the surface.The CO2 laser is an ideal surgical scalpel because of its high absorption by tissue water content. It is therefore a surface laser that vaporizes superficially and allows a what-you-see-is-what-you-get type of tissue interaction similar to a cold steel scalpel or the electrocautery. It is less hemostatic, however, especially when encountering blood vessels that exceed the diameter of

Figure 14-4 Different laser wavelengths at a given power and spot size will penetrate to different tissue levels with varying degrees of thermal spread and destruction.

the laser spot size.At high power settings, the CO2 laser primarily will vaporize tissue with a great deal of precision and little lateral thermal injury and char. In contrast, the Nd:YAG laser energy will transmit through water with little attenuation, being more selectively absorbed by pigmented tissue.The Nd:YAG laser tends to penetrate more deeply into tissue planes, resulting in a field of thermal injury much deeper and less visible than that achieved by the CO2 laser (Fig. 14-4) The Nd:YAG laser is therefore a much less precise tool for use as a surgical scalpel but is one of the most hemostatic of all lasers. However, tissue necrosis can occur well beyond what is initially visible and therefore requires considerable training and experience for safe use. Similarly, the visible light lasers, the argon and KTP lasers, are more selectively absorbed by hemoglobin and pigmented tissues. Their precision as a surgical scalpel and hemostatic properties fall somewhere between the Nd:YAG and CO2 laser energies (see Table 14–2).

POWER

In addition to the physical properties of the specific laser energy, tissue interaction is user controlled by adjusting the power, spot size, and exposure time of

TABLE 14-2 RELATIVE TISSUE EFFECTS OF DIFFERENT LASERS

CO2, carbon dioxide; KTP, potassium-titanyl-phosphate; YAG, yttrium- aluminum-garnet, increasing (*) asterisks the effect.

the laser beam. Power is the least frequently altered parameter during a treatment session. In general, the highest safe power setting should be used when the laser is needed as a scalpel or for tissue ablation. At high power settings, most of the tissue ideally is vaporized, leaving a clean incision with minimal char and thermal injury. However, for laser welding (e.g., microvascular anastomoses and microflap, vocal fold phonosurgery), very low power settings may be used (milliwatts) to allow photocoagulation and denaturization as the predominant tissue effect.

SPOT SIZE AND POWER DENSITY

Because all of the laser energy is concentrated in the area of beam contact, altering the spot size will spread the same amount of energy at a given power setting (watts) over a greater or smaller surface area (cm2) and reduce or increase the power density or irradiance (watts/cm2). Irradiance equals power in the focal spot divided by area of the focal spot. Surface area and irradiance vary with the square of the beam diameter. Therefore, if the spot diameter is doubled, the irradiance will decrease to one fourth at a given power setting. If the spot diameter is cut in half, the irradiance will increase fourfold.This change in power density can be accomplished by focusing the beam with lenses and working within the focal point of the lens for greatest power density (smallest spot size) or defocusing the beam to reduce power density (larger spot size). In summary, the irradiance or power density can easily be altered in an exponential fashion by either changing the focal length of the lens or changing the working distance from laser to tissue plane (Fig. 14-5).

TREATMENT TIME AND FLUENCE

Although the total amount of energy delivered to the tissue and power density, or irradiance, is important, the rate of delivery may be the most crucial user-defined variable in determining the laser’s ultimate biological effect. With a given spot size and power setting, the surgeon can vary the exposure time to achieve the desired result. The rate of energy delivery by the laser is called fluence. Fluence equals power density multiplied by time and is measured in watts (W s/cm2) or joules (J/cm2). For any given total amount of energy delivered per application, the rate of energy delivery will have the greatest biological effect. Control over fluence is, in actual practice, the most difficult concept to master and requires training, supervision, and experience. For example, a delivery of 100 J of energy can be achieved using either 25 W/cm2 for 4 seconds or 100 W/cm2 for 1 second, with a major difference in biological effect (Fig. 14-5).The majority of adverse tissue effects with laser technology occur because the inexperienced surgeon will tend to use an insufficient power setting over an excessively long exposure time.This tends to create a greater degree of thermal injury for the same degree of tissue ablation achieved at higher power settings over briefer exposure times.This results in excessive char, colateral tissue destruction, and subsequent scar tissue formation. Therefore, when using the laser to cut or ablate tissue, the surgeon should always use the highest level of fluence that he or she is comfortable with (Fig. 14-6). The fluence delivered to tissue also can be modified by using the laser in a pulsed delivery mode rather than using it in a continuous mode.

PULSED DELIVERY

The more commonly used lasers in the head and neck—argon, KTP, Nd:YAG, and CO2—operate in the continuous wave mode. The novice will often use a pulsed delivery mode in the order of seconds to feel more in control of the energy delivery. Short-pulse sequences or super-pulsed modes will often allow higher energy delivery with less thermal injury by using the heat sink effect of the surrounding tissue and blood flow during the interpulse intervals. Some lasers are pulsed by rotating or removing one of the end mirrors. Q-switched lasers rely on this technique to produce bursts of laser emissions in nanosecond pulses. Q-switched pulsed lasers are most useful in achieving fine control over surface ablation, an important attribute for laser skin resurfacing.

LASER TRANSMISSION AND INSTRUMENTATION

OPTICAL FIBERS

The energy emitted from the laser tube may interact with its target directly or more commonly is focused with lenses and transmitted through optically reflective wave guides, articulating arms, or fiberoptic cables (Fig. 14-7A,B). Not all laser wavelengths can be transmitted through true optical fibers, where there is total internal reflection and close to 100% transmission (with little or no heat generation). A wave guide is a type of flexible optical cable with a highly reflective, internal metallic coating. It differs from true fiberoptic light cables in a lower efficiency of light transmission and higher

A

Figure 14-7 (A) A laser bronchoscope.The laser beam is reflected through a prism, and the spot position within the lumen of the scope is adjusted with a pivoting mirror attached to a joystick. (B) Laser energy (argon) may be transmitted with little energy losses through a

heat generation, often requiring higher power outputs and air cooling with miniature pumps built into the laser. For example, a cost-effective fiberoptic cable is not yet clinically available for the CO2 laser. To reach areas within the nasal cavity, a wave guide is used instead.The laser energy also can be focused to a smaller, more intense microspot through the use of lenses within handpieces or the operating microscope.

FLASH SCANNERS

To spread the laser energy more uniformly over a target area, the flash scanner was developed. This is essentially a moving laser beam within a defined area created by two nearly parallel, rapidly rotating mirrors.With this technology, laser energy may be spread uniformly over an area with a diameter of 3 mm in 1 millisecond. Similarly, the laser energy may be pulsed rapidly over a defined surface area achieving a similar effect (see later discussion on skin resurfacing). Lasers merged with this technology are capable of precise surface ablation with little or no char at depths as little as 0.15 mm and is ideally suited for epithelial resurfacing (tattoo removal, wrinkle removal, lip vermilionectomy for leukoplakia, surface ablation of tonsillar crypts, etc.).

LASER INSTRUMENTATION

Laser hits from a reflected beam can cause both skin burns and eye damage. Metallic instruments that appear dull in visible light may in fact act like a mirror when exposed to the far infrared wavelength of the CO2 laser. Reflected, misdirected laser hits can be avoided by using

B

fiberoptic light cable. Not all laser wavelengths can be transmitted in this way and require less efficient wave guides, which achieve less efficient energy transmission and generate more heat within the carrier.

instrumentation that has a low specular or direct reflectance. Laser energy striking this type of instrument will produce a large diffuse or scattered and misdirected laser beam, with little risk of tissue injury. Attempts to blacken or ebonize and roughen the surfaces of metallic instruments will afford some but not complete protection. Ebonized instruments often lose their black coating after several cycles of sterilization and may have no real-life protective benefit over nonebonized instruments.

Some laser handpieces used within the oral cavity have a backstop to prevent laser hits beyond the target once vaporization is complete. It is essential that continued, prolonged laser exposure of the backstop be avoided because this may cause excessive heating and potentially burn the patient. Instruments should be lightweight to facilitate unencumbered movement, especially when attached to smoke evacuator tubing (see below).

LASER SAFETY CONTROL MEASURES

EDUCATION

The potential for disaster and the likelihood of litigation should not be underestimated when a medical laser is used by either inexperienced or careless individuals in an office setting or in an operating room. It is essential that every member of the surgical team, including the patient, be educated and informed. The patient should understand the specific benefits of the laser over other existing technology, and it should not be used unless those benefits have been well documented through clinical trials and peer review. The patient also must understand the unique risks associated with the use of laser energy and the potential for injury away from the operative field. This information should be included in the process of informed consent.

SAFETY GUIDELINES AND CREDENTIALING

In 1988, safety standards for laser use in medicine were first outlined in an American National Standards Institute (ANSI) report titled “Laser Safety in the Health Care Environment.”The standard itself outlines specific procedural and administrative controls necessary to ensure the safety of patients and health care professionals working with lasers and intended as a guide to aid the manufacturer, the consumer, and the general public. Although the ANSI report has defined the current standard of care for the safe use of lasers in the health care environment, compliance in general is voluntary unless required by a specific organization (e.g., hospital or ambulatory facility).

Administrative controls include the establishment of a laser safety committee and appointment of a laser safety officer.The laser safety committee generally consists of a multidisciplinary group, including physicians, nurses, biomedical engineers, and hospital administrators, who meet on a regular basis to establish and enforce adequate protective measures against laser-induced injury and provide in-service training for the management of laser-induced catastrophes (e.g., fires, burns, and explosions). Credentialing procedures must be set up and monitored by the committee for physicians, anesthesiology staff, nurses, technical support staff, and other health care personnel. Educational programs of at least 16 to 20 hours in duration and with 50% of the time dedicated to hands-on experience have been suggested as a minimum requirement for credentialing. The program must include exposure to all of the specific wavelengths of energy that will be used, as well as comprehensive training in all aspects of laser biophysics and safety.As new wavelengths of laser energy are introduced, specific additional hands-on training would also be required.

The laser safety officer must ensure continuing surveillance and enforcement of safety regulations and credentialing requirements. Any laser-related complications or problems are documented and reported directly to the committee for review and appropriate corrective action. New laser installations require inspection by the laser safety officer, in conjunction with the manufacturer and/or biomedical engineer, and should include assessment of other special considerations such as electrical hazards, fire and explosion hazards, eye exposure risks, laser smoke evacuation, and the flammability of anesthetic agents and drapes.

Indeed, the incidence of serious laser-related injuries at institutions adhering to the ANSI guidelines remains astonishingly low despite an increase in laser use across surgical subspecialties. Accidents occurring during laser surgery are almost always related to breaches in safety protocol and surgical accidents. Medical assistants or nursing staff in the office must have already received laser credentials and hands-on training in laser safety, or they must attend courses for certification prior to assisting physicians in performing laser procedures. All personnel should have in-service training from the manufacturer of the specific laser(s) being used in the office.

GENERAL SAFETY CONSIDERATIONS IN THE

OFFICE OR OPERATING ROOM

The treatment or operating room must be of adequate size to allow adequate dissipation of heat from the laser

unit and permit enough room around the patient to allow unencumbered movement of the laser articulating arm or laser fiber. Specific electrical and plumbing requirements must meet local building codes and be in place prior to installation of a laser in the office. This may require consultation with an engineer or electrician to ensure the presence of adequate circuit breakers and fire protection. Smoke detectors and fire extinguishers should be present at all times and regularly tested for proper function.

In the event of laser malfunction, traditional surgical instruments and hemostatic capabilities must be readily available. An electrocautery unit should always be present as well as silver nitrate to control minor bleeding.To avoid any potential fire hazard, all flammable liquids (e.g., ethyl chloride, alcohol, and acetone) should be removed from the treatment room when using the laser. Nonflammable drapes and water-saturated towels should be used to protect both the patient and anesthesia circuit tubing when appropriate. In the event of an endotracheal tube fire, a bronchoscope should be readily available both to reestablish the airway after immediate removal of the endotracheal tube and to inspect the endobronchial tree for thermal and smoke injury. All basic life support and emergency equipment must also be available.

Because the laser is capable of causing combustion within the patient’s airway and in the operating room, special precautions must be taken to avoid a fire hazard. Also, because most patients undergoing upper airway surgery with the laser require general anesthesia and the delivery of oxygen through an endotracheal tube, the least flammable mixture of inhalational agents should be used whenever possible. Mixtures of helium, nitrogen, or room air plus oxygen are often used to minimize the oxidizing effects of pure oxygen. Combinations of nitrous oxide and oxygen are particularly dangerous and should never be used because a “blowtorch effect” could cause serious injury to the tracheobronchial tree (Fig. 14-8). The risk of an airway fire may be minimized by the use of nonflammable laser-safe endotracheal tubes. Metal and coated tubes are available, but all have their advantages and disadvantages, and none are totally without risk. In addition, the use of double-cuffed endotracheal tubes filled with saline both prevent loss of airway protection due to inadvertent puncture by the laser and will help extinguish an airway fire. The proximal cuff is often filled with dilute methylene blue dye to help warn of a cuff puncture. Protecting the endotracheal tube from stray laser hits is essential. The use of saline-saturated cottonoids, laser suction platforms, and nonreflective, ebonized instrumentation are all essential safety

Figure 14-8 A demonstration of the “blowtorch effect” resulting when flammable anesthetic gas mixtures are ignited by the laser.

precautions. Eliminating the use of an endotracheal tube during surgery by jet ventilation or apneic technique with intermittent reintubation is the safest method but requires the participation and cooperation of an experienced anesthesiologist.

LASER QUALITY CONTROL AND

LOCKOUT FEATURES

The U.S. Food and Drug Administration (FDA) heavily regulates the development and introduction of medical devices for use in the health care industry. All lasers manufactured or imported into the United States are regulated by and must conform to all safety regulations established by the Center for Devices and Radiological Health, a division of the FDA.These regulations classify each laser by power and wavelength and specify its mechanical and electrical requirements. Laser manufacturers are required to classify their laser by one of four major hazard categories, depending on the type and power output. Each classification has specific operational safety guidelines. All lasers must have an identifying decal stating the specific class and the need for eye protection. The majority of medical lasers, with the exception of low-power diode lasers and lasers used specifically for alignment purposes [e.g., the helium-neon (HeNe) laser], fall into class IV. Class IV lasers are hazardous to view either directly or indirectly, will cause skin burns, and are a fire hazard. Approved laser safety glasses of the appropriate spectral range must be worn at all times when the laser is turned on and in the treatment mode (see below).

All lasers must have a key switch interlock or lockout feature to ensure that only qualified individuals use them. Most lasers will have a key-actuated master control switch. The key is removable, and the laser cannot be

operated when the key is removed. The laser should always be tested for proper functioning, and in the case of the CO2 laser, the aiming beam and treatment beams should be in reasonable alignment and can be tested on a wet tongue depressor. If there is any doubt about the proper functioning of the laser, either the procedure should be rescheduled or more traditional surgical techniques should be used until it can be professionally serviced. Medical lasers should be serviced by their manufacturer on at least a biannual basis to ensure proper output and alignment.

LASER WARNING SIGNS AND

BLACKOUT SHADES

A focused laser beam can traverse a room with very little attenuation and cause significant eye injury. It is essential that windows have blackout shades and entrance and/or exit doors be closed at all times to protect personnel outside the treatment or operating room.The ANSI-approved laser warning sign indicating the laser’s specific class, power, and wavelength should be hung in clear view outside the room, and ideally a “laser in use” status be indicated by either a lighted sign or flashing red light to ensure that the appropriate safety glasses will be selected.The laser warning sign ideally is affixed to the room door using Velcro strips, which permit repeated attachment and removal without damage to painted surfaces. If the door is metallic, a magnetic pad may be glued to the back of the sign to allow repeated removal. Safety glasses should be available in a box outside the door for visitors not present at the beginning of the procedure.

The use of laser safety glasses must be mandatory when using wave guides, optical fibers, optical telescopes, and the microscope. Eye injuries from cracked fibers and malfunctioning mechanical shutter filters have been reported. Only when using CO2 energy are the lenses within the optical telescopes and the microscope sufficient to prevent corneal injury.

The best protection against inadvertent laser hits away from the target area is coordination of laser actuation and standby modes.Any pause in laser activity should be followed immediately by a depression of the standby switch. The surgeon always must have an assistant to operate the laser mode and have the standby mode actuated as soon as active lasing is suspended. For example, when working in the oral cavity or nasal cavity, the laser should be in the standby mode as soon as the foot pedal is no longer depressed and prior to removal of the laser handpiece or fiber from the treatment area. Furthermore, when the laser is in the standby mode, confusing the

laser foot switch with the foot pedal for the electrocautery or bipolar cautery will not cause any harm.

EYE AND SKIN PROTECTION

Eye injury either to the cornea (focal cataract) or retina (blind spot or permanent blindness) can occur from a direct hit from the laser beam, a side hit, or a reflected beam hit.The specific injury will depend entirely on the wavelength of the laser energy and the energy density of the beam. Laser energy in the visible (argon, KTP, HeNe, etc.) and near infrared (Nd:YAG) regions of the electromagnetic spectrum (400–1400 nm) will tend to pass through the cornea and cause a retinal burn, whereas the CO2 laser in the far infrared spectrum will be absorbed by the water content of the cornea and cause a thermal injury (cataract/scar). Protective eyewear dedicated to the specific wavelength of the energy being used must be available for the patient, the surgeon, and any other personnel present in the operating or treatment room. The safety glasses should have side shields to prevent a side hit and be ANSI-approved, with their optical density and wavelength stamped on the frame. Although most plastic lenses are acceptable for the CO2 laser, glass lenses tend to resist scratching and will better withstand a laser hit. Laser safety glasses are essential for eye protection, but deeply colored lenses used for visible and near infrared lasers can obscure the operative field either by inadequate light or by color distortion.The operating surgeon must correct for these visual impairments and resist the temptation to operate the laser without safety glasses. Any of the currently available visible or near infrared lasers are capable of emitting a laser beam of sufficient power and within a time frame of such short duration that an aversion reflex or blink will not be sufficient to prevent an irreversible retinal injury.

Protection of the patient’s eyes from the laser is also mandatory. Besides wearing appropriate laser safety glasses, patients should keep their eyes closed during laser use and be additionally protected with moist saline-saturated eye pads whenever possible.

Facial skin burns represent the second most frequently reported complication. This complication occurs when the skin is inadequately protected and the laser beam is misdirected, either by user error or specular reflection from a metallic instrument in the surgical field. The use of a double layer of saline-soaked gauze sponges, lap pads, or towels is effective for the patient under general anesthesia. However, for office-based laser surgery on an awake patient, this is seldom used. It is therefore crucial that the patient hold perfectly still

during the procedure. For example, a rapid head turn during intraoral laser-assisted surgery could result in a facial or lip burn. Careful patient education with a videotaped demonstration of the procedure is quite helpful and reinforces the importance of a team approach.

LASER PLUME BIOHAZARD AND THE NEED

FOR UNIVERSAL PRECAUTIONS

Although stringent regulations concerning eye protection have been established by various regulatory agencies, there has been little written about protection from smoke inhalation during laser use. There has been increasing concern within the medical community that the noxious smoke plume generated by laser surgery may represent a significant health hazard both to the patient and to operating room personnel. The composition of plume generated during use of the CO2 laser has been shown to contain particles ranging in size from 0.10 to 0.80 . These particles are too small to be effectively filtered by currently available surgical masks, although there are some commercially available laser masks that claim higher efficiency in filtering. Independent studies have shown some of these masks to be no better than standard surgical masks. Several studies have shown the laser plume to contain numerous gases and hydrocarbons that are toxic, potentially mutagenic, and carcinogenic. Bacteria and viral particles also have been isolated and may remain viable for up to 72 hours. In addition to obscuring the operative field and causing reflection of laser energy, laser smoke can be irritating to the eyes. Inhaled particles from laser plume fall into the size range of “lung-damaging dust” or particles that can travel to the most peripheral parts of the lung parenchyma. Inhalation of laser-generated smoke may cause transient nausea, hypoxia, depression of pulmonary defense mechanisms, and delayed airway inflammation. It is conceivable that repeated long-duration exposures to unfiltered laser plumes cause or exacerbate existing lung disease or cause the commonly termed black lung disease. Live viral deoxyribonucleic acid (DNA),including papilloma viruses, hepatitis viruses, and human immunodeficiency virus (HIV) have been isolated from the airborne contents of the laser plume and may be infectious. Therefore, laser plume must be treated like any body fluid that may contain bloodborne pathogens, and universal precautions should be instituted. This should be considered when handling and disposing used smoke evacuator filters.

SMOKE EVACUATION

The best way to minimize the risk of smoke inhalation during laser surgery is to ensure adequate smoke evacuation

at the site of generation.This will prevent the generation of airborne particulate matter and eliminate direct inhalation by the surgeon, patient, or operating room assistant. Specially designed laser handpieces, nasal specula, laser fiber holders, and metal tongue depressors must all incorporate smoke evacuation channels.When not using one of these instruments, the smoke evacuator tubing should be connected to a pool tip suction (to prevent suction of skin or sponges) and held as close to the operative site as possible without interfering with the laser beam.The instruments are connected via tubing to high efficiency particulate air (HEPA) laser smoke evacuators capable of eliminating 99% of all particles in the range of 0.1 .To maintain high efficiency and prevent malfunction, filters must be changed according to the manufacturer’s recommendations, and blood or secretions must never be suctioned into the smoke evacuator tubing.When working in the upper airway on an awake patient, laser treatment should be coordinated with breathing, so that tissue vaporization takes place while the patient exhales. This will divert the smoke plume toward the evacuation aperture of the laser instrument and prevent smoke inhalation.

Adequate room ventilation is essential and must exchange and filter the room air according to local standards.The laser generates heat, and in a small treatment room, the addition of fans and freestanding HEPA air cleaners may be needed. Ventilation ducts and vents should be positioned strategically relative to the treatment chair or table to maximize smoke evacuation.

SPECIFIC LASER APPLICATIONS IN THE HEAD AND NECK

CUTANEOUS APPLICATIONS

Skin laser treatment may be performed in an office setting using topical anesthesia and several highly specialized new laser technologies. In an attempt to improve initial treatment results for vascular skin lesions (e.g., telangiectasias, port wine stains, hemangiomas, and venous lakes), pulsed lasers with more selective chromophore or pigment absorption spectra were developed to replace the KTP, argon, and Nd:YAG lasers, which often caused scarring or hypopigmentation.The “yellow” wavelength (577–585 nm) dermatological lasers (copper vapor and flash lamp pumped-dye lasers) evolved by necessity for treatment of vascular skin lesions. These pulsed lasers allowed a higher peak instantaneous delivery of energy than the average power. By pulsing the energy, decreased thermal spread and tissue injury are possible by using the heat sink effect of the circulation between pulses.

A more recently introduced generation of lasers is now capable of delivering high-intensity, short energy bursts that can pass through the epidermis with minimal superficial injury and permit even more selective wavelength absorption of either melanin (694 nm) or oxyhemoglobin (585 nm). The Q-switched YAG, Q-switched ruby, or Q-switched alexandrite (694) lasers are more melanin pigment selective, and the candela flash lamp- excited-dye (585) laser is more hemoglobin selective. These newer pigment-selective lasers have significantly improved the treatment of a variety of superficial skin lesions by reducing scarring and hypopigmentation, problems occasionally encountered in the past with argon and KTP lasers. Although many pigmented skin lesions can be cured or lightened with the laser, suspicious or recurrent lesions are still best treated by careful excision.

The use of lasers to achieve reproducible and predictable skin resurfacing has become a major component of cosmetic surgery and is performed routinely by dermatologists, general plastic surgeons, and facial plastic surgeons. The development of computerized, pulsed or scanning technology, for example, Silktouch (Sharplan Lasers, Inc., Allendale, NJ) and Ultrapulse (Coherent Inc., Palo Alto, CA), has added a new dimension to laser surface ablation. By pulsing the laser beam or scanning the laser beam over a defined area of skin, the laser’s energy can be delivered at a relatively high power for brief periods of time.This results in superficial surface vaporization without char or thermal injury. Control over surface tissue ablation can now be achieved with a degree of precision not previously possible. Although chemical exfoliation, or chemical peel, continues to be a popular method for skin rejuvenation, more control over the desired depth of resurfacing is now possible when the CO2 laser is coupled to this new technology. The CO2 laser can be used to exfoliate the epidermis and dermis by superficial vaporization to renew sun-damaged skin and to ablate superficial, static wrinkles. Deeper, dynamic wrinkles or skinfolds formed by the underlying muscles of facial expression cannot be treated effectively by the laser but are amenable to botulinum toxin injections, selective muscle lysis, and skin tightening procedures (e.g., rhytidectomy and forehead lifts).The CO2 laser is being used to debulk large keloids and mild to moderate acne scars and to “resurface” other skin areas such as superficial traumatic scars, pigmented solar keratoses, xanthelasma, spider hemangiomas, and other vascular and benign tumors. Laser treatment of rhinophyma, a particularly deforming sebaceous skin lesion of the nose, has also met with much success.

LARYNGEAL AND TRACHEOBRONCHIAL

APPLICATIONS

The use of the CO2 laser in otolaryngology procedures was first introduced in the early 1960s by Jako and Strong. The laser provided a unique tool for bloodless, sterile, no-touch microlaryngeal surgery for a variety of lesions. The management of recurrent laryngeal papillomatosis, webs, scar and stenosis, and telangiectasias are often best managed by combining traditional microsurgical techniques with the laser.The popularity of the laser for benign vocal cord lesions has declined, primarily because of accruing evidence of vocalis muscle scar and vocal cord stiffness. However, newer microspot focusing lens systems and application of microflap, mucosal welding techniques at low power settings (milliwatt) have refined use of the laser in phonosurgery.

Although there is continued controversy concerning postoperative voice quality, the use of the laser for ablation of early vocal cord cancers is a welcome and oncologically sound addition to open conservation laryngeal procedures and primary radiation therapy. In many situations, the transoral laser excision of superficial vocal cord cancers can be curative, with the lowest morbidity of any treatment modality.The laser is often useful for debulking obstructing laryngeal and endobronchial tumors. The CO2 laser is usually used for the larynx and subglottic airway and the Nd:YAG laser for bronchial lesions. The Nd:YAG laser can be used with a fiber passed through a flexible bronchoscope.

ORAL CAVITY AND OROPHARYNGEAL

APPLICATIONS

Tumors of the tongue, gingiva, floor of the mouth, palate, and tonsils can be resected with excellent hemostasis and control using the CO2 laser. Lack of muscle stimulation from the electrocautery can be of benefit in controlling tongue tumor margins. Because large vessels in the oral cavity cannot be controlled with the CO2 laser, the electrocautery must always be on the field. For palliation of bulky, nonresectable tumor, the Nd:YAG can accelerate tumor necrosis and help debulk obstructing lesions or control bleeding from raw tumor beds.

The use of the CO2 laser for tonsil surface ablation can be very effective for controlling or eliminating food collection in deep tonsillar crypts. It can be performed in the office with local anesthesia. Laser-assisted uvulopalatoplasty has become a popular office-based procedure for the management of habitual snoring and mild cases of obstructive sleep apnea.