Laser Safety
Sameer Menda
Berklee Robins
Deborah Carter
Vishal Khemlani
▪ INTRODUCTION
Laser light is a form of energy that has been used for surgery by many medical subspecialties for decades. Lasers may provide distinct advantages over other surgical techniques because of their ability to target difficult-to-reach regions of the body and provide a high amount of energy to a very small surface area. The result is a precise surgical target that is heated, often to the point of vaporization, with minimal swelling and trauma to surrounding tissues. This may result in reduced postoperative pain. Another advantage of laser surgery is its ability to minimize bleeding and destroy small blood vessels at the target area by photocoagulation. Photocoagulation is the coagulation (clotting) of tissue using a laser that is selectively absorbed by hemoglobin, a component of red blood cells.
Otolaryngologists often use lasers to target areas such as the larynx (voice box) and trachea. Urologists often use a different type of laser to destroy kidney stones in the ureter and kidney. Other medical fields that commonly use lasers are ophthalmology and dermatology, targeting the eye and skin, respectively.
Though laser surgery has provided remarkable benefits to the medical field and patients, the use of laser is not without risks. It is important for the anesthesia technologist to be familiar with the various types of lasers used in medical practice today, as well as the particular risks and protective measures that are unique to each.
▪ LASER TECHNOLOGY
Laser is an acronym for light amplification by stimulated emission of radiation. It describes the process of producing and amplifying light energy. Laser light, like all forms of light, from x-rays to ultraviolet radiation, travels in waves. The length of each wave, known as wavelength, determines the amount of energy of the laser and its unique properties. Laser energy commonly used in medicine is either visible light with a distinct color or invisible.
Three main components are required to produce laser light:
An energy or power source
An active medium energized by the power source (solid, liquid, or gas)
Mirrors used to amplify and channel the energy from the active medium to the light that is emitted
The active medium in a laser is the material (solid, liquid, or gas) containing atoms, which can be energized by a power source. Examples of active mediums used include gas mediums such as carbon dioxide, argon, or krypton and solid mediums such as neodymium (Nd), holmium (Ho), or chromium used to produce a ruby laser. Liquid mediums can contain dyes, which produce a distinct color and wavelength of laser light.
The energized atoms of an active medium release photons of energy, which are amplified by mirrors. The photons then exit into a delivery system as a beam of laser light, with specific properties. The waves of this laser energy have the same wavelength, travel in the same direction in synchronization, and do not diverge or spread out with distance. In contrast, ordinary light is a combination of waves of varying wavelengths traveling out of synchronization spreading out in all directions. By understanding how laser light differs from other light sources, it is clear why such an intense amount of energy can be focused on a small target from a distance.
▪ LASER INTERACTION WITH TISSUE
Laser energy has a variable interaction with a target tissue depending on its wavelength and the composition of the target substance. Laser light energy may
Travel through a substance without affecting the substance
Be absorbed by the substance at the point of impact, generating heat in the affected tissue
Reflect off the target substance
The goal of laser use is to produce the desired effect on the target tissue without transferring heat to adjacent tissues. Laser light energy absorbed as heat at the desired target tissue can start to produce a smoke plume once the tissue reaches temperatures near 100°C. Effects such as protein remodeling and coagulation of the tissue occur at lower temperatures.
Surgeons often take advantage of a laser’s unique wavelength and characteristics to selectively treat a target tissue (Table 53.1). A particular laser may be used because its wavelength is absorbed by certain colors (e.g., hemoglobin in vascular lesions such as port-wine stains or a particular pigment in the skin during removal of a colored tattoo). Laser beams with long wavelengths, such as a carbon dioxide laser, are readily absorbed by water in the superficial tissue layers. This minimizes deeper penetration, making it ideal for targeting only the surface of a tissue. Other lasers such as the Nd-YAG and KTP laser, both with shorter wavelengths, can both target deeper structures in the tissue since they are not readily absorbed by water at the superficial layers. The main factors determining the effect of a laser on a given tissue are listed below:
Power (watts) of the laser beam
Duration of exposure
Surface area exposed
Wavelength
Target tissue composition
It is important for the anesthesiology technologist, as well as all operating room personnel, to have a basic understanding of the type of laser in use. This will assist them in determining safety precautions to prevent possible injury.
▪ SAFETY CONCERNS
Laser surgery has many hazards associated with its use including the risk of eye injury, fire hazard, and air contamination. Deaths have been reported related to venous gas embolism, particularly when a gas coolant other than carbon dioxide for the laser was used. Other risks include damage to soft tissue, such as skin burns, and perforation of the trachea, if the laser beam is misdirected or used inappropriately.
Laser usage should be limited to trained personnel in the operating room. The delivery system of many lasers is composed of small mirrors necessary to carry the laser beam from a laser unit to a handpiece or scope. It is important to handle the machine carefully since the mirrors can easily be misaligned, resulting in a laser malfunction or a misdirected laser beam. The laser unit should always be in the standby mode when not actively being used.
Eye Injury and Protective Eyewear
Lasers used during surgery have the potential to damage both the superficial (cornea) and deep structures of the eye (retina). Certain lasers with longer wavelengths, such as carbon dioxide and holmium, are incapable of penetrating fluid. The result is such that most of their effect is on the superficial layers of the eye (cornea). Other lasers, such as the Nd-YAG and diode lasers, are capable of penetrating fluids and act upon the deeper structures of the eye. Ophthalmologists often use diode lasers to treat the retina. If a laser beam able to penetrate fluid contacts an unprotected eye, the eye structures can focus that beam onto the retina, causing injury.
It is important to wear protective eyewear specific to the type of laser being used in the operating room because the eyewear has been designed to absorb the specific wavelength originating from that particular laser. The area where injury from a laser can occur is called the nominal hazard zone. Laserspecific protective measures, including laser eyewear, should be used in this area. The room where a laser is used must have a standardized sign, as mandated by the American National Standards Institute, posted at each entrance. The wavelength of the high-powered treatment laser being used should be listed on these signs. Protective eyewear should be worn before entering this area. The manufacturer must specify the wavelength, in nanometers (nm), or a range of wavelengths, that
the protective eyewear is designed to absorb. The wavelength number (or range) on the eyewear must match the nanometer number for the treatment laser in use. It is important to note that the color of the protective eyewear itself is not a reliable indicator of which wavelengths are absorbed; the wavelength number on the eyewear and the wavelength number of the laser must be the same. Laser protective eyewear may not protect against exposure to a direct beam of laser energy. Lasers can easily reflect off shiny mirror-like surfaces, causing unintended harm. Most operating room instruments used during laser surgery are nonreflective with a dulled finish to minimize the risk of laser beam reflection. Many of the lasers used in the operating room can penetrate glass, so an opaque covering should be used on all windows.
the protective eyewear is designed to absorb. The wavelength number (or range) on the eyewear must match the nanometer number for the treatment laser in use. It is important to note that the color of the protective eyewear itself is not a reliable indicator of which wavelengths are absorbed; the wavelength number on the eyewear and the wavelength number of the laser must be the same. Laser protective eyewear may not protect against exposure to a direct beam of laser energy. Lasers can easily reflect off shiny mirror-like surfaces, causing unintended harm. Most operating room instruments used during laser surgery are nonreflective with a dulled finish to minimize the risk of laser beam reflection. Many of the lasers used in the operating room can penetrate glass, so an opaque covering should be used on all windows.
TABLE 53.1 CHARACTERISTICS, HAZARDS, AND USES OF MEDICAL LASERS | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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