Safe Use of Medical Lasers (2024)

HAZARDS WHEN USING LASERS

Risk to the eyes

The American National Standards Institute (ANSI) has classified lasers into four categories, according to their potential to damage the eyes.

Class I: A laser that does not exceed the maximum permissible exposure (MPE) of the eye even when exposed to direct sunlight for a long time. As a self-contained unit used in general laboratories, it does no harm under normal limits.

Class II: IIa: It is safe to be exposed as a visible light laser within 1000 seconds.

IIb: As a visible light laser, blinking eyes are safe to be exposed within 0.25 seconds. It is not capable of emitting and output of 1 mW or more. They include He-Ne alignment light (CO2 or Nd: used for YAG lasers), and laser pointer light. There is no harm if they have not seen the light directly for a long time.

Class III: Class IIIa is a laser that cannot have an output of 1mW or more like Class II, and is used in aim beams such as architectural badges. It does not cause harm when the eyes are exposed within 0.5 seconds.

Class IIIb can output up to 0.5W CW, and when exposed directly to the intra-beam, it can harm the eyes and skin, and belongs to the infrared solid-state laser that eliminates wrinkles for molding. These types of lasers must be tested before use and can be harmful, so they must be operated with care and protective devices are required when operating them.

Class IV: As a laser with an output of 0.5 W or more, even if it is exposed momentarily, it damages both the eyes and the skin. Like a CO2 laser, it can cause damage such as fire, images and eye damage, either directly as a potentially dangerous laser or by reflected light rays.³

The FDA and Rockwell reported that 75% of 134 laser accidents in 1984-1989, and 73% of 272 laser accidents in1964-1994, respectively, were eye injuries.⁴ Eye damage is completely preventable.

The eye is very sensitive to the laser beam and the type and extent of damage caused by laser irradiation depend on the wavelength of the light and the energy absorption characteristics of the ocular tissues. Far infrared lasers, such as CO2 lasers, are absorbed by the cornea, lens, and vitreous body. While they do not cause damage to the retina, they cause damage to the cornea (If the corneal damage is not deep, it can be recovered within a few days).

Visible light lasers, such as the Argon, KTP/532, and krypton lasers, are focused on the retina by the cornea and lens. They damage the retina, causing blind spots in the field of view and damages to the fovea. On the optic nerve, it causes far more serious visual impairment. The injury may occur immediately after beam irradiation, or it may be a chronic degenerative injury resulting from repeated exposure to a low power laser beam. Near infrared lasers with wavelengths between 800 and 2000 nm, such as Diode Laser, Nd: YAG, and Ho: YAG, are focused to the retina by the cornea and lens, and cause damages to the three tissues. The maximum permissible corneal exposure (MPE) of the eye is determined by the wavelength and duration of exposure, and protective goggles should be used when there is a risk of exceeding the MPE (Fig. 1). The eyes are vulnerable to visible light due to specific physiological factors. Parallel laser beams are focused in a similar manner as the light rays, the direct entry of these rays is called intra-beam exposure. While surgical laser beams are usually not parallel, unfortunately, since the eye can accept a wide range of rays, they can be focused on the retina like 10 μm sized spot.⁵ However, even though the light beam reflected by the non-smooth surface of the laser beam also enters the eye, this light beam enters the eye at a wide angle, and therefore the image generated on the retina also occupies a wide area. This is called an extended source. It is easy to see that the risk of the retina is lower for extended sources when the exposure time is shorter than for intra-beam exposure.

Figure 1. Protective goggles (A) and patient’s eye protection (B).

Previous reports on eye damage indicated that only those with inefficient protective goggles were injured.⁶ Therefore, each time a Class IIIb and IV laser is used, to reduce the risk of eye damage, you must use matching protective glasses and goggles (with goggle side shields). Extra precautions should also be taken when using an endoscope that does not have an automatic filter. Even with these protective goggles, they do not protect you from being exposed directly to the laser beam for extended periods of time. The patient's eyes should also be protected with a saline-moistened sponge or metal eye cover or appropriate eyeglasses.

Long time exposure

When exposed to a laser for an extended period (10 seconds or longer), there is a significant risk of photochemical effect, rather than the effect of high temperatures, at visible light wavelengths, especially in the blue region of the spectrum. However, this can be prevented with protective goggles.

Protective goggles

Practical use of all surgical lasers will always exceed MPE if exposed to intra-beam during.⁸ Therefore, protective eyewear including goggles (with a side shield) suitable for the laser in use must be worn. Protective eyeglasses are comfortable to wear; however, eyeglasses alone do not provide sufficient protection. Optical density appropriate for the specific length must be displayed on the protective goggles. It should be known that any filter can penetrate the filter if it is exposed to the intra-beam for a long time.

Generally, the optical density of protective goggles appropriate for an argon laser is 10, and that of a CO2 laser is usually about 15, which is far beyond the level of safety. Notably, in some cases red therapeutic or guide beam do not show when performing laser surgery with protective goggles.

Effects on skin

Since it is largely exposed, the skin is more prone to laser damage, but the resultant damage is less serious than that of the eyes. The skin damage, which is clearly visible as redness or black carbonization on the tissues varies depending on the laser wavelength, the exposure time, the beam density and the skin color. While laser damage on the skin can result from either the photochemical effect or thermal effect, the primary cause of laser damage on the skin is high temperatures. The high temperature alters the protein to necrotize the tissue, boils the cellular components, evaporates the tissue, and the dried tissue forms carbonization. Therefore, normal tissues other than operation site should always be overwritten with a drape or sponge soaked in water. Dried drapes and sponges are prone to ignition and need to be re-wet with distilled water or saline on a regular basis during surgery.

Gas embolism

Gas embolism was reported to have occurred during intrauterine surgery using tip of Nd:YAG fiber. Gas-cooled fibers should be restricted for use on the body surface only, as gas embolism has been reported during liver surgery.

Laser plume

The smoke generated by the laser is composed of small particles of approximately 0.1 micrometer. The smoke has a strong odor, and reaches the bronchioles and alveoli, causing damage similar to that of asbestos and tobacco.^9,10 Exposure to smoke can irritate the eyes, nose and throat, causing discomfort and chronic coughing.¹¹ Garden detected HPV DNA in laser smoke, therefore it important to have a thorough suction. Proper position of the smoke evacuator is essential for effective smoke suction and should be placed within 2-5 cm of the laser surgery site if possible. Inserting a 0.3 μm filter between the wall suction and the suction bottle is necessary in some situations where the smoke inhaler is not used.

A laser mask (0.3 μm filtration) must always be worn when using CO2 lasers. In the room using Q-switched lasers, normal masks are sufficient. All tubes, connectors and adapters must be changed after the surgery.

Reflected or incorrectly emitted laser

Accidentally laser beam can be reflected off surgical instruments and surrounding materials, and while such mistakes are rare, they are serious mistakes that should be avoided at all cost. To avoid the risks, all instruments using the laser and the reflective surfaces of surrounding materials must be thoroughly investigated. All reflectors (such as endoscopes) must be replaced with non-reflective ones, deformed, or covered in black.

A laser that penetrates the target tissue or spreads too far to the side will destroy the non-target tissue. For example, Nd:YAG penetrates 5-7 mm and therefore not suitable for the treatment of thinner tissues instead, holmium, CO2 lasers and Nd:YAG contact mode have can be used since they have weaker penetration than Nd:YAG. In addition, auxiliary equipment such as a platform that prevents and absorbs the over-penetrated laser behind the target tissue can be used to prevent over-penetration (especially when using an endoscope).

Fire and electrical hazards

A fire caused by a shot wrongly laser or an electric shock caused by high-voltage electricity is unpredictable and horrific accidents during laser treatment. According to experts, 100 fires occur in the operating rooms in the United States, each year. Among them, 10-20 cause severe injury to patients with 1-2 deaths.¹² The drape that covers the patient in the operating room is easily ignited by the laser since the oxygen levels are high. To prevent this, drapes with weak ignition qualities should be used. In addition, the cover of the laser site should always be kept wet.¹³ The endotracheal tube fire will be described separately.

Many lasers are high voltage electric devices that can easily shock handlers, especially when the protection plates are removed. There is also a risk of unnecessary disruption in case the devices come into contact with water that can short-circuit the system wiring. For these reasons, it is important that users receive appropriate training from the manufacturer. Types of laser hazards is summarized in Table 1.

Table 1 . Types of laser hazards

Types	Hazards
Laser irradiation	Eye, skin, or airway injury Primary or scattered beam
Chemical hazards	Laser plume Irritation to eyes, nose and throat Spread of viral materials
Fire and electrical hazards	High voltage, flammable materials Anesthesia tube, patient’s hair or clothes