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What are the safety rules for using a laser for surgical procedures in a veterinary practice?

During surgical procedures using a laser or electrosurgical unit, there are unique hazards that staff members face. Among them are the smoke byproduct produced by the thermal destruction of tissue and the danger from the laser itself. As this tool becomes more commonplace in the veterinary practice, controlling the hazards to the staff is just part of the job.

Smoke Dangers

Research studies have confirmed that this smoke plume can contain toxic gases and vapors such as benzene, hydrogen cyanide, and formaldehyde, bioaerosols, dead and live cellular material (including blood fragments), and viruses. At high concentrations the smoke causes ocular and upper respiratory tract irritation in staff members, and creates visual problems for the surgeon. The smoke has unpleasant odors and has been shown to have mutagenic potential. Fortunately, research has shown that airborne contaminants generated by these surgical devices can be effectively controlled by two methods: adequate ventilation and appropriate work practices.

Ventilation: Ventilation controls include a combination of general room and local exhaust ventilation (like a scavenger system.) General room ventilation is not sufficient in itself to capture contaminants generated at the source, therefore, process-specific exhaust ventilation is also required. The two major exhaust ventilation approaches used to reduce surgical smoke levels for staff members are portable smoke evacuators and scavenger-type suction systems.

Smoke evacuators contain a suction unit (vacuum pump), filter, hose, and an inlet nozzle. The smoke evacuator should have high efficiency in airborne particle reduction and should be used in accordance with the manufacturer's recommendations to achieve maximum efficiency. A capture velocity of about 100 to 150 feet per minute at the inlet nozzle is generally recommended. It is also important to choose a filter that is effective in collecting the contaminants. A High Efficiency Particulate Air (HEPA) filter or equivalent is recommended for trapping particulates. Various filtering and cleaning processes also exist which remove or inactivate airborne gases and vapors. The various filters and absorbers used in smoke evacuators require monitoring and replacement on a regular basis and are considered a possible biohazard requiring proper disposal.

Scavenger suction systems used to capture generated smoke are different from waste anesthetic gas scavengers because of the amount of air drawn into the system and the method by which the fumes or smoke are captured. In a waste gas scavenging system, the flow rates are measured in liters per minute, corresponding to the flow rate of the anesthetic and the gas never leaves the system’s tubes (hence a closed scavenging system.) In a smoke scavenger suction system, the flow rates are usually higher (in cubic feet per minute) so that the smoke can be removed from the air surrounding the open end of the suction hose. In some cases it may be possible to modify existing scavenging systems to perform both functions. Once captured in a scavenger suction system, the smoke is exhausted outside the work environment at a safe location.

Work Practices: The smoke evacuator or scavenger suction hose inlet must be kept within 2 inches of the surgical site to effectively capture airborne contaminants generated by these surgical devices. The scavenger or smoke evacuation system should be activated at all times when airborne particles are produced during procedures. At the completion of the procedure all tubing, filters, and absorbers must be considered contaminated and cleaned, disinfected or disposed of appropriately. Of course, regular maintenance and inspection of the scavenger or evacuator is essential for preventing leaks that could release the harmful smoke back into the room.

Laser Light

Eye safety is the most immediate concern for anyone working with or near a laser. As quick as it takes to blink, the laser can severely damage the eyes of anyone standing within range of the laser. Though the injuries are rare, they are permanent. Engineering controls are the preferred method of protection but cannot be relied on as the only protection. Protective eyewear may also be necessary, especially during the alignment of a laser beam.

Engineering controls, such as protective housings, remote controls, or enclosed laser-beam paths, ensure protection for the operator except when the operator needs to set up, adjust or maintain the beam. Any practice which uses a laser should appoint a Laser Safety Officer (LSO) who is responsible for monitoring and enforcing the control and operation of laser hazards.

Eye damage from a laser beam happens primarily because the cornea and lens focus the light beam to a very small spot on the retina. Vision damage is usually severe, and can result in blindness; therefore, direct viewing of the laser and its reflections should be avoided by all practical means available. A laser's reflective beam intensity may approach its direct beam intensity so it’s also important to remove any reflective objects or surfaces from the area of the procedure.

The four main points determine the type of eyewear required for a laser are:

• Wavelength
• Pulse vs. continuous laser
• Laser type (carbon dioxide, ruby)
• Wattage

A laser consists of a resonant optical cavity filled with an active medium. The medium is acted upon by some source of excitation energy. The media could be one of three types: a solid state, a gaseous state, or a semiconductor or injection-type. Solid lasers use a crystal (i.e. ruby), glass or a semiconductor (argon) as the light amplifying substance, producing a pulsating laser beam. A gaseous state laser (helium-neon) produces a continuous beam.

A laser produces an intense beam of light of a single wavelength (or color) and frequency. The American National Standards Institute (ANSI) classifies lasers into categories and gives guidelines on laser safety in their standard Z136.1.

• Class 1: Cannot emit laser radiation at known hazard levels.
• Class 2: Low-power visible lasers. Emit laser radiation above Class 1 levels and radiant power not above 1mW. The human aversion reaction to bright light will protect the person from this level. Example: a supermarket laser scanner.
• Class 3A: Intermediate-power lasers. Only hazardous for intrabeam viewing. Some limited controls are usually recommended. Example: a helium-neon laser used for pointing.
• Class 3B: Moderate-power lasers. Not generally a fire hazard and usually not capable of hazardous reflection, except in instances of intentional staring at close distances.
• Class 4: High-power lasers. Hazardous to view under any condition (directly or diffusely scattered). Potential fire hazard and a skin hazard. Significant controls are required for Class 4 laser facilities. Example: an Excimer laser operating in the ultraviolet.

A laser's eye-damaging ability varies depending on which area of the light spectrum it is generating. The ultraviolet radiation laser (180-400nm) causes corneal burns. Infrared radiation lasers (780-1800nm) cause retinal damage; these are usually Class 2, 3A, 3B and 4 lasers. The high-powered lasers, Class 3B and 4, can also cause electrical shock and skin burns. For information on the laser's wattage or power of the laser, refer to the instruction/maintenance manual. A skin cover, like opaque gloves and tightly woven fabrics, and or a "sun screen" may be recommended for Class 4 lasers.

Protective Eyewear

The lens of laser protective eyewear is a filter/absorber designed to reduce light transmittance of a specific wavelength. The lens can filter out (or absorb) a specific wavelength while maintaining adequate light transmission for other wavelengths. The absorption capability of the filtering media is called the optical density (OD). The OD is always expressed as a factor of 10. An OD of 5 means the filter has reduced the power of the beam to 1/100,000 of its original power. The required OD is the minimum OD necessary to reduce the beam to a non-hazardous level.

When choosing appropriate eyewear, time is also a consideration. Unlike protective goggles for x-rays, which are designed to protect from scatter radiation, laser protection eyewear is designed for protection against the primary laser beam but only for a short time: e.g., where the beam is reflected into the eye accidentally. Some considerations you must take into account when selecting the proper eyewear are how long will the eyewear protect the eye before the beam goes through and how long will you have to react if you are hit with a direct beam? According to the ANSI standard, protective eyewear shall exhibit a damage threshold for a specified exposure time (typically 10 seconds). The eyewear shall be used in a manner so that the damage threshold is not exceeded in the worst case exposure situation.

Other Hazards

In addition to the smoke and eye protection issues, there are these considerations when using lasers in the veterinary practice:

• A potential explosion hazard may occur from the buildup of high pressures of gases in the flash lamp when it is fired.
• Sometimes cryogenic gases (liquid nitrogen or liquid helium) are used to cool the crystal (ruby, neodymium, etc.). Skin burns can result from contact with these gases. If these cryogenic gases leak into a closed room, they are capable of replacing the oxygen in the air, thus creating an oxygen-deficient atmosphere.
• Electrical shock or electrocution may occur from contact with exposed utility power. Exposures can occur during setup, installation, maintenance and service of the laser. The protective covers are often removed to allow access to the components.
• Fire is also potential hazard with Class 4 laser systems. The use of flame-retardant materials should be encouraged.

Given the ease and results of this tool, it’s easy to see why lasers are becoming more prevalent in the average veterinary practice. Even with the potential risks of using lasers, many practices use them with excellent safety records and clinical results. The key to establishing an effective and safe laser program is to prepare the location properly and follow all the procedural instructions supplied by the manufacturer.

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The information on these pages is excerpted from
The Veterinary Safety & Health Digest,
Copyright 2000 Philip J. Seibert, Jr., CVT  All Rights Reserved
No part of this publication may be reproduced for distribution without prior permission from the publisher.