<title>Optimal surface characteristics for instruments for use in laser neurosurgery</title>

Abstract

In recent years, the C02 laser has proved to be a valuable instrument in neurosurgery. Its primary role has been in the ablation of tumors, although it may also be used in intricate dissection of other tissues. The C02 laser beam can be focused and used with a microscope and micromanipulator. This, coupled with the principle that 90% of the radiation is absorbed in the first 0.03 mm. of water makes the instrument exquisitely precise in Lumor removal while sparing tissues which must be preserved. This precision makes for an instrument which usually has a high degree of safety. However, while it usually is quite innocuous, this powerful tool carries the potential for injury.(2) The otolaryngologists report serious injury by inadvertent ignition of endotracheal tubes by laser.(1) This can result in extensive injury to the airway and lungs due to heat and smoke. In the neurosurgical operating room, injury can occur either by the beam striking structures directly or indirectly. Other instruments are usually present in the surgical field during laser use. Hand-held or self-retaining retractors, suction devices, or probes are used to retract or manipulate structures or to evacuate smoke or fluids. These may be inadvertently passed into the path of the beam or may be struck by a moving beam. The injury can be divided into that in which tissues in contact with the instruments are burned by the instrument which absorbs the energy and heats up, and injuries which occur by energy which is reflected off of an instrument. Both the patient and the surgical personnel are at risk from this reflected energy. Reflected power can even ignite surgical drapes. Measures are routinely taken to help reduce the risks of injury. These include the requirement that safety glasses are used by all operating room personnel. Delicate structures within the surgical field are covered with moist cottonoids. Instrument design should incorporate features which reduce the risk of injury due to reflection and absorption of energy. Many companies offer the service of ebonizing instruments with the claim that they will improve the safety of laser surgery. Unfortunately, there have been few studies performed which ascertain the ideal characteristics of instrument design. This study was performed to determine whether varying certain characteristics of the surface of an instrument can reduce surgical risks. Flat brain retractors were used to control for variation in the beam striking a curved surface. Identical retractors were prepared 128 / SPIE Vol. 1428 Three-Dimensional Bioimaging Systems and Lasers in the Neurosciences (1991) O-8194-0518-3/91/$4.OO with surfaces with various grades of roughness and with different surface materials. Each retractor was tested for absorption and for reflection of energy.