NdYAG Laser

The Nd:YAG laser has a wavelength of 1.06 microns, which is poorly absorbed by water and, therefore, penetrates tissue deeply. It is well absorbed by pigment (deep purple), vascular tissue, and the char of carbon deposits (see Table 37-1). The energy is not dissipated at the surface, as is the case with the CO2 laser; it scatters within the tissue depending on the degree of tissue pigmentation for absorption. The YAG laser in a noncontact mode is a "cooker" or coagulator of tissue as opposed to the more precise cutting effect of the CO2 laser. In the less common contact mode, the YAG laser is somewhat wavelength independent and the energy concentrates at the tip of the fiber and causes limited vaporization of tissue and little damage to the surrounding tissue. The contact mode is good for coagulating blood vessels less than 1 mm in diameter; its effect on soft tissue is similar to the CO2 laser.6

The YAG laser can be transmitted through commonly available flexible quartz fibers that make possible its use in the tracheobronchial tree. Using the nonfocused fiber, the laser beam diverges approximately 10° as it leaves the fiber; the closer the fiber is to the tissue, the smaller the spot size. The fiber is normally used at 0.5 to 1 cm from the target. The fiber can be connected to a series of contact tips of differing geometric shapes for contact mode use for the purpose of cutting, coagulating, and ablating. Care must be taken to deliver the beam in short exposures of 1 sec or less at a power setting at 40 W or less. Continuous exposure of the Nd:YAG laser at a high power setting (above 40 W) may result in an explosion of tissue, caused by concentration of high energy below the tissue surface that creates an expanding cavity.

The Nd:YAG laser wavelength has little visible effect on colorless tissue; the laser beam readily traverses it, causing thermal damage to the more pigmented underlying tissue or structures, such as blood vessels. It is important to note that the white color of the normal tracheal cartilage will not absorb the laser energy unless it becomes dehydrated from the continuous heat and char to form an absorbing element. The laser will otherwise pass through the unpigmented wall and may be absorbed by the underlying vascular structure and lung tissues. It is well known that the thermal effects of the Nd:YAG laser go well beyond its immediate area of visible impact; what is seen is not necessarily what you get.6 A study by Shapshay, comparing the CO2 laser with different Nd:YAG delivery systems, points out the pitfalls in using the Nd:YAG laser.6 Thermal damage from using the YAG laser in the normal tracheobronchial tree delays healing and reepithelialization, and may cause scarring. Mucosal charring and blood deposition on the tracheal wall enhance the absorption of the Nd:YAG laser beam. Rapid propagation of thermal energy can ensue, causing tracheal perforation.

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