COMPLICATIONS OF LASER SURGERY

Abstract

Newly applied concepts in technology and physics have popularized modern lasers both within industry and in the field of medicine. High-energy laser light can now safely be used for a variety of tasks, from metal welding to cosmetic surgery. Today's lasers are safe and versatile because they have been designed based on unique principles that have evolved from photobiology and tissue dynamics. It is the knowledge of these principles that has allowed physician–scientists to manipulate the type of laser energy produced and the manner in which it is delivered, in order to destroy specific tissues while sparing damage to surrounding vital structures. The first medical lasers to be developed were continuous wave lasers that produced a continuous beam of radiation that was subsequently absorbed by a target. Although this constant laser light could effectively treat certain dermatologic conditions, its use was limited by the fact that the laser energy not only altered the target but also spilled over into adjacent issues, causing unwanted collateral damage and scarring. As our understanding of the interplay between living tissue and laser physics evolved, however, so did our ability to restrict laser damage to a specific target. The concept of selective photothermolysis developed by Anderson and Parrish in 1983 gave us the tools necessary to be more precise and safer with laser energy. 12 Selective photothermolysis states that a specific chromophore or target can be selectively destroyed with minimal collateral thermal tissue damage if the laser wavelength matches that absorbed by the chromophore, and if the target is exposed to the laser energy for an interval less than its thermal relaxation time. The thermal relaxation time is the time it takes a given target chromophore to lose 50% of its absorbed heat energy. Selective photothermolysis revolutionized laser technology and paved the way for a new generation of lasers that are designed to deliver a set wavelength for a precise duration, resulting in greater specificity and safety. The pulsed, quality Q-switched, and scanned systems are examples of such laser technology. Other so-called quasi-continuous laser systems also attempt to adhere to the theory of selective photothermolysis by limiting pulse durations from a continuous beam source through shuttering or chopping of the emitted laser beam. The usefulness of these systems is often limited owing to their high repetition rates or moderately long pulse durations, causing the target to experience the laser's energy as if it were a continuous wave. With the previously mentioned concepts in mind, the side-effect profile of a specific laser can be predicted in general terms, based on its wavelength and mode of operation. As a group, continuous wave and quasi-continuous lasers have a higher risk of scarring and textural changes through thermal buildup and heat diffusion to normal skin structures (Table 1). Lasers designed on the theory of selective photothermolysis are more specific and have a lower risk profile. Depending on the wavelength and pulse durations delivered, pigmentary changes, epidermal cell injury, textural changes, and crusting and tissue splatter can potentially occur (Tables 1 and 2). It is important to remember that even the safest lasers can cause injury if used incorrectly. Repetitive or overlapping pulses, excessive energy or power settings, and improper patient selection can potentially result in a high rate of morbidity with the use of any medical laser. This article provides an overview of the complications encountered with currently available laser systems.