Ablative Laser Skin Resurfacing

Carbon Dioxide Laser
Skin resurfacing with the CO₂ laser remains the gold standard technology for production of the most dramatic clinical and histologic improvement in severely photodamaged and scarred facial skin [5]. It was the development of highenergy pulsed CO₂ systems in the early 1990s that revolutionized aesthetic laser surgery and ushered in a new decade of rapidly evolving laser technology. Producing a wavelength of 10,600 nm, the CO₂ laser penetrates approximately 30 µm into the skin by absorption and vaporization of water-containing tissue. Older continuous-wave CO₂ lasers produced an unacceptable amount of thermal destruction (up to 200 µm–2 mm beyond the target area) [6]. The new generation of pulsed and scanned CO₂ lasers limit this thermal damage by delivery of high-energy laser light with tissue dwell times shorter than the thermal relaxation time of the 30 µm of targeted tissue (about 1 ms). Energy densities of approximately 5 J/cm² must be applied in order to achieve tissue ablation [7].Vaporization of very thin (20–30 µm) layers of skin occurs with each laser pass, leaving a small amount of residual thermal necrosis [8].With each subsequent laser pass, further tissue ablation occurs, but because the area of residual thermal necrosis increases (effectively reducing the amount of tissue water), the amount of ablation with each pass diminishes until a peak of approximately 100 µm is reached [9]. Delivering more than three to four passes or use of excessive energy densities significantly increases the risk of excessive thermal injury and subsequent scarring [10].
Use of the CO₂ laser for skin resurfacing yields an additional benefit of collagen tightening through heating of dermal collagen. The triple helical structure of collagen is altered, resulting in shortening of the fibers by one third [11]. Persistence of this collagen contraction results, in part, from these shortened fibers serving as a scaffold for neocollagenesis. Beyond this time, wound healing and fibroblast up-regulation of immune modulating factors leading to persistent collagen remodeling may explain continued clinical improvement seen up to 1 year after the procedure [12, 13, 14].

Several CO₂ laser systems are available and can be separated into two distinct groups: pulsed and scanned. The high-energy pulsed CO₂ lasers (e.g., Ultrapulse by Lumenis, Santa Clara, CA, USA) produce single short (1 ms) pulses of very high energies (up to 7 J/cm²). Scanned laser systems (e.g., FeatherTouch) utilize a computerized scanning device to deliver the laser energy rapidly over the skin, thus limiting the tissue dwell time in any one area. A study comparing four different CO₂ lasers found that the pulsed systems produced the least amount of thermal necrosis with the greatest subsequent collagen formation (compared with the scanned systems), but equivalent clinical outcomes between all four lasers were observed [13].

Although techniques and applied settings vary with each patient, practitioner, and type of laser used, general principles should be followed to maximize outcome while minimizing postoperative complications. Care must be taken to avoid overlapping or stacking of laser scans or pulses in order to reduce the risk of tissue scar formation and subsequently scarring. Similarly, it is important to thoroughly remove partially desiccated tissue between each laser pass. If only a single pass is performed, partially desiccated tissue can remain intact to serve as a biologic wound dressing [15]. It is best to avoid resurfacing areas such as the neck and chest due to the scarcity of pilosebaceous units in these regions with resultant slow re-epithelialization and potential for scarring [16].

Careful patient selection is critical in optimizing outcomes from laser skin resurfacing. Non-movement-associated rhytids, especially in the periorbital and perioral areas (Fig. 7.1a–c), are very responsive to laser resurfacing whereas movement-associated rhytids, such as in the glabella and forehead areas, fail to show as dramatic a response to laser treatment. In addition to ameliorating facial rhytids, the CO₂ laser has been shown to provide tissue tightening even as much as to exert a lifting effect on tissue. Upper eyelid dermatochalasis has been shown to be significantly improved after periocular CO₂ laser skin resurfacing [17].When used with traditional surgical lifting techniques, it enhances the overall cosmetic outcome [18]. The CO₂ laser has also been used effectively to treat atrophic and other scars [12, 19]. Sculpting of scars with the laser yields a more uniform skin texture and stimulates new collagen formation within the dermal defects. Patients can expect a mean improvement of 50–80% in moderate atrophic scars,with continued collagen remodeling and scar effacement for 12–18 months postoperatively [12, 19]. Patients with scars previously treated with dermabrasion or deep chemical peels may have additional fibrosis, which is more difficult to vaporize, thereby reducing their potential outcome. In addition, these patients also may have concealed hypopigmentation that could become more apparent after laser skin resurfacing [16, 19]. Although patients with paler skin tones are at lower risk for developing postoperative hyperpigmentation, those with darker skin tones can successfully undergo CO₂ laser resurfacing. Finally, and perhaps most importantly, patients must have realistic expectations of postoperative outcomes and mentally prepare themselves for the convalescence and potential for prolonged erythema and skin sensitivity.