Are more passes better? Safety versus efficacy with the pulsed CO2 laser

Whether greatly increasing the number of passes with the pulsed CO2 laser compromises safety or enhances effectiveness is unknown. Intuitively speaking, more passes should produce a greater depth of injury with better removal of wrinkles but greater likelihood of scarring. A chamois color has been said to signal laser penetration of the reticular dermis and has been recommended as an end point for safe treatment. Isolated case reports and anecdotal stories suggest that the potential for scarring from deep thermal injury remains significant. With the Coherent Ultrapulse laser at our usual therapeutic settings (300 mj, density of 4 with the Computerized Pattern Generator), the authors treated multiple test panels on in situ breast skin (one to 16 passes) and eyelid skin (one to eight passes) and then compared the panels in the excised skin histologically. The depth of injury did not increase after three passes, and no full-thickness injury was observed even in the thin eyelid skin. After treating severely wrinkled upper lips with up to 11 passes without scarring or other adverse effect, the authors treated a small series of patients with four passes on one side of their lips and 10 passes on the other side. No difference could be detected either at the time or after final healing. The authors believe that injury depth in using the pulsed CO2 laser is automatically limited by progressive dessication of the superficial dermis. The chamois color indicates dessication, not increasing depth. Although more than three or four passes will not produce injury under ordinary circumstances, they do not improve the final result.