Depth of morphologic skin damage and viability after one, two, and three passes of a high-energy, short-pulse CO2 laser (Tru-Pulse) in pig skin

Background: CO2 laser energy is absorbed by water, which is present in all tissue. The depth of penetration of CO2 lasers is narrow with minimal reflection, scatter, or transmission. However, thermal damage has limited the usefulness of conventional, continuous-wave CO2 lasers for debridement as demonstrated by wound healing studies. The development df high-energy CO2 lasers, with pulse durations that are less than the thermal relaxation time of tissue, have made vaporization of skin for resurfacing and wound debridement possible because of the decreased risk of thermal damage. Objective: This study was performed to evaluate thermal damage produced by a CO2 laser. Methods: Routine histopathologic examination and nitroblue-tetrazolium chloride (NBTC) staining were used to evaluate the depth of tissue damage and viability in weanling pig skin after one. two, and three passes of the laser. Results: At a pulse energy of 300 mJ, with a pulse duration of 60 mu sec, one pass of the laser produced vaporization of the epidermis with minimal thermal damage. Two passes produced areas of denatured collagen with loss of viable cells in the superficial papillary dermis. Three passes extended the damage into the papillary dermis. Conclusion: Hyalinization of collagen appears to correspond well with the level of thermal damage as measured by NBTC staining. Our findings suggest that the energy necessary to vaporize the dermis may be greater than that needed to vaporize epidermis.