Effects of overlap and pass number in CO2, laser skin resurfacing: A studyof residual thermal damage, cell death, and wound healing

Background: Newer CO2 laser systems incorporating short pulse and scanning technology have been used effectively to resurface the skin. As the number of resurfacing cases has increased, hypertrophic scarring has been reported more commonly. Previous dermabrasion and continuous wave CO2 studies have suggested that depth of injury and thermal damage are important predictors of scarring for a given anatomic region. To determine whether rapid overlap ping of laser pulses/scans significantly altered wound healing, we examined residual thermal damage, cell death, and histologic and clinical wound hea ling in a farm pig. Methods and Materials: Two popular CO2 systems were used, with a range of r adiant exposures, degrees of overlap, and numbers of passes. Thermal damage was assessed by histology, and dermal cell viability was measured with nit rotetrazolium blue staining. Presence or absence of clinical scarring was d etermined by textural change and loss of skin markings. Results: We observed that dermal thermal damage did not increase significan tly with pass number when performed as in the normal clinical setting (for 2-4 passes); however, by delivering rapidly overlapping pulses and scans, r esidual thermal damage and cell death depth were increased as much as 100% over areas without immediate overlap of laser impacts. Conclusions: Immediate overlapping of CO2 laser pulses and scans is a signi ficant risk factor in increasing thermal damage, cell death, and possibly s carring. Lasers Surg. Med. 24:103-112, 1999. Published 1999 Wiley-Liss, Inc .dagger