Effects of overlap and pass number in CO2 laser skin resurfacing: a study of 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 overlapping of laser pulses/scans significantly altered wound healing, we examined residual thermal damage, cell death, and histologic and clinical wound healing in a farm pig. METHODS AND MATERIALS: Two popular CO2 systems were used, with a range of radiant exposures, degrees of overlap, and numbers of passes. Thermal damage was assessed by histology, and dermal cell viability was measured with nitrotetrazolium blue staining. Presence or absence of clinical scarring was determined by textural change and loss of skin markings. RESULTS: We observed that dermal thermal damage did not increase significantly with pass number when performed as in the normal clinical setting (for 2-4 passes); however, by delivering rapidly overlapping pulses and scans, residual 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 significant risk factor in increasing thermal damage, cell death, and possibly scarring.

The effect of wiping on skin resurfacing in a pig model using a high energy pulsed CO2 laser system.

BACKGROUND: The impact of wiping in laser skin resurfacing has not been systematically studied. METHODS: We examined the effects of wiping during single- and multiple-pass high energy pulsed CO2 laser skin resurfacing in a farm pig. Consequences of wiping were evaluated with regard to depth of residual thermal damage, tissue necrosis, and fibroplasia. Also, the impact of wiping on gross wound healing was observed. Wounds were followed for 21 days and biopsies were obtained on postoperative days 0, 1, and 21. RESULTS: Immediate postoperative biopsies of single-pass wounds showed equivalent residual thermal damage regardless of wiping; in contrast, biopsies from multiple-pass sites without wiping showed more extensive and variable residual thermal damage than wiped sites. On postoperative day one, single pass sites without wiping were grossly less erythematous than wiped sites, and biopsies showed less extensive necrosis and inflammation. In contrast, multiple pass sites without wiping were grossly more erythematous than corresponding wiped sites, and biopsies revealed significantly increased and variable necrosis. After 21 days, multiple pass sites without wiping were grossly more erythematous and showed a thicker band of fibroplasia microscopy. CONCLUSIONS: For single pass wounds, not wiping decreased the level of wounding. In contrast, not wiping in multiple pass wounds significantly increased the depth and variability of residual thermal damage and necrosis, resulting in prolonged healing.

Laser ablation of burns: initial clinical trial.

BACKGROUND: Scanning, high-powered carbon dioxide laser ablation of eschar may facilitate blood conservation in patients with burns. METHODS: Twenty-one children with full-thickness burns that required serial excisions were enrolled in a Human Studies Committee approved protocol in which a full-thickness wound was ablated with a rapidly scanned continuous wave carbon dioxide laser system. A control wound was sharply excised, and both wounds were immediately autografted. End points were engraftment at 7 days and serial Vancouver scar scores. RESULTS: The children had an average age of 8.3 +/- 1.2 years, weight of 36.3 +/- 4.9 kg, and burn size of 40% +/- 5.1%. The study wounds were ablated with an average energy of 99.2 +/- 5.7 W; there was no bleeding from 19 successfully ablated wounds. Initial engraftment averaged 94.7% +/- 3.5% in the control sites and 94.7% +/- 3.3% in the study sites (P = 1.0). There was no significant difference in Vancouver scar scores at an average follow-up of 32.0 +/- 5.2 weeks. CONCLUSIONS: This pilot study follows a successful trial of this concept in a porcine model and demonstrates the technical feasibility of laser vaporization of burn eschar in humans with immediate autografting. Further refinement of the technique is required before it can be generally recommended.

Carbon dioxide laser ablation with immediate autografting in a full-thickness porcine burn model.

OBJECTIVE: To compare the long-term clinical and histologic outcome of immediate autografting of full-thickness burn wounds ablated with a high-power continuous-wave CO2 laser to sharply débrided wounds in a porcine model. SUMMARY BACKGROUND DATA: Continuous-wave CO2 lasers have performed poorly as tools for burn excision because the large amount of thermal damage to viable subeschar tissues precluded successful autografting. However, a new technique, in which a high-power laser is rapidly scanned over the eschar, results in eschar vaporization without significant damage to underlying viable tissues, allowing successful immediate autografting. METHODS: Full-thickness paravertebral burn wounds measuring 36 cm2 were created on 11 farm swine. Wounds were ablated to adipose tissue 48 hours later using either a surgical blade or a 150-Watt continuous-wave CO2 laser deflected by an x-y galvanometric scanner that translated the beam over the tissue surface, removing 200 microm of tissue per scan. Both sites were immediately autografted and serially evaluated clinically and histologically for 180 days. RESULTS: The laser-treated sites were nearly bloodless. The mean residual thermal damage was 0.18+/-0.05 mm. The mean graft take was 96+/-11% in manual sites and 93+/-8% in laser sites. On postoperative day 7, the thickness of granulation tissue at the graft-wound bed interface was greater in laser-debrided sites. By postoperative day 180, the manual and laser sites were histologically identical. Vancouver scar assessment revealed no differences in scarring at postoperative day 180. CONCLUSIONS: Long-term scarring, based on Vancouver scar assessments and histologic evaluation, was equivalent at 6 months in laser-ablated and sharply excised sites. Should this technology become practical, the potential clinical implications include a reduction in surgical blood loss without sacrifice of immediate engraftment rates or long-term outcome.