title: Effects of overlap and pass number in CO2 laser skin resurfacing: a study of residual thermal damage, cell death, and wound healing.
abstract: 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
  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.
authors: Dermatology Laser Center and Wellman Laboratories of Photomedicine, Massachusetts General Hospital, Boston 02114, USA. vross@snd10.med.navy.mil
authors: E V
authors: EV
authors: Ross
authors: D J
authors: DJ
authors: Barnette
authors: R D
authors: RD
authors: Glatter
authors: J M
authors: JM
authors: Grevelink
mesh_terms: D000818:Animals; D017209:Apoptosis; D002056:Burns / Q000209:etiology / Q000473:pathology; D016923:Cell Death; D062109:Dermatologic Surgical Procedures; D004195:Disease Models, Animal; D005500:Follow-Up Studies; D053685:Laser Therapy / Q000009:adverse effects; D009336:Necrosis; D011183:Postoperative Complications / Q000209:etiology / Q000473:pathology; D013518:Surgery, Plastic / Q000009:adverse effects*; D013552:Swine; D014945:Wound Healing / Q000502:physiology*