Depth of vaporization and the effect of pulse stacking with a high-energy, pulsed carbon dioxide laser.
BACKGROUND
Laser resurfacing of photodamaged skin has become popular, but questions regarding its safety with regard to the risks of scarring have arisen.


OBJECTIVE
This study was designed to investigate the depth of vaporization and residual thermal necrosis of single-pulse vaporization and multiple passes versus pulse-stacking and multiple passes. The potential significance of operator technique and laser parameters is considered.


METHODS
Skin samples from surgical excisions were treated by means of a Coherent Ultrapulse carbon dioxide laser at 250 mJ per pulse and 500 mJ per pulse with a 3 mm collimated beam and a repetition rate of 10 Hz. A total of 70 treatment areas were performed. Blinded analysis of the histologic effects of single-pulse, double-pulse, and triple-pulse vaporization after 1 through 10 passes was undertaken.


RESULTS
A plateau of vaporization was observed after 3 passes at both 250 and 500 mJ whether single-, double-, or triple-pulse vaporization was used. This plateau occurs at approximately 100 to 250 microm from the skin surface. Thermal necrosis is well controlled only with single-pulse vaporization. There is a direct linear increase in the depth of thermal necrosis both with the number of pulses stacked and the number of passes.


CONCLUSIONS
Pulsed carbon dioxide laser resurfacing is a safe and self-limited procedure if a pulse width of less than 1 msec is used with single-pulse vaporization and fluences of 3.5 J/cm2 and 7.0 J/cm2. There appears to be little justification for performing more than 3 or 4 passes. Pulse stacking may significantly increase residual thermal necrosis, thereby increasing the risk of scarring. Operator technique may be significant in avoidance of this occurrence.
Fitzpatrick
R E
RE
Department of Medicine, University of California, San Diego, USA.
Smith
S R
SR
Sriprachya-anunt
S
S
D002921:Cicatrix / Q000473:pathology; D046508:Culture Techniques; D006801:Humans; D053685:Laser Therapy / Q000009:adverse effects* / Q000295:instrumentation; D009336:Necrosis; D012867:Skin / Q000293:injuries* / Q000473:pathology