Abstract
Several published reports describe the benefits of using the carbon dioxide laser for cutaneous resurfacing. The mechanisms on which skin resurfacing work are still not completely understood. This study was performed to obtain quantitative and qualitative information describing the thermal response of skin during high-energy, short-pulsed CO2 laser irradiation. A Tissue Technologies TruPulse CO2 laser was used to irradiate an in vivo rat model. The laser parameters that were used were a 100-micros pulse width, a 1-Hz repetition rate, a 3 mm x 3 mm square spot size, and 2.4 J/cm2 and 3.9 J/cm2 radiant exposures. A 3-5 microm thermal camera was used to obtain temperature information during irradiation. Single spots were irradiated with one pulse, and the temperature-time history was obtained. In a different experiment, 15 pulses were applied to single spots, and both thermal and video images were obtained. Irradiation with one pulse at 2.4 J/cm2 and 3.9 J/cm2 led to peak temperatures >100 degrees C. The temperature relaxation time was approximately 25-150 ms. Multiple-pulse irradiation at 2.4 J/cm2 led to a slight rise in the peak temperature with each pulse. At 3.9 J/cm2, the peak temperature increased with successive pulses until pulse 10, after which the peak temperature oscillated between 300 and 400 degrees C. Video images showed concurrent burning events that occurred during pulses 10-15. Temperatures >100 degrees C were measured during CO2 laser irradiation of skin. Pulse stacking can lead to peak temperatures approaching 400 degrees C and to tissue charring with as few as three stacked pulses. It is crucial for the physician to manipulate the laser handpiece at parameters with which he or she can avoid pulse overlap.
Highlights
This study examines the thermal response of skin to CO2 laser irradiation in terms of an in vivo study performed on a rat model
Representative examples of the temperature response of in vivo rat skin to single ablative pulses are shown in Figure 2 for radiant exposures of 2.4 J/cm2 (Fig. 2a) and 3.9 J/cm2 (Fig. 2b)
The surface temperature of in vivo rat skin during CO2 laser irradiation was measured with a band-limited thermal camera for single and multiple pulses
Summary
The theoretical advantages of the pulsed CO2 laser for skin resurfacing are that it: (1) ablates tissue precisely (10 m per pulse at a radiant exposure of 5 J/cm2 [1]); (2) leaves a minimal zone of residual thermal necrosis (∼50 m) when operated at high irradiances (>1,000 W/cm2) and short exposure times [2,3]; (3) seals small nerve endings, which may lead to a reduction in postoperative pain [4]; (4) seals small lymphatics, resulting in less postoperative edema [5]; (5) increases the operative speed [6]; and (6) seals small blood vessels, leading to decreased hemorrhage, improved vision in the surgical field, and less postoperative bruising and swelling.The short-pulsed aspect of these resurfacing lasers is derived from the idea of selective photothermolysis [7]. The optical-thermal response of skin to laser resurfacing is complicated by the need for multiple passes in order to obtain the desired clinical effect. We examine the response of a single spot to irradiation with multiple pulses. This study was performed to obtain quantitative and qualitative information describing the thermal response of skin during high-energy, short-pulsed CO2 laser irradiation. Single spots were irradiated with one pulse, and the temperature-time history was obtained. 15 pulses were applied to single spots, and both thermal and video images were obtained.
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