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Figure 1A. Pre treatment patient infraorbit with multiple ines and wrinkles. |
Figure 1B Same patient three weeks post laser resurfacing showing effacement of fine lines and wrinkles with smooth skin texture. |
Photoaging is an inevitable occurrence for people who have a fair skin type, who live in a sunny climate, and who enjoy the outdoors. In the past the remedies for this condition were limited to dermabrasion, or chemical peeling. Both dermabrasion and chemical peels have hazards of their own. With phenol peels, cardiac and renal toxicity were real concerns. With dermabrasion, inadvertent trauma and scarring were concerns. Since the early 1990's the CO2 laser has emerged as one of the "tools" of choice for treating the effects of photoaging1. For this reason we will explore the basics of how CO2 lasers work, what they can be used for, and what the down sides of laser resurfacing might be.
The theoretical basis for development of the laser is Einstein's theory of photoelectric stimulation2. In brief, stimulation of atoms or molecules may raise electrons from a stable electron resting state to a higher, unstable state of excitation. Photons are released as the electrons decay to a stable steady state.
Clinically, Goldman3 introduced the use of lasers as a destructive modality in 1970, predominantly for warts, and actinic chelitis. Unpredictable levels of heat conduction with scarring limited the dermatologic application of early lasers.
Laser function is based on the principle that stimulation of electrons leads to photon emission. If the photons are generated in a specific metal, gas or liquid lasing medium, they will have a specific wavelength. These stimulated photons are then reflected by a sequence of mirrors, and released through a single, small aperture. This allows the coherent light to travel in a parallel column with almost no dispersion. The light reaching a target has the spectral characteristics of the source and virtually no loss of energy by interference or divergence. Specific chromophores in the skin absorb light energies at specific wavelengths. Oxygenated hemoglobin absorbs light at 542 and 577 nm. Melanin also absorbs light of similar but slightly shorter wavelengths (see article this issue by Harris and Randle). Intracellular water absorbs laser energy in the near and far infrared spectrum, ranging from 2000 nm to 10,600 nm.2
The clinical effects of the CO2 laser are based on the principal of the incoming light being converted to heat. Enough heat is generated to vaporize the intracellular water, in essence, vaporizing the skin cells as well. Heat is then further transmitted past the point of incidence. This heat stimulates type one collagen bands to shorten their length approximately 30 percent. This collagen shortening may be one of the factors responsible for the tightening effect of the resurfacing laser4.
The extinction length is defined as the thickness in water that absorbs 90% of the incident beam's radiant energy. The extinction length for the CO2 laser in tissue is approximately 30 microns4. Histologic studies using three different CO2 laser delivery systems have shown fairly certain depths of penetration with CO2 laser energy. One pass of the Coherent Ultrapulse 5000® completely vaporized a 20- 30 micron depth layer of tissue, and did not ablate entirely through the epidermis. A second pass resulted in vaporization to the level of the superficial papillary dermis. The depth of residual thermal injury increased with the number of passes regardless of which CO2 laser was used. One pass with the Coherent Ultrapulse® produced 20 microns of thermal damage. The second pass produced a zone of thermal necrosis to 50 microns in depth and the third pass extended the zone of thermal necrosis to 70 microns deep. The above data is significant, as scarring may well be dependent for the most part on the degree and depth of residual thermal damage.
The development of pulse technology has allowed the laser to evolve from a glorified cautery to a useful tool for correcting photoaging, wrinkles and actinic damage5,6,7,8. Lasers needed to be developed that could shoot a pulse faster then the time needed for the target tissue to cool down to prevent excess heat transmission and scarring potential. The time needed for the target tissue to cool down to 50% of its heated temperature is called the thermal relaxation time. For human skin this time is 1 millisecond. Pulses that are less then the thermal relaxation time minimize the transmission of repetitive thermal transmission and acoustic vibratory shock waves. This limits unintentional nearby tissue destruction by heat. Pulsing below thermal relaxation time also enhances the uniformity of incipient energy dispersion and vaporization without charring.
In addition to pulse technology the computerized pattern generating scanner has been a significant advancement in resurfacing technology. A pattern generator spreads the laser beam uniformly so it becomes practical to treat a surface instead of cutting or creating a hole. This has allowed for fairly easy standardization of treatments, as well as speeding up the time necessary to perform these procedures.
Areas such as the periorbital regions and perioral creases7, which were difficult or fairly risky to treat with TCA or phenol peels, can now be more aggressively treated with less patient risk. Actinic damage, fine lines, deep lines, acne scars, and traumatic and post surgical scars can be treated by laser resurfacing. (Figure 1a and 1b) Dr. Thomas J. Baker9 recently told the American Society of Plastic and Reconstructive Surgery that laser resurfacing may produce dermal/epidermal changes similar to the phenol peel and may be as durable.
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Figure 1A. Pre treatment patient infraorbit with multiple ines and wrinkles. |
Figure 1B Same patient three weeks post laser resurfacing showing effacement of fine lines and wrinkles with smooth skin texture. |
It is important for patients to realize that the CO2 resurfacing laser is not a magic wand. This unit produces a controlled "sunburn" that causes tissue damage. Any time tissue is damaged there is a risk of scar formation, bacterial or monilial infections, or a flare up of latent herpes simplex3. Patients may develop contact dermatitis from the applied postoperative dressings as well. There is always a risk of damage to the pigmentary unit with either hypo or hyper pigmentation. This is more likely if the patient enjoys a sun-oriented lifestyle.
In that regard, the Erbium-YAG laser may play a greater role in the future of laser resurfacing. The erbium laser is noted to have ten times the water absorption of the CO2 laser. There is a 10- 40 micron layer of vaporization with each tissue impact, with minimal collateral thermal damage10. Teiknemeir's study, while small, showed acceptable results, with no documented reports of scarring or pigmentary change.
There are also risks from the anesthesia. It is sometimes necessary to obtain conscious sedation when performing full face laser resurfacing. Of course conscious sedation should be performed by appropriately trained personnel, with appropriate backup equipment. Injectable local anesthesia poses a risk too, with allergies uncommon but documented. Finally, there is also a risk of nerve damage when performing regional blocks.
Perhaps the most pervasive risk is that of not achieving the patient's expectation. It is important to counsel the patient that 100% correction is probably not a realistic expectation. One may also consider cautioning the patient that it is safer for the patient to undercorrect and repeat then to "push the envelope" too far and risk scarring. The procedure can be repeated in the future, but is difficult to be undone if overapplied the first time. Occasional reports of ectropion3 have been noted when periorbital lasering has been performed. As a rule, patients with lower lid lag should be approached cautiously, if at all3.
REFERENCES
1. Roberts T, Weinstein C, Alexandrides J. Aesthetic CO2 Laser Surgery: Evaluation of 907 Patients. Aesthetic Surgery. 1997; 17(5): 293-303.
2. Herd R, Dover J, Arndt K. Basic Laser Principles. Dermatology Clinics. 1997; 15(3): 355-72.
3. Weinstein C, Pozner J, Ramires O. Complications of carbon dioxide laser resurfacing and their prevention. Aesthetic Surgery Journal. 1997; 17(5): 216-225.
4. Kauvar A, Waldorf H, Geronemus R. A Histopathological Comparison of "Char-Free" Carbon Dioxide Lasers. Dermatologic Surgery. 1996; 22: 343-348.
5. West T. Laser Resurfacing of Atrophic Scars. Dermatology Clinics. 1997; 15(3):449-459.
6. Apfelberg D. a Critical Appraisal of High Energy Pulsed Carbon Dioxide Laser Facial Resurfacing for Acne Scars. Annals of Plastic Surgery. 1997; 38(2): 95-100.
7. Fitzpatrick R. Laser Resurfacing of Rhytids. Dermatology Clinics. 1997; 15(3) 431-448.
8. Trimas S, Ellis D, Metz R. The CO2 laser: an Alternative for the Treatment of Actinically Damaged Skin. Dermatologic Surgery. 1997; 23(10): 885-890.
9. Branch D. Laser Resurfacing Yields the Same Result as Phenol Peel. Skin and Allergy News. 1997; 11:43.
10. Teikemeir G, Goldberg D. Skin Resurfacing with the Erbium YAG Laser. Dermatologic Surgery. 1997; 23(8):685-689.
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