The role of the chromophore in the treatment of vascular pathologies is played by the hemoglobin of erythrocytes located in the blood vessels. The aim of the procedures is to cause thermal damage to blood vessels with a diameter of 20-50 microns while maintaining the integrity of the surrounding tissues. For this, light with wavelengths of about 520-600 nm is used, which is well absorbed by hemoglobin, several times weaker by melanin and practically not absorbed by the rest of the skin components.
Vladimir Alexandrovich Tsepkolenko
MD, Professor, Honored Doctor of Ukraine,
President of the Ukrainian Society of Aesthetic
Medicine, General Director of the Ukrainian
Institute of Plastic Surgery
and aesthetic medicine "Virtus"
When treating vascular pathologies, the laser wavelength should be selected depending on the average depth of the vessels: the longer it is, the longer-wavelength laser should be preferred (taking into account the weaker absorption of long waves by hemoglobin), since short waves simply do not reach deep layers of the skin due to scattering and absorption in the upper layers. Even a small increase in dye laser wavelength from 575 to 595 nm results in a clinically noticeable improvement in treatment of deep vessels.
Another factor affecting the efficiency of coagulation of vessels located in the deep layers of the skin is the number of vessels located above them. This is due to the fact that the blood of the upper vessels absorbs most of the light before it reaches the target vessels, and there is simply not enough energy to heat them up. Therefore, for effective treatment, several procedures spaced apart in time are often required. The use of epidermal cooling not only reduces the risk of unwanted injury, but also allows the use of more powerful pulses than usual, thereby increasing the selectivity of photothermolysis.
The main vascular lasers and their brief characteristics
Potassium titanium phosphate (KTP) laser, 532 nm
Due to the relatively short wavelength, the light of this laser does not penetrate deep into the skin, which dramatically reduces the effectiveness of treatment of deep-seated formations. However, the extremely strong absorption of 532 nm light by hemoglobin makes it possible to successfully treat superficially located vascular formations. The main complication is postoperative erythema in all treated areas, scarring and ulceration are practically not observed. Histological analysis shows that the selective closure of the vessels proceeds without bleeding.
Pulsed dye laser (PDL), 575-600 nm
Laser radiation is excellently absorbed by both oxyhemoglobin and deoxyhemoglobin, and the disadvantages are a very sharp time profile and short pulse duration, which increases the likelihood of prolonged erythema. The relatively small penetration depth does not allow treatment of deep-seated vessels (especially when they are densely packed): at a power of 8 J/cm2, vessels are coagulated at a maximum depth of 0.7 mm, even in cases where they are not blocked by higher-lying vessels.
Nd:YAG and Nd:YVO4, 1064 nm
Long-wavelength radiation penetrates deep enough into the skin, but the selectivity of its absorption is relatively low. The latter is associated with absorption by hemoglobin and melanin close in intensity. Water absorption is not so great, but already noticeable. Thanks to these factors, coagulation of superficial and deep-lying vessels with a diameter of even more than 1 mm is possible.
The relatively weak absorption by hemoglobin requires the use of a high energy density of radiation, so there is a need for epidermal cooling of the skin, and in some cases, local anesthesia. However, in many cases it is still not possible to avoid atrophic scarring.
Copper vapor laser, 510, 578 nm
The laser generates radiation with two wavelengths – 511 nm (green) and 578 nm (yellow) with a power ratio of 3:2. As a result, the action of the radiation of this laser occupies an intermediate position between KTP and PDL, that is, it is intensively absorbed by hemoglobin at a small penetration depth. On the other hand, the pulse duration is about 20 ns (hundreds of times less than the relaxation time of even small vessels), resulting in low non-specific thermal and significant mechanical damage.
Argon laser, 488, 514 nm
The main argon laser radiation chromophores are melanin and hemoglobin, which are ubiquitous in the skin, which, given the continuous operation and relatively low radiation power, does not allow the use of selective photothermolysis and leads to a high risk of hypertrophic scarring. This combination of factors makes this laser ineffective in the treatment of vascular pathologies.
Recommendations for treatment of vascular lesions
First, it is recommended to test the formation response to pulses with different energy densities in order to determine the most effective and safe settings. If there is no change in the color of the irradiated skin – probably, the radiation energy density is insufficient. In the event of swelling, blistering or blackening at the site of exposure – the energy density is excessively high. As a rule, 3-5 settings are tested, and the result is evaluated after approximately 6 weeks. As a result, they choose the option that led to the maximum clarification of the treated area, but did not cause unwanted side effects.
Laser spot repositioning may be used during treatment to eliminate missed areas of skin. The amount of overlap depends on the spatial profile of the laser beam (with a Gaussian profile - up to 20%), but is usually recommended at 10% of the spot diameter. It is important to remember that more heat than expected enters the overlap area (especially with a flat beam profile), which, in the event of an error, greatly increases the risk of side effects. It should also be taken into account that modern scanning tips usually include a beam blocking mechanism that is appropriate for a particular type of laser. In this case, no additional overlap is required.
Side effects of laser treatment of vascular tumors and malformations
Pigmentary changes
Due to competing uptake by melanin, there is a possibility of hypopigmentation on the treated areas of the skin (especially in patients with Fitzpatrick skin phototypes IV-VI). Light skin, on the contrary, is prone to hyperpigmentation (up to 25-30% of cases), which usually disappears within a few months. With an increase in the length of the radiation used, its absorption by melanin weakens, which leads to a decrease in the risk and intensity of pigmentation changes. Persistent hypopigmentation is most common in the neck, legs, and chest. In most cases, hypopigmentation resolves on its own within 6-12 months, but additional treatment with UV sources may be required. To prevent the occurrence of significant pigment changes before and after laser treatment, it is recommended to use depigmentation agents and avoid skin insolation. Postoperative trauma to the treated area can also cause unwanted effects.
Scarring of the skin
Hypertrophic scarring, although not common, does occur when high energy density radiation is applied and the treatment areas are on the neck, arms, or shoulders. The appearance of depressed scars is also possible due to injury to the treated area within a few days after treatment. The likelihood of developing scarring is influenced by the localization of stress, the energy density of the radiation, the duration of the pulses (depending on the diameter of the vessels) and postoperative care. Experience with the copper vapor laser also showed a high incidence of scarring of the skin in the treatment of vascular pathology of the skin and the need for more treatment procedures compared to KTP (532 nm).
Keloid formation is especially likely in the case of previous use of isotretinoin (the process is not fully understood), it is considered advisable not to use laser therapy for 1-2 years after taking this drug.
To be continued.
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