Áreas de cobertura y requisitos relativos al suministro de datos

Though most of the aspects mentioned under CO₂ laser surgery are common some unique aspects apply to the Er:YAG laser.

1. Wherever full face resurfacing is needed modulated Er:YAG is superior to CO₂ laser.

2. Although the superficial ablation and minimal collateral thermal damage achieved with the Er:YAG laser allow physicians to treat patients with more confidence, careful patient selection is still essential.

3. For most dermatological indications except vascular and lymphatic disorders Er:YAG is the ideal laser.

Patient Selection

Absolute contraindications to laser resurfacing include active bacterial or viral infections, impaired immune system, use of isotretinoin in the past year, and history of poor healing, especially hypertrophic scars or keloids in the treatment area. Skin that has received extensive radiation therapy or patients with scleroderma show decreased amounts of adnexal structures and should not be resurfaced because of risks of poor healing. Patients with unrealistic expectations should not be resurfaced.

Pregnant patients are also not treated due to the unknown risk of anesthesia on the fetus.

Relative contraindications include history of prior skin dyspigmentation, skin types V and VI, and koebnerizing diseases such as vitiligo or labile psoriasis. Patients who had a prior blepharoplasty or who have significant eyelid laxity should be approached cautiously, since the tightening achieved during laser resurfacing may result in ectropion formation.

Pretreatment Regimen

All patients undergoing laser resurfacing of the face are typically prophylactically given either acyclovir 400 mg PO tds, valacyclovir 500 mg PO bid, or famcyclovir 250 mg PO bid. The antiviral is started 2 days prior to the procedure and continued for 10 days after the procedure. We though do not follow this as a rule and if there is no elicitable history of herpes labialis there is no need to administer antivirals.

Prophylactic use of systemic antibiotics, such as dicloxacillin, cephalexin, or azithromycin in penicillin allergic patients, should be given 2 days prior and continuing until the skin has re-epithelialized, to diminish the incidence of postoperative infection. We prefer levofloxacin 750 mg HS.

A moist, warm wound environment also promotes candidal infections. Occasionally,a single dose of fluconazole may be given on the day of surgery to patients, especially those with a significant history of recurrent vaginal discharge.

Intraoperative

Anesthesia: Infiltration anesthesia Treatment Technique

The basics have been described in the text and today resurfacing is not the primary indication. For almost all ablative indications except vascular and lymphatic, Er:YAG is better than CO₂ laser. This is specially true of the new variable pulse lasers where the pulse duration can be increased to match the coagulative effects of CO₂ laser.

Method

1. Er:YAG resurfacing can be performed either freehand or with a scanner. If the freehand method is used, it is important to ensure that overlapping of pulses is moderate, but not great. Significant overlapping and stacking of pulses will increase the depth of ablation and collateral thermal damage.

2. The number of passes necessary to vaporize the epidermis depends on the fluence and spot size used. In general, a fluence of 5–7 J/cm 2 _will

ablate the epidermis in two to four passes and a fluence of 8–15 J/cm 2

will do so in one or two passes. Subsequent passes will ablate between 5 and 40 mm of tissue depending on the energy fluence used. This is based on a rough estimation of an ablation of 5µm of the skin per J/cm2

of energy.

3. To minimize thermal damage subsequent passes should be oriented perpendicular or at an angle to the preceding passes to further enhance the uniformity of the ablation.

4. The margins of the treatment areas can be blended into the untreated skin by using pulses of lower fluence or by defocusing the handpiece or scanner (which, in effect decreases the fluence).

5. A quick wipe between passes with moistened gauze is recommended to remove the fine tissue debris, to rehydrate the skin, and to allow better visualization of the plane being treated. This process only takes a few seconds and does not require the time and effort associated with wiping between CO₂ passes.

Dose/Depth

With a of 5 J/cm2_{, the following ablation depths are usually achieved: one}

pass, 20–40 µm or down to the granular layer of the epidermis; two passes, up to 60 µm or down to the basal cell layer; three to four passes, 80–120 µm or down to the papillary dermis, and deeper into the papillary and superficial reticular dermis after five to six passes (Alster, Perez).

Weinstein (1997) described the following ablation depths using a scanner of 20 Hz and 30% pulse overlap: 5 J/cm2_{, superficial epidermal injury (30–40}

µm) with negligible thermal necrosis; 10 J/cm2_{, epidermal injury to the level}

of the basal layer (50 µm) with minimal thermal necrosis (5 mm); 15 J/cm2_,

full-thickness epidermal injury through the basement membrane, minimal ablation of the papillary dermis (20 µm), and a narrow band of thermal necrosis (10–15 µm). These schematic histological ablation depths provide an approximation of the real ablation depth achievable with different fluences and numbers of passes.

End Point

The visual endpoint for treatment with the Er:YAG laser differs from that of the CO₂ laser. The chamois yellow color seen with CO₂ resurfacing, which indicates that the deep papillary dermis or superficial reticular dermis is reached, is not seen with Er:YAG laser resurfacing.

Epidermis: Resurfacing within the epidermis produces a yellowish brown appearance on the epidermis.

Epidermo-dermal junction: Once the epidermis is removed, a pinkish appearance of the upper papillary dermis will be readily appreciated. The follicle openings look small and regular like a fine sponge.

Lower papillary dermis: When proceeding in to the papillary dermis, pinpoint bleeding and a transudate develops, indicating injury to the small

capillaries. The follicle openings become wider and begin to stand out from the surrounding dermis.

Upper reticular dermis: When the upper reticular dermis is reached, bleeding increases and the transudate becomes more profuse. Follicle openings become much wider and the collagen bands become coarser and

more haphazard in orientation. At this point it is generally best not to proceed no further.

Therefore, the physician must be mindful of the estimated depth of ablation associated with each pass of the laser at the fluence being used, and compare that with the average depth of the epidermis and dermis of the area being treated. As the collateral thermal injury induced by the Er:YAG laser is insufficient to coagulate medium-sized vessels, a common visual clue indicating that ablation has reached the mid-dermis is pinpoint bleeding. This bleeding will often inhibit further treatment beyond a certain level.

Thus if the rhytides, acne scars, or other lesions are adequately effaced before the bleeding and exudate limit further treatment, then one or two additional passes are done to compensate for the impact edema. If oozing is remarkable, gauze soaked with 1% lidocaine with epinephrine can be placed over the resurfaced area at the end of the procedure.

Postoperative Care

For small lesions, we recommend topical antibiotic ointments or ointments specifically designed to accelerate wound healing (e.g., Fucidin). This should be used until complete re-epithelialization has occurred and prevents the formation of irritating crusts.

For extensive lesions as in skin resurfacing, either the open technique (application of ointments several times a day, following irrigation with water or vinegar solutions) or the closed technique (application of various kinds of occlusive dressings for several days) can be used.

Pearls/Pitfalls

To complement the effect of Er:YAG and CO₂, a combination approach is a useful concept. This helps to balance out the advantage of fine ablation of Er:YAG and coagulation of CO₂.

A often asked question is whether this may lead to accentuated thermal damage. This has been answered by the histological examinations of Utley et al., who found the following residual thermal damage zones after ablation with an Er:YAG and a pulsed CO₂ laser (at 4.7 J/cm2 _each).

a. CO₂ alone (four passes) 89 µm, Er:YAG (four passes) and CO₂ (two passes) 97 µm.

b. Er:YAG alone (eight passes) 43 µm, and CO₂ (two passes) and Er:YAG (four passes) 56 µm.

Thus a simple protocol is to combine Er:YAG initially followed by CO₂ for deep pathologies while Er:YAG suffices for most superficial indications.

This helps to maximise results by using the almost predictable ablation of Er:YAG with coagulation of CO₂ lasers.

BIBLIOGRAPHY

1. Alster TS. Clinical and histologic evaluation of six erbium:YAG lasers for cutaneous resurfacing. Lasers Surg Med. 1999;24:87-92.

2. Hohenleutner U, Landthaler M. Er:YAG Lasers. Principles and practices in cutaneous laser surgery/ed, Kauvar ANB; Associate ed, Hruza GJ. Taylor and Francis; 2005.

3. Perez MI, Bank DE, Silvers D. Skin resurfacing of the face with the erbium:YAG laser. Dermatol Surg. 1998;24:653-9.

4. Ross EV. Continuous Wave and Pulsed CO₂ Lasers. Principles and practices in cutaneous laser surgery/ed, Kauvar ANB; associate ed, Hruza GJ. 2005. Taylor and Francis.

5. Tse Y, Manuskiatti W, Detwiler SP, Fitzpatrick RE, Goldman MP. Tissue effects of the erbium:YAG laser with varying passes, energy and pulse overlap. Lasers Surg Med. 1998;22(suppl 10):70.

6. Utley DS, Koch RJ, Egbert BM. Histologic analysis of the thermal effect on epidermal and dermal structures following treatment with the superpulsed CO₂ laser and the erbium:YAG laser: an in vivo study. Lasers Surg Med. 1999;24:93- 102.

7. Weinstein C. Computerized scanning erbium:YAG laser for skin resurfacing. Dermatol Surg. 1998;24:83-9.

8. Weinstein C. Erbium laser resurfacing: current concepts. Plast Reconstr Surg 1999;103:602-16.

ATLAS

Fig. 1: A case of epidermal nevus, a test spot is treated with Er:YAG (10 J/cm2_{; 4 Hz).} Note the healing with residual and transient pigmentary loss.

Fig. 3: Intraoperative procedure using the “paintbrush technique” with the Up CO₂

lasers (350 mJ; 5 J/cm2_{; <1ms). Note the almost bloodless field due to the coagulative} effect of the laser

Fig. 5: Immediate postoperative view using a Up CO₂ lasers (350 mJ; 5 J/cm2_{; < 1ms).} Note the complete lack of bleeding. Concomitant thermal necrosis is visible as charred tissue on the periphery

Fig. 6: Immediate postoperative photograph of a melanocytic nevus using the Er:YAG

(10 J/cm2_{; 4 Hz). Note the capillary bleeding seen at the level of papillary dermis. The} lack of coagulation is an useful tool to determine a reliable end point

Fig. 7: A preoperative photograph of lympho (hemangioma) circumscriptum

Fig. 8: Intraoperative use of CO₂ (superpulsed mode; paintbrush technique) which is the ideal laser for coagulation of lymphatic vessels

Fig. 9: Healing with hypertrophy of the skin due to the concomitant thermal tissue

effect of the CO₂ laser

Fig. 11: Single spot technique using Up CO₂ (350 mJ; 5 J/cm2_{; < 1ms). End point is} mild crusting

Fig. 12: Syringoma are eccrine gland tumors. Ideal laser is Er:YAG due to its better

Fig. 13: Post-treatment with Er:YAG (5 J/cm2_{; 2 Hz; single spot technique) healing} with pigmentary alteration, which is an inevitable but reversible sequelae

Fig. 14: A case of bilateral xanthelasma palpebrum. Plan (Er:YAG; 10 J/cm2_{; 4 Hz).} End point is ablation of the tumor

Fig. 15: Postoperative view after 4 months. Note the healing and the variable

OVERVIEW

Laser-Tissue Interactions in Pigmented Skin

Selective photothermolysis was originally applied to the treatment of vascular lesions with oxyhemoglobin as the target chromophore. Thereafter, selective photothermolysis was applied to pigmented lesions by targeting endogenous melanin and exogenous carbon particles as target chromophores.

As a target chromophore, melanin has a broad absorption spectrum within the ultraviolet, visible and near-infrared light range (Fig. 3.1). Thus, while most lasers can be used for treating pigmented disorders, the light absorption in melanin decreases steadily with increasing wavelength. Also, there are competing chromophores, thus the “window of opportunity” is between the wavelengths of 630–1100 nm where the melanin absorption exceeds that of Hb. But as the absorption of melanin falls with a higher wavelength, a higer fluence is needed.

The melanin containing melanosomes are 0.5 µm in diameter and are predicted to have a thermal relaxation time between 50 ns and 500 ns. Thus, ideally Q-switched lasers would be effective in treating the disorders. With increasing wavelengths, melanin absorption decreases but the required threshold laser exposure dose increases. This is relevant (Fig. 3.1) as the lasers that is used in India QS Nd:YAG (1,064 nm) would require a higher fluence than the other lasers. This can lead to PIH, which is a decidedly common feature. More importantly is the sequelae of hypopigmentation and thus the authors do not recommend using this laser for melasma.

When treating pigmented lesions, Q-switched lasers generate an immediate ash-white color at the site of impact (Fig. 3.2). The cause of this tissue response is due to heat-induced steam cavities in melanosomes which cause a scattering of visible light, producing a white color. The adequate laser exposure dose for melanosome damage correlates well with the clinical threshold for immediate skin whitening. In other words, if the clinical ash- white color is not visible, the laser exposure dose is not sufficient. Darker skin has a lower threshold for whitening due to a higher epidermal melanin

Kabir Sardana, Rashmi Ranjan, Payal Chakravarty, Khushbu Goel, Anuj Tenani, Anjali Madan

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