Throughout the last decade, cutaneous laser resurfacing has gained popularity among laser surgeons and the public alike. Based upon the principles of selective photothermolysis, resurfacing lasers selectively target water-containing tissue resulting in controlled tissue vaporization. Associated residual thermal injury in the dermis results in collagen shrinkage and remodeling. See the image below.
Lasers currently available for cutaneous resurfacing include a high-energy pulsed or scanned carbon dioxide laser, a short-pulsed erbium:yttrium-aluminum-garnet (Er:YAG), [1, 2] and modulated (short-and-long-pulsed) Er:YAG systems. High-energy pulsed or scanned carbon dioxide laser skin resurfacing can achieve excellent clinical improvement of photodamage, rhytides, and atrophic scars. However, this resurfacing is associated with an extended reepithelialization period and, in some cases, prolonged erythema that may persist for several months. Of greater concern is the potential for delayed permanent hypopigmentation seen in as many as 20% of patients when multiple-pass carbon dioxide resurfacing is performed. The demand for less aggressive modalities for skin rejuvenation led to the development of the Er:YAG laser. 
The 2,940-nm wavelength emitted by the Er:YAG laser is absorbed 12-18 times more efficiently by superficial (water-containing) cutaneous tissue than is the 10,600 nm wavelength of the carbon dioxide laser. With a pulse duration of 250 microseconds, a typical short-pulse Er:YAG laser ablates 5-20 µm of tissue per laser pass at a fluence of 5 J/cm2 with minimal residual thermal damage (compared with 20-60 µm of tissue ablation and up to 150 µm of residual thermal damage per pass with the carbon dioxide laser). The precise tissue ablation and small zone of residual thermal damage results in faster reepithelialization and an improved side effect profile.
Because of these advantages, many thought the short-pulsed Er:YAG laser would supersede the carbon dioxide laser as a superlative ablative modality. However, initial enthusiasm for the short-pulsed Er:YAG laser was tempered by poor intraoperative hemostasis and less impressive clinical improvement (reduced tissue tightening) when compared to traditional high-energy pulsed or scanned carbon dioxide laser resurfacing. 
In an attempt to overcome the limitations of the short-pulsed Er:YAG laser, modulated (short-and-long-pulsed) Er:YAG systems were introduced to facilitate deeper ablation of tissue, improve hemostasis, and increase collagen remodeling. With the addition of significant coagulative properties, modulated Er:YAG systems combined precise control of ablation with the ability to induce dermal collagen formation by means of thermal injury. 
The concept of fractional photothermolysis revolutionized cutaneous laser resurfacing when introduced by Manstein et al in 2004.  Using a nonablative, 1550-nm Er-doped fiber laser, full-thickness columns of thermal injury (termed microthermal treatment zones or MTZs) are created in a pixelated pattern just below the level of the stratum corneum, with the surrounding skin left intact. Because epidermal barrier function is intact, healing is rapid, without oozing or crusting. Patients typically require a series of treatments for the best response for a variety of conditions such as photodamage and atrophic scarring. However, with the deepest scars or rhytides, the amount of overall improvement may be marginal with this nonablative approach. A study has shown that multiple sessions are effective in facial rejuvenation, stimulating the formation of new collagen and resulting in better skin texture and finer wrinkles. 
Most recently, ablative fractional resurfacing treatments with either a carbon dioxide or 2940-nm Er:YAG laser have demonstrated good clinical outcomes with significantly less recovery time and adverse effects compared with traditional ablative laser skin resurfacing. Research is ongoing to determine the most effective treatment protocols for this exciting new technique.
Indications and Treatment Areas
As with any cosmetic procedure, the surgeon should be completely familiar with the indications and limitations of the treatment being considered. [8, 9] The Er:YAG laser is a powerful tool in the cosmetic surgeon's armamentarium that can have beneficial effects when used properly for the correct indication. Mild-to-moderate photo-induced rhytides, superficial pigmentation, atrophic scars, and a variety of epidermal and dermal lesions can be treated successfully with the Er:YAG laser. Treatment with the short-pulsed Er:YAG laser is particularly well suited for patients with darker skin phototypes. Several studies have documented a lower risk of pigmentary alterations as compared to carbon dioxide laser resurfacing. Although studies suggest modulated Er:YAG lasers are associated with a lower risk of pigmentary alterations than carbon dioxide laser resurfacing, long-term data regarding the risks of delayed hypopigmentation are not yet available.
Skin resurfacing with a short-pulsed Er:YAG laser is most commonly used for the improvement of fine rhytides. For moderate photodamage and rhytides, modulated Er:YAG laser skin resurfacing results in greater collagen contraction and improved clinical results as when compared to short-pulsed Er:YAG systems. Clinical improvement of severe rhytides treated with a modulated Er:YAG laser can be impressive. However, the improvement seen is not equivalent to that of pulsed or scanned carbon dioxide resurfacing, even when equal depths of ablation are obtained. Newman and colleagues  compared a variable pulse Er:YAG laser to traditional pulsed or scanned carbon dioxide resurfacing for the treatment of perioral rhytides. Although a reduced duration of reepithelialization was noted with the modulated Er:YAG laser (3.4 d vs 7.7 d with carbon dioxide), the clinical results observed were less impressive than those following carbon dioxide laser resurfacing.
Er:YAG laser systems may greatly improve atrophic scars caused by acne, trauma, or surgery.  In a series of 78 patients, Weinstein  reported 70-90% improvement of acne scarring in the majority of patients treated with a modulated Er:YAG laser. Pitted acne scars may require ancillary procedures, such as subscision or punch excision, for optimal results. These procedures can be performed either prior to or concomitant with Er:YAG laser resurfacing.
A variety of benign epidermal and dermal conditions respond favorably to Er:YAG laser resurfacing, including sebaceous hyperplasia, eruptive hair cysts, adenoma sebaceum, angiofibroma, hidradenoma, xanthelasma, and syringomas.
Laser surgeons can combine Er:YAG lasers and carbon dioxide lasers to take advantage of the unique properties of each laser. The addition of Er:YAG laser following carbon dioxide laser resurfacing may decrease the duration of postoperative crusting and edema presumably by reducing the amount of thermal necrosis induced by the carbon dioxide laser.
Ablative laser skin resurfacing can be combined with surgical lifting procedures to provide complete rejuvenation in appropriate patients. When combination techniques are performed, the dermatologic surgeon must consider the potential for reduced vasculature in facial flaps. Therefore, a lighter treatment with the laser is recommended.
The success of cutaneous laser resurfacing relies upon the presence of adnexal structures (eg, pilosebaceous units, sweat glands) to function as a reservoir of epithelial cells that can migrate upward to form a new epidermis. Er:YAG laser resurfacing is most suitable for facial skin, which has more adnexal structures and, thus, a greater capacity to regenerate new cells than the skin of the trunk. Several studies document successful rejuvenation of the neck, chest, arms, and hands with the Er:YAG laser. However, the risk of scarring is significant because of the paucity of adnexal structures in these areas. Therefore, resurfacing of nonfacial areas remains a challenge and must be approached with caution, especially by the novice laser surgeon. To date, ablative fractional photothermolysis with an Er:YAG laser has been used successfully on the neck; however, clinical studies are ongoing to determine the most effective protocols.
Patient Selection, Contraindications, and Cautions
Appropriate patient selection and reasonable patient expectations are the cornerstones of any successful cosmetic procedure. At the initial consultation, a complete medical and surgical history should be obtained. Contraindications to laser resurfacing include unrealistic patient expectations, tendency toward keloid or hypertrophic scar formation, isotretinoin within 6 months prior to surgery, and when a patient cannot comply with postoperative instructions. Patients with reduced numbers of adnexal skin structures, such as those with scleroderma, burn scars, or history of prior ionizing radiation to the skin, are not good candidates for ablative resurfacing. [3, 13, 14]
A history of previous laser skin resurfacing, dermabrasion, or deep phenol peel is noteworthy because these procedures could potentially slow the wound healing process due to the presence of fibrosis. Patients who have undergone prior transcutaneous lower lid blepharoplasty or have limited infraorbital elasticity may be at increased risk for postoperative ectropion. When applicable, patients who smoke should be discouraged from doing so before and after surgery to reduce the risk of delayed or impaired wound healing.
A thorough examination of the skin to be treated includes careful attention to skin phototype and specific areas of scarring, dyschromia, and rhytide formation. For patients desiring periorbital laser treatment, the eyes must be examined for scleral show, lid lag, and ectropion. Other cutaneous disorders should also be noted, including seborrheic keratoses, solar lentigines, actinic keratoses, and cutaneous carcinomas. The latter must be treated adequately before any resurfacing procedure is performed.
Antibiotics and Antiviral Agents
Oral antiviral agents
Laser skin resurfacing can lead to reactivation of latent herpes simplex virus infection or predispose the patient to a primary infection during the reepithelialization phase of healing. It is recommended that prophylactic antiviral medication be prescribed during the postoperative period, regardless of a patient's herpes simplex virus history. Commonly used regimens include famciclovir 250 mg twice daily, acyclovir 400 mg 3 times a day, or valacyclovir 500 mg twice daily. The medication may be administered the day before, or morning of, laser resurfacing and continued for 7-10 days until reepithelialization is complete.
Cutaneous laser surgeons may prescribe antibiotics for bacterial prophylaxis; however, little data exist to support their use because of the relatively low incidence of postoperative bacterial infections reported. Moreover, the routine use of antibiotic prophylaxis may increase the incidence of antibiotic resistance and predispose patients to organisms of increased pathogenicity. When used, a cephalosporin (cephalexin), semisynthetic penicillin (dicloxacillin), macrolide (azithromycin), or quinolone (ciprofloxacin) is administered one day before, or on the morning of, surgery and continued until reepithelialization is complete. The use of topical antibiotics on the laser-induced wound is not routinely recommended because of the increased risk of contact dermatitis.
Commonly Used Laser Parameters
Appropriate laser parameters depend upon the type of Er:YAG laser system utilized and the indication for resurfacing. No consensus is reached regarding the optimal laser parameters to use in every clinical setting. Laser surgeons commonly rely on their own experience to determine the most appropriate laser parameters to use in each case.
At a fluence of 5 J/cm2, a typical short-pulsed (250-microsecond) Er:YAG laser ablates 15-20 µm of tissue and creates a zone of thermal damage not exceeding 15 µm. Alster et al assessed the clinical and histologic changes following cutaneous resurfacing with 6 different short-pulsed Er:YAG laser systems and found that 3 laser passes were necessary to produce total epidermal ablation. 
Modulated Er:YAG laser systems have enabled laser surgeons to gain greater control over the tissue reaction and induce more thermal damage. The hybrid Er:YAG/carbon dioxide Derma-K laser delivers ablative Er:YAG pulses with fluence up to 28 J/cm2 and a 350-microsecond pulse. The coagulative carbon dioxide pulse can range from 1-100 milliseconds with 1-10 W power. The dual-mode Contour Er:YAG laser combines short ablative pulses (200-350 microseconds) and long coagulative pulses to achieve up to 400 µm of ablation and 100 µm of coagulation per pass. The touch screen control panel allows the operator to program clinically relevant depths of ablation and coagulation depending upon the patient's needs. The variable-pulsed carbon trioxide (CO3) Er:YAG laser delivers pulse durations from 500 microseconds to 10 milliseconds. Shorter pulse durations are used for tissue ablation, and longer pulse durations are used to induce collagen contraction through thermal injury.
Treatment parameters of the most advanced ablative fractionated Er:YAG lasers are dependent on several factors including area to be treated, severity of the condition, and the brand of laser used. Referral to the most recent laser guidelines for each individual laser system is advised.
Pain associated with laser resurfacing results from the vaporization of tissue and thermal injury. For small areas, local infiltration using 1% lidocaine with epinephrine or tumescent anesthesia using a dilute lidocaine suspension is usually sufficient to produce adequate anesthesia. Patients having a single-pass resurfacing procedure may be able to tolerate the Er:YAG well with topical anesthetic (EMLA, Ela-MAX) alone. For large areas, such as full-face resurfacing, or when several laser passes are performed, nerve blocks are used. Some laser surgeons may use tumescent anesthesia, with or without nerve blocks, to provide local anesthesia, while others prefer to use conscious sedation (twilight anesthesia) alone, or in conjunction with, other techniques.
Postoperative Wound Care and Complications
Postoperative wound care
Although postoperative wound care varies among laser surgeons, it is well established that wounds heal more quickly in a moist environment. It is crucial that the laser-treated area be kept moist and not allowed to desiccate during the reepithelialization period. Postoperative wound care can follow an open or closed method.
With the closed method, a semiocclusive dressing (usually involving hydrogel) is placed on the denuded skin. These wound dressings have been shown to accelerate the rate of reepithelialization by maintaining a moist environment. In addition, decreased postoperative pain has been reported with their use. However, some surgeons believe occlusive dressings also create a low-oxygen environment that may promote the growth of anaerobic bacteria and subsequent infection. As such, many proponents of the closed technique currently endorse removal of the dressing with wound inspection 24-48 hours after the procedure followed by topical emollients.
Advocates of open wound care recommend frequent soaks with cool saline or dilute acetic acid. These soaks are followed by the application of copious amounts of ointment to promote reepithelialization while allowing adequate visualization of the resurfaced wound.
Complications after laser resurfacing
Er:YAG laser resurfacing ablates superficial cutaneous tissue and imparts a thermal injury to denuded skin. Therefore, adverse effects are to be expected and should be differentiated from complications. Minor adverse effects of cutaneous laser resurfacing include transient erythema, edema, burning sensation, and pruritus. Short-pulsed Er:YAG resurfacing procedures are associated with a significantly shortened period of reepithelialization and erythema when compared to the carbon dioxide laser. However, when equivalent depths of ablation and coagulation are achieved with the aforementioned modulated systems, postoperative healing times are comparable.
Mild complications of Er:YAG laser resurfacing include milia, acne exacerbation, contact dermatitis, or perioral dermatitis. Moderate complications include localized viral, bacterial and candidal infection, prolonged erythema, transient posttreatment hyperpigmentation, and delayed hypopigmentation. The most severe complications include fibrosis, hypertrophic scarring, disseminated infection, and the development of ectropion. Diligent evaluation of the patient is necessary during the reepithelialization phase of healing. This is important because a delay in recognition and treatment of complications can have severe deleterious consequences such as permanent dyspigmentation and scarring.
Although short-pulsed Er:YAG laser resurfacing has a significantly better adverse-effect profile and complication rate when compared to pulsed or scanned carbon dioxide resurfacing, long-term data for the modulated Er:YAG systems are not yet available. Because the modulated Er:YAG systems may be used to create zones of collateral thermal damage similar to those created by the carbon dioxide laser, further studies are necessary to determine the incidence of delayed hypopigmentation.