Key points

Videos are provided of animation of combined deep fractional and superficial ablative treatments; resurfacing of the upper neck; and resurfacing of deep perioral rhytids accompanying this article at http://www.facialplastic.theclinics.com/

Introduction

The author of this article uses the pulsed ablative CO ₂ laser regularly for skin rejuvenation, despite the body of literature describing its adverse effects and the growth of less ablative fractional laser procedures. This decision is based on the gold standard status of the CO ₂ modality and an innovative posttreatment plan shown in the author’s practice to minimize postoperative side effects commonly associated with fully ablative laser resurfacing. Depending on the patient and the severity of the skin condition, the author customizes each treatment, which may also include deep fractional and fully ablative CO ₂ lasers, fat grafting, facelifting, and any combination of these techniques. A summary of the evolution of ablative pulsed CO ₂ technology is presented to prepare the reader for a detailed description of the author’s approach to skin rejuvenation.

Skin resurfacing refers to the removal of the outer layers of photodamaged skin to stimulate re-epithelialization and collagen remodeling. Aesthetic procedures for resurfacing facial skin may be surgical or nonsurgical. Rhytidectomy and blepharoplasty are time-honored surgical techniques to eliminate unwanted jowls, facial laxity, and facial puffiness. Nonsurgical modalities include dermabrasion, chemical peeling, and lasers. Dermabrasion and chemical peeling improve scarring and facial rhytids by burning (chemical ablation) or abrading the superficial layers of skin. Results, however, can be unpredictable because it is difficult to control the depth of tissue removal with absolute precision.

Introduction

The author of this article uses the pulsed ablative CO ₂ laser regularly for skin rejuvenation, despite the body of literature describing its adverse effects and the growth of less ablative fractional laser procedures. This decision is based on the gold standard status of the CO ₂ modality and an innovative posttreatment plan shown in the author’s practice to minimize postoperative side effects commonly associated with fully ablative laser resurfacing. Depending on the patient and the severity of the skin condition, the author customizes each treatment, which may also include deep fractional and fully ablative CO ₂ lasers, fat grafting, facelifting, and any combination of these techniques. A summary of the evolution of ablative pulsed CO ₂ technology is presented to prepare the reader for a detailed description of the author’s approach to skin rejuvenation.

Skin resurfacing refers to the removal of the outer layers of photodamaged skin to stimulate re-epithelialization and collagen remodeling. Aesthetic procedures for resurfacing facial skin may be surgical or nonsurgical. Rhytidectomy and blepharoplasty are time-honored surgical techniques to eliminate unwanted jowls, facial laxity, and facial puffiness. Nonsurgical modalities include dermabrasion, chemical peeling, and lasers. Dermabrasion and chemical peeling improve scarring and facial rhytids by burning (chemical ablation) or abrading the superficial layers of skin. Results, however, can be unpredictable because it is difficult to control the depth of tissue removal with absolute precision.

Ablative CO ₂ laser resurfacing

Ablative resurfacing with the CO ₂ laser is considered the gold standard for skin rejuvenation. CO ₂ lasers, continuous wave (CW) or pulsed, emit light at 10,600 nm and target tissue water, which has a high absorption coefficient at this wavelength. Ablation is limited to the upper 20 μm of skin during any single pulse and residual thermal damage (collateral heating) typically occurs at depths of 0.2 to 1 mm. CW CO ₂ lasers use low-power densities (50 W/cm ² ) and gated exposures to successfully reduce wrinkles.

The adverse effects of CW CO ₂ laser irradiation are multifactorial. Commonly reported complications include the following:

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  Persistent erythema

  
  
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  Acneiform eruptions

  
  
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  Pustules

  
  
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  Milia

  
  
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  Hyperpigmentation

  
  
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  Hypopigmentation

  
  
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  Overall lack of satisfaction with the procedure

The degree of thermal damage depends on laser wavelength, irradiance, and duration of exposure. Researchers in the 1980s suspected that tissue could be suitably ablated and thermal damage could be reduced by short pulses rather than long-pulsed, CW CO ₂ radiation. Walsh and colleagues measured the widths of thermally damaged zones in guinea pig skin after irradiation with pulse durations ranging from 2 microseconds to 50 milliseconds. The 50-millisecond pulse durations produced damaged zones 750 μm wide, whereas the short pulse durations resulted in zones of 50 μm in width.

Selective photothermolysis

The results of Anderson and colleagues were consistent with the concepts of selective photothermolysis and thermal relaxation time (TRT) of target tissues. In selective photothermolysis, the laser energy is confined to the target tissue for a shorter time (because of short pulse duration) than that required for the laser-induced heat to diffuse to surrounding tissue. The TRT is the time required for the highest temperature rise in a heated area of tissue to decrease to 37% of its peak value. If the pulse duration is less than the TRT of the target tissue, thermal damage to the surrounding tissue is minimized and more desirable thermal effects are achieved. By using pulses shorter than the TRT of the vaporized layer (0.8–1 ms, the TRT of skin), thermal damage zones are reduced to 20 to 150 μm in width. The TRT of the target tissue may be used to select the appropriate laser pulse duration time.

Pulsed ablative CO ₂ lasers permit precise control of tissue vaporization; minimal (controlled) thermal damage; dermal collagen contraction; and hemostasis. CO ₂ energy instantly vaporizes the surface layer of cells, thermally induces coagulation necrosis of cells and denatures proteins in the subjacent residual layer, and damages cells in deeper zones. Similar clinical results can be obtained by scanning a tightly focused CW beam of CO ₂ energy. With this modality, a beam scanner moves the laser spot at a speed that covers the treatment site at an exposure (dwell) time commonly reported as 0.8 to 1 milliseconds, resulting in effects similar to those of a pulsed ablative laser.

The erbium:YAG laser

Also an ablative laser, the 2940-nm erbium (Er):YAG device was developed to reduce adverse effects associated with CO ₂ laser treatment. The 2940-nm wavelength is absorbed 16 times more strongly by water than the 10,600-nm energy of the CO ₂ laser. Because the penetration depth of 2940-nm energy is only 1 μm, thermal damage is reduced, and ablation is more precise compared with the CO ₂ laser, whose skin penetration is 20 μm. Research has shown, however, that although wounds heal more quickly and ablation is more superficial compared with the CO ₂ laser, efficacy of Er:YAG treatment is less when the number of passes and fluences per pulse are comparable with those of the CO ₂ laser. Dermal collagen remodeling is also less with the Er:YAG laser. Because efficacy of the Er:YAG laser increases with the depth ablation and surrounding thermal damage, pulse duration must be increased to reach the appropriate depth for rhytid ablation and provide some degree of thermal injury. When treatment depths of the Er:YAG laser are increased to those of the CO ₂ laser, healing times are comparable with the CO ₂ laser.

Adverse effects of ablative lasers

Traditional ablative lasers have high efficacy but an unfavorable adverse effects profile. Adverse effects of ablative CO ₂ lasers have been described in numerous reports and include the following :

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  Prolonged erythema

  
  
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  Pruritis

  
  
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  Hyperpigmentation and hypopigmentation

  
  
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  Acne flares

  
  
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  Milia

  
  
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  Contact dermatitis

  
  
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  Infections

  
  
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  Pain during treatment

  
  
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  Scarring

With fractional and ablative CO ₂ resurfacing, treatment parameters must by altered because of the variables associated with each anatomic zone. For example, the risk of scarring is greater in the neck, chest, and extremities than in the face because these nonfacial areas have fewer pilosebaceous units than the face. The depth of the epidermis and dermis vary significantly even within specific facial zones and must be considered to minimize the risks previously discussed.

Nonablative lasers were developed to further reduce adverse effects of rejuvenation procedures. Although nonablative laser treatment stimulates collagen remodeling in the dermis and improves clinical manifestations of photodamage, efficacy is unpredictable and usually less than that of ablative lasers.

Fractional photothermolysis

To address the adverse effects of ablative lasers and the limited efficacy of nonablative lasers, the concept of fractional photothermolysis (FP) was developed. With this technology, the laser beam, rather than completely vaporizing a layer of superficial tissue, creates an array of microscopic wounds at specific depths of the skin with controlled collateral damage to the surrounding tissue. The result is microablation, tissue contraction, neocollagenesis, and rapid healing caused by small wounds and the short migration distances for keratinocyte during re-epithelialization. The first FP device was the nonablative 1500-nm erbium glass laser. It soon became apparent that patients needed multiple successive treatments at 3- to 4-week intervals to achieve clinical results comparable with those of a single treatment with an ablative laser.

With the success of the nonablative fractional laser came the development of an ablative fractional resurfacing CO ₂ laser whose encouraging histologic and clinical effects have been reported. Reilly and colleagues recently reported upregulation of matrix metalloproteinases after ablative fractional resurfacing CO ₂ laser, similar to the molecular alterations observed after fully ablative CO ₂ laser resurfacing, The fractional CO ₂ laser combines FP with the ablative 10,600-nm wavelength to thermally ablate a fraction of the skin while carefully heating the surrounding tissue, which after treatment “repopulates” the ablated columns of tissue. Hantash and colleagues showed that collagen remodeling occurred for at least 3 months after treatment. These authors and others subsequently demonstrated that the ablative fractional resurfacing CO ₂ laser device also tightened skin and improved texture more than that observed with the original nonablative FP devices. Histologic evidence showed that wound repair and neocollagenesis also occur.

Adverse effects of fractional lasers

Compared with traditional ablative resurfacing devices, reepithelialization after Ablative Fractional Treatment is more rapid, infections are less frequent, duration for posttreatment skin care is shorter, fewer acneiform eruptions occur, and the duration of postoperative erythema is shorter. Fractional laser treatments, however, are not without risk. Avram and coworkers observed hypertrophic scarring of the neck in five patients referred to them after fractional laser treatment. These authors speculated that the scarring may have been caused by reduced wound healing capacity (ie, because of fewer pilosebaceous units for reepithelialization and fewer cutaneous vessels) of the neck compared with the face; facelifting and necklifting procedures that may have produced a “subtle fibrosis” that would have adversely affected the cutaneous blood vessels; and plastic surgery that may have placed underprivileged neck skin on facial sites. They suggested that treating physicians closely monitor posttreatment wound care to minimize adverse effects.

In a retrospective study of 374 patients who received a total of 490 treatments with a deep fractional CO ₂ laser, Shamsaldeen and colleagues reported adverse events in 16.8% of patients and in 13.6% of treatments of the face, neck, chest, arms, abdomen, and back. Adverse events in order of decreasing frequency included the following:

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  Acneiform eruptions, 5.3%

  
  
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  Herpes simplex outbreak, 2.2%

  
  
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  Bacterial infections, 1.8%

  
  
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  Yeast infections, 1.2%

  
  
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  Hyperpigmentation, 1.2%

  
  
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  Erythema persisting longer than 1 month, 0.85%

  
  
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  Contact dermatitis, 0.8%

In a similar study with the fractionated CO ₂ laser, Campbell and Goldman reviewed records of 287 patients who received 373 treatments. Adverse effects were recorded in 13.9% of patients and 12.6% of treatments. These effects included the following:

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  Allergic or contact dermatitis, 4.6%

  
  
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  Acneiform breakout, 3.5%

  
  
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  Prolonged erythema, 1.1%

  
  
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  Herpes simplex virus outbreaks, 1.1%

The risk of adverse events increased when three consecutive treatments were given to multiple body sites.

Adverse effects have also been found with the 1500-nm erbium doped fractional laser. In their review of 961 successive treatments in 422 patients treated on the face, neck, chest, and hands, complications were observed in 7.6% of treatments. Adverse effects included the following:

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  Acneiform eruptions, 1.87%

  
  
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  Herpes simplex virus outbreaks, 1.77%

  
  
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  Erosions, 1.35%

  
  
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  Postinflammatory hyperpigmentation, 0.73%

  
  
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  Prolonged erythema, 0.83%

  
  
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  Prolonged edema, 0.62%

  
  
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  Dermatitis, 0.21%

  
  
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  Impetigo, 0.10%

  
  
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  Purpura, 0.10%

The ablative CO ₂ laser revisited

The availability of these different treatment options enables physicians to customize treatment, depending on the severity of photodamage and the downtime the patient can tolerate. With modern lasers treatment parameters can be more easily controlled and tailored to the needs of each patient.

The author prefers to use the ablative pulsed CO ₂ laser over other modalities for skin rejuvenation. The scientific evidence is clear that the fully ablative CO ₂ laser is the most effective in creating the desired effect in skin rejuvenation for the following reasons: (1) greater long-term wound contraction and fibroplasia per micrometer depth of injury compared with the Er:YAG laser ; (2) superior clinical improvement after equivalent-depth dermal wounding with the Er:YAG laser ; (3) greater posttreatment neocollagenesis with the pulsed CO ₂ laser compared with the Er:YAG or scanned CO ₂ modalities ; and (4) a study of quantitative molecular changes in dermal remodeling after treatment of photodamaged forearm skin with a pulsed CO ₂ laser showed increased production of messenger RNA for type I procollagen, type III procollagen, interleukin-1β, tumor necrosis factor-α, transforming growth factor-β1, and matrix metalloproteinases-1, -3, -9, and -13. Levels of fibrillin and tropelastin were also observed after treatment. These molecular changes during wound healing were reproducible and resulted in changes in dermal structure of the treated areas.

The treatment conditions necessary to optimize clinical benefits and minimize adverse effects with the ablative CO ₂ laser can be understood from the following considerations. The energy needed to ablate skin tissue without charring is approximately 2500 J/cm ³ . This amount of energy must be delivered to the targeted tissue for duration equal to or less than the TRT of the skin. Delivery of energy must stop “on time” to minimize transfer of heat to the underlying tissue and prevent charring. When prolonged dwell times are used, superheating of adjacent tissues occurs, which may result in prolonged erythema, extended healing times, and dismay by physician and patient.

The equations describing the energy and pulse duration needed to ablate the uppermost layer with minimal injury to underlying tissue are beyond the scope of this article but may be summarized as follows :

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  The heat of vaporization for water is 2260 J/g, which is numerically close to the 2500 J/cm ³ to ablate skin tissue without charring.

  
  
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  For tissue ablation to occur, the applied fluence must be 2500/α, where α = 500/cm, the absorption coefficient of water at 10,600 nm.

  
  
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  The quotient, 5 J/cm ² , is the pulse fluence to ablate the uppermost layer of tissue.

  
  
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  To minimize thermal injury to underlying tissue, the 5 J/cm ² fluence must be delivered in a short pulse.

  
  
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  The optical penetration depth is limited to 20 μm because much of the incident radiation is absorbed by water.

  
  
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  The TRT for the CO ₂ -heated superficial layer under these conditions is calculated to be approximately 0.8 milliseconds.

  
  
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  To completely ablate the uppermost 20-μm thick layer of tissue with minimal controlled thermal injury to underlying tissue, at least 5 J/cm ² fluence must be delivered with a pulse duration of 0.8 milliseconds or less.