16 Maximizing Safety with Ablative Lasers

10.1055/b-0040-177258

16 Maximizing Safety with Ablative Lasers

E. Victor Ross, Erez Dayan, and Rod J. Rohrich

Abstract

Lasers are among the most precise and powerful tools available in facial rejuvenation. Through selective photothermolysis, lasers are able to target specific tissue chromophores based on their absorption wavelength (i.e., hemoglobin, water, melanin). Laser technology and safety have evolved significantly since the continuous wave CO₂ laser developed in 1964, which had less control of energy parameters, leading to frequent injury and scarring. The pulsed mode (and subsequent superpulse and ultrapulse lasers) was a significant advance in safety and efficacy. This technology uses electronic shutters to interrupt the continuous wave of energy into pulses, thereby limiting thermal damage. The introduction of the Er:YAG laser in the mid-1990s offered a more selective absorption of water (12–18 x) than CO₂ lasers with less collateral heat injury to surrounding tissues.

Perhaps the most significant modern advance in the safety and efficacy of lasers was the evolution of the fractional laser in 2003. Fractional thermolysis resurfaces microtreatment zones (MTZ) within a target area (typically 20%); maintaining intervening uninjured epidermis and dermis that preserves the skin’s barrier function while speeding re-epithelialization.

Key Points

The most common ablative lasers used in facial aesthetics are CO₂ and Er:YAG. Both target water as a chromophore. Er:YAG is more specific (12–18 x), leading to less surrounding heat dissipation and collateral tissue damage. ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵
The goal of ablative lasers is to eliminate or reduce damaged collagen and encourage new collagen formation and remodeling through a combination of tissue vaporization and collagen denaturation secondary to thermal damage. ⁶ ^, ⁷ ^, ⁸
Ablative fractional lasers lead to microthermal zones of injury, with surrounding areas reaching temperatures of 55–62°C. This denatures existing collagen, leading to neocollagenesis, elastogenesis, and remodeling. ¹ ^, ⁹ ^, ¹⁰ ^, ¹¹
Ablative lasers can be used on patients of all skin types; however, to avoid permanent hypo or hyperpigmentation and scarring, treatment should be avoided or approached with extreme caution in patients with > Fitzpatrick type III skin. ⁹ ^, ¹⁰

16.1 Safety Considerations

CO₂ Laser (10,600 nm)
CO₂ lasers have a higher ablation threshold than Erbium lasers, which means that greater thermal heating is required to achieve effect. ⁹ ^, ¹⁰
Ablation is achieved at 5 J/cm² for CO₂ lasers with a residual 70–150 µm area of heating. ⁹ ^, ¹⁰
Depth of ablation depends on the number of passes, the fluence, the pulse duration, and the amount of cooling time between passes. ¹ ^, ¹¹
As more passes of the CO₂ laser are performed, less water (target chromophore) is present to be vaporized. This leads to additive heat accumulation and increased potential for thermal injury/scarring.
Clinical endpoint depends on color assessment of tissue (as in chemical peels) rather than dermal bleeding. ¹ ^, ⁶ ^, ¹¹ ^, ¹²
Fractional CO₂ lasers allow for the creation of microthermal zones (MTZ) of pixilated tissue damage to the underlying dermis while leaving epidermal elements intact. This allows for more rapid re-epithelialization and dermal collagen remodeling. Thus, multiple treatments can be achieved with less risk for pigmentation changes. Coverage density ranges from 10 to 60% per pass depending on the area being treated. ³