The energy delivery time or exposure time during laser treatment is termed the “pulse width” and achieving the correct pulse width is key to successful laser outcomes. The energy provided to the tissues by the laser must be introduced into the target faster than it can dissipate to adjacent tissues. The thermal relaxation time is defined as the time for the target tissue to dissipate 51% of the energy absorbed. The pulse width must be less than this and the ideal pulse time is usually half of the thermal relaxation time. If the process of heating to the required thermal temperature takes too long, then surrounding tissue temperature will build up causing unwanted damage and the target chromophore will not be adequately treated either. Laser light works at different wavelengths and the longer the wavelength, the longer the absorption length observed in the tissues, rather than the two properties being inversely proportional to one another. Each given wavelength will propagate to a specific tissue depth due to its own unique absorption characteristic. Laser light has a number of specific qualities including coherence (light is in phase), monochromaticity (light is one color only), and it is collimated (within a tight formation). In contrast, intense pulsed light (IPL) has the opposite features; it is noncoherent, polychromatic, and noncollimated. Fluence does not relate to the speed of energy transfer to the tissues, but instead refers to the energy density as measured in joules/cm2. It is a product of the power and the spot size used. Laser energy delivery was previously continuous but is rarely so anymore because this is likely to cause scarring secondary to thermal damage. Instead, pulsed energy delivery is commonly used such that the timing can be matched between the size of the target and its thermal relaxation time.1,2
2. Farkas JP, Hoopman JE, Kenkel JM. Five parameters you must understand to master control of your laser/light-based devices. Aesthet Surg J 2013;33(7):1059 • Vascular lesions—hemoglobin and oxyhemoglobin • Pigmented skin lesions—melanin • Tattoo pigment—tattoo pigment • Ablative resurfacing—water • Laser liposuction—water and fat Hair removal works best on dark hairs given the chromophore target is melanin within the hair. Water is the chromophore for ablative lasers such as CO2 and Er:YAG. The target chromophores for vascular lesions are hemoglobin and oxyhemoglobin. Skin constituents such as collagen or elastin are not chromophores, but may be affected by laser treatment. For example, use of a resurfacing laser, such as CO2, will target water in the dermis and stimulate the regeneration of collagen and elastin which can tighten the skin.1–3
3. Nahai F. The Art of Aesthetic Surgery: Principles & Techniques. 2nd ed. St Louis: Quality Medical Publishing; 2011 The electromagnetic spectrum relevant to lasers in plastic surgery includes the ultraviolet (UV) (200–400 nm), visible (400–750 nm), near-infrared (750–1400 nm), and mid-infrared (1400–20,000 nm). Most vascular lasers are within the visible range (as this corresponds to the wavelength of hemoglobin), and most that target melanin are in the near-infrared spectrum. Those that target water are within the mid-infrared spectrum. Nd:YAG is in the near-infrared spectrum and can target both oxyhemoglobin and melanin as well as tattoo pigment. The wavelengths of common lasers are shown in Box 11.1. Wavelengths of commonly used lasers are often asked in written examinations.1–4 BOX 11.1 WAVELENGTHS OF COMMON LASERS Vascular KTP: 532 nm Pulsed dye: 585 nm Nd:YAG: 1064 nm Ablative Resurfacing CO2: 10,600 nm Er:YAG: 2940 nm Melanin Target (hair removal, solar lentigines, or tattoo removal) Alexandrite: 755 nm Ruby: 694 nm Diode: 810 nm KTP, Potassium titanyl phosphate; Er:YAG, erbium-doped yttrium aluminum garnet; Nd:YAG, neodymium-doped yttrium aluminum garnet.
4. Stübinger S, Klämpfl F, Schmidt M, Zeilhofer HF. Lasers in Oral and Maxillofacial Surgery. SpringerLink; 2020 When using a laser for therapeutic interventions, it is vital that strict safety measures are in place. The responsibility of this falls on both the surgeon and operating room (OR) lead to ensure the safety measures are maintained. It is important to have formal training and accreditation in laser prior to using it in clinical practice. A key component to achieving adequate safety is ensuring that laser specific signs are placed at all entrances to the treatment room or operating room. These signs must indicate that a laser procedure is in progress and that eye protection is required. They must also show what wavelength and power of laser is being used. Furthermore, they should not be permanently posted, but instead should be removed when the laser treatment session is complete. The windows of the room must also have opaque coverings that correspond to the wavelengths of any laser being used. Eye protection with laser specific goggles/glasses is mandatory for all personnel in the treatment room or operating room. It is not limited to those actually giving the treatment. The optical density should be 5 or more (not less than 2) to adequately protect the eye. In addition to eye protection, masks should be worn, particularly in cases with malignancy or risk of viral transmission. Plume evacuation is required when using CO2 or erbium lasers. Wet swabs should be placed around the operative site to reduce the chance of local burns and ignition risks when using the CO2 laser. In this case a reinforced endotracheal tube must also be used with low FiO2 flows (less than 30%) to reduce the risk of flash burn or inhalation.1–3
The main goal of cooling tissues during laser treatment is to protect them from unwanted damage, specifically the skin at the dermal–epidermal junction. Complications of damage to the dermal–epidermal junction are blistering and subsequent hypo- or hyperpigmentation. Cooling does have a secondary benefit for patients in that it can provide anesthesia, but this is not usually its primary purpose. Treatment speed is not affected by cooling and excessive cooling is not effective because the target chromophore will be less responsive to the treatment being given and therefore will itself require higher energy to achieve a result. There would be no benefit in using a higher-powered laser to account for overcooling of the tissues.1,2
KTP is a popular choice for laser treatment of spider nevi. A spider nevus is an enlarged artery with radiating vessels supplied by it. This gives the appearance of a spider body with legs. On examination, pressure on the area makes the spot disappear and then on release it reappears as blood fills the empty vessel lumen. The cause is not known but they can be associated with liver or thyroid disease. Most commonly, they present as an isolated condition and can often resolve spontaneously. Laser therapy can be useful for the treatment of persistent spider nevi in a single visit. Other vascular lasers may also be considered such as yellow pulsed dye, ruby, alexandrite, and diode as they all target hemoglobin and cause local coagulation to the main source vessel.1–4 Green dye is used for café au lait macules. Er:YAG, fraxel, and CO2 are all used for resurfacing.2
Nd:YAG is a very versatile laser choice because it can be used to target both oxyhemoglobin and melanin chromophores. Therefore, it can be effective in treating hemangiomas, telangiectasia, and spider veins, as well as pigmented skin lesions, tattoo pigment, hair removal, and scar management. Yellow dye is a good choice for vascular lesions including hemangiomas, port-wine stains, and telangiectasia. However, it is best for superficial lesions and is associated with a higher rate of post-treatment purpura. Green dye is useful for managing café au lait macules, rather than vascular lesions, given its chromophore is melanin. Ruby also targets melanin and is popular for tattoo removal. Er:YAG uses water as its target chromophore and is used for skin resurfacing, not vascular lesions.1–3
There are a number of vascular lesions which are effectively treated with isolated laser modalities. The target chromophores for such lesions are hemoglobin and oxyhemoglobin. Laser causes damage to the vessel intima, coagulation, and stasis. Most vascular lesions, particularly more superficial ones, will respond well to treatment, although multiple sessions are usually required. However, venous and mixed venous lymphatic malformations tend to respond less well to laser therapy alone, because they are often too large or too deep for isolated laser therapy to be effective. Their management is more commonly combined with other nonlaser techniques such as surgical debulking or intralesional sclerotherapy with agents such as bleomycin or OK451.1,2 Early stage, ulcerated, and regressed hemangiomas can be treated with laser monotherapy. However, its use is contraindicated when the hemangioma is in the proliferative phase as the treatment itself can induce ulceration and tissue necrosis. Nonlaser mainstays of treatment are now propranolol, which is taken orally, or intralesional injection with substances such as bleomycin or steroid. Capillary venous malformations, facial telangiectasia, rosacea, and spider veins are generally all effectively treated with laser monotherapy. Common laser types for such treatments are KTP, Nd:YAG, or intense pulsed light (IPL).3–6
effective? The patient described has a port-wine stain or capillary malformation. Port-wine stains represent a collection of abnormally formed capillaries within the skin, resulting in a red or purple colored mark. Most port-wine stains are present at birth, as in this case, but they can also be acquired. They are relatively common and occur in 1:300 infants with an equal sex distribution. The pulsed dye laser is commonly used to improve the appearance of port-wine stains as it targets oxyhemoglobin within the abnormal vessels using a 585 nm wavelength. Cases generally require a series of treatments at regular intervals. These often require general anesthesia in children. Treatment outcomes can be quite successful although most lesions never fully disappear. In general, the outcome following treatment with pulsed dye laser is best in lighter colored lesions, in children, and in patients with lighter skin tones (Fitzpatrick I– III). Treatment can be started from the age of 6 months. Better responses are observed in the head and neck region with the exception of the trigeminal nerve V2 distribution. The anatomic area associated with the poorest response is the extremities.1–3 Long-term follow-up shows that these lesions darken again over time once treatment has finished. In most cases the port-wine stain at 10 years after treatment has an appearance midway between the before and after injury color. For this reason, patients must be informed of the risk of darkening over time.4
10 years after pulsed-dye-laser treatment. N Engl J Med 2007;356(12):1235–1240 There are a number of different laser types used in hair removal, each with its own advantages and disadvantages. These lasers include Diode, Alexandrite, and Nd:YAG. Ruby is not a hair removal laser choice and is indicated for tattoo removal and treating pigmented skin lesions. Alexandrite is commonly used for hair removal in patients with lighter skin tones. Nd:YAG is safest for darker skin tones to reduce the risk of hypopigmentation.1,2 In general, laser hair removal is most effective in patients with fair skin and dark hairs because the target chromophore is melanin. Laser is therefore generally less effective in blonde patients although it does still work. Intense pulsed light (IPL) is an alternative option for hair removal and can be quite effective in fair-skinned, fair-haired individuals such as in this patient.2,3
Green tattoo inks are best treated with a laser of wavelength 650 nm. Suitable choices include alexandrite (755 nm) and ruby (694 nm). Q-switched lasers are preferable over pulsed for tattoo removal. They use high bursts of energy in short time intervals and create acoustic waves that result in mechanical pigment disruption. The pigments that are fragmented can then be phagocytized by macrophages.1,2
Multicolored tattoos are very difficult to treat and will require multiple therapies with different lasers. Of the colors listed, yellow will be most difficult to treat as this and orange are highly resistant to treatment. These colors best absorb light in the UV range which is absorbed by, and damages, melanocytes. This affects the ability of light to penetrate the dermis.1–3
Scars that remain erythematous due to increased vascularity may be treated with either pulsed dye, Nd:YAG, or KTP lasers. These cause coagulation necrosis and decrease the number and proliferation of fibroblasts as well as the deposition of type III collagen. Sometimes, ablative lasers such as Er:YAG or CO2 are used for scars to reduce the texture and thickness, but their effects on decreasing the pink coloration within a scar are very limited.1,2
Water is the target chromophore for ablative resurfacing and the two key traditional options for this are Er:YAG (2940 nm) and CO2 (10,600 nm). Of the two, Er:YAG is generally preferred currently because energy absorption by water is far more efficient (by about 13 times) with ER:YAG compared with CO2 lasers. It allows for a more controlled depth penetration without collateral thermal damage. It is also more suitable for areas of the face that have thinner skin and is associated with less erythema and an overall reduced downtime compared with CO2. Nd:YAG is a nonablative resurfacing laser. Fraxel and intense pulsed light (IPL) are also nonablative techniques that may be used for less aggressive resurfacing.1–3
Isotretinoin is related to vitamin A and is taken orally to treat acne. The precise mechanism of action is not known but it works by suppressing activity in the sebaceous glands of the skin and by decreasing the amount of oil produced. It can make the skin fragile and cause delayed wound healing and scarring. This may be a direct result of damage to the epithelial cells of the adnexal structures which usually provide cells that repopulate the resurfaced skin wound. It can also increase the risk of wound infection and sensitivity to UV light. Therefore, isotretinoin should be stopped 6–12 months before resurfacing treatment to minimize the risk of scarring, poor wound healing, and hyperpigmentation. Using tretinoin and hydroquinone for 4–6 weeks pretreatment will stimulate rapid healing and help prevent post-treatment hyperpigmentation. Antivirals, such as Acyclovir, should be given 48 hours before and 7–10 days after ablative laser resurfacing. Use of sunblock before and after treatment is normally also advised. Metronidazole is used for treating acne and does not specifically need to be stopped for laser surgery. However, laser therapy should not be given during a bout of active acne as it will likely result in poor scarring.1–3
Laser liposuction can be performed with either Nd:YAG or Diode lasers. The Nd:YAG has the longest track record for use and can be useful for providing a skin tightening effect due to effects on collagen. Diode at 980 nm can be particularly effective on areas with large amounts of fat. However, although laser liposuction is purported to have benefits of causing adipocyte membrane rupture, coagulation of small blood vessels, and coagulation of dermal collagen, there is not enough evidence to show an increased efficacy compared with standard liposuction approaches. It can be associated with a steep learning curve for the operator and risks thermal injury, although this is only 1% rather than 10%. It can be used in the head and neck areas including the face, neck, and chin. In general, laser liposuction is associated with a longer, not shorter, operating time.1–3