Laser Debridement: Can It Have An Impact For Chronic Wounds?
Offering pertinent insights on key principles and the biological effects of laser technology, these authors examine the possibilities of this modality for the debridement of lower extremity ulcerations.
Ever since its emergence in early 1960s, laser technology has occupied an important niche in medicine and surgery. Today, a great number of specialties utilize lasers. These specialties include dentistry, dermatology, ophthalmology, otolaryngology and vascular surgery. Laser applications include the treatment of hypertrophic scars, removal of skin lesions, laparoscopic surgery, vein ablation and many others.1 Unfortunately, to date, the use of lasers in the field of podiatry has mostly been limited to the treatment of onychomycosis.2 Meanwhile, a deeper integration of the laser technology into the podiatric practice may offer the means of improving therapeutic outcomes of many difficult to treat conditions.
Chronic lower extremity ulcers affect a significant portion of the adult population worldwide and represent one of the most common problems podiatrists see.3 Debridement is the cornerstone of wound management. Studies suggest that wounds treated with serial debridements demonstrate lower infection rates and heal faster in comparison to wounds that receive less frequent debridement or no debridement at all.4,5 Researchers have commonly attributed these effects to the role of debridement in reducing bacterial bioburden, eliminating excessive pressure, the stimulation of cytokine and growth factor release, and the facilitation of drainage.6
While many types of debridement are currently available, sharp debridement is the method of choice for the majority of physicians due to its efficiency and convenience.7 The major drawbacks of surgical debridement are the lack of uniform technique and procedural pain. In a retrospective study of 143 patients with diabetic foot ulcers treated by different providers in wound care centers across the country, Saap and Falanga noted significant inconsistency in the quality of surgical debridement, which strongly correlated with the variability in the wound closure rates.8 Procedural pain is another limiting factor commonly associated with sharp debridement. While neuropathic patients generally tolerate sharp debridement well, individuals with venous and arterial ulcers may experience significant debridement-associated discomfort, which could limit the extent of the procedure and deem the treatment less effective.9
Laser debridement is one of the lesser known wound debridement techniques and it has mostly been limited to burn treatment so far.10-13 Its advantages include precision and uniformity of tissue ablation, which reduces trauma to the wound bed, improved patient comfort, and potentially the promotion of wound healing. Accordingly, let us take a closer look at the rationale for using lasers in the management of chronic lower extremity wounds and present the preliminary data that suggest the efficacy of such treatment.
A Primer On The Principles Of Laser Technology
Lasers are electro-optical devices that emit a focused beam of intense monochromatic light in visible and infrared radiation spectrums. Laser technology is based on the principle of stimulated emission of radiation postulated by Einstein in 1917. The first laser was built by Maiman in the early 1960s. Since then, people have utilized lasers successfully in many fields, including medicine and surgery.14
The human body absorbs laser energy to a different extent depending on the wavelength of laser radiation and specific properties of light-absorbing molecules or chromophores within the target tissues. Chromophores are a diverse group that include melanin, hemoglobin and most importantly, water.14
With the majority of medical lasers, the absorbed energy converts to heat, which produces characteristic zones of injury within the target tissue and around it.1 The superficial layer of laser-irradiated tissue is exposed to the temperatures above 100 Cº and undergoes carbonization, disintegration and vaporization. The adjacent zone heats to around 65 Cº, which leads to protein denaturation, thermal necrosis and coagulation. The zone of thermal conductivity and repair is the tissue layer farthest from the heat source and it has the best chances of remaining viable following irradiation. Various laser applications rely on different zones of injury for their desired effect. For example, in laser skin resurfacing, the target tissue is the papillary dermis, where the zone of conductivity and repair is induced in order to stimulate the formation of new collagen for healthier and younger appearing skin.15
Understanding The Biological Effects Of Different Laser Types
Understanding the differences between various laser types is important in order to select the device that is best suited for the specific clinical application. Different types of lasers create different patterns of tissue destruction. In general, laser beams with a longer wavelength are better absorbed by target tissues and produce less scattering over the adjacent tissues. In contrast, shorter wavelength laser beams are more likely to be scattered by the tissue and will affect a larger surface area.1
Carbon dioxide lasers emit light with a wavelength of 10.6 μm. The energy of these lasers is strongly absorbed by water and all biological tissues with high water content. This leads to increased vaporization of surface layers and reduced damage to underlying cells.1 Physicians commonly use carbon dioxide lasers for excisional surgery due to their precision. However, perhaps one of the most significant contributions of carbon dioxide lasers is to the field of skin resurfacing, where they have been established as the gold standard.16
Neodymium-doped yttrium-aluminum-garnet (Nd:YAG) lasers produce light with a wavelength of 1.06 μm, which is poorly absorbed by water. The beam of these lasers transmits efficiently through clear fluids, which makes them well suited for applications in eye and urinary bladder surgery.1 Due to the selective color-dependent absorption of Nd:YAG lasers, dermatologists commonly utilize these modalities for the treatment of pigmented skin lesions and tattoo removal.14 Since the discovery that the Nd:YAG laser beam successfully penetrates the nail plate and produces superheating of fungal material, this laser became widely used for the treatment of onychomycosis.17 Despite the initial success of this treatment, however, randomized controlled clinical studies are necessary to draw any conclusions about its efficacy.
Erbium-doped yttrium-aluminum-garnet (Er:YAG) lasers emit light with a wavelength of 2.94 μm. The water absorptive properties of these lasers are even better than those of carbon dioxide lasers. Therefore, these devices are extremely efficient at vaporization of epidermal skin layer, which consists of almost 90 percent water.18 Studies suggest that Er:YAG lasers produce a narrower zone of thermal necrosis than carbon dioxide lasers do, which potentially makes these lasers a better alternative to CO2 lasers in skin resurfacing.18 The potential disadvantage of this laser is the lack of tissue coagulation properties, which makes it unsuitable for use in highly vascularized tissue.
A Closer Look At The Literature On Laser Debridement In Wound Care
Laser debridement is based on controlled vaporization of superficial layers of the wound bed containing unwanted microbial and necrotic particles. The depth of the tissue ablation depends on the type of laser as well as the number of passes one performs, and ranges from 2 μm to 150 μm per pass.18 Unlike other types of wound bed preparation that rely on manual control, laser debridement is controlled electronically, which improves precision of ablation and reduces the risk of incidental damage to healthy tissue.
The use of lasers for wound debridement dates back to the beginning of the 1970s. In one of the first studies published on the subject, Stellar and colleagues reported successful use of a continuous-beam CO2 laser for preparation of infected decubitus ulcers for skin grafting.19 Smith and coworkers demonstrated improved healing rates in a porcine model of sulphur mustard burns treated with a pulsed CO2 laser.20 Lam and co-workers reported a fourfold acceleration in re-epithelialization rates of porcine Lewisite burn wounds debrided with a pulsed-beam CO2 and Er:YAG lasers.12 Researchers have demonstrated similar outcomes in several other studies in both animal and human models.10,11,13,21
One potential disadvantage of laser wound debridement is damage to surrounding tissues from thermal diffusion. Heat transmission beyond the target tissue results in characteristic zones of injury, as we described earlier, and it is an inevitable side effect of all thermal lasers.1 Recognition of this phenomenon in early models of carbon dioxide lasers led to numerous studies comparing healing rates of skin incisions created using a laser versus a surgical blade.22-24 Histological studies in animal wound models demonstrated that epithelialization was initially delayed in incisions produced by a laser due to formation of a charred eschar in the zone of thermal necrosis. However, researchers showed that epidermal cell migration resumed after 10 days once the necrotic zone had dissolved and the final appearance of the incision resembled that produced by a blade.24,25
In an attempt to reduce thermal damage to healthy tissue, laser manufacturers have introduced several improvements to conventional lasers. One such improvement is a pulsed beam system, which delivers laser energy in a quick succession of high-power pulses.25 Since the thermal energy delivered in this way is equal to or even higher than that produced by continuous beam devices, optimal vaporization properties are present. However, due to the shorter duration of target tissue exposure to high temperatures, thermal injury is minimized. Studies in animal models and human skin have demonstrated a reduction in thermal damage in tissues treated with pulsed-beam carbon dioxide lasers in comparison to the tissues irradiated with conventional continuous beam CO2 devices.25
The Erbium-doped yttrium-aluminum-garnet (Er:YAG) laser was another innovation in laser technology aimed at the reduction of thermal damage to irradiated tissue.18 Since water absorbs their energy 12 times more efficiently than it absorbs CO2 lasers, Er:YAG lasers have very limited tissue penetration. In addition, due to the rapid expansion of water within the irradiated tissue, charred debris gets ejected from the surface of the wound without leaving a necrotic eschar behind as most lasers do.18 Reduction in residual necrotic tissue burden as well as finer ablation properties are some of the distinct advantages of Er:YAG laser, which make it one of the best suitable devices for wound debridement.
While a lot is already known about the biological effects of laser debridement, new research is currently underway focusing on molecular regenerative pathways taking place within the tissues farthest from the laser heat source, a so-called zone of thermal conductivity and repair. Capon and colleagues observed accelerated healing and decreased scar appearance of a skin incision in a hairless rat irradiated with a diode laser at temperatures below 50 Cº.15 The authors have postulated that these effects occurred due to temporary changes in cellular metabolism in thermal conductivity and repair zone, which led to induction of a heat shock protein (Hsp 70) and overexpression of an inflammatory mediator (TGF-beta 3). Better understanding of this phenomenon could lead to a more targeted application of laser technology in wound healing.
What Preliminary Case Study Results Reveal
While numerous case reports have described the benefits of laser wound debridement, no systematic study comparing the effects of laser debridement to other forms of wound bed preparation has occurred to date. Below, we present three case studies that begin to address this question.
Patient A is a 62-year-old male with history of diabetes mellitus and hypertension, who had treatment for a chronic venous leg ulcer that he had for four years. The patient’s wound care regimen consisted of biweekly sharp debridements that he found very painful. In contrast to sharp debridement, laser debridement was associated with significantly reduced procedural discomfort. The reduction in debridement-associated pain allowed us to perform a more meticulous wound bed preparation, which led to complete removal of yellow film, fibrotic tissue and exposure of a underlying healthy and bleeding granulation tissue base.
Patient B is a 70-year-old male with multiple bilateral chronic venous leg ulcers. He reported intense discomfort during sharp debridement, which prevented thorough wound bed preparation. When we performed laser debridement, the patient was able to tolerate the entire treatment session. The appearance of the ulcers post-debridement was remarkably improved in comparison to the results that routinely occurred using a scalpel. In addition, the duration of the procedure was noticeably reduced.
Patient C is a 65-year-old male with diabetes mellitus and peripheral neuropathy, who was treated for a chronic full-thickness ulcer of neuropathic etiology. As in previous cases, laser debridement enabled us to remove fibrotic tissue and callus, exposing a healthy granulation tissue base efficiently and rapidly without damage to surrounding tissue.
Although these results are only preliminary, they suggest that laser debridement enables successful wound bed preparation while significantly reducing procedural pain. More extensive studies are necessary to address efficacy of this treatment in comparison to sharp debridement.
Dr. Bazarov is a first-year resident with the San Francisco Bay Area Foot and Ankle Residency Program at Kaiser Permanente in San Francisco.
Dr. Vartivarian is an Adjunct Assistant Professor in the Department of Medicine at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Ca.
Dr. Reyzelman is an Associate Professor in the Department of Medicine at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Ca. He is the Co-Director of the UCSF Center for Limb Preservation in San Francisco and is a Fellow of the American College of Foot and Ankle Surgeons.
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