Histologic effects of laser-assisted topical anesthesia in a porcine model

A handheld laser device that removes the stratum corneum, the major barrier to transdermal absorption, has recently been approved to assist with topical anesthesia before painful procedures such as intravenous cannulation. The authors assessed the cutaneous histomorphologic effects of the laser device and the ability of the laser-treated skin to resist infection in a porcine model.

This was a blinded, randomized animal experiment using isoflurane-anesthetized young domestic pigs. The ventral surface of the animals was irradiated multiple times with a lightweight, portable erbium yttrium-aluminum-garnet unit or a sham laser. One third of the wounds were inoculated with a Staphylococcus aureus suspension. The treated areas were then covered with a dry dressing, and full-thickness biopsy specimens of the treated areas were obtained immediately after treatment and at three, seven, ten, and 14 days for blinded histopathologic evaluation using hematoxylin and eosin staining and electron microscopy. Quantitative bacterial counts were obtained at three days in wounds exposed to bacteria. Main outcomes were quantitative bacterial counts, presence of cellular necrosis, epidermal integrity, and dermal scarring. Data analysis was conducted with descriptive statistics.

Laser irradiation resulted in immediate disruption of the cornified layer of the skin and necrosis of the stratum spinosum in all treated areas. There were also focal areas of vacuolar alteration of the basal one third of the epidermis. There was no evidence of any damage to the basement membrane or the underlying dermis. At three days, the epidermis had healed and there was evidence of epidermal hyperplasia and hyperkeratosis that was completely resolved by 14 days. There were no infections and no scarring. Sham laser had no histomorphologic effects on the skin. There was no bacterial growth from all sham laser-treated wounds challenged with bacteria. Three of 20 (15%; 95% confidence interval = 0% to 31%) laser-irradiated wounds that were challenged with bacteria grew between 280,000 and 1,600,000 colony-forming units/g.

Laser irradiation results in ablation of the stratum corneum and a superficial burn to the epidermis that heals by three to 14 days without any scarring or infection in pigs. Challenging laser-irradiated cutaneous wounds with a large bacterial inoculum resulted in bacterial growth in a minority of wounds.