Single or multiple pulses in the use of the pulsed dye laser for the treatment of port-wine stains

The pulsed dye laser was developed for the treatment of vascular cutaneous lesions using single non-overlapping pulses. However, in practice, overlap and multiple pulses to the same site are commonly used. This study was undertaken to examine the effects of single vs two, three and five pulses to the same site on penetration depth of the laser beam and vascular selectivity. Two albino pigs were treated with a 577 nm, 450s, 3 mm-diameter pulsed dye laser. The effect of multiple pulses to the same site over a range of fluences was analysed histologically from biopsies acquired immediately and at 1 and 4 days after laser irradiation. The results show that multiple pulses to the same site do not increase the penetration depth (maximum depth from the dermo-epidermal junction where damaged blood vessels are observed) of irreversible vascular injury. Cumulative pulses do increase the extent of tissue injury, including both desired vascular changes and unwanted effects such as extravasation. No clinical changes were observed following multiple pulses below 2 J cm^–2. It was concluded that 577 nm, 450s multiple pulses to the same site do not increase penetration depth of vascular injury of the laser beam.