Abstract
The successful treatment of port wine stain (PWS) patients undergoing laser therapy is based on selective thermal coagulation of blood vessels without damaging the normal overlying epidermis. Cryogen spray cooling of skin may offer an effective method for minimizing epidermal thermal injury. Inasmuch as the density of melanosomes and depth of PWS blood vessels can vary considerably, an optimum cooling strategy is required on an individual patient basis. The authors present a theoretical study of the thermal response of various pigmented PWS lesions to spray cooling in conjunction with flashlamp-pumped pulsed dye laser irradiation (585 nm). Results of the authors' model indicate that precooling of skin using tetrafluoroethane as the cryogen spray is sufficient to eliminate epidermal thermal injury when using incident fluences less than 10 J cm-2 and 8 J cm-2 on patients with intermediate and high epidermal melanin content, respectively. Cryogens that have lower boiling points than tetrafluoroethane may allow successful treatment when using fluences equal to or greater than those indicated.
Highlights
Successful laser treatment of port wine stain (PWS) birthmarks is based on selective photothermolysis whereby absorption of the laser light by haemoglobin in PWS blood vessels results in irreversible thermal injury (Anderson and Parrish 1983)
Epidermal thermal injury has been reported to be prevented with use of these cooling methods, deeper layers of skin including PWS blood vessels may be cooled and as a result remain resistant to photothermolysis (Nelson et al 1995a)
Calculated thermal responses indicate that precooling by tetrafluoroethaneis sufficient to eliminate epidermal injury on category II PWS when the incident laser fluence is less than 10 J cm-'
Summary
Successful laser treatment of port wine stain (PWS) birthmarks is based on selective photothermolysis whereby absorption of the laser light by haemoglobin in PWS blood vessels results in irreversible thermal injury (Anderson and Parrish 1983). The ideal laser treatment should cause irreversible laser injury to the PWS blood vessels without damaging the overlying epidermis. In recent years, cooling of skin has been used as a technique for preventing thermal injury to epidermis. Epidermal thermal injury has been reported to be prevented with use of these cooling methods, deeper layers of skin including PWS blood vessels may be cooled and as a result remain resistant to photothermolysis (Nelson et al 1995a). An appropriatecooling and irradiation method should cool selectively the epidermal layer but allow photocoagulation of deeper
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