LAS VEGAS Laser treatment complications can come not just from the light; they can result from the cryogen cooling as well.
Cooling with ice offers a safe alternative for laser therapies, Dr. Ranella Hirsch said at the annual meeting of the American Society of Cosmetic Dermatology and Aesthetic Surgery.
Ice packs are cheap, reliable, and they work, she said.
The use of cryogen and other forms of cooling has been a major advance, but it is not entirely without risk, said Dr. Hirsch, who practices in Cambridge, Mass., and is president of the society.
"As any dermatologist who has performed cryotherapy knows, you can get bullae and epidermal necrosis just from the cryogen cooling," she said.
Because of the risk, Dr. Hirsch uses ice packs instead of cryogen for just about every use of the laser, she said in an interview.
She first started using the technique for hair removal, and now she has an assistant whose main job is just to do the ice cooling. The risk of cooling injury is slight, but "a little extra safety goes a long way," she said in the interview.
To test the efficacy of ice cooling, Dr. Hirsch conducted a study to look at the effects of contact cooling with ice at different skin depths, a study that was supported by a research grant from laser maker Candela Corp.
Dr. Hirsch is a clinical investigator for Candela Corp., Cynosure Inc., and Palomar Medical Technologies Inc.
In that study, she placed thermocouples connected to a computer monitoring system in ex vivo pigskin to acquire temperature and time data after ice was applied to the surface.
The top of the epidermis adequately cooled almost instantaneously, but there was very little cooling beyond 0.51.0 mm unless the ice was kept in place for 15 seconds or longer, suggesting that the areas generally targeted by the laser would not be adversely cooled.
She found that cooling the temperature of the skin by 10° C at a depth of 1 mm, the usual depth of sebaceous glands, took 15 seconds with the ice in place, and that the temperature at 3.3 mm did not change even when the ice was kept in place for as long as 60 seconds.
It took about 4 seconds to cool a depth of 0.75 mm by 10° C and about 6 seconds to cool that depth by 15° C.
The study "strongly supports" the idea that ice-pack cooling protects the epidermis without compromising the laser's ability to heat the deeper regions where most laser targets are found, Dr. Hirsch said in the interview.
"The general take-home message with ice is that longer is better," she noted.
Cryogen cooling, on the other hand, can lead to scarring, she said in her talk at the meeting.
Dr. Hirsch showed photos of some presumably permanent injuries caused by cryogen cooling, including a small spot of hypopigmentation around the umbilicus of one patient and scarring on the back of another patient's knee that had lasted 24 months after laser treatment for a spider vein.
These types of injuries can occur when the cooling sprays get overlapped as the operator moves from one area to the next while treating.
The way to avoid any injuries when using cryogen cooling and a laser is to pay close attention to proper technique and to the changes occurring in skin as it is treated, and to be wary when patients complain of disproportionate discomfort, Dr. Hirsch said.
Dr. Hirsch said another technique that can prevent overcooling is using the back of her hand to judge skin temperature as she is cooling and treating. One can get quite good at judging when skin is too hot or too cold, she said.