Biomedical Engineering Reference
In-Depth Information
Scarring
In contrast to CO
2
laser resurfacing, most series utilizing the
short-pulsed Er:YAG for facial resurfacing have reported neg-
ligible rates of scarring (5,7,11,13). In her large series of 625
patients, Weinstein observed a 0.8% incidence of scarring. In
her study, scarring developed on the chest, lower eyelid, and
upper lip. All of these scars responded well to a 50/50 mixture
of intralesional triamcinolone (10 mg/kg) and 5-fl uorouracil.
Resurfacing of the neck and other nonfacial areas with the CO
2
laser has resulted in a high incidence of scarring and hypopig-
mentation in a number of studies. A study by Fitzpatrick and
Goldman reported a 33% incidence of hypertrophic scarring
after resurfacing of the lower neck with a single pass of the Ultra-
Pulse CO
2
laser. Another study by Rosenberg et al. also reported
scarring of the lower neck after single-pass resurfacing with the
UltraPulse CO
2
laser. The increased risk of scarring of nonfacial
skin is thought to be due to the relative lack of pilosebaceous
units in nonfacial skin as compared with facial skin (269,275).
In contrast to CO
2
, skin resurfacing of nonfacial areas
including the neck, arms, and hands with the Er:YAG laser has
been demonstrated to be safe and moderately effective in sev-
eral studies.
McDaniel et al. used the short-pulsed Er:YAG with a 5-mm
spot diameter and a fl uence of 2.5 J/cm
2
to resurface the dorsal
hands of three patients and the neck of one patient (two or
three passes) and observed an improvement in the appearance
of 48% and 44%, respectively, and no cases of scarring or
hypopigmentation (236). Goldberg et al. treated 11 necks and
4 dorsal hands with multiple passes of the short-pulsed Er:YAG
laser at fl uences of 4-5 J/cm
2
and reported signifi cant clinical
improvement of photodamage (25%-100%) and no adverse
sequelae (14). Goldman et al. treated the neck of 20 patients
with two passes of the short-pulsed Er:YAG at higher fl uences
(up to 13.5 J/cm
2
) and reported an overall patient satisfaction
of 51%, an average improvement in the skin texture of 39%,
and an average improvement in the skin color of 37%. All their
patients healed within 7-10 days had resolution of their ery-
thema within 2 weeks (except for one patient who developed
an infection) and reported no permanent adverse effects (15).
Jimenez et al. treated seven patients with photodamage of the
forearms and hands and fi ve patients with photodamage of the
neck with one to three passes of the short-pulsed Er:YAG laser
using a 5-mm spot size and a fl uence of 5 J/cm
2
. They reported
no permanent adverse side effects with these laser parameters.
However, they noted that the cosmetic improvement achieved
was only mild, the healing time was signifi cantly longer
(2-3 weeks) than for Er:YAG facial resurfacing, topical anes-
thesia was inadequate, and two of the seven patients who
underwent hand and forearm resurfacing experienced infec-
tions that required oral antibiotics (270).
neck) in their large series of 625 patients resurfaced with a
short-pulsed Er:YAG laser. Alster et al. reported one instance of
herpes simplex reactivation in a series of 12 patients who under-
went facial cutaneous resurfacing with short-pulsed Er:YAG
lasers. Teikemeier et al., Khatri et al., Ziering et al., and Bass et al.
observed no infections in their respective series of 20, 21, 25,
and 50 patients resurfaced with the short-pulsed Er:YAG laser
(5,7,10,11,13). A detailed discussion of the treatment of the
complications described above is provided in the section “Com-
plications of CO
2
Laser Resurfacing.”
Modulated (Coagulative and Ablative)
Er:YAG Laser Systems
Despite the initial enthusiasm for the Er:YAG laser, clinicians
quickly came to realize that clinical results achieved with the
conventional short-pulsed Er:YAG lasers were considerably
less impressive than those attained with CO
2
lasers. The hopes
of those who had envisioned the Er:YAG laser as the resurfac-
ing tool that would entirely replace the CO
2
laser were swiftly
shattered.
There were a number of factors that limited the resurfacing
potential of early generation Er:YAG lasers. First, early short-
pulsed Er:YAG lasers were slow and underpowered. They had
low repetition rates of only 1-2 Hz, produced modest fl uences
no greater than 10 J/cm
2
, and had small beam diameters of
1-2 mm. Multiple passes were required to achieve epidermal
ablation with these systems (244,276,277). Alster et al. tested
six different early generation short-pulsed Er:YAG lasers in
skin resurfacing and found that with all of them, three passes
were needed for complete epidermal ablation (5).
The low ablation rates of early generation Er:YAG lasers,
which typically hovered at around 20 mm per second, repre-
sented a signifi cant disadvantage when compared with the
high peak power, short-pulsed CO
2
lasers (276). Second,
although early Er:YAG lasers proved effi cacious for superfi cial
ablation, their limited coagulative effect precluded good hemo-
stasis and signifi cantly limited depth of ablation (23,24,278).
However, early Er:YAG lasers proved to be excellent tools
for resurfacing of mild-to-moderate rhytides. Furthermore,
postoperative erythema and reepithelialization time after
Er:YAG resurfacing turned out to be signifi cantly less than
seen after CO
2
resurfacing (11). Despite its advantageous side
effect profi le, clinicians quickly came to realize that skin
resurfacing with the Er:YAG laser produced results that were
considerably inferior to those attained with the CO
2
laser
(11,19-22,236,279).
A number of studies suggested that thermally induced effects
on the dermal collagen contributed to the benefi cial effects of
CO
2
lasers in the treatment of facial rhytides and perhaps
underlie the superior results achieved after CO
2
laser skin resur-
facing. Tissue contraction, tightening of facial skin, synthesis of
new collagen, and collagen remodeling were demonstrated after
CO
2
laser skin resurfacing in several studies (2,6,280,281).
Therefore, a number of authors hypothesized that the relative
lack of effi cacy of traditional short-pulsed Er:YAG laser skin
resurfacing was related to a relative lack of thermally mediated
coagulative effects in the upper dermis (6, 19-22, 54,279). Sev-
eral studies demonstrated less coagulative effect and thermal
residual damage after Er:YAG laser skin resurfacing as compared
Infection
As with any other cutaneous resurfacing method, infection is a
potential risk of Er:YAG laser resurfacing. However, the reported
infection rates have generally been low. Most infections occur
during the fi rst week, prior to reepithelialization.
S
. aureus and
P. aeruginosa
are the most common bacterial pathogens and
Candida
is responsible for most of the fungal infections. Wein-
stein et al. reported only one case of bacterial infection (on the
