Biomedical Engineering Reference
In-Depth Information
studies (165), respectively. This may sometimes be a near per-
manent complication. The incidence of hypertrophic scars
and keloids is comparable to that of fair-skinned patients.
These later complications are usually the results of poor tech-
nique, postoperative infection, or other intrinsic patient
factors.
We believe that the advantage of preoperative treatment is
not so much in the prevention of PIH but in determining what
medications a patient is sensitive to so they can be avoided in
the postoperative period. A study by West and Alster (169)
noted no signifi cant difference in the incidence of post-CO
2
laser resurfacing hyperpigmentation between subjects who
received pretreatment with either topical glycolic acid cream
or combination tretinoin/hydroquinone creams and those
who received no pretreatment regimen.
In our experience, PIH may occur in spite of careful preop-
erative treatment. Similarly, a retrospective study on facial
resurfacing in patients with skin type IV indicated no correla-
tion of pretreatment or types of laser used to incidence of PIH
(168). However, PIH appears to respond to appropriate treat-
ment once it has developed.
The application of broad-spectrum sunscreen and sun
avoidance postoperatively is also benefi cial in minimizing
hyperpigmentation. The advantage of sun avoidance has been
demonstrated in a study showing that preoperative and post-
operative UV exposure on laser-treated skin resulted in a poor
cosmetic appearance, including textural change and hyperpig-
mentation (170).
In 1996, the introduction of the Er:YAG laser represented an
alternative to the pulsed and scanned CO
2
resurfacing lasers.
Er:YAG laser resurfacing requires a shorter, less painful recov-
ery time, and causes fewer long-term adverse effects. In gen-
eral, the recovery time and the incidence of adverse sequelae
are proportional to the extent of tissue injury, including the
total anatomical depth of necrosis, ablation, and residual ther-
mal damage (171-173). A layer of residual thermal damage
observed after a typical Er:YAG laser resurfacing procedure is
less than 50 µm versus the 80-200 µm typically observed after
multiple passes of pulsed CO
2
laser resurfacing (174). There-
fore, one advantage of the Er:YAG laser over the CO
2
laser is
that it appears to offer a higher margin of safety when treating
patients with darker complexions (skin phototypes III and
higher), because the resultant infl ammatory reaction caused
by less extensive thermal trauma stimulates less melanocytic
activity (93).
The incidence of transient PIH following CO
2
laser resurfac-
ing ranges from 3% to 7% for all patients and nearly 68%
among those with skin type IV and higher. Although postop-
erative hyperpigmentation and prolonged erythema seem to
occur at roughly the same rate among patients with darker
skin after Er:YAG laser resurfacing, it is often less severe and
resolves more quickly compared with the CO
2
laser treatment
(94). The Er:YAG laser, therefore, appears to be better suited
for resurfacing of Asian skin.
With equal energy fl uence and number of passes, the Er:YAG
laser produces less total depth of tissue necrosis and hence less
effective treatment of deeper wrinkles. The greater immediate
collagen contraction effect and the hemostasis property pro-
vided by the CO
2
laser are the advantages of this laser resurfac-
ing system over the Er:YAG laser. To combine the benefi cial
properties of these two systems, Goldman and Manuskiatti
(175) successfully developed a resurfacing technique using the
combined CO
2
and Er:YAG lasers in the same treatment ses-
sion. By using the Er:YAG laser to vaporize a portion of the
layer of residual thermal damage created by the CO
2
laser, one
can achieve a better cosmetic response with faster healing time
and shorter duration of postlaser erythema, and hence a
decreased incidence of adverse sequelae. The favorable result
of this combined treatment method has also been confi rmed
by a study on the treatment of atrophic scars in Korean patients
with skin phototypes IV-V (176).
The single-pass CO
2
or Er:YAG laser has been performed to
help lessen the risks associated with multipass CO
2
, Er:YAG, or
combination techniques of laser skin resurfacing (177-179).
Ruiz-Esparza and Gomez (179) evaluated 15 Hispanic patients
after single-pass CO
2
laser resurfacing for a follow-up period
of 18 months. All the patients were re-epithelialized by 7 days,
and continued clinical improvement of rhytides was observed
throughout the length of the study. However, the near univer-
sal incidence of transient postoperative hyperpigmentation
has still been observed in patients with dark skin tones after
CO
2
single-pass resurfacing. Although superfi cial resurfacing
is defi nitely safer than deep resurfacing, it is no guarantee that
PIH will not develop.
A less-aggressive technique in ablative facial resurfacing has
emerged that offers modest clinical improvements in rhytides
and atrophic facial scars with reduced postoperative morbidity
and shorter recovery times, that is, the variable-pulsed, dual-
or thermal-mode Er:YAG lasers emit light with extended pulse
durations (up to 250 ms) producing larger zones of dermal
heating compared with traditional short-pulsed Er:YAG laser
systems (180-183). These larger zones of dermal collagen
coagulation result in benefi cial tissue effects that approximate
those of the CO
2
laser. In addition, increased thermal coagula-
tion of dermal vessels is effected, permitting deeper tissue pen-
etration and improved intraoperative fi eld visualization. The
use of these newer methods are associated with a shorter and
less severe postoperative course compared with traditional
multipass CO
2
and short-pulsed Er:YAG laser skin resurfacing.
The intensity and duration of such adverse sequelae as ery-
thema and PIH are also reduced, making the variable-pulsed
Er:YAG a potentially better choice when treating patients with
darker skin tones (Fig. 13.19).
Studies on CO
2
(184-186), Er:YAG (94,181,187,188), and
combined CO
2
and Er (176,189) lasers resurfacing on Asian
skin (skin phototypes III-V) have shown that these proce-
dures can be performed effectively and safely when proper
pre- and postoperative management is implemented. Pre- and
postoperative treatment regimens are necessary to achieve
optimum results and reduce the incidence of PIH (190,191).
In addition to topical retinoic acid applied each night, patients
with skin phototypes III-VI are given topical preparations of
hydroquinone, kojic acid, azelaic acid, or vitamin C to be used
for 1-2 months preoperatively. Although an arbitrary mini-
mum preoperative treatment time of 2 weeks is often recom-
mended, achieving maximum benefi t requires months of use.
These agents are restarted as soon as possible postoperatively
(2-4 weeks). Reinstitution of these topical preparations too
early may induce infl ammation on the newly regenerated
treated skin and should be avoided (173,190).
