Biomedical Engineering Reference
In-Depth Information
longer pulse mode of 10 ms and a fl uence of 5 J/cm
2
, thermal
damage zones of 30-40
The Derma-K laser is a hybrid laser system that delivers
ablative Er:YAG laser pulses followed immediately by coagula-
tive CO
2
laser pulses. The Er:YAG component produces a fl u-
ence of up to 28 J/cm
2
with a 350-
m have been reported.
The CO
3
laser is no longer made by Cynosure but may be in
use by some practitioners. Rostan et al. performed a split-face
study comparing resurfacing with the variable-pulsed (CO
3
,
Cynosure) Er:YAG laser versus the 950-
μ
s pulse. The CO
2
component
can deliver a subablative/coagulative pulse varying from 1 to
100 ms at 1- to 10-W power, providing excellent hemostasis.
The CO
2
coagulative component can be programed to be
delivered during a fraction or all of the time between the abla-
tive Er:YAG laser pulses.
Energy can be delivered using either a CPG with a 3-mm
spot or a noncollimated 0.2- to 8-mm spot. Zones of thermal
necrosis of up to 50 mm in depth have been observed after
resurfacing with this laser system (30,292).
Goldman et al. performed full-face resurfacing of 10 patients
with the Derma-K hybrid laser. They performed four passes
with a 4-mm spot, Er:YAG laser parameters of 350
μ
s UltraPulse CO
2
laser. Sixteen patients were randomized to receive resurfacing
with either UltraPulse CO
2
or CO
3
laser with a 10-ms pulse on
one side of the face, followed immediately by a pass with the
short-pulsed Er:YAG laser. Two passes with the CO
3
parame-
ters set at 2 J, 10-10.5 J/cm
2
, 10-ms pulse, 4-10 Hz, 5-mm spot
were performed. One additional pass with the CO
3
laser (same
settings) over the areas of greatest scarring and photodamage
was followed by a single pass with a 500-
μ
s Er:YAG at 1.5 J,
7.7 J/cm
2
, 5- to 7-mm spot, and a repetition rate of 10 Hz.
UltraPulse CO
2
treatment was performed utilizing the CPG
for two or three passes at settings of 596, 595, and 584 followed
by a single pass with a short-pulsed Er:YAG at 14-16 J/cm
2
with a 4-mm spot size and up to 50% overlap. Overall clinical
improvement was found to be equal for both the sides treated
with UltraPulse CO
2
and variable-pulsed Er:YAG (CO
3
) lasers,
with an average improvement in photoaging scores of 57%.
Moreover, decreased erythema and edema and faster healing
were observed on the side treated with the variable-pulsed
(CO
3
) Er:YAG laser (26).
Newman et al. performed a side-by-side comparison study
of the histologic and clinical effects of the variable-pulsed
CO
3
-Er:YAG versus the UltraPulse CO
2
laser after perioral
resurfacing. Four ablative-mode passes with the CO
3
laser
(5-mm spot size, fl uence of 5.2 J/cm
2
, and a 500
μ
s, 1.7 J/cm
2
,
and the CO
2
component set at 5 W, 50 ms with a frequency of
10 Hz. Their patients experienced a 44% and 38% improvement
in perioral and periorbital rhytides at their 3-month follow-up
and an overall improvement of 39% in their facial photoaging
score. Histology revealed a 20-
μ
m zone of thermal damage
immediately after treatment and an average depth of collagen
of 54-
μ
m (86% increase from baseline) 3 months postopera-
tively. Weinstein et al. have also reported good-to-excellent
results after facial resurfacing with the Derma-K Er:YAG-CO
2
hybrid laser. They noted a mean reepithelialization time of
11.3 days and postoperative erythema that lasted an average of
8.3 weeks, in their study (30).
Trelles et al. performed single-pass resurfacing of 102 patients
with skin phototypes I-V with the Derma-K hybrid laser. They
used an ablative Er:YAG laser pulse (350
μ
s pulse
width) were followed by a single coagulative mode pass (5-mm
spot, fl uence of 2.6 J/cm
2
, and a 10-ms pulse width). A fi nal
pass, designed to remove the thermally damaged tissue par-
tially, used parameters identical to the initial ablative passes.
Histology showed a 90-
μ
s, 28 J/cm
2
) followed
immediately by a coagulative CW CO
2
laser shot (4-6 W,
50 ms) through a 3-mm collimated handpiece (3-mm spot)
with 50% overlapping and a repetition rate of 10 Hz. In total,
67 patients scored their results as very good, 25 as good, and 10
as fair and the patient's rating correlated well with those of the
treating physician and three independent observers. Mean
duration of follow-up in their study was 1.76 years. Mild, tran-
sient side effects were seen in only four of their 102 patients.
Histology 2 months postoperatively demonstrated a band of
well-oriented newly synthesized collagen underneath a healthy
epidermis (293).
As previously described, one of the main benefi ts of cutane-
ous resurfacing with a CO
2
laser is tissue contraction, which is
believed by a number of authors to underlie the superior resur-
facing results achieved with the CO
2
laser. All of the new modu-
lated Er:YAG laser systems have demonstrated the capability to
produce “CO
2
-like” tissue contraction not only clinically but
also histologically. Kist et al. studied collagen contraction after
CO
3
laser treatment in a bovine tendon collagen model. The
depth of irreversible and reversible collagen fi bril changes
(measures of collagen contraction) was assessed by electron
microscopy. With a constant fl uence of 6.1 J/cm
2
, the maxi-
mum irreversible collagen fi bril change was achieved at the
highest pulse duration (10 ms) and it measured 3.25
μ
m layer
of residual thermal damage. The authors postulated that the
fi nal ablative pass partly removed the zone of thermal necrosis
generated by the 10-ms coagulative pulse. Two months after
treatment, there was a 54% improvement in rhytides treated
with the variable-pulsed CO
3
-Er:YAG laser, compared with
63% improvement with the CO
2
laser. Reduced duration of
crusting (3.5 vs. 7.8 days) was observed on the sides treated
with the variable-pulsed CO
3
-Er:YAG laser. They observed no
cases of permanent hyperpigmentation, hypopigmentation, or
scarring (27).
Christian et al. conducted a six-patient, split-face study that
evaluated the impact of single-pass resurfacing (“micro-
resurfacing peel”) at two different pulse durations (500
μ
m layer of ablation and a 10-
μ
s vs.
4 ms) of the variable-pulsed (CO
3
) modulated Er:YAG laser.
Six of eight peels were performed at a fl uence of 7.1 J/cm
2
.
Erythema was found to be signifi cantly greater on the 4-ms
side at postoperative days 3-4, but this difference was no lon-
ger signifi cant at postoperative day 7. Average time to reepithe-
lialization was found to be 3.6 days (290).
Finally, the Derma-K (ESC Medical Systems, now Lumenis)
hybrid Er:YAG-CO
2
laser was available commercially in the
USA. Given that some clinicians continue to utilize the Derma-K
system for skin resurfacing and reports of its effi cacy continue
to appear in the literature (291), we will briefl y review this
laser system as well.
μ
m. The
maximum depth of reversible collagen change at the same fl u-
ence was found to be 9.52
μ
m and it was attained at the 7-ms
pulse duration. Their study showed that when pulse duration
or fl uence was increased while the other variable was held con-
stant, there was a steady increase in the mean maximum tissue
μ
