Biomedical Engineering Reference
In-Depth Information
(
A
)
(
B
)
Figure 2.21
(
A
) Port-wine stain before and (
B
) after 12 treatments in type V skin with pulsed dye laser (10 mm, 7 J/cm
2
, 1.5 ms, 50 ms spray, 30 ms delay with
cryogen spray).
pulsed dye laser
The PDL remains the most studied device in PWS treatment.
Over the years various pulse durations and wavelengths have
been applied. Today, most PDLs emit 595 nm light over a range
of pulse durations and pulse structures. The most commonly
applied pulse duration is 1.5 ms; however, for lighter PWS,
0.45 ms has been advocated. Although the risk of general anes-
thesia (typically required in young children for larger lesions
and lesions around the eye) increases risks to the patient, the
typical course is to initiate treatment within three months of
birth- the arguments for early intervention include the likeli-
ness that the vessels are smaller and more superfi cial and the
smaller overall size of the lesion (78,100,101). Those that argue
for later intervention note that studies do not clearly show that
earlier intervention is more effective than later treatments.
Treatment intervals are normally about 3 to 6 weeks apart.
A recent study showed that more frequent treatments might be
preferable (100,101). Treatment responses are variable accord-
ing to anatomic areas and the gross and microscopic anatomy of
the lesion. Facial lesions generally respond better than nonfacial
lesions, and lesions on the mid-face respond more poorly that
those lesions at lateral facial locations. There are multiple rea-
sons for the multiple treatment requirements for PWS. One is
the variable depth so the lesions and the likelihood that the most
superfi cial vessels must be reduced fi rst to allow for deeper light
penetration and heating of deeper lesions. Also, angiogenesis
between treatments might account for some resistance and is
currently becoming a target of biologic strategies in PWS man-
agement. Some providers suggest that PWSs respond better
once they are “broken up”; that is, the initial treatment creates
islands or pixels in initially confl uent lesions. Once the “break
up” is achieved, light more readily propagates down the skin and
can “hit” the PWS vessels from all sides (Fig. 2.22).
One study examined the use of multiple pulses (passes) in the
same session (102), starting with a longer pulse and progressing
to a shorter pulse. In this manner, a layered approach was sug-
gested to accelerate PWS clearance and decrease the total num-
ber of treatment sessions. In the study, a fi rst pass was made at
1.5 ms and 595 nm followed by treatment at 585 nm at 0.45 ms.
In a recent study (103) the PDL was applied with two passes
30 minutes apart and with 0.45-3 ms and reducing the fl uence
by 0.5-2 J/cm
2
in the second pass (from, e.g., 12 J/cm
2
with
7 mm spot to 10 J/cm
2
). Tanghetti et al. found that multiple
passes with a short interval (10 minutes) allowed for deeper
injury in vessels. In all of these studies, epidermal damage was
avoided or mitigated by the dynamic cooling device (DCD) or
contact cooling. Tanghetti et al. also found that by increasing the
interpulse interval that the level of vascular damage was greater
(104). Another study found that multiple passes might be supe-
rior to one pass in a single session (103). However, a more recent
tightly controlled prospective study of PDL treatment of PWS
found that two passes were not superior to one pass (105). Acces-
sories to increase the effi cacy of PWS clearance with PDL include
vacuum assist (Serenty Pro, Candela, Wayland, Massachusetts,
USA) (106-108). In one study the increase in blood fraction was
signifi cant and more purpura was observed after PDL; however,
the vacuum chamber precludes the use of DCD and therefore
would limit use in darker skin types.
PDLs contain a rhodamine dye excited by a xenon fl ash lamp
that produces light at 585-600 nm; the most commonly used
wavelength is 595 nm. A lack of controlled studies with a single
parameter difference has made it diffi cult to optimize pediatric
treatment settings (109). Pulses of 1.5 ms (long-pulsed) are
most commonly applied; however, for lighter PWSs 0.45 ms
(short-pulse PDL) has been advocated. Short-pulse widths
(<3 ms) generally cause immediate purpura (a clinical end-
point), an effect that may take fi ve to 10 days to resolve. Longer
pulse widths tend to cause less bruising. Fluences range from 4
to 12 J/cm
2
and spot sizes range from 2 to 10 mm with 7 mm
being a popular choice because of laser power limitations.
In these ranges, light penetrates the dermis to approximately
1.2-1.5 mm in depth, with deeper penetration possible with
higher wavelength and longer exposure durations.
While PDLs are a relatively safe and effective treatment,
patient and parental anxiety will often require physician reas-
surance. Potential adverse events, including postinfl ammatory
pigmentary changes (especially in darker-skinned patients),
immediate postlaser purpura, recurrence, and infection should
be addressed prior to treatment. Sun exposure can drastically
affect pigmentary changes, and sun avoidance/protection is
essential to optimizing outcomes. Blistering, crusting, and,
rarely, hypertrophic or atrophic scarring may also occur. Surface
cooling has markedly diminished this side effect. Swelling and
erythema are frequently present immediately after treatment,
especially around the eyes, but resolve within 24-48 hours.
Hypopigmentation occurs infrequently and, in the absence
of textural changes, usually resolves spontaneously over 3 to
6 months. Cutaneous depressions or atrophic scars have
occurred in isolated laser impact sites and have been associated
with excessive delivery of energy, absence of cooling, excessive
