Biomedical Engineering Reference
In-Depth Information
with a 1-mm spot directed toward individual lesions. A reason-
able approach with a maximum benefi t-to-risk ratio is treating
individual larger lesions with a directed therapy followed
immediately by fractional laser.
Becker's nevus (BN) has been treated with fractional CO
2
laser in a recent study of 11 patients. The authors performed
three treatments 6 weeks apart at 10 mJ with a 120-
fractional treatments are less than that reported with fully
ablative treatments, they are still reported at between 0.3% and
2% of cases (38,39). The risk can be mitigated by beginning
prophylaxis 1 day prior to the procedure and continuing treat-
ment for a total of 7 days. Patients who present the day of
treatment with an active herpes infection should not be treated
due to the risk of HSV exacerbation (40).
Rates of bacterial infection are generally low with a reported
incidence of 0.1% of cases. Patients with infection will generally
present 1-4 days postoperatively with complaints of increas-
ing pain, erythema, erosions, and crusting. Wound occlusion can
increase the likelihood of infection, primarily with
Staphylococcus
aureus
and
Pseudomonas aeruginosa
. Although there are no clear
guidelines for the use of prophylactic antibiotics, strong consid-
eration should be given in situations where the patient is immu-
nocompromised. Where wound infection is suspected, cultures
should be performed and antibiotic therapy initiated. Candidal
infections occasionally occur and may manifest primarily as an
increase in pruritus and/or erythema. A small case series by Alam
et al. examined the relationship between posttreatment pruritus
and positive fungal cultures. They found a signifi cant relation-
ship between positive culture and the development of signifi cant
pruritus but not with physician ratings of clinical signs (41). Fun-
gal infections will generally present later than viral and bacterial
infections—most often 1 to 2 weeks after the procedure with
complaints of increased pruritus. Antifungal therapy should be
initiated to mitigate any risk of scarring (42,43). An atypical
mycobacterial infection has also been reported after AFR (44).
m spot
microbeam and 35-45% coverage with only moderate success:
the risk of PIH was high and only 4 of 10 patients who com-
pleted the study would recommend it to fellow BN patients (34).
μ
complications
The nature of fractional devices leads to a lower complication
rate than that observed with fully ablative lasers. Most compli-
cations have occurred on the neck and chest and included
scarring and infection. Facial complications with microspot
treatment have usually been associated with too high a density
and/or depth. It follows that the wounds mimicked “punch”
biopsy-type wounds and resulted in thick scars. With the
larger 1.3-mm macrospot applications (broad superfi cial inju-
ries with only 100-200
m total depth), wounds covering
greater than 90% surface area have been associated with pro-
longed healing and greater infection risks.
One drawback of fractional treatments is the lack of clear
clinical endpoints. Once a series of passes is applied, the cumu-
lative number of pixels and therefore percent surface coverage
must be followed closely by the provider. Most devices can dis-
play the total energy applied but cannot record exactly
where
that energy was delivered. Accordingly, the operator is treating
by recipe rather than clinical endpoints.
μ
Scarring
Although hypertrophic scarring and keloid formation are less
common in ablative fractional treatment versus conventional
laser interventions, there have been reports of posttreatment
scar formation. Infection is the most prevalent cause, as dis-
cussed in the previous section. The majority of primary scar-
ring in fractional cases has occurred on the neck, likely due to
the relatively poorer vascular supply and lower density of
pilosebaceous units in the skin of the neck (Fig. 7.13). For this
Prolonged Erythema
Erythema posttreatment is normal. However, it is expected
that most erythema will resolve after an ablative treatment
within 4 weeks (12,34). Various treatments have been reported
to reduce the duration of the erythema, including exposure to
590-nm light emitting diode (LED) light (36) and the applica-
tion of ascorbic acid posttreatment (37). Patients should be
advised to avoid potential irritants or sensitizers and to limit
the degree of sun exposure through the use of protective cloth-
ing and sunscreens. We recommend that any topical prepara-
tions applied to the face have a minimal number of ingredients.
Plain petrolatum serves this function well. Transition to a
bland moisturizer after reepithelialization occurs (generally
5 to 7 days posttreatment depending on the aggressiveness of
the treatment) and tends to maintain patient comfort and
expedite healing without prolonging erythema. One of the
editors (MPG) has found the nightly application of 0.1% fl uo-
cinolone in white petrolatum starting at postoperative day 2
and continuing to day 7 to be helpful in minimizing erythema
secondary to infl ammation. In addition, the use of a lower
density setting and/or shorter pulses minimizes the degree of
non specifi c thermal damage and resulting erythema.
Infection
One of the most common infections is cutaneous herpes sim-
plex virus (HSV). In general, these infections will present
within the fi rst week posttreatment. It is imperative that these
infections be recognized and treated expeditiously to avoid
potential long-term sequelae, such as delayed wound healing
and scarring. Although the rates of infection after ablative
Figure 7.13
Approximately 3 weeks after treatment, the neck of a patient
treated with carbon dioxide ablative fractional resurfacing (treated at a pulse
energy of 20 mJ (630-μm depth) with 30% coverage of the exposed skin and a
total treatment energy for the neck of 5.0 kJ) displays fi rm linear bands over
the treated area consistent with multiple vertical and horizontal hypertrophic
scars.
Source
: From Ref. 43.
