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Page 8 of 15 Ali et al. Plast Aesthet Res 2021;8:35 https://dx.doi.org/10.20517/2347-9264.2021.29

camera, scope holder, 4K high definition monitor, and 3D glasses. In comparison, operating microscopes
[50]
can vary in cost, with start-up ranges from approximately $250,000 to over $500,000 . A justification for
this cost may be the utility of this technology by multiple surgical specialties, ability to use in both dissection
and microvascular anastomosis, and improved ergonomics for the operative surgeon to increase overall
career longevity.

In our institution, we have trialed the exoscope technology, but have not utilized this in routine practice.
The operative microscope continues to be our standard of practice. There are various technologies that can
provide comparable magnification during FTT; the exoscope may have advantages as far as ergonomics.

Fluorescent angiography
Fluorescent angiography using indocyanine green (ICG) can be an excellent resource in assessing flap
vascular perfusion. ICG is a fluorescent dye that is administered intravenously and remains in the
intravascular compartment. After injection, the dye can perfuse through vascular pedicles into the
subdermal and subcutaneous plexus. It has an absorption spectrum of 800 nm and can be detected using an
infrared camera to confirm adequate flap perfusion. Historically, it was used to measure hepatic and cardiac
[51]
function but has been widely adopted for use in ophthalmology and microvascular surgery .

There are multiple companies that utilize this technology: IC View (Pulsion Medical Systems, Munich,
Germany), PDE (Hamamatsu Photonics, Shizuoka, Japan), Quest Spectrum (Quest, Middenmeer,
Netherlands), among many others. At our institution, we use the SPY Elite (Stryker, Kalamazoos, MI),
which is a standalone camera system mounted onto a workstation for video output and data storage. There
are also portable handheld models as well as systems integrated into operating microscopes that work via an
[52]
infrared camera (Leica, Wetzlar, Germany) . Typically, ICG is stored in powder form. This is reconstituted
in saline or sterile water and given through a rapid intravenous bolus. For free flap imaging, we typically use
a standard dose of 10 mg. After injection, the camera system is directed into the area of interest and
perfusion can be assessed.

ICG has a well-established safety profile. In a large study from 1994, Hope-Ross et al. examined 1923 tests
[53]
in 1225 patients and found an incidence of 0.15%, 0.2%, and 0.05% for mild, moderate, and severe reactions,
respectively. No deaths were noted. While rare cases of anaphylaxis have been described , intraoperative
[54]
use should be quite safe given that the patient remains under monitored anesthesia care for an extended
time following exposure. Caution should be taken in patients with iodine allergy, pregnancy, liver disease,
uremia, and previous anaphylaxis to intravenous dye . ICG is metabolized by the liver and has a short half-
[53]
life of 3 to 4 min. The rapid turnover allows for repeated use throughout the same case, if necessary.

Fluorescence angiography has multiple applications in free flap surgery. It can be used to assess arterial
perfusion of the flap through the overall fluorescence of the skin paddle. This gives confirmation that the
arterial anastomosis is patent, and that perforators have been preserved. It can also be used to look for
relative venous insufficiency by comparing the flap to surrounding native tissue. Oversaturation can suggest
some level of venous congestion. Finally, it is a useful adjunct in determining the pattern of perforator
distribution. This allows the surgeon to split the skin paddle safely as well as discard distal areas of skin that
may have suboptimal blood supply .
[53]

Some surgeons use ICG angiography routinely in every FTT. At our institution, we have found clinical and
visual assessment to be adequate for most cases. We reserve the SPY for use in complex cases involving large
skin paddles, multiple perforators, or if there is a clinical concern for inadequate perfusion.