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Page 10 of 17 Cevallos et al. Plast Aesthet Res 2023;10:30 https://dx.doi.org/10.20517/2347-9264.2023.01

between oxygen delivered at the capillary level and mitochondrial consumption, providing a direct
estimation of oxygen availability at the cellular level [102,103] . To achieve tissue oxygen tension monitoring, an
implantable probe and microcatheter are typically used, with the microcatheter containing an electrode
[104]
functioning as an oxygen sensor . When the apparatus is placed in the flap, it measures the reduction of
molecular oxygen using a cathode and polarized circuit [101,105] . Rapid declines in oxygen tension detected by
[106]
these sensors indicate potential vascular compromise .
Oxygen tension monitoring devices offer real-time measurements of oxygenation, allowing for trend
analysis over time. These measurements are easily understandable by all members of the care team and are
considered highly sensitive indicators of end-organ tissue perfusion [107-109] . However, these devices require
invasive procedures for placement and removal of probes, which carries the risk of flap infection.
Furthermore, the temperature calibration of probes makes them susceptible to the influence of external
environmental factors and subtle temperature variations within the flap. Consequently, some authors have
suggested that these systems may be more prone to bias and could benefit from the integration of other flap
monitoring approaches, particularly in cases involving large areas of skin or significant temperature
gradients within the flap [101,110] .

Fluorescence imaging
[111]
Fluorescein angiography was one of the early applications of fluorescence in measuring flap perfusion .
Depending on the specific use case, different fluorophores can be leveraged to monitor perfusion quality
and flap viability. Indocyanine green fluorescence angiography (ICG-FA) has been extensively used for
peri-operative assessment of anastomotic patency and has found applications in various fields, such as
cardiac function monitoring, liver function testing, neurosurgery, and ophthalmology. As a non-toxic,
water-soluble dye with a half-life of 3-4 min, ICG can be safely injected into patients to visualize
microvascular patency and tissue perfusion. Adelsberger et al. conducted a study involving 210 free flaps to
assess vascular thromboses post-operatively. They used a handheld infrared camera in a dark room to
visualize the distribution of the dye after injection over a 4-hour interval for the first 72 h . The
[112]
combination of ICG-FA and clinical examination yielded an 85% success rate in detecting vascular
thromboses. Revision rates decreased from 19% to 12%, with a false negative revision rate of 4.8% over a
span of 3 years, accounting for a training and habituation period. Others have combined ICG injection with
scanning of flap using a near-infrared camera with an additional pinprick test to evaluate perfusion status
by fluorescent imaging of bleeding. This approach facilitates the need for repeated pinpricks and may lead
to subsequent complications, such as hematoma. However, it is particularly useful in patients with
questionable perfusion . Hitier et al. determined that intraoperative fluorescence after anastomosis to the
[113]
recipient vessels serves as a reliable predictor of post-operative flap viability, capable of indicating abnormal
values 16 hours prior to clinical evidence of flap failure using fluorescence signal thresholds . Despite its
[114]
usefulness, ICG-FA has certain limitations. It does not allow for continuous monitoring and requires repeat
injections. Exploring other fluorophores with increased circulation time may enable continuous monitoring
and provide activation at different wavelengths.

Other monitoring techniques
Given the significant advancements in post-operative monitoring techniques for autologous breast
reconstruction proven to have a high sensitivity and specificity, there has been a shift away from more
outdated and costly monitoring techniques. These include the use of biochemical markers, microdialysis,
technetium-99m sestamibi scintigraphy, and perfusion-weighted MRI. While we include them here for a
comprehensive perspective, it is important to note their limitations in terms of invasiveness, cost, and lack
of continuous monitoring.