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Page 10 of 15 Ali et al. Plast Aesthet Res 2021;8:35 https://dx.doi.org/10.20517/2347-9264.2021.29

particular in crowded anatomic spaces in the head and neck, as well as overall caregiver consciousness of
protecting the external segment of the monitoring probe. Future upgrades may include more widespread
use wireless monitoring capabilities, potentially reducing existing issues with probe dislodgement.

Color duplex doppler ultrasonography
Color doppler ultrasound is a non-invasive, cheap, and repeatable tool that can be used to assess arterial and
venous flow as an adjunct for overall FTT assessment. Studies have typically described utilizing a 5 or
5.5 MHz linear transducer ultrasound probe with a real-time high resolution ultrasonography machine .
[60]
Knowledge of the location of the pedicle (denoted by a stitch or marker) allows the user to perform real-
time ultrasonography to identify and trace the pedicle from its origin in the free flap to its course into the
recipient vessel. From a flap monitoring perspective, the proposed advantages of this technology include the
ability to monitor buried or covered flaps, assess the health of the artery and vein in parallel to one another,
and assist with assessing the exact site of obstruction in the event of a geometrical issue or an occluded
[60]
vessel [60-62] . A case series discussion by Seres et al. demonstrates how color ultrasonography can provide
additional information when venous congestion is of concern, particularly in cases of hematomas or free
flap swelling. In all three of their described cases, the authors were able to avoid returning to the OR by
confirming adequate flow through the vein via color doppler ultrasound. Further studies have found a role
for color ultrasonography as a means of evaluating the loss of implantable Doppler probe signals in buried
free flaps, where clinical assessment cannot distinguish between device malfunction and true flap
[62]
compromise .
Limitations of color Doppler ultrasonography relate to the overall cost of owning the machine and degree of
[61]
knowledge and skill required to perform the imaging and accurately assess the flow through the pedicle .
While it is likely not feasible to train nursing staff in performing ultrasonography as part of FTT assessment,
as ultrasound use becomes more widespread overall, a greater proportion of residents are becoming familiar
with its use. Additionally, as ultrasound technology becomes increasingly mobile where touch-screen
devices and personal cellphones are being utilized as the screens, the need for transporting larger and more
costly equipment will decrease.

At our center, we do not currently utilize color ultrasonography as part of routine free flap assessment.
However, as the technology becomes increasingly portable and the imaging techniques become more
ingrained within the training curriculum, we do feel that it has an important role as an adjunctive measure
for flap monitoring, particularly for re-operative decision making.

Near-infrared spectrophotoscopy
Near-infrared spectrophotoscopy (NIRS) technology employs a light source to emit energy at specific near-
infrared wavelengths in order to measure relative changes in concentration of oxygenated and deoxygenated
hemoglobin . The spectrometer typically measures relative changes in tissue concentrations of hemoglobin
[63]
and presents the findings as an alteration in percentage of saturated hemoglobin (StO ). This requires
2
attachment of a probe to the patient’s free flap, with the use of a light-blocking shield to prevent ambient
light intrusion, typically placed at the time of initial surgery . The surgical team must then decide a
[63]
threshold value where the spectrometer will alert the clinician, typically an absolute reading of StO below
2
[64]
30% to 50% or a certain drop rate percentage over a set amount of time . Proposed advantages of this
adjunctive technology include its overall reliability, noninvasive nature, and ability to distinguish the source
of the vascular crisis . A systematic review demonstrated an improvement in surgical salvage rate and flap
[65]
failure rate between NIRS monitored groups and those that did not use NIRS . Disadvantages associated
[64]
with NIRS system include inconsistency in alarm threshold values, potential need for repositioning of the
spectrometer sensors, retail price of the sensor and the spectrometer, and inability to be used for buried