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Page 6 of 17 Cevallos et al. Plast Aesthet Res 2023;10:30 https://dx.doi.org/10.20517/2347-9264.2023.01

Table 3. Invasive techniques for flap monitoring, including main benefits and limitations
Invasive technique Benefits Limitations
Implantable doppler & ● Cost effective ● May cause vessel damage
venous coupler ● Usable on all types of flaps ● Complex operative technique
● Ease in signal reading ● High false positive rates
Transcutaneous oxygen ● Very sensitive to declines in tissue oxygenation ● Invasive, requires tunneling with some extra dermal
tension monitoring ● Easy to monitor components
● Can be used for monitoring of buried flaps ● May be unreliable in large cutaneous flaps or flaps
● Provides a direct measurement of oxygen availability at with large within-flap temperature gradients
the cellular level
Biochemical markers ● Cost effective ● Limited efficacy among diabetic patients
● Reflect the flap’s local environment ● Not applicable for buried flaps
● Patterns of known metabolites exist to direct thresholds
and clinical decisions
Microdialysis ● Can be used when clinical examination is not possible ● Causes local tissue trauma
● Detects flap failure hours before it becomes clinically ● Cost
evident ● High false-positive rates
● Gives a quantitative metric ● May require an equilibrium period
● Securing the catheter can be difficult
Fluorescence imaging ● Broadly used with clinical applications beyond plastic ● Additional staffing requirements are not as high as
surgery other techniques
● Can leverage different fluorophores ● Continuous monitoring is difficult
● Handheld devices and probes have been developed ● Repeat injections of dyes may be required
● Ease of use ● Limited circulation of fluorophores
Technetium-99m sestamibi ● Can monitor muscle flap viability reliably ● Limited to a majority of case reports and series with
scintigraphy ● Reveals distal ischemia or hypoperfused area in muscle the need for more robust studies
tissue ● May need to be combined with other techniques,
● Short half-life of ~6 h such as Doppler, to visualize the blood vessel integrity
Perfusion-weighted MRI ● Is relatively non-invasive, and risks to the patient are ● Resource intensive
limited to those imposed by the administration of contrast ● Requires support staff at each step
● Provides a picture of entire-flap perfusion ● Requires serial studies if flap is to be monitored over
time

pathologies . However, its specificity in identifying vascular compromise, like other Doppler devices, is
[54]
limited. Color duplex ultrasound machines are more expensive, less portable, and require trained personnel
for operation. Typically, the presence of a microsurgeon is necessary to aid in the anatomical orientation of
the transmitter, while a radiology technician is required for consistent image acquisition and interpretation.

Surface temperature monitoring
In addition to tactile assessment in the clinical exam, flap temperature can be measured and monitored
using temperature probes placed on the skin surface. The arterial blood supplying the flap carries heat,
[63]
which is released into the surrounding extravascular tissue through convection . Congested flaps exhibit
distinct temperature drop patterns compared to ischemic flaps. A temperature drop of 3 °C (37 °F) at the
center of a skin paddle indicates arterial thrombosis, while a uniform temperature drop of 1-2 °C (33.8-35.6
°F) across the skin surface of a flap suggests venous compromise . Typically, surface temperature
[64]
[65]
monitoring can detect flap compromise starting from the eighth hour post-operation . Measurement of
flap temperature can be easily performed using inexpensive strips (~1$ per strip) placed on the surface of
[66]
free flaps, and the values can be compared to the temperature of adjacent non-operated skin .

Recently, infrared thermography has emerged as a novel method of post-operative flap monitoring in breast
reconstruction [67,68] . This thermal imaging technology converts the detected temperature values through
infrared radiation into pixel values, resulting in a visual display of cutaneous blood flow. Infrared
thermography has demonstrated a sensitivity of 96% and a specificity of 75%, indicating its potential as a
valuable adjunct to clinical assessment .
[67]