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Ali et al. Plast Aesthet Res 2021;8:35 https://dx.doi.org/10.20517/2347-9264.2021.29 Page 9 of 15

POSTOPERATIVE
While overall success rates for FTT exceeds 95%, the need for revision surgery remains significant at 10% to
[55]
12% . Timeliness is particularly important in identifying a potential issue with a FTT, as there exists a finite
window where the flap can be salvaged while under-perfused or congested. While clinical assessment by an
experienced microvascular surgeon is the gold standard, it is not practical to have this be the only measure
of flap monitoring during the critical 48 to 72 h window where there is greatest risk for arterial or venous
thrombosis. As such, the need for a sensitive and specific adjunct flap monitoring technique is crucial,
particularly in the era of strict resident duty hour monitoring and increasing turnover of nursing staff.
These adjunct techniques serve to complement a basic clinical examination and provide objective data with
which microvascular surgeons can assess the need for possible revision surgery. The techniques vary greatly
in terms of ease of use, cost of implementation, and overall specificity and sensitivity. This section will
explore the basics of newer technologies in adjunct free flap vascular monitoring, as well as their advantages
and disadvantages.

Implantable dopplers (arterial and venous)
The implantable doppler technology consists of a 20-MHz pulsed ultrasonic probe within a silicone cuff that
[56]
can be secured to the vascular pedicle (either artery or vein) via sutures, surgical clips, or tissue sealants .
The potential advantage of this technology is that it provides real-time assessment of flow through the
vascular pedicle and can alert clinicians to alteration of arterial flow or compromise of venous drainage in
advance of clinically detectable changes in the free flap. The disadvantage largely relates to over-reliance on
the technology in lieu of clinical assessment, leading to a potentially significant false-positive rate in the
event of device dislodgement or failure. A meta-analysis of 22 articles comparing post-operative outcomes
between an implantable doppler group and a clinical assessment group found a significantly lower free flap
[57]
failure rate (2.11% vs. 4.21%) and an improved flap salvage rate (83% vs. 59%) .
At our institution, we utilize implantable dopplers for the majority of our mucosal reconstructions. We have
found that continuous, real-time monitoring in the OR after microvascular anastomosis has allowed us to
identify alterations in flap perfusion related to fluctuations in the patient’s blood pressure. This helps
establish a minimum blood pressure goal for the anesthesiologist to titrate toward to maintain ideal flap
perfusion. Specifically, if there is an alteration or loss of signal correlated to a decrease in blood pressure, we
will titrate the blood pressure up to establish a minimum perfusion goal. Furthermore, the continuous
monitoring while completing inset or closing the neck wounds provides an additional safeguard against
unfavorable pedicle positioning, potential compression with skin flaps, or alterations in flow secondary to
placement of a suction drain. Postoperatively, we have found that it provides reliable monitoring of flow
through the arterial anastomosis, however we do not rely on it for assessment of the venous pedicle.

[58]
A study by Swartz et al. demonstrated that relying on an arterial probe to detect downstream venous
thromboses led to an increased rate of false negatives; further laboratory analysis demonstrated that an
arterial probe required a mean 220 ± 40 min to detect venous thromboses, compared to a mean
6.08 ± 2.4 min for a venous probe to detect venous thromboses. The caveat with this, however, is that
utilization of venous probes can lead to a higher false-positive rate (up to 33%), secondary to probe
[57]
dislodgement, fibrin coating, or global device malfunction .

The implantable doppler has proven itself to be a useful adjunct in the overall assessment of free flaps post-
operatively, particularly for monitoring of flap perfusion where there is evidence for earlier time to flap
salvage and resultant improved overall outcomes . It is additionally useful for buried free flaps, providing
[59]
continuous and reliable monitoring. Effective utilization does require troubleshooting pedicle geometry,