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Carter et al. Plast Aesthet Res 2020;7:33 I http://dx.doi.org/10.20517/2347-9264.2020.81 Page 11 of 15

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Figure 8. We use the T-Stat VLS Tissue Oximeter (Spectros; Portola Valley, CA) for postoperative flap monitoring in all patients, and
sometimes for intraoperative decision-making. It provides continuous quantitative measurements of total hemoglobin concentration [Hgb]
and hemoglobin oxygen saturation

Early identification of vascular compromise is directly correlated with successful flap salvage rates [35-37,39] .
Typical postoperative flap monitoring includes bedside physical exam in combination with handheld
Doppler monitoring of the arterial signal [35,37,39] . The clinical exam includes flap skin color, capillary refill,
and surface temperature [11,37] . If necessary, pinprick bleeding may be used, although we do not routinely use
this at our center. Cutaneous handheld Dopplers are used to detect intravascular arterial and venous blood
[37]
flow . These checks occur every 1-2 h at the bedside for the first few days postoperatively. Flaps that are
concerning for incipient vascular compromise are monitored even more frequently. While clinical evaluation
[37]
and Doppler alone are generally effective and have negligible additional cost , there are drawbacks to this
method. Clinical examination can vary between observers, require trained staff, and may not be able to
detect vascular compromise until relatively late physical findings become apparent . At that time, damage to
[36]
the flap microvasculature may be irreversible. Additionally, while Doppler is sensitive to arterial compromise,
it is less sensitive to venous compromise [35,36] . This is problematic given that venous congestion is the most
common cause of flap failure [35-37] . Furthermore, the strength of the arterial Doppler signal does not correlate
with sufficient oxygen delivery to the flap and loss of the Doppler signal can be a relatively late finding [35,38] .
Neither clinical examination nor handheld Dopplers are able to continuously monitor the integrity of the
flap, which could delay detection of vascular compromise [35,36] .

The ideal flap monitoring system is noninvasive, continuous, reliable, sensitive, and easy to interpret [37,39] .
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Our group uses the T-Stat VLS Tissue Oximeter (Spectros; Portola Valley, CA) to augment routine bedside
clinical examinations and handheld Doppler checks [Figure 8]. The T-Stat oximeter uses visible light
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spectroscopy (VLS) to continuously monitor total hemoglobin concentration [Hgb] as well as hemoglobin
saturation (StO ) of tissue at the capillary level in real time [35,36] . [Hgb] approximates the total blood volume
2
[36]
in the flap, and an increased value indicates obstruction of venous drainage . StO measurements correlate
2
directly with arterial tissue perfusion, and a decreased value indicates diminished arterial inflow from
[36]
an arterial thrombus or is a later finding in the case of venous drainage obstruction . In this way, VLS
monitoring is able to continuously quantify the arterial inflow, venous outflow, and perfusion status of the
[36]
flap .
Multiple groups have demonstrated an initial gradual increase in StO detected with VLS in the first ~8 h
2
after surgery before the value stabilizes, attributable to mild ischemia-reperfusion injury [35,36] . The mean