Table 2. Overview of free flap monitoring technologies.
| Technology | Mechanism | Advantages | Disadvantages |
|---|---|---|---|
| Abbreviations: Hb, hemoglobin; LSI, laser speckle imaging, NIRS, near-infrared spectroscopy; SFDI, spatial frequency domain imaging; US, ultrasound; VLS, visible light spectroscopy. | |||
| Handheld Doppler US | Detects sound proportional to flap blood flow | Inexpensive Easy to use Noninvasive Rapid assessment With experience, can differentiate venous from arterial signal |
Operator dependent Not quantitative Intermittent monitoring Cannot surveil buried flaps |
| Color duplex US | Visualizes blood flow using US | Relatively inexpensive Noninvasive Rapid assessment Can differentiate venous from arterial blood flow |
Operator dependent Not quantitative Intermittent monitoring Typically requires technician Cannot surveil buried flaps |
| Implantable Doppler probe | Detects sound proportional to flap blood flow, near anastomosis on pedicle | Relatively easy to use Continuous monitoring Rapid assessment Can monitor buried flaps |
Has to be placed intraoperatively Not quantitative High cost |
| Flow coupler | Implantable Doppler incorporated into venous coupler | Same as “implantable Doppler probe” | Same as “implantable Doppler probe” |
| Laser Doppler flowmetry | Blood flow velocity is estimated by illuminating a tissue sample with laser light and then analyzing the frequency distribution of the backscattered light | Continuous monitoring Semiquantitative Very accurate Rapid assessment |
Operator dependent Typically requires technician Cannot surveil buried flaps Very high cost |
| NIRS or VLS | Light of specific wavelength is emitted toward tissue and changes in intensity attributable to relative changes in hemoglobin concentrations, which correlate with tissue oxygenation | Continuous monitoring Quantitative Rapid assessment |
Operator dependent Cannot surveil buried flaps Extremely high cost |
| Microdialysis | Catheter is placed into tissue, sample extracted and presence of metabolites like lactate analyzed | Quantitative Accurate Used in buried flaps |
Sample variability Intermittent monitoring Invasive Not real time Requires technician High cost |
| SFDI | Near infrared light projected and collected in real time, converted into spatial maps of O 2 Hb and Hb concentrations | Real time Quantitative Continuous Can distinguish arterial from venous complications |
High cost Cannot surveil buried flaps |
| LSI | Laser light reflected into video camera produces speckles that correlate with tissue blood flow | Continuous Real time Noninvasive Can distinguish venous from arterial complications |
Cannot surveil buried flaps |
| Oxygen-sensing bandage | Molecule within paint detected by camera creates 2-map of oxygenation | Real time Noninvasive Can be applied to high topography regions Low cost |
Intermittent monitoring Not for acute use Sample variability |
| Thermal imaging | Temperature of skin measured by infrared sensor on handheld device | Real time Noninvasive Low cost |
Operator dependent Intermittent monitoring Only useful for flaps with cutaneous island |