Improving intraoperative perfusion reliability in anterolateral thigh free flap reconstruction for diabetic foot ulcers

Table 1 Multimodal perfusion assessment toolbox for patients with diabetic foot ulcer undergoing anterolateral thigh free-flap reconstruction

Modality	Physiological target	Core quantitative readouts	Key strengths in DFU/ALT flap setting	Major limitations/sources of bias	Recommended role in an integrated workflow
ICG-FA: Static intensity	Superficial microvascular filling	Relative intensity, perfused area ratio	Real-time intraoperative “perfusion map”; margin tailoring; identifies gross hypoperfusion	Highly sensitive to camera gain/distance, ambient light, ICG dose/injection, tissue thickness/edema; intensity saturation/pooling	Screening/visual guidance only; avoid using a single brightness snapshot as a stand-alone threshold in DFU
ICG-FA: Time-intensity kinetics (FTC metrics)	Dynamic inflow/outflow kinetics	Wash-in slope, Tmax, AUC, Fmax, half-time, washout	More robust to device settings than static intensity; supports reproducibility; captures “exchange efficiency” beyond brightness	Still affected by ROI selection, timing, motion, and protocol heterogeneity; requires standardized acquisition and curve extraction	Primary quantitative layer for intraoperative decision support; should be standardized and validated against outcomes
Toe pressure/TBI	Distal macrocirculatory capacity (digital arteries)	Toe pressure (mmHg), toe-brachial index	Less distorted by medial arterial calcification than ABI; linked to healing/amputation risk	Toe deformity, ulcer location, temperature, pain; not intraoperative-real time	Baseline distal inflow gatekeeper; interpret ICG-FA within the “distal capacity” context
SPP	Microvascular perfusion reserve (skin)	SPP (mmHg)	Useful when toe pressure unavailable; healing prediction utility	Operator dependence; site-specific; not continuous	Pre-op ischemia stratification and post-revascularization reassessment
TcPO2	Tissue oxygenation (skin oxygen diffusion)	TcPO2 (mmHg)	Strong wound-healing prediction literature in DFU; anchors perfusion to oxygen delivery	Placement/temperature/thickness sensitive; slower response; limited intraoperative feedback	Oxygenation “ground-truth” adjunct to interpret ICG-FA and plan revascularization/optimization
NIRS/tissue oximetry	Local hemoglobin oxygen saturation	StO2 trends, desaturation events	Early warning for perfusion compromise; continuous monitoring potential	Device/probe variability; thresholds not standardized; depth limited	Continuous trend monitoring peri-/post-op; complements ICG-FA kinetics
LDF/LDI	Superficial microvascular flow (RBC flux)	PU, spectral indices	Detects microvascular dysregulation; noninvasive	Motion artifacts; small sampling area; limited depth	Microcirculation trend assessment; research/adjunct use
LSCI	Superficial perfusion mapping	Relative perfusion maps, flow index	Wide-field perfusion mapping; can complement ICG-FA	Susceptible to motion/Lighting; standardization needed	Cross-validation of ICG-FA in centers with capability
Doppler waveform (handheld/duplex)	Arterial hemodynamics	Waveform morphology; velocity indices	Adds hemodynamic context; supports PAD grading	Requires expertise; may miss microvascular failure	Macrovascular characterization together with toe pressure/TBI/SPP/TcPO2
FLIR	Surface temperature proxy for perfusion	Temperature gradients, thermal asymmetry	Rapid, non-contact; potential adjunct with TcPO2	Confounded by ambient temp, inflammation, dressings; indirect marker	Adjunct screening, especially when paired with TcPO2 in angiosome-based assessment

ABI: Ankle-brachial index; ALT: Anterolateral thigh; AUC: Area under the curve; DFU: Diabetic foot ulcer; FLIR: Infrared thermography; Fmax: Maximum fluorescence intensity; FTC: Fluorescence-time curve; ICG-FA: Indocyanine green fluorescence angiography; LDF/LDI: Laser Doppler flowmetry/imaging; LSCI: Laser speckle contrast imaging; NIRS: Near-infrared spectroscopy; PAD: Peripheral artery disease PU: Perfusion units; RBC: Red blood cell; ROI: Region of interest; SPP: Skin perfusion pressure; StO₂: Tissue oxygen saturation; TBI: Toe-brachial index; TcPO₂: Transcutaneous oxygen tension; Tmax: Time to maximum fluorescence intensity.

Table 2 Proposed minimum reporting set for standardized quantitative indocyanine green fluorescence angiography in diabetic foot ulcer anterolateral thigh free-flap reconstruction

Reporting domain	Minimum items to report (recommended)	Why it matters	Outcome anchoring
Patient and limb ischemia phenotype	Diabetes duration/type; PAD history; prior revascularization (type, timing); ulcer location/angiosome; infection status	Baseline heterogeneity strongly shapes perfusion signals and failure risk	Stratify analyses by ischemia phenotype and revascularization status
Distal perfusion capacity (pre-op baseline)	Toe pressure/TBI, SPP, TcPO2 (site, temperature settings, timing); Doppler waveform	Interprets ICG-FA within a “distal capacity ceiling”; mitigates ABI distortion in medial calcification	Use clinically meaningful thresholds and report proportion meeting targets
ICG agent and administration	ICG dose (mg/kg), concentration, injection rate/flush volume, injection site, repeat-injection interval	Dose/rate substantially change curve shape and saturation; critical for reproducibility	Report adverse reactions; document repeated runs and reasons
Imaging system and acquisition settings	Device model; excitation/emission band; working distance; gain/exposure; frame rate; ambient light control; start time relative to injection	Controls systematic measurement drift across platforms and cases	Provide calibration/QA steps if available
ROI definition rules	ROI anatomical landmarks; size/shape; number of ROIs (central vs peripheral, suspected hypoperfusion zones); method for background subtraction	ROI selection is a dominant source of between-study variability	Predefine ROI plan; avoid “post-hoc ROI fishing”
Primary kinetic parameters (FTC-based)	Wash-in slope; Tmax; AUC; Fmax; time-to-10%/90% rise (if used); normalization method	Kinetic metrics are less sensitive than intensity-only metrics and reflect inflow/exchange dynamics	Specify how curves are extracted (software, smoothing, interpolation)
Decision rules during surgery	Criteria for margin trimming, re-anastomosis, supercharging, warming/vasodilator use; whether decisions were blinded to kinetics	Enables evaluation of clinical utility and prevents circular reasoning	Link each decision to subsequent necrosis/complication endpoints
Systemic physiology at imaging	MAP/vasopressors; temperature; hemoglobin; SpO2/PaO2; PaCO2/ventilation strategy; fluid balance	ICG-FA reflects a systemic-regional-microcirculatory continuum; systemic variables confound kinetics	Report concurrent systemic targets and deviations
Comparator modalities (if available)	NIRS StO2 trends; TcPO2/TcPCO2; LDF/LSCI; thermography	Multimodal validation improves credibility and mechanistic inference	Predefine primary/secondary validation endpoints
Clinical endpoints	Partial/total flap necrosis (definition, timing); take-back/re-exploration; wound healing time; limb salvage; LOS	Avoids endpoint heterogeneity, enabling meta-analysis/registry utility	Mandatory follow-up window and adjudication process

ABI: Ankle-brachial index; AUC: Area under the curve; FTC: Fluorescence-time curve; ICG-FA: Indocyanine green fluorescence angiography; LDF/LSCI: Laser Doppler flowmetry/Laser speckle contrast imaging; LOS: Length of stay; MAP: Mean arterial pressure; NIRS: Near-infrared spectroscopy; PaCO₂: Partial pressure of arterial carbon dioxide; PAD: Peripheral artery disease; PaO₂: Partial pressure of arterial oxygen; QA: Quality assurance; ROI: Region of interest; SpO₂: Peripheral capillary oxygen saturation; SPP: Skin perfusion pressure; StO₂: Tissue oxygen saturation; TBI: Toe-brachial index; TcPO₂: Transcutaneous oxygen tension; Tmax: Time to maximum intensity.