How is flap perfusion assessed intraoperatively during breast reconstruction, including the use of indocyanine green (ICG)?

Intraoperative Flap Perfusion Assessment in Breast Reconstruction

Indocyanine green (ICG) fluorescence angiography is the primary method for intraoperative flap perfusion assessment during breast reconstruction, providing real-time objective visualization of tissue perfusion to guide surgical decision-making and reduce complications.

ICG Angiography Technique and Protocol

The standard approach involves intravenous administration of ICG with near-infrared fluorescence imaging to assess mastectomy skin flap and DIEP flap perfusion 1. Based on recent high-quality evidence:

Dosing and Timing

• Standard IV dose: 0.3 mg/kg body weight for perfusion assessment 2, 3
• Ophthalmic/specialized applications: Up to 40 mg in 2 mL aqueous solvent 1
• Critical timing window: Perfusion assessment must occur at 60-90 seconds post-injection for accurate interpretation 4
  • Assessments at ≤30 seconds are unreliable and should be avoided
  • Fluorescence intensity increases with time, requiring time-adjusted thresholds

Imaging Protocol

• Perform ICG angiography after temporary skin closure
• Record for 120 seconds to capture complete perfusion dynamics 5
• Control modifiable factors: standardize ambient lighting, camera distance, and ICG dose 4
• ICG binds 95-98% to plasma proteins (primarily albumin) and is hepatically cleared with no extrahepatic circulation 1

Perfusion Assessment Metrics

Quantitative Thresholds for Mastectomy Skin Flaps

Two validated approaches exist for predicting flap necrosis:

1. Absolute perfusion values (SPY Elite® system):

   • ≤7 units predicts full-thickness necrosis with 88% sensitivity and 83% specificity 6
   • In patients without smoking history or epinephrine use: 83% sensitivity, 97% specificity
   • Critical caveat: Smoking and epinephrine-containing tumescent solutions cause false-positive low readings 6

2. Perfusion score threshold:

   • <40% perfusion score indicates high necrosis risk 7
   • Strict adherence to 40% threshold eliminated mastectomy flap necrosis in recent series 7

3. Ingress time metric:

   • ≥70.5 seconds for complete flap perfusion predicts full-thickness necrosis 5
   • Sensitivity 82%, specificity 84%, accuracy 83%
   • Mean ingress time: 104.6 seconds (necrosis group) vs 47.6 seconds (no necrosis) 5

Dynamic Parameters for DIEP Flaps

For fasciocutaneous flaps, quantitative fluorescence-time curve analysis identifies compromised perfusion 8:

• Time-to-peak (Ttp): Prolonged in compromised flaps (209 vs 48 seconds in distal flap, p=0.001)
• Normalized inflow slopes: Reduced in compromised tissue (1.6 vs 4.2%/s, p=0.002)
• Outflow slopes: Decreased washout indicates venous congestion

Clinical Outcomes and Impact

ICG guidance significantly reduces complications compared to clinical assessment alone:

• Mastectomy flap necrosis: Reduced from 24.3% to 4.0% (p=0.0048) 7
• Overall complication rate: 24% (ICG) vs 36% (clinical assessment) 9
• Readmission rates: Decreased from 27.3% to 4.9% (p=0.0071) 7
• Wound complications: Reduced from 39.4% to 9.8% (p=0.0026) 7
• Fat necrosis in DIEP flaps: 8% with 100% flap survival 2

Practical Application Algorithm

Step 1: Administer ICG 0.3 mg/kg IV after flap elevation and temporary closure

Step 2: Wait 60-90 seconds before assessment (not ≤30 seconds)

Step 3: Record fluorescence for 120 seconds

Step 4: Apply decision thresholds:

• If absolute perfusion ≤7 units OR perfusion score <40% OR ingress time ≥70.5 seconds → Resect poorly perfused tissue
• If smoking history or epinephrine use present → Interpret low values cautiously (may be false-positive)

Step 5: Reassess after tissue adjustment if needed

Critical Pitfalls to Avoid

1. Premature assessment: Do not evaluate perfusion before 60 seconds post-injection 4
2. Ignoring confounders: Smoking and epinephrine cause falsely low readings 6
3. Unstandardized technique: Maintain consistent ambient lighting and camera distance 4
4. Subjective interpretation alone: Use quantitative thresholds, not just visual assessment 9, 8
5. Single time-point assessment: Dynamic parameters (ingress time, time-to-peak) provide additional predictive value 5, 8

Additional Applications

Beyond mastectomy flap assessment, ICG enables:

• DIEP flap perforator selection: Streamlines intraoperative perforator choice 2
• Post-anastomotic patency verification: Confirms vascular connections 7
• Contralateral symmetry assessment: Guides tissue resection 7

The evidence strongly supports ICG as superior to clinical judgment alone, with the most robust data showing elimination of necrosis when strict quantitative thresholds are applied 7.