Reply: Intraoperative Assessment of DIEP Flap Breast Reconstruction Using Indocyanine Green Angiography: Reduction of Fat Necrosis, Resection Volumes, and Postoperative Surveillance.

Abstract

Sir: We thank the authors for their comments and for taking the time to respond to our recent article.1 We certainly agree that a set fluorescence intensity criterion would be beneficial to allow maximal objectivity and reproducibility for this study. Although several attempts have been made to define a critical threshold of fluorescence intensity to predict optimal tissue perfusion postoperatively, we are far from a consensus on the exact threshold that will best prevent fat necrosis in the subcutaneous tissue of free flaps for breast reconstruction. An additional obstacle for using objective intensity numbers for free flaps with large amounts of subcutaneous tissue is adequately assigning cutoffs for both the fat and the skin, which frequently have different intensities on indocyanine green angiography. Commonly, the skin of deep inferior epigastric perforator (DIEP) flaps will be well perfused in entirety, but areas of fat will still become necrotic postoperatively. This current study is the first analysis of a homogenous population of DIEP flaps that correlated the reduction of fat necrosis in the free flap to the use of indocyanine green angiography. Therefore, during the period from 2010 to 2017, which was when the procedures were performed for this study, we used a subjective assessment of perfusion in the tissue of our DIEP flaps in 1 to 2 minutes. The next step for future studies, now that we have established the reduction of fat necrosis with indocyanine green angiography use in DIEP flap breast reconstruction, is to establish specific objective indocyanine green criteria for both the skin and fat signals that best predict fat necrosis. Sixty-two percent of the DIEP flaps underwent indocyanine green angiography and did not have any areas of relative hypoperfusion, and thus no portion of the flap was resected. These flaps were not included in the comparison of average weights. The average weights of the resection specimens only included flaps that had indocyanine green–guided resections versus flaps that had resections based on clinical signs and symptoms of hypoperfusion alone without indocyanine green angiography. We did analyze the percentage of flaps (38 percent) that had excisions in the indocyanine green angiography cohort versus the percentage of flaps (27.1 percent) that had excisions based on clinical signs of hypoperfusion (poor bleeding, venous bleeding, poor capillary refill of overlying skin) instead. The issue with this comparison is that we believe that clinical signs and symptoms of hypoperfusion are inadequate alone to guide excision of certain zones or portion of a flap, and therefore a surgeon may frequently not excise any portion of the flap or the fat of the flap even though it is hypoperfused. This is our explanation for why there were fewer excisions for the non–indocyanine green angiography cohort. This does not, however, mean that indocyanine green angiography is not effective for avoiding overresection. In light of also reducing fat necrosis, it simply means indocyanine green angiography offers a more accurate depiction of which portion of the flap is hypoperfused and needs to be resected. We maintain that comparing the weights of the excised portions between both cohorts is a more accurate way of supporting the accuracy of excision guided by indocyanine green angiography. We hope that our explanations and discussion help clarify our research methodology. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. No funding was received for this communication. Austin Hembd, M.D.Department of Plastic Surgery Yulin Liu, Ph.D.Department of Population and Data Sciences Sumeet S. Teotia, M.D.Nicholas T. Haddock, M.D.Department of Plastic SurgeryUniversity of Texas Southwestern Medical CenterDallas, Texas