Reply: Optimizing Perforator Selection: A Multivariable Analysis of Predictors for Fat Necrosis and Abdominal Morbidity in DIEP Flap Breast Reconstruction.

Abstract

Sir: We thank Drs. Li and Long for their interest and comments on our recent publication, “Optimizing Perforator Selection: A Multivariable Analysis of Predictors for Fat Necrosis and Abdominal Morbidity in DIEP Flap Breast Reconstruction.”1 We certainly agree with them that there were certain assumptions made when we calculated the total flow rate of these flaps based on the visual estimates of the perforator diameters. We opted to utilize physiologic normal values for blood pressure, blood viscosity, and the general length of an anastomosis or venous coupler. We do agree that a patient with hypertension may have a different total flow rate value versus a normotensive patient, even with the same perforator numbers and perforator diameters. However, our main aim was to accurately assess the importance of changing perforator diameters on the perfusion of a flap. Previous studies had looked at perforator diameters and sizes and found mixed results, the reason for which we believe is the failure to take into account the exponential increase in blood flow to a flap due to an increasing vessel diameter.2 Several studies have analyzed the role of perforator numbers as well, the additive effect of which would pale in comparison to increasing the diameter of a single perforator based on the Hagen-Poiseuille equation.2–4 Thus, the salient finding comes not from comparing the absolute values of flow rates for each patient based on their respective blood pressure, but rather from comparing the overall trend of how these flow rates changed from adding more perforators versus including larger perforators. This is why we kept the other variables in the Hagen-Poiseuille equation static from patient to patient. In addition, hypertension was one of the 28 variables we included and controlled for in our statistical analysis.1 If increased blood pressures had indeed confounded the statistical relationship we found between total flow rate and fat necrosis, this would have been elucidated in our multivariable model. We agree that color duplex ultrasonography is an interesting technology that has promising results for assessing hemodynamic information for perforators. This retrospective study did not utilize this for perforator assessment. Therefore, this would be an avenue for future research. Despite this, we believe our finding that increasing total flow rates of the flap decreased the odds of fat necrosis is significant,1 particularly in the setting of prior evidence suggesting that increasing the number of perforators could have a similar effect. In our study, perforator number was not a significant factor in reducing the odds of fat necrosis. In addition, we classified the row of perforators as medial, lateral, or both not as a novel scheme for our research, but because it is an established classification system in the literature analyzing fat necrosis in abdominal free flap breast reconstruction for the last several decades.2–11 We agree that it has its limitations in regard to the exact position of perforators within a given flap; however, creating a new classification system or reporting perforator locations in terms of positional measurements not only is outside the scope of this retrospective study but also runs the risk of losing relevance in the current established schema within deep inferior epigastric perforator flap literature. In regard to their comments about our primary outcome measures, we looked at not only fat necrosis in the free flap itself but also abdominal bulge and abdominal donor-site complications.1 Flap loss rates and venous congestion were not analyzed in this study as primary outcome measures and will be the subject of future publications. DISCLOSURE The authors have no commercial or financial associations related to this communication, and no commercial or financial conflicts of interest. No funding was received for the performance of this research or production of this communication. Nicholas T. Haddock, M.D.Austin S. Hembd, M.D.Sumeet S. Teotia, M.D.Department of Plastic SurgeryUniversity of Texas Southwestern Medical CenterDallas, Texas