Reply (2014)

Sir: We thank you for allowing us to respond to the letter by Tambasco et al. regarding our original article “The Effect of Pressure and Shear on Autologous Fat Grafting.”1 This letter attempts to explain differing results between our original peer-reviewed publication in Plastic and Reconstructive Surgery in May of 2013 and a letter written to Plastic and Reconstructive Surgery in April of 2013 by Tambasco et al.2 These are (1) differences between our syringe suction pressure curves and those printed in a letter to Plastic and Reconstructive Surgery in August of 2012 by Rodriguez and Condé-Green, and (2) stating that Poiseuille’s law only affects machine liposuction and not syringe suction. We can explain the differences in suction pressure curves using Boyle’s law, which states the following: Pressure1 × Volume1 = Pressure2 × Volume2 where Pressure1 is 1 atmosphere at sea level, Volume1 is the starting volume of a closed system, Pressure2 is the ending pressure, and Volume2 is the ending volume of the same closed system. For accurate pressure curves, it is imperative that the starting volume (i.e., Volume1) is accurate. In clinical fat grafting, the starting volume is only the volume in the Coleman suction cannula because there is nothing in the syringe. Fortunately, the same suction cannula was used in both experiments and we measured the volume of the cannula to be 0.6 cc. In these pressure experiments, the starting volume is the volume in the manometer system including any tubing between the syringe and the manometer. We can solve for the starting volumes using Boyle’s law in the 3-cc syringe data point from both our original article and that found in the letter by Rodriguez and Condé-Green3 as shown in Table 1.Table 1: Calculation of Starting Volume (Volume1) Using a 3-cc SyringeBy our calculations, our starting volumes were much more similar to those seen in clinical fat grafting using the standard Coleman cannula and thus reflect more accurate pressure curves. As mentioned in the Discussion of our original article published in Plastic and Reconstructive Surgery in May of 2013, introducing any additional volume to the system such as tubing will alter the starting volume enough to dramatically alter the pressure curves. Therefore, we believe the pressure curves of Rodriguez and Condé-Green inaccurately reflect the pressure curves that are seen in clinical fat grafting using a Coleman syringe suction cannula. The second point that Tambasco et al. discuss is Poiseuille’s law, which states that there is a pressure drop in a fluid flowing through a cylindrical pipe. By this law, the suction pressure seen at the cannula tip is weaker to some degree than that seen in the canister of a machine liposuction device. What has been overlooked is that the same principle also applies to syringe suction where a cannula with a much smaller radius is used. Furthermore, if the suction pressure seen at the cannula tip is lower than that measured in the canister, we would argue that this only serves to support our conclusion that high machine suction is equivalent to low machine suction. No one has ever reported harmful effects of lower suction pressures. We have reviewed the letter to Plastic and Reconstructive Surgery in April of 2013 by Tambasco et al.4 discussing histology of fat harvested with various degrees of suction pressure. Having performed similar experiments, we can appreciate the time and effort involved in undertaking such research. It is true that the conclusions of our original article differ than those in the letter to Plastic and Reconstructive Surgery by Tambasco et al. Before agreeing or disagreeing, however, we would need more information. First, what type of statistical analysis was conducted to calculate statistical significance between the sample groups, and was there more than one sample per study group that was analyzed for histology? It would be difficult to claim that there was a statistically significant difference if the p value was not less than 0.05 or if n = 1. Second, how can the authors differentiate in their histology the cytoplasmic membrane rupture versus sectioning artifact that is very commonly seen in adipocyte histology? We have looked at countless histologic slides for membrane rupture and have determined that it cannot be reliably used as an endpoint. Instead, we look at the degree of inflammation, fibrosis, and vacuoles, which are all markers of graft injury and much more easily determined. Third, how can the authors infer long-term fat graft survival at day 0? Most in the field agree that a long-term model is needed. We too have investigated day-0 data, but they clearly do not reliably relate to long-term graft survival. Therefore, we have published long-term data using a proven small-animal model. We aim to answer clinically relevant scientific questions. In this case, what effect do these variables have on long-term fat graft survival in vivo? We agree wholeheartedly that standardizing a procedure is difficult. Our intention is to provide a deeper understanding of the variables that significantly affect fat grafting and to stimulate much needed research. We all look forward to the day when there is a standard technique that optimizes all of the significant variables, but the data do not yet exist. There are numerous variables that still warrant investigation and peer review before we can comfortably support or claim a “ standard” technique. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Jeffrey H. Lee, M.D. Michael C. McCormack, M.B.A. William Gerald Austen, Jr., M.D. Massachusetts General Hospital Boston, Mass.