Quantification of Negative Pressures Generated by Syringes of Different Calibers Used for Liposuction

Sir:FigureThe procedure of “fat grafting” is composed of a series of discrete steps and principles: choice of donor site, harvesting, processing, preparation of the recipient area, and injection techniques.1,2 Each of these steps has an impact on the degree of success of the intended outcome (i.e., fat engraftment). The process of analyzing and optimizing each of these principles individually is called “process engineering.” For the purpose of this Viewpoint, we focused on the harvesting step, specifically, lipoaspiration with the syringe. There are questions about the amount of negative pressure generated by a syringe, which is variable, compared with a vacuum pump that has a constant and measured negative pressure.3 It is believed that small syringes exert less negative pressure than large ones.4 Our intent was to provide a guide to negative pressures generated by syringes of different calibers and with various degrees of pullback on the plunger (a step that is routinely done with minimum control). We evaluated the negative pressures generated by syringes of 1, 3, 6, 12, 30, and 60 ml. Each of these syringes was connected to a vacuum pressure gauge (Compound Meter Fuel pump and vacuum tester; U.S. General, Camarillo, Calif.) by means of a 1-cm noncompliant silicone tube in a closed system (Fig. 1). Negative pressures were measured by pulling the plunger of each syringe at 1-cc intervals. The negative pressures generated correlated directly with the number of cubic centimeters aspirated, independent of syringe caliber. For example, at 1 cc of retraction of the plunger, the pressure recorded was –165 mmHg (–0.21 atm) in all syringes; and at 3 cc of retraction, the pressure recorded was –349 mmHg (–0.45 atm) in all syringes (3, 6, 12, 30, and 60 ml). Furthermore, negative pressures increased rapidly as the plunger was pulled back, reaching –559 mmHg (–0.735 atm) at 10 cc of retraction. Thereafter, the increase was slower and reached a plateau at 30 cc of retraction, approximating –667 mmHg (–0.877 atm). Maximum negative pressure of –718 mmHg (–0.944 atm) was reached with the 60-cc syringe. Thus, a small syringe can generate relatively high negative pressure and a large syringe can generate low negative pressure and vice versa, depending on the volume pulled back by the plunger. We hereby provide a practical, easy-to-follow graph to help surgeons apply the desired negative pressure regardless of syringe used, whether it is used for a small- or large-volume harvest (Fig. 2).Fig. 1: Vacuum pressure gauge used to measure the negative pressure generated in syringes of 3, 6, 12, and 30 cc.Fig. 2: Graph showing the parabolic curve generated by the negative-pressure increase inside a syringe as volume is aspirated by pulling the plunger back, regardless of syringe size.Our findings demonstrate that negative pressure generated by a syringe is determined by the volume or number of cubic centimeters introduced in the syringe by pulling back the plunger. Syringe caliber is a secondary consideration. The pressure increase generated inside the syringe as the plunger is pulled back is not linear but parabolic in accordance with Boyle's law (PV = K), with rapid increases in negative pressure generated initially at low volumes and leveling off after approximately 13 cc of plunger pullback. This study establishes a fact-based guideline for further understanding and engineering the step of syringe lipoaspiration. Ricardo Luis Rodriguez, M.D. Cosmeticsurg Alexandra Condé-Green, M.D. Division of Plastic Surgery, University of Maryland Medical Center, Baltimore, Md. DISCLOSURE The authors have no financial interest to declare in relation to the content of this article. No outside funding was received.