The process of liposuction involves some intuitive and some non-intuitive features. While a negative pressure gradient or suction Is fundamental to this process, there are some concepts that merit further understanding. Suction is necessary but not sufficient for the process. A mechanical abrasive effort Is required to establish the flow of fat. This technique is described as either shaving or rasping and figures prominently in the design of liposuction cannulas. The disruptive energy is either delivered through mechanical oscillation of the cannula tip or the delivery of acoustic energy that results in the destruction and elaboration of the fat.
While formal analysis of the components of liposuction could be evaluated by classical physics, the discussion rapidly becomes esoteric and lacks clinical relevance. Some very important conclusions can be made with respect to cannula characteristics, tissue characteristics, and the tumescent anesthetic milieu.
The features of cannula design are based on a fundamental principle borrowed from fluid dynamics: Poiseuille’s Law. This pillar of fluid science is loosely applied to our clinical situation as fat far from an ideal fluid. However, the fact that the flow of fat through a cannula and tubing arrangement is proportional to the fourth power of the diameter of the conduit and inversely related to its length, is clinically useful. Also, the number of ports or holes in the cannula is important. It has been observed that the number of entry sites in the tip of the cannula is of greater significance than the aggregate surface area available for aspiration. A short thick cannula with more ports is more efficient than a narrow long cannula with fewer ports. It is reasonable to discuss the pressure gradient at this time. In a general sense, the suction gradient established for liposuction is the difference between the ambient air pressure and the vacuum created by the pump. While we can’t realistically alter our ambient pressure, except by varying altitude, we can adjust the pump. In most centers, this is approximately 1atm of vacuum.
Tissue characteristics are also pertinent to the conversation. Resistance to flow has ethnic variances which manifest as the density of investing fibrostroma. This reality can be substantial clinically. Also, within an individual regional anatomic variation exists. The tissues of the thorax tend to be more fibrous and stubborn for aspiration than the abdomen. Any prior surgery, liposuction or percutaneous cryosurgery efforts will noticeably augment resistance to aspiration.
The tumescent milieu also mechanically affects aspiration efforts. The injected fluid (anesthetic, vasoconstricting agent, diluent carrier) serves to equilibrate and stabilize the tissue with an elevated interstitial (tissue) pressure. This stabilizes the fat tissue for more effective mechanical disruption. It also serves as an acoustic medium for disruptive energy (ultrasound). Another important physical concept is that of viscosity. Viscosity is a fluid’s intrinsic resistance to flow or movement. When a mixture of fluid and fat is created and mixed (homogenized), the resultant mixture approximates the fluid characteristics of the proportional constituents. The fat(non-fluid) mixture flows more like water(fluid) and extraction becomes more expeditious.
While all these factors deserve a great deal more discussion for intellectual and professional mastery, the above serves as a simple basis in answering, “how does liposuction work”?
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