Reply to Blood Aspiration Test for Cosmetic Fillers to Prevent Accidental Intravascular Injection in the Face

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In reply, first, both tables mention ink aspiration results. The in vivo aspiration test in rabbit ear was a control to see whether positive results with ink in vitro could be replicated in small veins, which require a bigger vacuum for blood withdrawal.
Second I agree that, with blood, it should have been mentioned that needle gauges used were those that gave positive refluxes with ink, that is, in reply, 27-gauge for PLLA (Table 1) and 23-gauge for CaHa (Table 2).
Although human vessels are the ideal control, blood leaving a vessel undergoes immediate changes in viscosity; heparinized blood is also not adequate, as it shows different aspiration from a regular vessel and, in a tube, would have its own vacuum, possibly altering the test. Therefore, ink and rabbit ear were chosen as controls. To clarify, only gauges were altered, not needle length. Brands, also not mentioned, were from BD or Terumo.
Although injection techniques were not discussed, as reported by Carey and Weinkle, only the bolus or mini bolus techniques are available for blood aspiration. For aspiration, slow pulling is safer; however, I have found in human veins that pulling speed is not a factor but waiting will result in proper reflux. The snap technique does not usually work for the products tested, as it can take some seconds for reflux (Tables 1 and 2).1
Not all controlled studies are replicable in clinic, although this was my goal, and all products were tested in my own arm vein beforehand. I also conducted a case series with 5 HA and 1 CaHa products in which patient blood was withdrawn during regular filler application using gauges as recommended by my study,1 with some products having high viscosity. In this same spirit Sykes, 2015 showed high viscosity product reflux,2 despite the negative blood reflux showed in Dr Carey's controlled study.1–3 How could this be explained if the study3 not only was controlled but also used in vivo blood? I am not sure of the intent of your sentence? what was the finding and from what study? This is not clear.
I agree that more work and an aspiration test in patient blood are needed.
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