RESUMO
OBJECTIVE: Most of the doctors would regularly aspirate the plunger of a syringe before injection to make sure that the needle would not be mis-inserted into vessels. Yet pulling the plunger back only cannot guarantee the injecting status is safe. Injecting all of the non-fluid fillers, including colloidal hyaluronic acid (HA) into the vessel may cause "No blood return while pulling back the plunger," which is defined as false-negative aspiration. METHODS: In the first experiment, HA syringes were inserted into vessel simulators in vitro with standard needle sizes and residual dosages. In the second experiment, the lidocaine-primed syringe were inserted into the vessel simulator instead to observe its aspiration. RESULTS: There was no difference using different sizes of needles or dosages except for group 0.1 mL and the lidocaine-primed syringe. The rest of the groups need to wait more seconds to observe the blood return. CONCLUSIONS: The time lag does exist in every single aspiration and 88% of the blood return would happen in 10 s. We suggested that operators should aspirate regularly before giving an injection with at least 10 s of waiting or use the lidocaine-primed syringe instead. Blood returns could mostly be recognized in both ways.
