Comparison of hyaluronic acid filler ejection pressure with injection force for safe filler injection.

[BACKGROUND] Owing to the increase in the number of medical procedures performed every year, the frequency of filler injection-related complications has also increased. Although slow, gentle injections with low pressure are usually considered to be safe, the differences in ejection pressure during a filler injection remain to be determined. This study aimed to identify the optimal pressure during filler injections and evaluate its capacity to overcome the arterial blood pressure and reflux the filler material.

[METHODS] Twelve combinations of four hyaluronic acid (HA) fillers with different rheological properties and three needles of different diameters were assessed to determine the force exerted by the injection model. The ejection forces corresponding to varying injection forces were measured and HA filler ejection pressures were calculated.

[RESULTS] The highest and lowest injection forces were achieved using 30- and 25-G needles, respectively. In accordance with the expected ejection force, high ejection pressure was achieved by administering the HA filler under a high injection force. Irrespective of the injection force, the ejection pressure was likely to be higher than the vascular pressure at the time of entry into the vessel, rendering the injection dangerous.

[CONCLUSION] During filler injection, penetration of blood vessels and intravascular injection can be avoided by approaching the target area gently using a cannula or needle.