Embolism due to accidental intra-arterial injection of a soft tissue filler (STF) can lead to serious complications. Physicians practice aspiration as a safety test before injection to rule out intra-arterial placement of the needle tip. The value of aspiration as a safety test is evaluated in this study, which also considered the rheological properties of different STFs and their needle dimensions.

Aspiration with eleven different needle sizes and 24 different STFs was performed using Ringer's lactate (RL) colored with blue skin marking ink and secondly an empty saline bag containing anticoagulated blood, both pressurised to 150 mm Hg to mimic arterial blood pressure. Time between the start of aspiration and liquid in the needle hub was recorded.

A total of 340 individual aspiration tests with different STFs and needles were performed, of which 112 yielded true-positive results within 1-s and 128 yielded false-negative results after 10 s. Positive results between one and ten seconds were seen in 101 aspiration tests.

True-positive results were seen in 33% of the tests performed with STFs within 1 s of aspiration. Aspiration test results are influenced by needle diameter, needle length, and rheological properties of STFs. Additional safety measures are necessary to further reduce risk of inadvertent intravascular injection of STFs.