Factors influencing pre-injection aspiration for hyaluronic acid fillers: A systematic literature review and meta-analysis.

Pre-injection aspiration of hyaluronic acid filler is a well-recognized yet controversial safety technique. Many consider aspiration to be an important safety measure to prevent inadvertent intravascular filler injection. To assess factors influencing pre-injection aspiration by understanding the relationship between aspiration time and a range of product, needle, and procedural characteristics. We conducted a systematic review and meta-analysis of data, adopting the preferred reporting items for systematic reviews and metaanalyses guidelines. Our literature search identified four articles presenting data on variables associated with aspiration time for different HA filler brands. Statistical models pooling data from the four articles suggest a robust association between aspiration time and a filler's elastic modulus (G'), drop weight (cohesivity), and cross-sectional area of the needle lumen. However, there is insufficient evidence to confirm a robust association between aspiration time and HA concentration, viscous modulus (G″), needle length, and pullback volume. A deeper understanding of the relationship between product, needle, and procedural characteristics, and aspiration time can provide a sound base for discussing the role of pre-injection negative aspiration as a safety measure. The understanding of the effect of various factors on preinjection aspiration would further benefit from studies under clinical conditions.