False Sense of Safety: Blunt Cannulas Cause the Majority of Severe Vascular Complications in Hyaluronic Acid Injection.

Abstract

Vascular embolism is perhaps the most severe complication of hyaluronic acid injection.1 To avoid such catastrophic events, blunt cannulas were introduced.2 Theoretically, cannulas are considered safer than needles, as cannula tips are blunt rather than beveled and therefore less likely to penetrate vascular walls. However, as a matter of fact, the majority cases of severe hyaluronic acid–related intravascular events referred to our department were performed with cannulas instead of needles. Over the past 3 years, 28 severe cases of hyaluronic acid embolism were referred to our department (nine cases of unilateral blindness, one case of unilateral blindness with cerebral infraction, and 18 cases of a large area of soft-tissue necrosis). According to patient histories, 25 of 28 patients (89.3 percent) were injected with cannulas (range, 27 to 22 gauge) instead of needles. This finding suggests that the safety of use of cannulas in hyaluronic acid injections may have been overestimated. According to previous studies, thinner cannulas, especially those smaller than 25 gauge, can still punch through vascular walls when enough force is applied.3 Also, some cannula tips are sharper than others with the same gauge because of different designs by varying manufacturers (Fig. 1). Other than their underestimated penetration capability, aspiration can be more difficult with cannulas than with needles. Cannulas used in hyaluronic acid injections are often 40 to 50 mm in length, as sharp needles are usually ½ inch (12.7 mm) in length. This indicates that once hyaluronic acid enters the cannula, higher negative pressure and longer aspiration time would be required for the hyaluronic acid to retreat to the cannula base than in needles. The smoothness of the internal lining of the cannula also impacts the chance of successful aspiration. From the authors’ own experience, and that of many of our colleagues, poorly made cannulas have a rougher internal lining that can prevent successful aspiration, giving the injector the false impression of safety. The viscidity and the particle size of the hyaluronic acid product can affect the aspiration as well.4,5 Products with higher viscidity and larger particle size require a larger bore cannula/needle and a longer aspiration time to achieve successful aspiration. Other than the above factors, the method of aspiration that is used by many injectors nowadays is also questionable. Some injectors do not allow enough time for aspiration when the cannula/filler product requires longer to retreat to the syringe. When injecting with a liner or performing a fanning injection technique with cannulas, many injectors never aspirate or do so only when the cannula reaches the endpoint of the injection path. If a blood vessel is penetrated along the passage, the hyaluronic acid could enter the blood vessel during the retrograde injection at the point of penetration, causing an embolism.Fig. 1.: Varying quality and details of blunt cannulas by different manufacturers. Five cannulas of three sizes (27, 25, and 23 gauge) are shown. Cannulas A and C are made by the same manufacturer, and cannulas B, D, and E are made by another manufacturer. Despite having the same size (cannulas A and B, 27 gauge; and cannulas C and D, 25 gauge), the roundness of the tip shape of the distal openings and the smoothness of their outer coating are different.To avoid hyaluronic acid embolisms, the authors propose the following: (1) injectors should have a solid understanding of anatomy; (2) inject gently and avoid using cannulas smaller than 25 gauge, especially when injecting into high-risk areas such as the periorbital and glabella regions; (3) when using retrograde/fanning injection technique, aspirate and maintain negative pressure on entry all the way to the designated site; (4) use the cannula cautiously in deep layer injections; and (5) inject slowly and closely observe the injection site and the patient. Stop immediately if an embolism is suspected. With these precautions applied, the authors believe that we can lower the possibility of embolism when injecting with cannulas to the minimum. ACKNOWLEDGMENT This research was supported by the National Natural Science Foundation of China (no. 81971848). DISCLOSURE None of the authors has a financial interest in any of the products or devices mentioned in this article.