Aspiration before tissue filling with hyaluronic acid‐safety enhancement by using a lidocaine‐primed syringe

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.

such as bleeding, pain, edema, bruise, pigment, asymmetry, asperity, and infection. These symptoms are not extremely serious and can be controlled easily by observation or supporting treatments. Most of the commonly seen side effects can be healed eventually. The specific side effects of HA includes vessel infarction, nodules, and nerve injury. Vessel infarction is the most severe specific side effect.
Once it has been diagnosed, the infarction needs to be cured immediately. Arteries located in the upper and middle face such as angular artery and lateral nasal artery would converge into the ophthalmic artery. If the fillers like HA, fat, and PLLA were injected into those arteries, the dose would flow along with the vessels causing local red swollenness, pain, and even necrosis and blindness. 2 It is a fatal specific side effect that needs to be carefully considered during the operating process.
The whole injecting process should be handled by operators to decrease the rate of side effects, including prevention, vessel avoidance, early diagnosis, and emergency treatment. Doctors should be familiar with the facial anatomy, the layers where the vessel is located, accurate diagnosis, and treatment of infarction to reduce side effects.
Unlike botulinum toxin solution or other liquid productions for cosmetic use, colloidal HA almost could not be degraded while it was mis-injected into vessels. Although hyaluronidase can be injected to avoid the infarction getting worse, However, an infarction could not be immediately discovered until clinical symptoms being diagnosed.
A severe damage to the body may occur during the time from an embolus happens to its diagnosis, which could be hours to days.
Fortunately, patients suffering from infarction can be cured with an injection or a minor surgery in most cases, which means they do not have to stay in the hospital, but still need to pay a heavy price physically and mentally. Hence, reducing the rate of infarction is also the most significant thing to do during the whole tissue filling process.
When it comes to the safety of injection, most of the studies emphasize facial anatomy or the treatments for infarction. There are only a few studies that have discussed the prevention of operating relatively, such as using a cannula 3 or ultrasound assistance, 4 which aim to prevent the needle from being mis-inserted into vessels. This study was designed for prevention as well. The following content would prove and provide a simple and safe way to avoid infarction effectively, which could enhance the safety during operations.

| ME THODS AND MATERIAL S
Pulling back the plunger of a syringe is a common approach to observe whether blood from the vessel is aspirated into the syringe or not. Such a method is used in intravenous injection, intramuscular injection, tissue filling, etc. Aspiration is the standard of operation that has been taught in medical schools. However, according to our clinical injecting experience of using HA as a tissue filler, there is a probability that no blood return from the syringe while pulling back the plunger with the needle inserted in the vessel. It might cause infarction with a high chance after injecting tissue fillers in this case. This situation, which is defined as false-negative aspiration, is regarded as a serious technical problem from misjudgment.
In our opinion, The better way to avoild false negative is to increase more seconds of the steady aspirating time. The blood would return anyhow in a few seconds in this way. The following experiment is designed to acquire the waiting time of the aspiration. and 30G are recommended, some studies indicated that tiny needles could cause certain influence, such as slowing down the blood flow, and the possibility of intravascular injection, which negates its clinical use. 8,9 Nonetheless, we used those needles in our experiment.

| Different sizes of needles
We aim to distinguish whether there are significant differences in using different-sized needles.

| Different residual dosages of HA
Most of the HA products on the market contain 1 mL, which is not for single disposable use but for multiple uses. Therefore, the residual dosages might differ in every single injection. Five groups were set for the test-0.1, 0.25, 0.5, 0.75, and 1.0 mL. These are considered the five most common volume sets used by clinics according to our study.

| Lidocaine-primed injection
Lidocaine is a liquid that will not mix with colloidal HA. The air running into the needle hub while sucking lidocaine formed a surface to separate lidocaine and HA. Consequently, the syringe contained lidocaine that was placed in the front (needle and needle hub) and HA gel placed at the back (barrel). We put a little lidocaine, approximately 0.05 mL, in the front of the syringe before giving every single injection. After the experiment, the 27G needle and 1.0 mL HA were chosen according to the results of Groups 1 and 2. We are continue using the setting in this group to test whether a immediate blood return occurs during the aspirating time.
Besides the 3 groups of experiments, the theme of artificial vessel is also important to discuss in this artical. The simulated vessel with HA is inserted in vitro. Several kinds of vessel simulators are in use. For instance, the vessel simulator made of silicone is commonly used by medical or nursing students. The biomaterials could be made by 3D printing 10 and the other materials of vessel simulator like PP or nanofiber 11 can be used as well. The current study chose the PP syringe filled up with 3 mL blood from a healthy person.

| PROCEDURE S
1. Before the experiment getting started, 10 mL of blood was drawn from a person with a vacutainer containing sodium citrate.

| Standardized force and speed of aspiration
The force was quantified by the volume mark (0.1 mL) on the barrel.
There are two reasons of choosing 0.1ml as the expiriment force.
First, it is similar to clinical trials. Second, there is no space for forces bigger than 0.1ml in a standard HA syringe. 12 Operators usually pull back the plunger with two fingers (index and middle finger or thumb and ring finger). The speed of aspiration is considered with the natural position of holding syringe. The process can be finished in 1 s in most of the aspirations.

| Blood sample
Blood was drawn by a registered nurse 10 min before the experiment started. Blood was sourced from the author himself who was healthy.

| DISCUSS ION
Ten milliliters of blood from a healthy person was drawn and collected in tubes containing sodium citrate. Sodium citrate was added to prevent blood solidification during 3 h of the experiment and to not influence the test results.

| Steady force
Steady force was used for reducing the testing deviation. The force was usually quantified by the volume mark on the barrel, which is 0.1 mL according to previous research. The steady force could be 0.1, 0.2, or even 0.5 mL. 12 We chose 0.1 mL as it is more practical and there is no space for additional force in a syringe that contained more than 0.1 mL of HA.

| Blood return
Blood return is determined according to the color changing in the front end of the HA syringe observed by naked eyes. Since the blood is red, the semitransparent HA gel became turbid after the draw with a color of light red. This happened instantly when blood returned.
The calculator stopped with the release of the plunger after blood returned. The time was measured as a single record. The front end of the HA dyed red need to be removed in order to do the next test under the same condition. The dyed part of HA gel should also F I G U R E 2 Group 1: Different-sized needles used in syringes.

F I G U R E 4 Group 3:
The lidocaine-primed HA syringe after air extraction. The mark-print part of the barrel is HA while the front of it is full of lidocaine. be pushed out; the syringe was then filled with 1.0 mL of fresh HA gel. Since some of the blood in the vessel simulator was sucked into the HA syringe, it needs to be replenished to 3 mL as well for reducing experimental deviation.
We analyzed the data with SPSS one-way ANOVA to test whether the average values of each group are different or not in Group 1. The results (p = 0.837) indicated no obvious difference between each group. In addition, since 88% of the false-negative aspiration happened within 10 s in our study, we suggest that the operators wait for at least 10 s during aspiration to avoid false-negative aspiration.
In Group 2 we used the commonly used 27G needle. Group  No single blood return happened instantly among the 270 tests.
Waiting for several seconds was a must for a blood return in all of the tests. The waiting time even lasted over 10 s in the 33 tests out of 270 (approximately 12%). However, the remaining 88% tests had a blood return within 10 s, especially those between 0 and 5 s had occurred 199 times (74%).
As for the 0.1 mL group, the blood returned instantly, which was too fast to measure in all of the tests. With the special result of this minor group, we decided to do two more experiments to doublecheck the results. The first experiment included 20 times of tests and the second included 10 times of tests in the same conditions additionally. The results showed that the blood returned immediately in all of the tests. We analyzed the data of 30, 20, and 10 experiments in the 0.1 mL group with the chi-squared test (p = 0.355). There was no obvious difference in this group, which means the blood would return immediately with 0.1 mL left only in a HA syringe. Hence, we inferred that while HA is less than 0.1 mL, blood return would occur instantly. We suggest that if the residual dosage is less than 0.1 mL during the treatment, the operators would only need to pull back the plunger to see if the blood is coming out or not, and do not have to wait for a few seconds to avoid false-negative aspiration.
Nonetheless, there were still two times of false-negative aspirations.
The reason is that the 27G needle had been used too many times before the test for this group, which could possibly cause some flaws. The reason why blood can be sucked into a lidocaine-primed HA syringe immediately is that We believe that since blood and lidocaine are liquid-liked, the surface tension is too small to avoid mixing. Moreover, lidocaine is used as a local anesthetic in surgery. As a liquid, lidocaine is better than saline or sterile distilled water for its remarkable anesthetic effect that comforts patients during the operation. The other advantage of lidocaine is that it is effective at a slight dosage that does not affect the therapeutic HA filling.
There are differences between the HA syringe this study mentioned and other products of HA which includes lidocaine. The latter was a complete mix with HA and lidocaine, which means the syringe is much easier to become fully red while the blood return occurs.
This result is different from ours which has a limited reddish only at the very front of the syringe. Unfortunately, there is no conclusion on evidence-based medicine so far. However, the concern can be ignored by placing lidocaine in the needle hub part of the syringe as this study showed.

| CON CLUS ION
According to the injecting situations of different operators or medical institutions, all medical tools and materials differ from the sizes of the needle, the residual dosages, the force of aspiration, the brands of HA, and even the types of HA filler. It is nearly impossible to standardize the whole operation, the tools and materials. Therefore, we suggest doing aspiration as a must no matter which equipment is used. Aspiration should be considered as a regular procedure before giving an injection. Preventing infarction with a simple action is not only a huge benefit to patients but operators.
We tested many different sizes of needles and different resid-

FU N D I N G I N FO R M ATI O N
This research received no external funding.

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation F I G U R E 6 Lidocaine was sucked into the front end of the HA syringe.
C H A R T 1 Pie chart of results in Groups 1 and 2.

12%
The distribution of time waiting of aspiration 0-5s 5-10s 10s and above of data; in the writing of the manuscript; or in the decision to publish the results.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.

E TH I C S S TATEM ENT
This study on humans (individuals, samples, and data) was performed in accordance with the principles stated in the Declaration of Helsinki. Ethical approval was obtained for all protocols from the local Institutional Review Board (IRB) from Changhua Christian Hospital to confirm the study meets national and international guidelines for research on humans (CCH IRB No. 220716).