Aspiration Revisited: Prospective Evaluation of a Physiologically Pressurized Model With Animal Correlation and Broader Applicability to Filler vascular Complications
Editorial Decision date: February 23, 2021; online publish-ahead-of-print Aesthetic Surgery Journal
Background: Aspiration testing before filler injection is controversial. Some believe that aspiration can help prevent in- advertent intravascular injection, whereas others cite false-negative results and question its value given that the needle position always changes somewhat during injection procedures.
Objectives: The authors sought to test the relation of false-negative results to the viscosity of the material within the needle lumen and determine whether a less viscous material within the needle lumen could decrease the incidence of false-negative results.
Methods: In vitro aspiration tests were performed utilizing 30-G and 27-G needle gauges, 2 cross-linked hyaluronic acid fillers, normal saline bags pressurized at 140 and 10 mmHg to mimic human arterial and venous pressures, and 3 needle lumen conditions (normal saline, air, and filler). Testing was repeated 3 times under each study condition (72 tests in total). For in vivo correlation, aspiration tests were performed on femoral arteries and central auricular veins in 3 rabbits (4–5 aspirations per site, 48 tests in total).
Results:In vitro and in vivo testing utilizing 30-G needles containing filler both showed false-negative results on aspiration testing. In vitro and in vivo testing utilizing needles containing saline or air showed positive findings.
Three priming conditions of the needle lumen. (A) Air, (B) normal saline, and (C) hyaluronic acid filler.
Conclusions: False-negative results from aspiration testing may be reduced by pre-filling the needle lumen with saline rather than a filler. This Study used 27 & 30 Gauge Needles only!
Word Of Wisdom
Theoretical facial anatomy accompanied by a negative aspiration offers neither evidence for stationary injection nor further protection against intravascular injection. There is much variability in the facial vasculature both within facial layers and between these layers. An understanding of anatomical vascular patterns at the depth of injection will help substantially, but there are flaws in a total reliance on depth.
A series of articles have led to questioning the value of a negative aspiration as an assurance of safety. In theory, negative aspiration (if it were reliable) should assure the injector that they are not in a vessel and ensure safe injection of the product.
The issues around negative aspiration as a safety maneuver can be summarized as follows:
- Insufficient negative pressure may lead to false-negative aspiration, especially in smaller vessels. The thickness and the G prime of the filler may likewise prevent accurate aspiration. Because there are so many small, low-pressure facial vessels, it is likely that many times the needle will enter one of these, which may result in 3 potential issues.
- Exceptionally quick pullback aspiration will have insufficient pressure to the filler column back into the syringe on aspiration;
- It is possible that a small caliber vessel may collapse under the pressure of an attempted aspiration and reopen when pressure is released, and the injection begun allowing an inadvertent intravascular embolism;
- After a reassuring negative aspiration, subsequent bolus injection may allow retrograde filling of the smaller upstream arteries leading to major vessels. On reaching significant vessels, the downstream flow may block the intricate tributaries producing tissue embolic ischemia. In rare cases, with pressure on the plunger and bolus formation, retrograde flow may progress into the ophthalmic arterial system. On the release of the plunger, this filler column may reverse direction with re-establishment of normal arterial flow, thus affecting all ophthalmic tributaries including the central retinal and ciliary vessels. Maintaining precise hand position is required after negative aspiration because even minor changes can shift needle position to the intravascular plane. This is particularly relevant when aspirating for a prolonged time, and considerable negative pressure is exerted to enhance the possibility of positive aspiration. The aspiration maneuver (0.5 mL vs 0.2 mL of pullback), performed as a single or a double-handed movement, inevitably shifts the instrument such that the tip position at the end of the maneuver is not going to be the same as at initiation. Furthermore, studies conducted in vitro do not take into account movement by the recipient of the injecting interaction. Patient movement, even minute reactive or mimetic actions such as head turning, grimace, flinch or vocalization, will also shift the tissue planes relative to the needle tip. Finally, it is also important to realize that a full 1-mL syringe only allows limited pullback.
- b. Currently, deep injections on bone are considered safer practice in the mid-face, deep pyriform space, and temple because deep injections bypass the middle lamella where mimetic or masticatory muscles and major vessels are found. However, foramina are found in the supraperiosteal plane in the mid-face. Cadaver studies have highlighted the relevance of these issues.
- c. Vertical needle insertion may lead to multiple layer injection, involving more superficial vasculature. Injecting a static bolus after negative aspiration may still cause tissue infarction or fill very small vessels like the supratrochlear artery. In a cadaver study, volumes as low as 0.04 mL (average of 0.085 mL) were sufficient to fill the supratrochlear artery. Given the proximate nature of the supratrochlear artery to the ophthalmic circulation, very little injection volume is required to reach the retinal vessels, making the injection of fillers near these ophthalmic artery branches much more dangerous than the branches of the external carotid arteries in the mid face and lower face d. Although larger bore needles are considered beneficial for decreasing false-negative aspiration, the longer bevel length poses potential problems due to the likelihood of entering multiple layers on vertical injection. This holds true especially for the thin tissues of the nose and forehead and also vulnerable deep vessels such as the temple.
- e. Priming or not priming the needle is also discussed in the literature. It would seem that priming the needle will lead to a more direct transmission of pressure in a hydraulic sense, but not priming removes the need to suck the intraluminal filler back up the needle. This may allow a vacuum to form in the hub, which will fill with blood quickly if a vessel is impaled or transited if negative pressure is transmitted through retraction of the plunger. Relying on an unprimed needle would obligate the injector to withdraw after every single injection point and replace the needle with another unprimed needle. In addition to this impracticality of relying on unprimed needles, if one is committed to this technique, it would tempt the practitioner to concentrate on bolus injection to limit how many needles and injection points were to be utilized. Relying on unprimed needles or newer needles that enable more effective aspiration adds nothing to the validity of the aspiration concept.
- Recommendations for Minimizing the Chance of Embolic Phenomena (After Visual Consensus Paper9 2020)
- Injectors should consider all mechanisms for avoiding intravascular complications.
- The choice of the implanting tool—either needle or cannula—would appear not to guarantee safety.
- It is also important to realize that aspiration may result in a false negative.
Rather than relying on aspiration, avoidance mechanisms such as continuous movement when injecting, slow injection speed, low extrusion force, and small volumes, in conjunction with an in-depth understanding of the safer injection planes pertaining to vascular anatomy, may mitigate intravascular incidents.