Aspiration: Is It Really the Last Word in Safety?

As practitioners of aesthetic medicine, we are always thinking about safety, especially about how we can best avoid ischemia and necrosis. Our understanding is that an ischemic event usually happens because a bolus of filler gets inside an artery. The exception is in the tip of the nose, where ischemia can happen because of compression. The nasal tip is an area of limited blood supply and space, so too much filler there can cause a compartment-like effect. For the most part, however, ischemia is an embolic event.

The usual model of ischemia is that a large intravascular plug travels intact downstream in an artery and obstructs a major branch, leading to a sudden halt in blood supply to the angiosome of that branch. Whether this truly is the primary mechanism of ischemic adverse events, however, is controversial. During surgery, we sacrifice arterial branches in the face routinely without ischemic consequences because large branches have so many collateral branches that take over blood supply if the branch is ligated. It seems likely that, in many situations, an intra-arterial bolus of filler fractures immediately upon hitting the bloodstream, under the shear forces of systolic blood pressure, and a shower of particles travels downstream to obstruct blood flow at the level of the smallest branches and capillaries.

Within this shower of particles scenario, when a sufficient quantity of particles is generated, this can obstruct a critical mass of capillaries within that vessel branch’s angiosome. The bigger the bolus, the more particles come through and more capillaries are obstructed. Unlike larger branches, terminal arterioles and capillaries have no collaterals, so an obstruction at this level misses out on the abundant collateral supply of larger branches in the face.

The other contributing factor to ischemic adverse events is vasospasm. Hyaluronic acid is quite irritating to arteries. The presence of filler inside the lumen results in significant vasospasm, limiting the delivery of blood to the tissues that the affected vessel supplies.

Blindness is, of course, the most frightening of the possible ischemic complications. There is some controversy over the exact mechanism, but the currently accepted most likely scenario is that a large bolus of filler is forced backward in an artery that connects to a branch of the ophthalmic artery. The bolus is propelled with enough force to travel retrograde down the ophthalmic branch (supratrochlear, supraorbital or dorsal nasal arteries) and into the central retinal artery. Another possible mechanism is that of filler traveling through arterio-venous shunt malformations to get to the retinal artery. Better modeling of embolic blindness needs to be developed in the laboratory to really understand how this rare event takes place.

When industry experts talk about preventing complications, they primarily discuss avoiding intravascular injection. A vascular map of the face shows why I believe this is not easy to do (Figure 1). Due to the extensive vascularity of the face, it is difficult to avoid vessel penetration. At some point we will probably be injecting with “smart” needles that will give us feedback when the tip is inside a vessel lumen. Ultrasound guided injections are also a possibility, but the current state of technology (image resolution and device ergonomics) makes routine performance of ultrasound guided injection difficult for most practitioners. I believe that, for now, we must accept that we are essentially injecting blind, but it seems that I am in the minority.

Figure 1. A vascular map of the face shows the challenge involved in avoiding intravascular injection.

In their desire to avoid vessel cannulation, many injectors believe that pre-injection aspiration is an effective way to know whether the tip of their needle is inside an artery. Many studies acknowledge that the technique is not reliable, but it is still widely recommended. I believe this recommendation to be a mistake.

Aspiration typically involves three steps: positioning the needle, pulling back the plunger for a few seconds, and then repositioning the hand to inject. Any movement during this process, which is nearly inevitable given the effort needed to aspirate thicker fillers, makes a negative result unreliable, giving a dangerously false sense of safety to the injector.

There is little solid evidence suggesting that aspiration can prevent complications like blindness or tissue necrosis. Although anecdotal reports from training sessions often claim that positive aspiration tests have helped avoid such outcomes, these stories are not supported by actual data. While aspiration is considered highly sensitive (i.e., if positive the tip of the needle is definitely inside a blood vessel), its specificity (i.e., the reliability of a negative test) is quite low, especially because the process requires the injector to keep the needle perfectly still—something that is very difficult to do when applying force during aspiration. Although this method might work in areas with larger blood vessels, like the gluteal region, facial vessels are much smaller, and even the slightest movement can change whether the needle is inside or outside a key artery. Therefore, even a positive aspiration test may not be truly reliable, since the site of aspiration and the site of injection are not exactly the same. Placing the needle on bone can improve stability and many advocates of aspiration recommend injecting only on bone where there is less chance of movement. The trouble with this recommendation is that there are several common injection areas without bony support, like the lips and the soft cheeks. Also, there are areas like the glabella and the antegonial notch where large vessels are located on top of the bone, making injection at that depth unsafe.

I believe that a better approach is to continuously move the needle during the injection process. This technique, combined with slow and low-pressure injections using fine needles, can significantly reduce the risks. Delivering small amounts of filler at low pressure makes it less likely that filler will reach the central retinal artery, reducing the chance of blindness. Additionally, small injections (0.1cc or less) lower the risk of filling larger arteries and obstructing blood flow to critical areas.

Many discussions about aspiration focus on the mechanics of how fillers flow through needles, often recommending larger needles to improve aspiration accuracy. However, using larger needles poses its own risks – it is much easier to accidentally inject a large amount of filler, increasing the chance of complications like blindness or necrosis.

The other advantage to moving the needle retrograde in a column is that it permits the injector to deposit product in more than one plane, improving tissue lift capability and permitting elevation of tissue with minimal lateral spread of product. This is critical to creating the kind of precise, defined contours that we need for exceptional non-surgical facial sculpting.

It is promising that the aesthetic literature is beginning to advocate against the routine use of aspiration. This shift in thinking is important, as patient safety must always be based on sound scientific evidence. So far, the evidence supporting aspiration simply isn’t strong enough.

Some practitioners take the approach that aspiration can’t hurt. I disagree. If you aspirate, you can’t move and vice versa. Logically, you have to choose one or the other.

New techniques, such as ultrasound guided injection, may one day improve injection safety, but further research and better ultrasound technology are needed before this becomes universally embraced. The future may lie in more advanced tools, such as smart needles that provide real-time feedback on needle positioning. These technologies have the potential to revolutionize injection safety, but it’s essential that future advancements remain firmly grounded in science.