There has been an on-going debate whether it is worth aspirating when injecting dermal fillers but the question is should you do it? One of our students recently had a positive aspirate in the training clinic and so it sparked the question.
To get to the bottom of this we should look at this in a logical way to try and come to a conclusion.
Aspiration is the drawing back of the plunger prior to injecting. If the needle tip is not within a blood vessel then you will get a negative aspiration (i.e. no evidence of blood in the needle hub/syringe) and it would be deemed more safe to inject. The converse would apply if the needle tip was within a blood vessel. In these cases you would not inject, reposition and therefore possibly prevent a vascular occlusion.
When put like this it would seem absolutely appropriate to aspirate before every injection but we need to make one BIG assumption regarding the way we administer and this is that the needle will not move when injecting the filler. As soon as a needle has moved there is a possibility that it has entered a blood vessel. If you look at the diagram above - at position 1 there will be a negative aspiration but if the needle inadvertently moved slightly to position 2 the needle tip would be intravascular and if the filler were to be injected there would be a risk of vascular occlusion. For this reason aspiration is only appropriate as a safety measure if placing a bolus injection because if you were placing a linear thread or using a fanning technique the tip of the needle would be moving. Furthermore when placing the bolus you would need confidence that the needle tip has stayed exactly where it was from beginning or aspiration to end of aspiration and had not moved after aspirating when depositing the filler.
When put like this you now may start to question the reason why you aspirate. Aspiration does not guarantee you will prevent a vascular occlusion but what it does is it may reduce the risk of one. When injecting dermal fillers there is no way you can guarantee prevention of a vascular compromise but instead there was lots of ways to try and reduce the chance of one (aspiration being one of these). These also include:
Try to keep the needle moving. By doing this if a needle has transverse a blood vessel, it will not be in the vessel very long and so the amount of filler introduced into the vessel will be very little and may be small enough to dissipate harmlessly into the circulation (NOTE: think about when a patient bleeds profusely after a linear thread of dermal filler. It is highly likely that the needle has transversed a blood vessel and so filler would have been introduced but as it would have been such a small amount it is less likely to be as serious than if more had been injected into the vessel). But as discussed before if you keep the needle moving then clearly aspirating has limited value.
Try and avoid bolus injections because if you are in a blood vessel then a lot of filler will be introduced and is much more likely to lead to a vascular occlusion. When you cannot avoid a bolus it would be wise to aspirate despite the limitations (i.e. regarding the possible movement of the needle tip). Make sure you aspirate for 5-10 seconds otherwise there will be more false negatives.
Understand your anatomy well. By using facial landmarks to help appreciate where major blood vessels may lie along with an appreciation of how deep these vessels lie will again help reduce risk. Clearly there may be anatomical variations and other vasculature present and so this alone cannot be relied on for safety.
Inject very slowly
Consider cannulas. Tips of cannulas are blunt ended and so are less likely to perforate a blood vessel than a needle but this is not to say that you cannot actually cannulate a blood vessel and cause a large vascular occlusion. For this reason it is best to use cannulas that are 25G or thicker. Cannulas are not safe for nasal injections.
Consider directing the needle/cannular perpendicular to the major blood vessels in the area to avoid the risk of cannulating them.
By doing all of the above you are less likely to cause an occlusion than if you opt not to do them. That means, on average, after a career of injecting you would have reduced the number of vascular occlusions.
So, when considering aspiration as a technique you cannot rely on it solely and in reality, as discussed above, is only potentially effective in limited scenarios. Although it can be of limited benefit it can slightly chip away at the risk of a vascular occlusion and so it would still be recommended by many.
We hope this helps but if you have any more questions please do not hesitate to contact us here.