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Page 4 of 10 Zein et al. Plast Aesthet Res 2020;7:44 I http://dx.doi.org/10.20517/2347-9264.2020.133

Principles of safe injection
A safe injection begins with selecting the appropriate needle. We advocate the use of smaller needles such
as 30 G for injecting into the superficial and mid-dermis, and 27 G for deeper injections. Some injectors
recommend the use of large (25 or 22 G) blunt cannulas as they may provide a lower risk of iatrogenic
vessel puncture. After the patient has been properly cleansed and anesthetized, digital pressure can be used
to mark and occlude vessels at anatomic landmarks to prevent inadvertent puncture and back flow [14,15] .
Needles should be introduced perpendicular or parallel to vessels with the tip pointed towards the direction
of arterial flow. If a cannula is being used, it should always be parallel to the vessel. Prior to injecting, the
syringe is gently aspirated to ensure no blood return, though the absence does not guarantee a vessel has
[16]
not been punctured . The product is then introduced at low flow to avoid overcoming mean arterial
pressure should intra-arterial cannulation occur. Keeping the needle in constant motion during injection
will also help prevent product from depositing inside a vessel. If resistance is felt, then the needle should be
repositioned.

As product is injected, the needle tip should be maintained at a depth to minimize contact with any
vessels. The appropriate depth depends on the region being treated. In the glabella the needle tip is kept
either superficially in the dermis or deep to the frontalis muscle to avoid vessels in the subcutaneous
plane. In the temporalis fossa, filler is placed under the temporalis muscle to avoid vessels coursing in the
[17]
temporoparietal fascia . As an alternative, a cannula can be used in more superficial tissues of the temple.
In the tear trough and midface, filler should be placed just above the periosteum with special care medially
where the infraorbital canal is located. If filler is needed medially, it can be injected laterally then massaged
into place.

Safely injecting along the nasolabial groove can be challenging due to the variable course of the facial
artery. In the lower two-thirds, the facial artery generally runs at the muscular plane or deeper. We
therefore advocate keeping the needle tip in the superficial subcutaneous plane in this region and then
moving deeper to the preperiosteal plane near and above the alar base. At the nasal dorsum the vascular
network is located entirely in the subcutaneous plane so injections are kept deep in the preperichondrial
and preperiosteal planes.

Vascular compromise must be treated urgently once recognized. All filler procedures must be performed
with a “filler crash cart” in the immediate vicinity. This kit should contain at minimum 10 vials of
unexpired hyaluronidase (e.g., Hylenex, Halozyme Therapeutics, San Diego, CA; Vitrase, Bausch & Lomb,
Irvine, CA). Other items recommended by many providers include aspirin to prevent clot propagation, and
warm compresses and nitroglycerin to promote vasodilation. A quick referral system for ophthalmic care
should be in place in the event the ophthalmic artery is injured.

Signs and symptoms of vascular injury
Vascular injury can cause a range of complications. Early signs that an artery has been punctured include
the appearance of blood upon aspiration, formation of a hematoma, skin blanching or discoloration,
[18]
and intense pain at the injection site . Should any of these occur, the procedure must be aborted
immediately. If not promptly recognized, continued injection after intra-arterial cannulation can lead to
vascular occlusion resulting in skin necrosis or worse, vision loss. Skin necrosis occurs in < 0.001%-0.5% of
patients but accounts for 43% of serious complications related to soft tissue filler injections in the MAUDE
[19]
database . Early on the skin takes on a blanched then mottled and dusky appearance in the distribution of
the injured vessel [Figure 2]. The surrounding area may also appear erythematous.

Emboli can also travel retrograde up through the ophthalmic artery resulting in ocular complications .
[20]
The first reported case of vision loss due to cosmetic soft tissue filler injection occurred in 1988 and was