NASHA™ family

Published on 16/03/2015 by admin

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Last modified 16/03/2015

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3 NASHA™ family

Basic science

HA or hyaluronan is an anionic, hydrophilic, non-sulfated glycosaminoglycan that is abundant in human connective tissue. The chemical structure of this substance is uniform throughout Nature and lacks a protein component allowing it to have little to no potential for immunologic reaction in humans when injected. As one of the chief components of the extracellular matrix, HA stabilizes intercellular structures and forms part of the fluid matrix in which collagen and elastic fibers become embedded. The average 70 kg person has approximately 15 g of hyaluronan in the body, of which one-third is degraded and synthesized daily.

HA contributes to cell proliferation and migration as well as tissue repair. With age, HA concentration in the skin decreases, resulting in reduced dermal hydration, which manifests as an increase in lines and folds. In addition, excessive exposure to ultraviolet B rays causes cells in the dermis to stop producing HA. In its natural form, the half-life of HA is 1–2 days and is metabolized by the liver to carbon dioxide and water. As a compound, it can absorb up to 1000 times its molecular weight in water; its mechanism of action as a filler is mainly through hydration.

The hyaluronic acid molecule is stabilized with cross-linked hydroxyl groups. It is this cross-linking that confers longevity to the product in the skin and the degree of cross-linking one of the distinguishing features of NASHA™ products. Because of this structural matrix, the degradation curve of implanted HA is not linear. Rather, the product retains its effect until the structural complex around the HA molecule is broken down. Once the unbound HA is exposed, efficacy is then lost (Fig. 3.1). As a result, patients will often suddenly notice a change in their appearance rather than experience a gradual loss over time. In addition, patients sometimes feel they look worse after HA injection than they did prior to it; however, this is more of a function of selective memory. This is why taking pre-injection photographs is so important. As with natural hyaluronan, HA fillers can be instantly dissolved with the enzyme, hyaluronidase.

Choosing the right NASHA™

The main difference between commercially available NASHA™ products on the current US market is the viscosity of the product. The higher the concentration of HA, the stiffer is the product and the longer it lasts in tissue (Table 3.1). The larger the particle and the greater the concentration of the filler, the greater the lift you get. It should be noted, however, that not all of the HA in a given filler is cross-linked. Some is free, fragmented or only lightly cross-linked so that the gel can actually flow out of the syringe with ease. As discussed above, the cross-linking is what confers longevity to the product and this does vary between brands. In Restylane® and Juvéderm®, 1,4-butanediol diglycidyl ether is the cross-linking agent, which forms ether linkages in the HA chain. This same type of ether linkage is formed by diglycidyl sulfone found in Prevelle® Silk. In addition to cross-linking, it is worth mentioning that not all HA products are packaged in the fully hydrated state. As mentioned earlier, NASHA™ fillers create volume via hydration and, for this reason, patients will often look better or more filled 24 hours after treatment with products like Restylane® and Juvéderm, which are not completely saturated in the syringe. With that in mind, it is prudent not to overcorrect when using NASHA™ products.

Table 3.1 Hyaluronic acid (HA) concentration of commercially available NASHA™ products

Trade name HA concentration Particle size*
Restylane® 20 mg/mL ~260 µm
Perlane® 20 mg/mL ~1000 µm
Juvéderm® 24 mg/mL 50–500 µm (very cohesive)
Juvéderm® Ultra Plus 24 mg/mL Homogeneous gel
Prevelle® Silk 5.5 mg/mL ~250 µm
Hydrelle® 28 mg/mL Not available
Hylaform® Plus 5.5 mg/mL ~700 µm

* Even very cohesive products are particulate. The particle sizes of commercially available NASHA™ fillers are shown. In comparison, the particulate sizes of non-NASHA™ products are as follows: Radiesse® (25–45 µm), Artefill® (over 30–50 µm), Sculptra® (40–60 µm), Dermalive® (20–120 µm).

Patient evaluation

Prior to injection with any dermal filler, a careful patient history should be obtained. Pertinent items to note in this history include a history of herpes simplex virus, pregnancy or breastfeeding, history of keloid formation, presence of any autoimmune disease, and allergy to lidocaine as most of the fillers now come pre-mixed with lidocaine (Box 3.1). A medication history should include use of multivitamins, fish oil, vitamin E, blood thinners, aspirin, ibuprofen, and Gingko biloba, as all of these can predispose the patient to bruising. Unless medically necessary, the patient should be advised to discontinue these medications 14 days prior to treatment. In addition, alcohol use within 48 hours of injection can cause an increase in bruising tendency.

If the patient has had fillers in the past, it is recommended that the physician document how long ago, where the fillers were placed, and if the patient was satisfied with the results. In addition to history, pre-injection photography is a must. These authors prefer at least three views: frontal, left side at an oblique angle, and right side at an oblique angle. If a patient is having a specific area corrected, a closeup picture of that area is also advisable. Informed consent must be obtained and the patient should be aware of the financial cost of the procedure prior to opening the first syringe. We also advise that baseline facial asymmetry be discussed with the patient and noted in the chart. From a physician standpoint, it is important to inform your malpractice coverage carrier of your intention to use fillers as many uses are considered off-label.