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Injection technique
Almost all of the injections mentioned here, unless specifically stated otherwise, are intramuscular and not subcutaneous. The cosmetic surgeon's experience is based on the initial management of patients with facial dystonia. Such patients suffer from involuntary and irregular contraction of one or several groups of facial muscles, often involving the orbicularis oculi and orbicularis oris.
The impulse, once sparked, is thought to travel from muscle fiber to muscle fiber by the sequential depolarization of adjacent fibers (ephaptic transmission). BTX-A injections are placed in such a way that they achieve the maximum blockage of impulse transmission with the minimum of side effects, by giving BTX-A to muscles along the line of transmission.
The placement of BTX-A around dangerous areas, such as the corner of the mouth where inadvertent diffusion to the levators of the labii superioris will cause drooling, requires careful analysis of the degree of diffusion of the injection by dose and by depth of injection. Intramuscular placement is essential for maximum effect and control, but subcutaneous treatment can be used gently in these areas.
Injection
I recommend using one ml tuberculin or insulin syringes. These are essential for the dose to be gauged accurately during injection. The doses recommended are given in units of volume. The finest mark on a one ml syringe is 0.01: we often recommend using 0.025 ml.
Dosage
The vial can be diluted with preservative-free normal saline to achieve the desired concentration. The doses recommended for cosmetic use have been established independently by several workers over the last six years and,while now based on experience,were initially derived from the doses used for blepharospasm.
Jean and Alastair Carruthers made their original observations about the ability of Botox to smooth rhytids while treating a patient with blepharospasm induced by facial palsy. Blepharospasm due to orbicularis oculi spasm is treated with injections into the muscle above and below the eye. The information leaflet provided with each vial of Botox or Dysport gives the optimal dose recommended to relax each part of the orbicularis muscle.
For blepharospasm,Allergan recommend a dilution of 2.5 ml to give 4 units per 0.1 ml. Dysport recommend a dilution of 2.5 ml to give 20 units per 0.1 ml.
Aspiration
Always use gloves for self protection. The solution should be aspirated freshly for each patient, although some doctors recommend pre-aspiration of botulinum in several one ml syringes, and then storing them in the refrigerator. Manufacturers recommend a single vial per patient which must be used within four hours of reconstitution.
Botulinum toxin is potent and very expensive, so each drop must be used to its maximum effect. Even 0.0125ml is effective in certain sites. Take care to remove the 25-gauge needle from the bottle after aspiration, particularly with Dysport where the combination of a small vial and a viscous solution encourage seepages from the needle.
Once aspiration is complete, attach a 30-gauge needle to the hub of the syringe. Take care that the batches of needles and syringes fit well together, and beware attachments so loose that the toxin dribbles from the hub during injection.
This is wasteful, and may be hazardous if the leaked fluid contacts the patient’s face (ingestion of botulinum toxin droplets have been suspected of causing mild gastroenteritis). Clear the air bubble from the syringe using minimal agitation. This requires more care with Dysport because of its greater viscosity.