This is the most critical step of CAS procedure and it requires careful attention because  at this stage embolic events are most likely to develop.
Post-dilation must be performed using low-profile balloon catheters on a 0.014" platform in a rapid exchange system.
Balloon diameter ranges from 5 to 6 mm according to the arterial and stent diameters with a length of 2 cm.
Dilation must be performed only inside the stent to avoid arterial wall damages (dissection, spasm).
The risk of embolization is correlated with the fact that while the stent is being dilated, the plaque suffers a squeeze, can slide beyond the stent meshes and migrate into the intra-cerebral circle.
As the final goal of the procedure is exclusively technical aiming at an increase of the blood flow, balloons with a too big calibre (> 6mm) should be excluded. Technical success is achieved when a residual stenosis <30% can be observed.
In case of ulcerated lesions no matter if the ulcer is still evident at the end of the dilation because having the stent excluded the blood flow, the ulcer too will be excluded within 48 hours.
It is very important to perform a rapid inflation and deflation of the balloon because many patients are unable to compensate as a consequence of controlateral carotid stenosis, occlusion or alteration of the Circle of Willis.
Balloon dilation must be performed using an inflator device so as to control the dilation pressure and consequently the balloon calibre.
Before balloon dilation, 1mg of Atropine must be administered to the patient in order to reduce bradycardia and hypotension correlated to the stimulation of the carotid baroceptors (carotid sinus reflex). Fig.1
Post-dilation should be performed in all cases except when using nitinol stents because Nitinol is a thermo sensitive material and nitinol stents undergo a steady and progressive dilation being influenced by the heat of the human body.
When the percentage of residual stenosis, after positioning a nitinol stent, is <30%, stent post-dilation can be avoided. Thus the most critical moment of the procedure is by-passed reducing the risk of ischemic and neurological complications.
Also the danger of hypotension and bradycardia due to the stimulation of the carotid baroceptors is excluded.

Technical Note:

- only a single dilation is suggested because if more than one dilation is performed a higher incidence of neurological complications has been observed.

- Before performing dilation, a complete aspiration of air bubbles from the interior of the balloon is recommended to avoid air-embolic complications  in case of balloon rupture.

- After balloon dilation and before removing the cerebral protection device, an angiogram should always be performed in order to flush the inner portion of the stent where some plaque materials may have protruded after dilation causing debris dislodgement into the brain.

References