After positioning the patient ipsilateral portion of the face to be painted with antiseptic solution carefully , as pain may be triggered by painting. The area is draped with surgical drape.
C-arm positioning should start from AP view then the fluoroscope position will me changed to cranio-caudal direction to get the submental-view. The Fluoroscope to be rotated to ipsilateral direction so that the foramen ovale can be seen in between the maxilla and mandible.
The Surface point that corresponds to the foramen ovale should be determined by putting a opaque pointer. The point of entry usually lies 2-3 cm lateral to angle of mouth. Local anesthesia (1% lignocaine) injected at the entry point.
After the area is anesthetized an 16-gauge intravenous catheter is first inserted followed by the RF cannula 10 cm in length 2-mm or 5-mm RF active tip by needle through needle technique. While introducing the needle, care should be taken so that it should not passes through oral cavity.
Needle is progressed towards the foramen ovale under tunnel view. Intermittent checking under lateral fluoroscopic view is to be done to make sure that the needle direction is towards the junction of clivus and the coincided shadow of petrous part of temporal bone of left and right side in true lateral view of the skull. The needle tip is not visible at the lateral view unless the tip has crossed the junction. And it should be remembered the tip should not cross more than 2mm above the junction. and in most cases the desired sensory and motor stimulation is usually find before that. Once close to the ganglion sensory and motor stimulation checked. Sensory stimulation is usually done at 0.5V and 50Hz, but in some patients we can get stimulation in lower voltage. The area of paresthesia should match with the area of pain for the best results. Motor stimulation is usually done at 2Hz and the voltage is the double of that of motor stimulation to up to 2 volt. Ophthalmic and maxillary do not have motor part so on motor stimulation we will get the contraction of masseter muscle.
After stimulation careful aspiration is done to avoid position in blood vessel.
Once the needle position is confirmed by stimulation 0.2 - 0,5ml of local anesthetic in injected, alternatively sedation can be given, to make the lesioning time pain free.
Usually three conventional RF lesions are done successively at 65, 70 and 75 degree centigrade and for 60-90 seconds.
Case should be taken for ophthalmic division, to not to lesion at high temperature, that may lead to corneal anesthesia leading to exposure keratitis. The needle is taken out post lesioning. The patient is shifted to post procedure care unit. And monitored for vitals, corneal reflex is checked and ice is applied in cheek to avoid hematoma formation.