Use of local anesthesia in middle ear surgeries:
2% xylocaine with 1:20,000 adrenaline is used for infiltration. The total dose of local anesthetic used should not exceed 7mg/kg body weight. 12 – 15 ml of the drug is used. The local anesthetic solution is prepared by adding 1 mg of adrenaline to 20 ml of 2% xylocaine. In pateints with pre-existing cardiac disorders the dose of adrenaline can be reduced.
Local anesthetic solution should be strictly injected extravascularly. This can be ensured by withdrawing the piston of the syringe to ensure that there is no blood flow into the syringe before infiltration. If there is blood flow into the syringe on withdrawing the piston of the syringe then it means that the needle is within a blood vessel. Post injection massage should be avoided at all costs as the drug could permeate to other areas there by reducing its local anesthetic effect to the surgical field. The preparation and administration of the local anesthetic should be performed by the operating surgeon in order to avoid complications.
Local anesthetic technique for ear surgeries:
Injection should be administered around 12 points.
1. 3-5 ml of local anesthetic solution is injected into the post auricular region
2. The needle is advanced anteriorly through the same point of entry to get under the concha and 0.5 ml of the solution is injected to cover the posterior, superior and inferior meatal walls
3. About 0.5 ml of the solution is injected in the front of the helix crus to block the auriculo temporal nerve and then at the site of the endaural incision at the incisura and the medial surface of tragus. Medial surface of tragus is infiltrated in order to reduce pain and discomfort when retractor is placed in this area. It also helps during harvest of tragal cartilage graft.
4. The external auditory canal is straightend using an aural speculum and 0.5 ml of anesthetic solution is infiltrated in the skin lining the bony portion of external auditory canal in the superior, anterior, posterior and inferior (at 12 o clock, 3 0 clock, 6 o clock and 9 o clock postions). Ideally the needle is introduced into the skin lining of the cartilaginous portion of the external canal, and then proceeded subcutaneouly until the bony meatus is reached. Half ml of the anesthetic solution is infiltrated here. This area is preferred because the skin lining is thicker in this area than the skin lining the bony portion of the canal.
5. The middle ear mucosa is anesthetized by trickling of the anesthetic solution through the ear drum perforation. In case of intact ear drum then the solution should be instilled into the middle ear cavity as soon as the annulus is elevated.
Pulse and blood pressure of the patient should be monitored during the entire process of infiltration.