Anesthesia for Ear Surgery

EAR SURGERY

Frequently performed ear surgeries include sta-pedectomy or stapedotomy, tympanoplasty, and mastoidectomy. Myringotomy with insertion of tympanostomy tubes is the most common pediatric surgical procedure.

Intraoperative Management

A. Nitrous Oxide

Nitrous oxide is not often used in anesthesia for ear surgery. Because nitrous oxide is more soluble than nitrogen in blood, it diffuses into air-containing cavities more rapidly than nitrogen (the major com-ponent of air) can be absorbed by the bloodstream . Normally, changes in middle ear pressures caused by nitrous oxide are well tolerated as a result of passive venting through the eustachian tube. However, patients with a history of chronic ear problems (eg, otitis media, sinusitis) often suffer from obstructed eustachian tubes and may, on rare occasion, experience hearing loss or tympanic mem-brane rupture from administration of nitrous oxide anesthesia.

During tympanoplasty, the middle ear is open to the atmosphere, and there is no pressure build-up. Once the surgeon has placed a tympanic membrane graft, the middle ear becomes a closed space. If nitrous oxide is allowed to diffuse into this space, middle ear pressure will rise, and the graft may be displaced. Conversely, discontinuing nitrous oxide after graft placement will create a negative middle ear pressure that could also cause graft dislodgment. Therefore,  nitrous  oxide  is  either  entirely avoided during tympanoplasty or discontinued prior to graft placement. Obviously, the exact amount of time required to wash out the nitrous oxide depends on many factors, including alveolar ven-tilation and fresh gas flows , but15–30 min is usually recommended.

B. Hemostasis

As with any form of microsurgery, even small amounts of blood can obscure the operating field. Techniques to minimize blood loss during ear sur-gery include mild (15°) head elevation, infiltration or topical application of epinephrine (1:50,000– 1:200,000), and moderate controlled hypotension. Because coughing on the endotracheal tube during emergence (particularly during head bandaging) will increase venous pressure and may cause bleed-ing (as well as increased middle ear pressure), deep extubation is often utilized.

C. Facial Nerve Identification

Preservation of the facial nerve is an important consideration during some types of ear surgery (eg, resection of a glomus tumor or acoustic neuroma). During these cases, intraoperative paralysis with NMBs may confuse the interpretation of facial nerve stimulation and should not be used unless requested by the surgeon.

D. Postoperative Vertigo, Nausea and Vomiting

Because the inner ear is intimately involved with the sense of balance, ear surgery may cause postopera-tive dizziness (vertigo) and postoperative nausea and vomiting (PONV). Induction and maintenance with propofol have been shown to decrease PONV in patients undergoing middle ear surgery. Prophylaxis with decadron prior to induction, and a 5-HT ₃ blocker prior to emergence, should be considered. Patients undergoing ear surgery should be carefully assessed for vertigo postoperatively in order to mini-mize the risk of falling during ambulation secondary to an unsteady gait.

Oral Surgical Procedures

Most minor oral surgical procedures are performed in a clinic or office setting utilizing local anesthesia,augmented with varying degrees of oral or intrave-nous sedation. If intravenous sedation is employed, or if the procedure is complex, a qualified anesthesia provider should be present. Typically, a bite block and an oropharyngeal throat pack protect the airway. For light to moderate levels of sedation, the oropha-ryngeal pack prevents irrigating fluids and dental fragments from entering the airway. Deep sedation and general anesthesia require an increased level of airway control by the anesthesia provider. Regardless of whether deep sedation or general anesthesia is inadvertent or intended, appropriate equipment, supplies, and medications must be immediately available to help insure that any anticipated or unex-pected anesthesia-related problem occurring in an office or clinic setting can be safely addressed with the same standard of care that is required in the hos-pital or ambulatory surgery center.

Minor oral surgical procedures, such as exodon-tias, typically last no more than 1 hr. The surgical field is amenable to a nerve block or infiltration by a local anesthetic. In adults, most oral surgeons use 2% lidocaine with 1/100,000 epinephrine or 0.5% bupivacaine with 1/200,000 epinephrine in quanti-ties no greater than 12 mL and 8 mL, respectively. The anesthesia provider must be informed by the surgeon of the local anesthetic used and its con-centration and volume injected so that the allowed dosage based on weight is not exceeded. Pediatric patients, in particular, are at risk of local anesthesia toxicity due to an actual overdose or an accidental intravascular injection.

Intravenous sedation during oral surgical procedures greatly increases the patient’s com-fort and facilitates surgery. A combination of fen-tanyl (1–3 mcg/kg) and midazolam (20–50 mcg/ kg) is usually adequate prior to injection of the local anesthetic. The sedation can be further aug-mented by additional small dosages of fentanyl, midazolam, or propofol. Propofol (20–30 mg is a typical incremental dose for an adult) is a good standby drug, if the surgeon requires a brief epi-sode of unconsciousness.less than ideal airway, or extent of contemplated sur-gical procedure, it is safer to perform the procedure in a hospital or ambulatory surgery center setting with general endotracheal anesthesia.