Anaesthesia for ear surgery
*notes taken from local master student program
Overview
• Frequently performed ear surgeries include stapedectomy (usually under local anesthesia), tympanoplasty, and mastoidectomy.
• Myringotomy with insertion of tympanostomy tubes is the most common pediatric surgical procedure and is discussed in Chapter 44.
Intraoperative Management
Nitrous Oxide
• Because nitrous oxide is more soluble than nitrogen in blood, it diffuses into air-containing cavities more rapidly than nitrogen (the major component of air) can be absorbed by the bloodstream (see Chapter 7).
• Normally, changes in middle ear pressures caused by nitrous oxide are well tolerated as a result of passive venting through the eustachian tube.
• Patients with a history of chronic ear problems (eg, otitis media, sinusitis), however, often suffer from obstructed eustachian tubes and may rarely experience hearing loss or tympanic membrane rupture during 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 ventilation and fresh gas flows (see Chapter 7), but 15–30 min is usually recommended.
Hemostasis
• As with any form of microsurgery, even small amounts of blood can obscure the operating field.
• Techniques to minimize blood loss during ear surgery include mild (15°) head elevation, infiltration or topical application of epinephrine (1:50,000–1:200,000), and controlled hypotension.
• The use of controlled hypotension in ear surgery is somewhat controversial because of its inherent risks and questionable necessity.
• Because coughing on an tracheal tube during awakening (particularly during head bandaging) will increase venous pressure and may cause bleeding, a deep extubation may prove helpful.
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 NMBAs may confuse the interpretation of facial nerve stimulation and should be avoided.
Postoperative Nausea and Vomiting
• Because the inner ear is intimately involved with the sense of balance, ear surgery may cause postoperative dizziness (vertigo), nausea, and vomiting.
• Induction and maintenance with propofol have been shown to decrease postoperative nausea and vomiting in patients undergoing middle ear surgery.
• Prophylaxis with decadron prior to induction, with administration of a 5-HT3 blocker prior to emergence, should be considered.
Overview
• Frequently performed ear surgeries include stapedectomy (usually under local anesthesia), tympanoplasty, and mastoidectomy.
• Myringotomy with insertion of tympanostomy tubes is the most common pediatric surgical procedure and is discussed in Chapter 44.
Intraoperative Management
Nitrous Oxide
• Because nitrous oxide is more soluble than nitrogen in blood, it diffuses into air-containing cavities more rapidly than nitrogen (the major component of air) can be absorbed by the bloodstream (see Chapter 7).
• Normally, changes in middle ear pressures caused by nitrous oxide are well tolerated as a result of passive venting through the eustachian tube.
• Patients with a history of chronic ear problems (eg, otitis media, sinusitis), however, often suffer from obstructed eustachian tubes and may rarely experience hearing loss or tympanic membrane rupture during 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 ventilation and fresh gas flows (see Chapter 7), but 15–30 min is usually recommended.
Hemostasis
• As with any form of microsurgery, even small amounts of blood can obscure the operating field.
• Techniques to minimize blood loss during ear surgery include mild (15°) head elevation, infiltration or topical application of epinephrine (1:50,000–1:200,000), and controlled hypotension.
• The use of controlled hypotension in ear surgery is somewhat controversial because of its inherent risks and questionable necessity.
• Because coughing on an tracheal tube during awakening (particularly during head bandaging) will increase venous pressure and may cause bleeding, a deep extubation may prove helpful.
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 NMBAs may confuse the interpretation of facial nerve stimulation and should be avoided.
Postoperative Nausea and Vomiting
• Because the inner ear is intimately involved with the sense of balance, ear surgery may cause postoperative dizziness (vertigo), nausea, and vomiting.
• Induction and maintenance with propofol have been shown to decrease postoperative nausea and vomiting in patients undergoing middle ear surgery.
• Prophylaxis with decadron prior to induction, with administration of a 5-HT3 blocker prior to emergence, should be considered.
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