EAR

Anesthesia for Otologic Surgery

Presented by: Elisha Coppens DNAP, Mpharm, CRNA, CHSE, COI

Anatomy of the Ear

  • Outer Ear:

    • External auditory canal

  • Middle Ear:

    • 1. Eardrum

    • 2. Malleus

    • 3. Incus

    • 4. Stapes

    • 5. Semicircular canals

    • 6. Auditory nerve

    • 7. Facial Nerve

    • 8. Vestibular nerve

    • 9. Cochlea

    • Cochlea - The spiral-shaped organ in the inner ear responsible for converting sound vibrations into neural signals.

    1. Eustachian tube

  • Inner Ear

Innervation of the Ear

  • Facial Nerve (CN VII):

    • Provides motor innervation to the stapedius (striated) muscle of the middle ear.

    • Courses through the ear after exiting the brainstem to perform functions related to facial expression, taste, and lacrimation.

  • Trigeminal Nerve (CN V):

    • Specifically, the mandibular branch carries sensory information from parts of the external ear.

  • Glossopharyngeal Nerve (CN IX):

    • Receives sensory fibers from the middle ear via the tympanic branch.

  • Vestibulocochlear Nerve (CN VIII):

    • Supplies the inner ear.

  • Vagus Nerve (CN X):

    • Provides sensory supply to the auricular nerve, innervating the inferior portion of the tympanic membrane.

Facial Nerve Paralysis

  • Incidence ranges from 0.6% to 3.0%.

  • Increased risk of injury during procedures involving the middle ear, mastoidectomy, parotidectomy, and acoustic neuroma surgery.

Reducing Risk of Nerve Injury

  • Surgeons often utilize a clear drape to continuously monitor the function of CN VII.

  • NIMS Monitor (Nerve Integrity Monitoring System):

    • Identifies and confirms motor nerve functions and monitors major motor nerves across the body including cranial nerves in the head, face, and neck.

    • Alerts surgeons and operating room staff through visual and audible warnings if there is any change in nerve function.

    • Electrodes are strategically placed on the face along the path of innervation to enhance monitoring.

Positioning for Ear Surgery

  • Patients are positioned supinately with the head turned to the side.

  • Avoidance of extremes in head/neck torsion is critical to prevent injuries to the brachial plexus or cervical spine.

  • Special considerations for children under age 4 due to the risk of atlantoaxial subluxation.

  • Patients with limited carotid blood flow may be vulnerable to decreased cerebral blood flow from their positioning.

  • Surgical manipulation of the head must be anticipated, and the table is typically positioned 180 degrees away from the anesthesia provider with airway management in mind.

  • Surgical approaches include:

    • Trans-canal approach

    • Microscope-assisted techniques

    • Post-auricular approach through the mastoid

    • Exceptions include myringotomy and tube placement.

Anesthetic Considerations

Nitrous Oxide and Middle Ear Pressure

  • The middle ear is an open body air cavity intermittently vented by the Eustachian tube (normal pressure 20-30 mm H2O).

  • N2O enters the middle ear more rapidly than nitrogen leaves when inhaled at high concentrations, leading to negative pressure.

  • Expansion effects come from the significant difference in blood/gas coefficients between nitrogen (0.013) and N2O (0.46).

  • If Eustachian tube function is compromised (due to surgical trauma, disease, or edema), pressures can rise to 375 mm H2O within 30 minutes of initiating N2O inhalation.

  • Following discontinuation of N2O, significant negative pressure can develop.

Anesthetic Selection

  • For pre-meatal operations, stapedectomy, and uncomplicated middle ear surgeries lasting less than 2 hours:

    • Local anesthesia with carefully titrated sedation may be used in select patients.

    • Regional anesthesia can block sensory nerves innervating the ear through topical or infiltration techniques.

    • The goal of sedation is to keep the patient calm, cooperative and comfortable while avoiding overmedication.

  • Regional anesthesia can reduce occurrences of nausea and vomiting, speed discharge, and provide lasting analgesia.

General Anesthesia

  • Often required for more complex otologic procedures.

  • Balanced anesthesia techniques are common:

    • Total Intravenous Anesthesia (TIVA) with Propofol.

  • Careful muscle relaxation requires communication with the surgical team, maintaining at least a 30% response when monitoring facial nerve function.

  • Usually best to avoid excessive muscle relaxation unless indicated; an LMA (Laryngeal Mask Airway) can be employed with select surgeons and patients.

Additional Anesthetic Considerations

  • Adequate positioning of head and neck is crucial.

  • Keep an eye on changes in middle ear pressure due to nitrous oxide, which should be turned off before tympanic membrane closure.

  • Monitoring CN II/CN III integrity is essential in the anesthesia protocol.

  • Avoid deep paralysis to mitigate risks.

  • Implement multimodal strategies for preventing or managing nausea, vomiting, and vertigo.

Microsurgical Considerations

  • Surgical procedures often conducted under a microscope necessitate clear visibility; any bleeding may hinder the surgeon’s work.

  • Optimal microsurgery conditions can include:

    • Postural changes (e.g., 15° head-up tilt).

    • Maintenance of systolic blood pressure around 85 mmHg.

    • Controlled ventilation with a volatile agent.

    • Use of topical or infiltration epinephrine.

  • Any movement might simulate an earthquake for the surgeon operating through a microscope.

Deliberate Hypotension

  • An alternative technique for creating a bloodless surgical field includes:

    • Reducing systolic blood pressure to 80-90 mmHg.

    • Lowering mean arterial pressure (MAP) to 50-65 mmHg (30% reduction from baseline MAP).

  • The combination of deliberate hypotension and head-up tilt may elevate the risk of venous air embolism due to reduced central venous pressure.

  • Potential complications include:

    • Impaired vital organ function.

    • Central nervous system thrombosis.

    • Renal vessel thrombosis.

    • Dizziness.

    • Prolonged emergence from anesthesia.

Common Ear Surgeries

  • Tympanoplasty: Reconstruction of the tympanic membrane utilizing graft material, often harvested from behind the ear.

  • Mastoidectomy: Removal of infected mastoid air cells situated in the bone behind the ear.

  • Stapedectomy: A procedure for conductive hearing loss where the stapes is excised and substituted with a prosthesis.

  • Myringotomy with Tympanostomy Tubes: The most common pediatric surgical procedure.

  • Communication challenges faced by patients with hearing loss can be addressed by:

    • Replacing the hearing aid in the non-operative ear.

    • Utilizing hand gestures for communication.

    • Pre-operative coaching.

    • Considerations should be made as leaving the hearing aid in may cause damage from fluids or create high-pitched ringing sounds.

Myringotomy

  • An incision in the tympanic membrane for fluid suctioning, typically followed by the insertion of a tube to prevent tympanic membrane rupture.

Anesthetic Considerations for Myringotomy

  • Bilateral myringotomy procedures with evacuation of middle ear effusions and tube insertions generally take 5-10 minutes.

  • Sedative pre-medications may linger beyond necessary and typically are not required.

  • Procedures can be performed using either LMA or by mask.

  • N2O is commonly avoided, as tubes are placed to relieve middle ear pressure, rendering N2O's effects irrelevant in this context.

  • IV access and equipment should be prepared despite many providers opting against intraoperative infusions for brief procedures due to risks.

  • Postoperative pain management may include Tylenol suppository or intranasal Fentanyl (1-2 mcg/kg).

Other Surgical Procedures

  • Parotidectomy:

    • Surgical removal of the parotid glands, the largest salivary glands, often necessitated by cancerous tumors but sometimes performed for infectious disorders or access to deeper lesions.

  • Requires oral endotracheal tube (ETT) or LMA for anesthesia.

  • The facial nerve's main trunk (CN VII) must be identified, exposed, and dissected along its exterior to prevent injury.

  • Muscle relaxants should be avoided to protect facial nerve functionality.

  • Temporary facial nerve weakness may occur in 20-50% of cases.

  • 100% incidence of greater auricular nerve damage, although recovery is typically observed within a year.

  • Frey’s syndrome affects 35% of patients as a result of auriculotemporal nerve issues leading to flushing and perspiration upon consuming spicy food (gustatory sweating).

Acoustic Neuroma

  • Benign tumors arising from the Schwann cells of the inferior vestibular nerve (CN VIII).

  • Hearing loss is the predominant symptom associated with these tumors.

  • Two primary surgical approaches for removal include:

    • Translabyrinthine: Approached through the middle ear.

    • Retrosigmoid: Navigated through the skull behind the ear.

  • Anesthesia Considerations:

    • General anesthesia is administered as this is an intracranial procedure.

    • Patients are typically positioned supine with the head rotated 45 degrees and secured in pins for fixation.

    • Extensively resection of nerves is generally required.

    • EMG monitoring is frequently employed, which usually precludes the use of muscle relaxants.

    • The use of N2O is contraindicated due to the risk of pneumoncephalus.

Emergence from Ear Surgery

  • It is essential for patients to emerge from anesthesia without coughing or straining to prevent damage to tympanic grafts or other surgical repairs.

  • This is particularly important following stapedectomies.

  • LMA usage has been advocated as a useful tool to prevent coughing and bucking during emergence.

  • IV Lidocaine is effective in mitigating coughing and bucking in patients.

  • Deep extubation is advised to reduce incidences of coughing and bucking upon emergence if patients have normal airways and can be well-ventilated with a mask.

  • Signs of tympanic membrane rupture include the presence of bright red blood in the ear canal.

Postoperative Nausea and Vomiting (PONV) in Ear Surgery

  • Procedures on the middle or inner ear can lead to PONV due to the ear's connection to balance.

  • Effective prophylactic regimens may include:

    • Propofol infusions.

    • Scopalamine patch.

    • Ondansetron.

    • Dexamethasone administered preventively.

  • Avoidance of N2O can help mitigate PONV occurrences.

  • Atropine and glycopyrrolate have been shown to occasionally reduce PONV by modulating vagal tone.

  • The use of TIVA with propofol and remifentanil is known to result in significantly lower PONV rates, albeit at higher expense.

  • A slow, deliberate transfer to the post-anesthesia care unit (PACU) is critical, especially when navigating turns.

Vertigo

  • The vestibular system operates as an internal reference system, informing the brain of head positioning, movement direction, and acceleration.

  • Labyrinthine-induced vertigo, stemming from the vestibular apparatus, commonly resolves within 24 hours.

  • Disturbances of the labyrinth may induce hypotension and could require:

    • Sedation.

    • Bed rest.

    • Maintenance of a 30° head-up position to help reduce perilymph leakage and eustachian tube edema.

  • Pharmacological treatments for vertigo may include:

    • Antihistamines (e.g., meclizine).

    • Anticholinergics (e.g., scopolamine).

    • Other agents (e.g., benzodiazepines, hydroxyzine, steroids).

  • Patients experiencing vertigo should avoid excessive motion and make deliberate movements when necessary.