Intraoperative Neurophysiological Monitoring Flashcards
What is intraoperative monitoring?
- Continuous, on-line electrophysiologic assessment, measurement, and interpretation of neural responses to intraoperative events
- Modality-specific, controlled stimulation during the course of surgery
- Assesses the integrity of a sensory (CN VIII) or motor (CN VII) modality during a surgical procedure
What is the audiologist’s job during IOM?
- Administer and interpret electrophysiologic measurements of neural function including:
- Sensory and motor evoked potentials
- Tests of nerve conduction velocity
- Electromyography
-These measurements are useful in differential diagnosis, pre- and post-operative evaluation of neural function, and neurophysiologic IOM of CNS, spinal cord, and cranial nerve function
What are indications for IOM?
- When there is a risk of surgical complications involving the CNS or PNS
- When surgical or anesthesia intervention (indicated by monitoring) could help prevent, reverse, reduce consequences
- PURPOSE: to improve post-operative by correlating changes in neurophysiological responses with intraoperative responses
Describe the pre-operative assessment.
1) Pre-op audiologic workup
- Audiogram
- Immittance
- OAEs
- Speech discrimination
- Auditory electrophysioloy
2) Pre-incision ABR/ECochG
- Check equipment
- Identify any noise
- Patient baseline
What personnel should be in the operating room?
- Surgeon
- Anesthesiologist
- Nurses
- Audiologist
Describe the electrical and magnetic environment of the operating room.
- Operating microscope
- Anesthesia machine
- Pulse oximeter machine
- Electroacutery machine
- Automated blood pressure machine
- Heart rate monitor
- Respirator rate monitor
What are some hearing preservation strategies?
- Cerebellopontine angle tumor removal
- Vestibular nerve resection
- Microvascular decompression of CN V or CN VII
- Cochlear implantation (electric ABR and facial nerve)
What types of damage could occur in the operating room?
- Mechanical: compression, tearing, cutting, stretching
- Ischemic: interrupted blood supply to cochlea or brainstem
- Thermal: electrocautery
What are the three surgical approaches?
1) Retrosigmoid (suboccipital)
2) Translabyrinthine
3) Middle Fossa
Describe the retrosigmoid surgical approach.
- Craniotomy is made behind the ear in the occipital bone
- Bone overlying the IAC is removed to expose and remove the tumor
- Best candidates: patients with tumors that do not involve the lateral 1/3 of the IAC and do not impinge on the brainstem
What are advantages of the retrosigmoid surgical approach?
- Allows removal of tumors of different sizes
- Offers the possibility of hearing preservation
- Approach offers the surgeon a wide view of the cisternal component of the tumor and thus good access to the root entry zone of the acoustic nerve
What are disadvantages of the retrosigmoid surgical approach?
- Necessity for cerebellar retraction
- Less access to the facial and cochlear nerves in the distal IAC
- Increases the potential to leave a residual tumor fragment behind
Describe the translabyrinthine surgical approach.
- Craniotomy is made through the ear in the mastoid bone
- SCCs are removed to expose the tumor in the IAC
- Because the canals are removed, complete hearing loss occurs in the affected ear
- Use: patients who already have hearing loss or when preservation of hearing is not possible
What are advantages of the translabyrinthine surgical approach?
- Size of the tumor not a limiting factor
- It offers early identification of the facial nerve in the auditory canal
- There is absolutely no need for cerebellar retraction
What are disadvantages of the translabyrinthine surgical approach?
-No hearing preservation
