Monitoring Flashcards
What are brainstem auditory evoked potentials (BAEP)?
used in resection of acoustic neuromas, decompression of facial nerve for hemifacial spasm, posterior fossa brainstem surgery, clipping of basilar artery aneurysm, operations of CN VIII
How do BAEPs work?
use sound waves to stimulate cochlea
What are SSEPs?
Somatosensory Evoked Potentials
Used to monitor the spinal cord function during high risk orthopedic and neurosurgical procedures
With stimulation of the peripheral nerves –> spinal cord via dorsal root –> brainstem –> regional cortex –> monitors dorsal column
SSEPs monitor what?
Dorsal spinal root, ascending pathway, afferent pathway positioned posteriorly in the spinal cord
Why has there been documentation of no changes in SSEP but seen some injuries?
because of differing vascular supply, damage to anterior spinal circulation may cause motor deficits with unchanged SSEP
What is EMG?
Test used to record the electrical activity of muscles
Used to determine location of weakness, paralysis and/or muscle twitching
What does EMG do?
Demonstrates the integrity of the nerve
Major structures are monitored
INTEGRITY OF ANTERIOR HORN NERVE ROOT AND MOTOR NERVE FUNCTIONAL UNITD
Done to find damage already done in the nerves from the brain to the spinal cord
Does EMG show brain or spinal cord diseases?
No
How is EMG used in spinal surgery>
used to PROTECT nerve roots during surgery
Extremely sensitive to nerve root irritation
Monitored to help identify the possible level or site of nerve root irritation
SPECIFIC TO NERVE ROOT FIRING
What are motor evoked potentials?
Monitoring device utilizng direct simulation of the spinal cord above the operative site and recording responses below operative site
What tracts and pathways do MEPs monitor?
Descending motor pathways (ventral)
GOLD STANDARD FOR MONITORING MOTOR PATHWAYS
especially used in corticospinal tract
What is the anesthetic management of a patient undergoing SSEPs?
No Nitric oxide
Decreases amplitude and increases latency
What is the anesthetic management for a patient undergoing a NIMs tube?
No more paralytic after intubation
What is the anesthetic management for a patient udenrgoing EMG?
Limit NMB to a level of 2-4 twitches
What is the anesthetic management for patient undergoing MEP?
NO NMB
TIVA or balanced technique (Inhalational agent <0.6MAC)
Preop:
- Premedication with 1-2 versed
Induction:
- Propofol 1.5-4 mg/kg
- Narcotic bolus prior to induction (fentanyl)
Maintenance:
- Volatile (0.5-0.5 MAC)
- Propofol infusion 50-75 mcg/kg/min
- Narcotic infusion
- NO NMB
- Amnesia supplementation (versed 1mg Q1H)
- Ketamine bolus
How does Inhalational agents affect SSEP, EMG and Transcranial MEP?
SSEP: Sensitive >1 MAC (decreased amplitude and increased latency)
TRranscranial MEP : Sensitive >0.6 MAC
How does N2O affect SSEP, EMG and Transcranial MEP?
SSEP: Sensitive (dose related decreased amplitude)
transcranial MEP: Sensitive (usually avoided)
How do opiates affect SSEP?
Mild depression, usually do not avoid
How does ketamine affect SSEP?
DESIRABLE AGENT
How does droperidol effect SSEP?
Minimal effect
How does etomidate affect SSEP?
None
How do you determine a worsening situation with amplitude and latency?
Amplitude: signal strength (height)
Latency: Time from stimulation (length)
indicated by change in evoked potentials
CRITICAL DECREASE in amplitude or increase in latency indicate early warnings of structures in danger
