IONM/Spine Flashcards
(25 cards)
purpose of IONM
-protect integrity of peripheral and central nervous systems during surgical manipulation
What is the order of most to least sensitive IONM modalities (from anesthetic impacts)
MEP>EEG/SSEP>BAEP
what are evoked potentials (EPs)/purpose
-electrical potentials that are measures in response to a particular stimuli
-used to guide surgical strategy and warn team of neurologic deficits
-can prevent irreversible damage
4 types of stimuli used for EP studies
auditory, visual, motor, somatosensory
4 surgical factors that can impact EPs (not anesthetics)
- electrocautery (heat) injury to neural structures
- mechanical stress/retraction
- ischemia (ligation, edema, vessel damage)
- loss of functional integrity (transection)
what is the elastic limit of nerves and what does this mean
20%, further stretching can cause irreversible damage
amplitude
-measurement of the intensity of evoked response to the signal
-measured in micro or millivolts (MEP)
-height of the waveform relative to baseline voltage
latency
-indicative of the time necessary for the evoked response to be measured in the brain
-measured in milliseconds
-represents the delay in response to stimulus, indicated how long it takes for the signal and response to travel along the neural pathway
what % changes in latency and amplitude suggest ischemia
50% decrease in amplitude or 10% increase in latency
type of anesthetic agents that depress EP waveforms in a dose dependent manner
-inhalation
-IV also does but to a lesser extent
(when IA and IV are used together, the depressant effect is synergistic on SSEPs)
what pathway does SSEP monitor
sensory pathway through DRG and posterior column
Effect of each on SSEP…
Inhalationals
IV
Ketamine
Etomidate
-senstiive to all IA
-less affected by IV
-ket and etomidate increase amplitude
4 common types of surgeries SSEP is used for
spine (wide variety), CEA, some intracranial tumors, some CV surgeries
SSEP: drugs that decrease amplitude and increase latency (5)
- halogenated agents
- N2O
- barbiturates (ok w/ burst suppression on EEG)
- propofol (least pronounced, still the best IV agent to use with SSEP)
- opioids (mild, occurs more with bolus vs gtt, still ok to use)
how does ketamine affect SSEP
inc amplitude, no change in latency
how does etomidate affect SSEP
increased amplitude and increased latency
do benzos affect SSEP
minimally
what pathway does MEP monitor
motor pathway…motor cortex, corticospinal tract, nerve root, peripheral nerve
should you use NMBDs with MEP
no
can you use inhalationals with MEP
over 0.5 MAC signals are suppressed –> Use TIVA
who should not undergo MEP via magnetic stimulation?
patients with spinal or bladder stimulators, metallic foreign bodies, pacemakers, previous craniotomy
what part of the spinal cord would MEP signal reflect poor perfusion of
anterior spinal cord
(bolded in the slides)
2 drugs contraindicated with MEP
Magnesium and NMBDs
(MMNM: MEP, mag, neuromuscular)
What type of anesthesia is contraindicated with IONM
Regional: spinal AND epidural
