Intraoperative Monitoring. Behrouz Zamanifekri , MD Neurophysiology Fellow KUMC March 2013. Intraoperative monitoring.
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The most primitive method of monitoring the patient
50 years ago were continuous palpation of the radial
pulsations throughout the operation or wake up test!!
What is IOM ?
1. Reduce the risk of postoperative neurological deficits
2. Identify specific neuronal structures and landmarks that cannot be easily recognized
3. Research purposes in basic science, pathophysiology and therapeutic management
Sensory: 1- visual
MONITORING SPINAL CORD
free run or spontaneous EMG (sEMG)
triggered EMG (tEMG)
ascending pathways, thalamus
and, finally, to the
primary sensory cortex
upper limb SSEP
lower limb SSEP
- Earlier peaks tend to be less sensitive to anesthesia
- used to differentiate SSEP monitoring changes resulting from anesthetic effects from surgical manipulation.
-50% reduction in amplitude
-10% increase in latency
Factors that affect the SSEP amplitude include halogenated agents, nitrous oxide, hypothermia, hypotension, and electrical interference
in nerve root function
Dermatomal stimulation is better
- Propofolincreases the latency by approximately10%
- Benzodiazepines reduce the amplitude of cortical SEP
- Etomidate : cortical SEP amplitude augmented 200–600%,
increases SEP latencies
- Opiates, cause a slight increase in SEP latency
- Muscle relaxants, notaffect SEPs
SEP changes due to surgical maneuvers (e.g., spinal distraction) or ischemia (e.g., after placement of an artery clamp) are abrupt and localizedand only one side of the body may be affected
SEPs obtained after cross-clamping of the internal carotid ,whichresulted in ischemia (time 9:45) that later deteriorated (9:55). After placement of a shunt,response amplitude is restored to within normal limits (time 10:01).
Median nerve SEPs
ACA or the A.Com artery?
the only way to assess corticospinal
tract during surgery was wake-up test
nerve (neurogenic MEP)
spinal cord ( D-wave )
-the newer technologies is continuous free-running EMG throughout the surgery
1) all-or-nothingcriterion: the most used method,
complete loss of the MEP signal from a baseline recording is indicative of
a significant event
2) amplitude criterion: 80% amplitude decrement in at least 1
out of 6 recording sites
3) threshold criterion: increases in the threshold of 100 V or more
required for eliciting CMAP responses that are persistent for 1 h or more
4) morphology criterion: changes in the pattern and duration of MEP
-deep brain stimulators or cochlear implants
Tongue biting is the most common complication
caused by continuous force applied to the nerve
Baseline recordings. Note the low
amplitude background activity
High amplitude spikes are present
Due to the variation in thickness and shape between thoracic and lumbar pedicles, different stimulation thresholds exist for these regions
In cervical and thoracic procedures, the spinal cord are of greater importance