Download Neuromonitoring for Spine Surgery

Neuromonitoring for Spine Surgery
Aim: To ensure the integrity of the spinal cord and nerve roots especially at the site of
surgery, while providing safe and adequate anesthesia.
The Problem: The nervous system is suppressed by anesthetics, hypothermia,
hypotension and anemia; depending on anatomical site, specific drug & dose, site of
stimulation, and site of monitoring.
Discuss the monitoring plan and anesthetic techniques with the surgeon AND the
neuromonitoring team prior to starting the case.
EMG: The EMG assesses the integrity of cranial/spinal nerve roots and indirectly
peripheral nerves from the site of stimulation to the muscle.
Anesthetic Implications. Avoid neuromuscular blocking drugs during the period of
monitoring i.e. after intubation and positioning. High dose vapor may have a
suppressive effect, and may skew sensory vs motor nerve root thresholds.
Somatosensory Evoked Potentials (SSEP): SSEPs monitor the integrity of sensory
pathways from peripheral nerves to the sensory cortex. Disruption along any part of this
pathway may disrupt normal SSEP responses.
Anesthetic Implications. SSEPs are progressively suppressed by inhaled anesthetic
(vapor or N2O) > 0.5 MAC. All intravenous agents (propofol, barbiturates, midazolam,
opioids, ketamine) have minimal effect and are preferred. Standard dose neuromuscular
blockers can be used.
Auditory Evoked Potentials (AEP): AEPs monitor the integrity of auditory pathways
from ear through brain stem to cortex. They are also referred to as brainstem auditory
evoked potentials (BAEP or BAER).
Anesthetic Implications. Similar to SSEP but are much less sensitive to inhaled
anesthetics so that most anesthetic options are acceptable.
Motor Evoked Potentials (MEP): MEPs involve transcranial motor cortex stimulation to
elicit a response from muscles and thereby assess the integrity of motor pathways.
Anesthetic Implications. MEPs are easily suppressed by inhaled anesthetics (vapor >
N2O). These should usually be kept to a minimum or not used. In patients with preexisting neuropathy <0.3MAC is preferred while in patients without neuropathy
<0.5MAC is usually acceptable. IV hypnotics are less suppressive. Propofol up to 120
mcg/kg/min is usually acceptable. Ketamine & etomidate have minimal effect or
increase amplitude. There is insufficient literature about dexmedetomidine but it seems
to work well in many patients.
Last revised 10/2007
Gelb