2a. EPs Monitoring Flashcards
What is the purpose of evoked potential monitoring?
detects injury to the spinal cord and measures neuronal function
what 4 things may affect EP monitoring?
hypotension
anesthetic drugs i.e. volatile agents
hypothermia
spinal cord retraction
latency
time of administration of stimulus to peak response (time necessary for the evoked response to be measured in the brain)
amplitude
magnitude of the peak response/intensity of the evoked response
how do VAs and N2O affect latency and amplitude of EPs?
↓ amplitude and ↑ latency
which is more sensitive to depressant effects of anesthetics between motor (MEP) and somatosensory (SSEP) EPs?
MEPs
what MAC may be used without altering signal quality of EPs?
MAC ≤ 0.5
effect of propofol on EP monitoring?
dampening of evoked potential response
effect of opioids and benozos on EP monitoring?
no interference
what type of injury can occur from transcranial stimulation and how is this prevented?
facial muscle activation causes pt to bite down with significant force and cause injury to tongue, lips, cheeks, teeth etc. Therefore a soft bite block should be inserted to avoid injury.
What is the purpose of the Hunt-Hess Scale
determines severity of a patient’s subarachnoid hemorrhage (a high grade corresponds to a higher severity)
what hunt-hess scale score corresponds to an asymptomatic patient?
1
A patient with SAH will require intubation if his Hunt-Hess score is (Select 2)
4 and 5
NIRS
Near Infrared Spectroscopy used to assess cerebral O2 Sat
* Used when cerebral perfusion could be compromised
NIRS goal parameter
maintain the NIRS value at a minimum of 75% of the baseline reading
Normal ICP
5 to 15 mm Hg in adults
intracranial hypertension values
20 to 25 mm H
gold standard for ICP monitoring
intraventricular catheter (it allows for drainage of CSF to lower ICP)
what is the most frequent complication of ICP monitoring
Infection
ICP should be monitored in patients with a normal CT scan with two or more of the following criteria…
- age older than 40
- unilateral or bilateral motor posturing
- systolic blood pressure (SBP) less than 90 mm Hg
Cushing’s triad
- systemic hypertension
- bradycardia
- irregular respiratory pattern
who else should undergo ICP monitoring?
- patients with severe traumatic brain injury (TBI)
- a Glasgow coma scale (GCS) sum score below 9
- an abnormal CT scan
What change in EPs is suggestive of the possibility of cerebral ischemia?
A 50% decrease in amplitude or a 10% increase in latency
effect of ketamine and etomidate on EP monitoring?
increases amplitude
no effect on latency
motor or sensory: descending (efferent) tracts
motor
motor or sensory: ascending (afferent) tracts
sensory
main voluntary motor tract
lateral corticospinal tract (2nd: ventral corticospinal)
sensory functions of the dorsal column
deep touch
vibration
proprioception
sensory functions of the lateral spinothalamic tract
pain and temperature
sensory functions of the ventral spinothalamic tract
light touch
SOMATOSENOSORY-EVOKED POTENTIALS (SSEPs)
MONITOR INTEGRITY OF PERIPHERAL & CENTRAL SOMATOSENSORY NERVE PATHWAYS OF BRAIN & SPINAL CORD
(DORSAL COLUMN & LATERAL SENSORY TRACT OF THE SPINAL COLUMN)
upper extremity monitoring
placing the stimulus at the median nerve
(located between the tendons of the flexor carpi radialis and the palmaris longus)
lower extremity monitoring
POSTERIOR TIBIAL NERVE
(Located between the Achilles tendon & medial malleolus of the ankle)
ALMOST ALL ANESTHETICS INCREASE LATENCY & DECREASE AMPLITUDE EXCEPT
KETAMINE, ETOMIDATE & OPIATES
anesthetic management during SSEPs monitoring
NARCOTIC BASED, TIVA, <0.5 MAC VAA
DOES ADMINISTRATION OF PARALYTIC AFFECT SSEP MONITORING?
NO
HOWEVER, MUST AVOID IF MOTOR RESPONSE BEING MONITORED
GOLD STANDARD FOR MONITORING FOR EP MONITORING
MOTOR-EVOKED POTENTIALS
(USUALLY COMBINED WITH SSEPs)
USED TO ASSESS FUNCTIONAL INTEGRITY OF MOTOR TRACTS:
CORTICOSPINAL TRACT
how do MEPs differ from SSEPs, VEPs, and BAEPs?
MEPs evaluate descending motor pathways from the cerebral cortex past the neuromuscular junction to peripheral muscle groups
(the others provide information about ascending sensory neural pathways from the periphery to the cerebral cortex)
BAEPs monitor basic brainstem function by monitoring which tracts?
ENTIRE AUDITORY PATHWAY FROM DISTAL AUDITORY NERVE TO MIDBRAIN
what cranial nerve is stimulated by BAEPs?
8
Vestibulocochlear
what can commonly effect on BAEPs during anesthesia and surgery?
hypothermia AKA patient temperature less than 35°C
(increased latency & prolonged interpeak intervals)
VISUAL-EVOKED POTENTIALS (VEPs) monitor the FUNCTION OF VISUAL PATHWAY along what tracts?
Retina to the occipital cortex and everything in between, including the optic nerve and the optic chiasm
WHY DO VEPS HAVE QUESTIONABLE USEFULNESS IN ANESTHETIZED PATIENTS?
VEPs are the most sensitive neuromonitoring modality with regards to anesthesia
WHAT IS ONE ANESTHETIC TECHNIQUE FOR VEPS MONITORING?
opioid-based TIVA with muscle relaxants & BIS monitoring
