Neuro Monitoring & Complications Flashcards
What is the purpose of Neuromonitoring?
Way to protect nerves during surgeries with increased risk of injury potential.
-Electroencepholagram
-Motor Evoked Potentials
-Somatosensory evoked potentials
-Electromyography
-Brainstem Auditory Evoked Potentials
-Visual Evoked potentials
What are the effects of anesthesia on EEG?
-Most anesthetics inhibit neuronal activity
-EEG requires 50% of the total oxygen consumed in the brain
-Changes in EEG patterns are similar with ischemia and deep anesthesia
-Baseline EEG, repeat after induction and before surgery start
-Communication with NM tech about changes in anesthetic depth to eliminate false positive EEG patterns
-Drug induced burst suppression can be cerebral protective
-Volatile anesthetics are dose dependent in how they reduce CMRO2
-Used for supratentorial tumors, aneurysms, Carotid, surgeries on aorta
What do Somatosensory Evoked Potentials monitor?
Monitor the function of the brain and spinal cord during certain surgeries.
-Evoked means the neuro monitor tech gives a stimulus to check recordings
-Do not make abrupt changes in anesthetic during periods of risk.
-Good communication is critical with Monitoring technician.
Describe Anesthetic Management during SSEPs?
-Inhalation agents can decrease amplitude and increase latency of EPs.
-Use 0.5 MAC isoflurane and then TIVA. Any more than that will affect neuromonitoring.
-No abrupt changes in anesthetic. Communicate with NM tech.
Nagelhout:
-Volatile anesthetics and N2O depress the SSEP waveform in a dose-dependent manner. Avoiding abrupt changes in inhaled gas concentration and bolus injection of hypnotic drugs during periods of risk minimizes difficulties in determining whether waveform changes are due to surgical manipulation. Furthermore, a concentration of less than 1 MAC of volatile anesthetics is recommended when monitoring SSEPs.
What surgeries use neuromonitoring?
-Surgeries involving the spine, repair of intracranial aneurysm, craniotomy for tumors
What will alter the SSEP reading?
If there is posterior cord or brain ischemia- transmission of action potentials through the posterior cord and brain is diminished, thereby reducing the intensity and delaying the arrival of the action potential that reaches the cerebral cortex.
-The SSEP reading will be altered.
(!!!)
Which spinal tract is measured by SSEPs?
-Cuneatus and Gracilis Tracts (Touch, pressure, Vibration)
-Posterior Dorsal Cord
-Integrity of this area/tracts assessed by SSEP Monitoring
-Remember SAD=sensory/afferent/dorsal
-Tibial nerve stimulated: Carried up on the ipsilateral side of cord until they cross over in brainstem to the contralateral thalamus up to primary cerebral cortex where Cuneatus and Gracilis tracts lie.
-Direct Route! Early peak of the wave. Recording leads are over these tracts.
What is the Indirect Route monitored by SSEPs?
-Reticular activating system is considered the Indirect route.
-When it goes through this tract it spreads throughout the cortex.
-All recording electrodes can pick up.
-Anesthesia effects the Reticular activating System.
-This is the system that keeps you awake.
-Coma is the complete loss of the Reticular Activating System.
-Seen as the Late peak of the wave.
What do Motor Evoked Potentials monitor?
-Assess anterior lateral spinal cord containing the corticospinal tract
-Useful during surgeries that could have compromise to anterior cord, spine cases, aneurysm repair, thoracoabdominal repairs
What is Anesthetic Management of Motor Evoked Potentials?
-Avoid Muscle Relaxants
-TIVA is the best
-Avoid high MAC of volatile. Discuss with Neuro monitor tech.
-0.5 MAC is usually okay
-Always get a baseline before surgery.
-If you use MR for induction they will want to know when it’s worn off so they can run a set of baseline motors before surgery
How do we monitor SSEPs?
-Stimulus given through the tibial, ulnar or median nerve usually bilaterally. Tiny needles that are taped in place.
-The critical recording electrodes are placed midline to record tibial nerve evoked potentials and laterally for ulnar and median nerve evoked potentials.
-Sensory evoked potentials: the stimulating electrodes are placed peripherally and detecting electrodes are placed centrally.
-Remember the homunculus? The toes, feet, leg are in the longitudinal fissure. In the center of the brain. That’s where the primary electrode for measuring if you stimulate the tibial nerve.
-If the median/ulnar nerve is stimulated, the primary electrode for recording is on the lateral side.
What is the major reason for monitoring SSEPs?
To detect Ischemia (!!)
What is Latency?
The time it takes for the action potential to traverse the peripheral nerves, cord and inner brain and cerebral cortex.
What is Amplitude?
Magnitude or size of the evoked potential.
What changes in Amplitude and Latency indicate ischemia?
-50% decrease in Amplitude
-10% increase in Latency
If during spine surgery the SSEP decreases and the latency increases where is the damage happening in the spinal cord?
Posterior Cord
How sensitive are SSEPs to anesthetics?
Somewhat Sensitive
What is Electromyography (EMG)?
Continuous assessment of cranial and peripheral nerves, not a measure of ischemia.
-No Muscle Relaxants.
-Otherwise, anesthesia has no effect
-Ex: Nims tube for thyroid, ACDF, acoustic neuroma or any surgery that could damage facial nerves
What do Brainstem Auditory (BAEP) monitor?
-Auditory pathway CN VIII
-Clicks in the ear, used in peds for diagnosing hearing issues
-Used in acoustic neuroma surgery,
-B = barely sensitive to anesthetics
What do Visual (VEP)s monitor?
-Cranial nerve II- difficult to obtain
-Very sensitive to anesthetics
-Pituitary , retro-orbital or occipital lesions
How does Hydrocephalus occur?
-CSF is made in the choroid plexus.
-CSF is made in the lateral, 3rd, and 4th ventricles.
-All 4 ventricles are connected by narrow passages. If there is a blockage in one of the passages or in the flow of CSF, it will accumulate in the ventricles and enlarge them.
-Enlarged ventricles push the brain against the rigid cranium and can cause an increase in intracranial pressure.
-CSF then flows to the subarachnoid space, creating a fluid cushion around the brain and spinal cord.
-It is then reabsorbed multiple times a day and the process continues.
-When there is an issue in any of these steps and pressure or volume is increased, it is called hydrocephalus.
-Congenital issues: Arnold-chiari malformation, Dandy Walker Syndrome.
What is Normal Pressure Hydrocephalus?
-There is still an accumulation of CSF.
-However, it does not cause an increase in Intracranial pressure.
-However, there is a triad of symptoms first named by a Dr. Hakims in 1964:
1) disturbance in gait
2) confusion or dementia
3) impaired bladder control
What is Non-Communicating Hydrocephalus?
There is a blockage somewhere.
-One of the most common causes is a narrowing of the aqueduct of Sylvius, mass occupying tumors, blood clots in the drainage system, inflammatory conditions like meningitis, encephalitis.
What is Communicating Hydrocephalus?
There is no blockage found.
-There is inadequate reabsorption of CSF.
-Often there is thickening of the arachnoid around the base of the brain.
-These patients can also get a shunt to help with volume of CSF.
