There is a covering of the cerebrum (brain). It is outside and is a superficial layer of cerebrum called the_________ ________.
cerebral cortex
What is the main site for human intelligence?
The cerebral cortex
What is the part of the cerebral cortex where sensory impulses project called?
somatosensory cortex
True or false. The brain stem is part of the midbrain?
True
What are the three main parts of the brain stem?
1. Midbrain
2. Pons
3. Medulla
Vital signs are maintained & control of intrinsic life processes occur in the ____ ______.
Brain stem
Name all the parts of the mid brain
Brain stem (including the is the reticular formation and the vestibular system not quite as major but important!)
Cerebellum
Diencephalon
The diencephalon includes what?
everything w/thalamus (hypothalamus, thalamus)
The reticular formation does what?
It is the relay station for descending motor control (of the extrapyramidal tract), except for that going down the pyrimidal tract.
The vestibular system does what?
coordinates limb and eye movements in response to body position.
Basal ganglia, consists of how many nuclei?
5
What does the basal ganglia do?
The basal ganglia is nvolved in planning and generating motor commands.
Then those motor signals (generated in the mid brain) are traveling down the reticular formation, and effect the muscle.
What is the thalamus?
The sensory integrative center.
Thalamus is part of the diencephalon.
What does the cerebellum do?
controls posture
Also adjusts muscle contraction on the ipsilateral side (the same side).
fibers that ater 15-20 micromters tend to be what?
muscle fibers
Fibers that are 0.5 micrometers are....
sympathetic type C fiber
It’s a very very small type C fiber.
In spinal anesthesia, we have differential blockade. What type of fibers are very easy to block?
small sympathetic fibers (They are 0.5micrometers and unmyelinated)
We know the sympathetic fibers are very small. What are the next two types of fibers?
Sensory fibers are the size in between the small sympathetic fibers and the Large motor fibers.
Small = sympathetic
Medicum = sensory
Large = motor
During spinal anesthesia, we give local anesthetics at the nerve root. Why is the sympathetic block higher than the motor block? How many dermatomes higher can the it be?
Because those fibers are smaller and easier to block
Sympathetic fibers can be blocked 4 dermatomes higher than motor fibers, mainly because of the size of the fibers.
If we give the pt a spinal and has sensory block at T10 (umbi), motor block is at ____.
T12
As a CRNA you can tell the aympathetic level is dropping because the pt moves it’s legs. Why is this so important to know?
If surgery is still going on and the pt has sympathetic and sensory blockade.
You know you don’t have much time because the block is wearing off.
SENSORY information enters the cord through ______________
dorsal nerve roots
Describe what happens (the sensory pathway) when you stub your toe
Sensory by peripheral nerve→ up sensory pathway, and synapses on dorsal (posterior) horn of the spinal cord.
Then it gives rise to afferent pathways which ascend through the spinal cord to the brain.
There’s two routes it can take. The dorsal (posterior) or the spinal thalamic (anterior) pathway.
There are two dorsal columns (for the sensory pathway) what are they?
Those dorsal columns consist of fasciculus gracilis and the fasciculus cuneatus
Describe the motor pathways from the brain to the periphery.
Descending from the brain to the spinal cord.
Mostly go down the corticospinal tract.
They synapse in the anterior horn of the spinal cord.
They then go down through the anterior nerve roots to the periphery.
If there is a lesion of the cerebellum, you’re weak to that side,
because it doesn’t cross that cord
(the spinocerebellar tract does not cross the spinal cord)
If you have a sensory lesion, it it on the same side or the opposite from the lesion?
If you have a sensory lesion, generally it’s the opposite side because it crosses the pathway
Describe the sensory pathway of the posterior (dorsal column)
Vibration touch →1st synapse→ crosses cord →into thalamus all the way to somatosensory area of the cortex.
What is an SSEP?
Provides info about sensory tract and the brain. Testing the sensory tract (the dorsal columns)
You have stimulus in periphery, (usually the foot) looking at how that signal moves to the brain and whether or not that’s normal.
If you stimulate pt at foot, and put monitor at somatosensory area of cortex and see how long it takes for it to get there.
Describe the sensory pathway of the Spinothalamic tract (aka the anterolateral tract).
where pain pathways travel up.
Pain impulses travel over small fibers, travel though Lissauer’s tract and up the anterolateral (Aka spinothalamic tract) and synpases in the thalamus (integrated center) and then up to the brain.
What are the three main sensory pathways?
Spinothalamic tract (anterolateral tract)
Posterior (dorsal) columns (there are two)
Spinocerebellar tract (not as major)
Spinothalamic tract (anterolateral tract) is one of the three main sensory pathways, what does it do?
carries sensations of pain and temperature.
Posterior (dorsal) columns (there are two) are main sensory pathway, what do they do?
carry proprioception.
Spinocerebellar tract (although not as major) is a main sensory pathway. What does it do?
carries unconscious proprioception. (walking w/out thinking uses this pathway)
Only goes up to cerebellum or midbrain.
Doesn't go up to cerebral cortex where intelligence resides.
It also doesn't cross the cord.
Where are motor tract impulses started?
So neuro impulses are modulated by the basal ganglia, cerebellum, and the brain stem
Describe the motor impulse pathway through the pyramidal tract. What does this do?
Motor impulses start up in the brain, come down through the brain stem, though the medulla, through the anterior horn, through the corticospinal (pyramidal) tract (aka the motor pathway).
Does precise movement and the larynx.
What is the extrapyramidal tract made up of?
rubrospinal
lateral vestibulospinal
reticulospinal
What does the extrapyramidal tract do?
This maintains postural tone and directs voluntary movement.
TRUE or FALSE. Both pyramidal and extrapyramidal cross the spinal cord.
TRUE!
This motor tract, transmits motor commands, all the way down though brain stem, crossing over the spinal cord at some point, it synapses, down at the bottom in the anterior horn of the spinal cord. Why is important to distinguish where this synapse is?
Motor neurons above synapse are upper motor neurons and below are lower motor neurons
Injuring this tract causes paralysis of different types depending on upper or lower
What happens if you injure an upper motor neuron? Give an example of this type of injury.
There is spastic paralysis and hyperreflexia.
This includes anything that’s high in the tract (brain = high)
Ex: Cerebral palsy
An upper motor neuron lesions interrupts signals between the spinal cord and the brain. What happens a few days after an upper motor neuron lesion/injury?
Reflexes return to the muscles and hyper reflexia and spastic paralysis result.
What is a lower motor neuron lesion? What does this cause?
Anything under the spinal cord.
Any interruption of neurons below L1 is a lower motor neuron lesions.
This causes flaccid paralysis and areflexia.
Does a lower motor neuron lesion have ANYTHING to do w/the brain?
Has nothing to do w/brain!has to do w/spinal cord and effected muscle.
Spinal cord contains neural circuits which produce reflexes. What is a reflex?
A reflex is a stereotyped action in response to a peripheral stimuli.
The spinal cord reflex : Withdrawing to pain is a spinal cord reflex.
The ANS has reflexes. What happens when there is SNS stimlation?
pupil dilation occurs. +inotropic and chronotropic effects on the heart.
The ANS has reflexes. Which is more localized, the parasympathetic or the sympathetic?
parasympathetic effects which tend to be more localized than sympathetic effects
Where does the PNS arise from?
The PNS arises from the brain stem and the sacral spinal cord.
Where does the SNS arise from?
sympathetic fibers (during spinals) come off the thoracic and lumbar spine.
What is the Pathologic autonomic reflex?
Mass reflex, aka denervation hypersensitivity or autonomic hyperreflexia (common term)
Occurs in the presences of a spinal cord transection.
When there is a stimulus to the skin or visceral organ below the spinal cord transection.
What happens pathologically is simultaneous excitation of all segmental reflexes.Means the sympathetic nerves and parasympathetic nerves are active.
Massive excitation of entire ANS.
Describe the risk of autonomic hyperreflexia in someone w/a transection at T5 vs T10
High risk at T5: Very common w/transections above T5.
Low risk at T10: Very unlikely to occur w/lesions below T10.
Which is more important, the level of transcetion of the spinal cord or how stimulating the procedure is?
Level is much more important than how stimulating the procedure is.
35 yr old pt w/hx of T5 spinal cord transections presents for cystoscopy. What is the anesthetic plan?
Avoid succinylcholine.
Give GA.
If the BP is very high, treat it w/direct acting vasodilator (Nipride-rapid onset and very titratable).
For the patient w/chronic pain, a spinal cord stimulator is placed in epidural space. What is the idea behind this?
Gate control theory: if you turn up the stimulus pretty high so it’s effecting the bigger fibers, then the patient doesn’t feel the pain of the small fibers being blocked.
Giving repetitive stimuli “numbed the area”
That’s why the neurosurgeons put the nerve stimulators in.
We do that under LA. Pt prone, placed in epidural space. Pt awake so we can monitor them. Tell us when the pain is covered.
Describe tests of neurological function that do NOT require special equipment or systems.
Check pupils.
Use local or do a block. Able to talk to the pt. Are they awake? Can they count to 20?
Wake up test: Scoliosis surgery, wondering if damage to cord. Have pt wake up during the procedure. If able to move and feel feet, then motor and sensory function. Not necessitate extra equipment.
How sensitive are the SSEP (somatosensory evoked potentials) to our anesthetic agents?
mid range, pretty sensitive
How sensitive are the visual evoked potentials (responses) to our anesthetic agents?
Most sensitive!
How sensitive are the brain stem auditory evoked potentials to our anesthetic agents?
Least sensitive
Why is it important to have a closed loop communication with the EEG tech when giving anesthetic drugs?
because anesthetic drugs change the EEG in same manner that hypoxia changes the EEG.
Describe alpha, beta, and delta rhythms on EEG. (when they occur)
Alpha rhythm: pt seen relaxed w/eyes closed
Beta rhythm: when pt is concentrating.
Delta waves: occur during normal sleep
When does burst suppression occur?
Occurs during deep anesthesia.
EEG then nothing then burst EEG then nothing.
Also can be d/t hypoxia or extreme hyperthermia.
What is a benefit of EEG monitoring during surgery?
to monitor cerebral flow and oxygenation
What could EEG changes mean?
may indicate injury or it may be anesthetic level has changed
What is the treatment of EEG changes?
Communicate about what’s causing it!
Bolus of anesthetic could cause it. Or surgeon has had clamps in, pressing carotid and clamps need to be moved.
Surgeon working on carotid, and other side is also stenosed so pt not getting enough flow to brain, in that case, shunt can be placed to work on vessels and still maintain flow
As a CRNA, what can we do if an EEG changes?
raise the BP because it will increase flow to the brain
Make sure the patient is on 100% FiO2
What are we really looking at when we look at somatosensory evoked potentials?
At the function of the peripheral nerve
The posterior column of the spinal cord
The brain.
Looking at how long it takes for stimulus to get to brain and the forces of the stimulus.
Major changes in the SSEP particularly in spinal surgery tend to indicate injury
to posterior column of the spinal cord.
Where is the equipment for a SSEP?
So they have a stimulator on the foot and then a monitor on the other (Contralateral side) of the pts brain.
What two things does the SSEP measure?
amplitude and latency
What does N1 measure on the SSEP waveform?
N1= amplitude
How high is the wave
Signal should not loose strength as it goes up the posterior column.
If we see increased latency or decreased amplitude on an SSEP, what does this mean?
There is problem w/a signal and may be damage to the posterior columns
What are the major anesthetic points during surgery w/SSEP?
Use infusion so we get steady state.
Use balanced technique.
Don’t go above 1 MAC of volatile
Don't go above 100mcg/kg of propofol.
Versed effects SSEP so don't use it (board question!)
If you see changes in the SSEP, what could you do?
Tell surgeons & dc anesthetic if possible.
Make sure oxygenation and ventilation are adequate.
Raise BP to ensure spinal cord perfusion.
Prepare to perform a wake up test
Why should we avoid bolusing drugs when monitoring SSEP?
Our anesthetic drugs can effect the SSEP waveform so try to use infusions vs bolusing
Why would we measure both SSEP and MEP?
SSEP is Monitoring posterior cord (sensory)
MEP is monitoring anterior cord (motor)
Name the anesthetic drugs that ALL EFFECT SSEP waveform in a dose dependent manner.
Fentanyl, benzos, propofol, N2O, volatiles
True or False. Responses are summed, they don’t have an exact accurate monitor.
TRUE. Look at the trend
MEP are sensitive to anesthetics. Most importantly to.........
our muscle relaxants (you wont’ have same movement of the foot)
So the way this is done in practice is to use a nerve stimulator and titrate in MR w/an infusion pump and keep 2/4 twitches the whole case.
A 12 yr old pt w/ scoliosis having a T4-T11 spinal instrumentation fusion. As the spine was fused the pt lost the MEP. Followed soon after by loss of MEP on the other side. The SSEP and MEP were both lost at this point. What would you do?
A wake up test, neurologic monitors aren't exactly accurate.
Not sure what to make of that info (say you just gave 100mcg of Fentanyl)
Or surgeon just wants wake up test
What are some very important points about a wake up test?
NEED to tell pt pre-op this is a possibility!
Need delicate balance in anesthetic. Want ¾ twitches but not 4/4 twitches because you don’t pt to wake up w/full strength.
Also want enough narcotic on board so pt doesn’t feel pain, wake them up w/out pain. Intra-op wake up test, titrate in a narcotic (fentanyl infusion).
Surgeons sometimes use electromyolography (EMG)? What type of surgery would need this and why do we care as CRNAs?
Plastic surgeon doing a face lift, and he wants to monitor facial nerve intra-operatively because they don't want to damage the facial nerve.
If the surgeon is doing EMG nerve monitoring, so they don't cut a nerve, we need to avoid muscle relaxants.
Describe a benign vs a big stimuli
Benign: calling persons name or light touch
Big stimuli: Rib retraction, abdominal exploration, laryngoscopy and intubation.
At 2-2.5MAC, what types of responses are our anesthetics blocking?
No BP or HR changes, no tears, no sweating, no movement, no memory
At 1 MAC, what is our anesthetic depth?
Ventilation.
We could see sweating or tearing.
No where near awareness.
May think pt might be getting light.
What is our anesthetic depth at 0.5MAC?
Less anesthesia. Pt won’t remember but pt will move.
Incidence of awareness overall is
0.15%
If muscle relaxants are used, awareness % is higher, what is it?
It’s higher (0.18%) if MR are used
Reason to avoid MR if surgeon doesn't need it
What is the % of awareness if no muscle relaxants are used?
0.10% (lower) if no MR are used
Describe the BIS at ~80-100
Awake, memory intact
Small amplitude, fast frequency wave
Describe the BIS at ~65-80
Sedation
Describe the BIS ~45-65
General anesthesia, deep hypnosis, near suppression
Large amplitude, slow frequency wave
Describe a BIS ~1-30
Increasing burst suppression
Deep anesthesia
Describe a BIS of 0
Cortical silence
Isoelectric EEG
What would you do if your patient had hypertension, tachycardia, movement, and autonomic responses with a light anesthesia clinical profile AND the BIS was high?
Assess level of surgical stimulation
Confirm delivery of hypnotics/analgesics
Consider increasing dosing of hypnotic/analgesic
Consider anti-HTN administration
What would you do if your patient had hypertension, tachycardia, movement, and autonomic responses with a light anesthesia clinical profile AND the BIS was in desired range of 45-60?
Assess level of surgical stimulation
Consider increasing analgesic dosing
Consider anti-HTN administration
What would you do if your patient had hypertension, tachycardia, movement, and autonomic responses with a light anesthesia clinical profile AND the BIS was low?
Consider anti-HTN administration
Assess level of surgical stimulation
Consider decreasing hypnotic and increasing analgesic dosinng
What would you do if your patient was HD stable with no movement/responses and you had an adequate anesthetic clinical profile but a HIGH value on the BIS?
Assess level of surgical stimulation
Consider increasing hypnotic dose
Consider increasing analgesic dosing
What would you do if your patient was HD stable with no movement/responses and you had an adequate anesthetic clinical profile & an adequate value on the BIS?
NOTHING! Continue observation
What would you do if your patient was HD stable with no movement/responses and you had an adequate anesthetic clinical profile but a LOW value on the BIS?
Consider decreasing hypnotic dosing
Consider decreasing analgesic dosing
What would you do if your pt was HD unstable, hypotensive, and/or arrhythmia and you felt the clinical anesthetic profile was deep but you had a HIGH BIS value?
Consider BP support
Assess other etiologies
Consider increasing hypnotic/analgesic dosing
What would you do if your pt was HD unstable, hypotensive, and/or arrhythmia and you felt the clinical anesthetic profile was deep but you had a an adequate BIS value?
Assess for other etiologies
Consider BP support
What would you do if your pt was HD unstable, hypotensive, and/or arrhythmia and you felt the clinical anesthetic profile was deep and you had a LOW BIS value?
