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Brainstem purpose
maintain VS and intrinsic control of life processes
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What does the reticular formation do and where is it located?
- brainstem
- -relay station for descending motor control
- -excludes that going down the pyramidal tract
- -extrapyramidal
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What other term is used synonymously with brainstem
mid brain
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What does the vestibular formation do and where is it located?
- -brainstem
- -coordinates eye and limb movement in response to body position
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What is the cerebellum's function
-controls posture and coordinates muscle contraction on the ipsilateral side (same side)
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Where is the diencephalon located?
What other structures are located within it?
- Midbrain
- -thalamus
- -hypothalamus
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Thalamus function
sensory integrative center
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Where is the basal ganglia located and what is its function?
- midbrain
- -planning and generating motor commands
- -motor signals generated here travel down the reticular formation and eventually to the muscle
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Differential blockade
- Not all fibers are blocked simultaneously with spinal anesthesia
- -first to be blocked are sympathetic fibers (small type C)
- -next are sensory
- -last are motor (large fibers)
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With a spinal, which will be higher, sympathetic block or motor block?
Sympathetic block (up to 4 dermatomes higher)
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T4 dermatome
T10 dermatome
- T4- nipples
- T10- umbilicus
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Can a pt have a sympathetic and sensory block and still have muscle movement?
Yes the large motor fibers are difficult to block
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Ascending pathway of the SC- sensory or motor?
sensory
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Descending pathway of the SC- sensory or motor?
motor
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Where does sensory information enter the SC?
- Dorsal nerve roots
- -travels from peripheral nerve to dorsal (posterior) horn where it synapses with the SC
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After sensory information enters the SC where does it go?
Travels via ascending pathways thru the SC to the brain
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What 2 routes can the sensory information travel to the brain?
- 1) dorsal (posterior)
- 2 dorsal columns
- a) fasciculus gracilis
- b) fasciculus cuneatus
2) spinothalamic (anterior pathway)
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Descending pathway
- -motor
- -descends to muscle which is then activated
- -brain to SC
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Where do the descending motor pathways synapse?
In the anterior horn of the SC
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What pathway (tract) do the motor impulses travel via?
corticospinal tract
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3 main sensory pathways
- -spinothalamic (AKA anterolateral)
- -posterior dorsal columns (there are 2 columns but we think of them as 1)
- -spinocerebellar
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Which 2 sensory tracts cross the SC?
- spinothalamic
- and dorsal columns
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What type of sensory sensations does the spinothalamic (anterolateral) tract carry?
- -pain and temperature
- -travel via small fibers
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Lissauer's tract
path that pain impulses take (in the spinothalamic tract) to travel from periphery to the brain
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What type of sensory sensations do the dorsal columns carry?
proprioception, "where is my limb?"
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What type of sensory sensations does the spinocerebellar tract carry?
unconscious proprioception (ie walking without thinking, no conscious thought is required)
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How does the spinocerebellar tract differ from the other 2 sensory SC tracts (spinothalamic and dorsal columns)?
- -does NOT cross the SC
- -so a cerebellar lesion causes weakness on THAT side
- -only travels as far as the midbrain (cerebellum)
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Does a lesion of the spinothalamic and dorsal columns cause an issue of the ipsilateral or contralateral side?
contralateral side (remember it crosses the SC)
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Where do the dorsal columns and spinothalamic tracts travel to (what part of the brain)?
Thalamus (sensory integrative center) and cerebral cortex
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Where within the brain does the anterolateral (spinothalamic) tract synapse?
- -synapses in the thalamus (posterior ventrolateral nucleus)
- -then travels up into the brain
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Where within the brain do the dorsal horns synapse?
-thalamus (ventral posterior nucleus)
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What part of the brain regulates motor impulses ?
- Basal ganglia
- Cerebellum
- Brain stem
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What path do motor impulses take (brain to periphery)
- -start in brain
- -travel thru brain stem
- -crosses SC
- -synapses in anterior horn
- -travel thru corticospinal tract (pyramidal)
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Does the reticular formation relay pyramidal or extra-pyramidal impulses?
Extra-pyradimal
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Pyramidal motor tract
- major motor pathway
- controls precise movement and laryngeal muscles
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Extra-pyramidal motor tract
- maintains postural tone
- directs voluntary movement
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Parts of the extra-pyradimal tract
- rubrospinal
- lateral vestibulospinal
- reticulospinal
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How are the upper and lower motor neurons differentiated?
- UMN are above where the corticospinal tract synapses with the anterior horn
- LMN are below
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What type of paralysis results with injury to the UMN?
spastic paralysis and hyperreflexia
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UMN injury
- Occurs high (like in the brain)
- Ex: CP
- lesion interrupts signals between the brain and SC
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What type of paralysis results with injury to the LMN?
flaccid paralysis and areflexia
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LMN injury
- any interruption below L1 (below SC)
- doesn't have to do with the brain, is between SC and affected muscle
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Reflex
- stereotyped action in response to a peripheral stimuli
- SC contains neural circuits which produce reflexes
- Ex: knee-jerk, brain is not involved, only the SC is
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SNS reflexes (pupils and heart)
- pupil dilation
- + inotropic and chronotropic effects on the heart
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Where do the SNS fibers originate from?
Thoracic and lumbar
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Where do the PNS fibers originate from?
Brainstem and sacral SC
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Pathologic autonomic reflex
AKA mass reflex
AKA denervation hyperreflexia
AKA autonomic hyperreflexia
- occurs in presence of SC transection
- occurs when there is a stimulus to the skin or a visceral organ (below the level of SC injury)
- get simultaneous excitation of ALL segmental reflexes (SNS, PNS, massive excitation of the entire ANS)
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At what level SC injury is autonomic hyperreflexia likely to occur at?
At what level is it unlikely?
- Likely - transection above T5
- Unlikely- lesion below T10
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What type of anesthesia is appropriate for a pt with a T5 SC transection having a cystoscopy?
- GA or spinal even though the procedure is often done under LA
- a stimulus below the level of the transection will stimulate ANS
- need to not let the pt feel it
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What needs to be considered for a pt with a SC injury?
The level of their injury (how stimulating the procedure is is less important)
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What symptoms are seen with mass reflex
- HTN
- bradycardia (due to carotid baroreceptor reflex)
- diaphoresis
- flushing
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How is mass reflex treated?
Treat HTN with direct acting VD (ex: nipride)
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Evoked potential
delivering a stimulus and looking at the result of that stimulus
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Which type of EP is most sensitive to anesthetic drugs? Least sensitive?
- Most- visual EP
- Least- brain stem auditory EP
- (sensitivity implies that our drugs will change the EP)
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What is SSEP
- somatosensory EP
- stimulate sensory system and see how it travels to the brain
- midrange sensitivity to anesthesia drugs
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Can anesthesia drugs affect an EEG tracing?
Yes they will cause burst suppression and slowing
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EEG rhythms: alpha
pt relaxed with eyes closed
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EEG rhythms: beta
pt concentrating
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EEG rhythms: delta
normal sleep
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EEG rhythms: burst suppression
- occurs during deep anesthesia
- spikes then flat inbetween
- also due to extreme hypothermia or hypoxia
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For what procedure might we use EEG monitoring?
- CEA
- monitors CBF and oxygenation
- EEG changes can indicate injury or that anesthetic level has changed
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If EEG changes are noticed during a CEA what should be done?
- Communicate with EEG tech
- Raise BP to increase flow to brain
- 100% O2
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If we're using SSEP and we stimulate the pt's left foot, are we monitoring the L or R side of the brain?
right
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When looking at SSEP waveforms what are we looking at?
- Latency (wave frequency) and how long it takes for stimulus to get to the brain
- Amplitude (wave height) force
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SSEP can tell us the functioning of what?
- Peripheral nerve
- Posterior column of the SC
- Brain
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Anesthetic management of a pt getting SSEP
- avoid giving a large amount of any 1 drug
- use infusions (steady state)
- avoid bolusing
- avoid versed
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T or F, SSEP gives us information about the anterior part of the SC?
F, information about the posterior (sensory) portion only
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What effect do our anesthesia drugs have on SSEP?
- All affect the SSEP waveform in a DOSE DEPENDENT manner!!
- volatiles, benzos, propofol, N20, opioids
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NMB considerations when using MEP
use an infusion and maintain 2 / 4 twitches
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MEP
a nerve stimulator is used and look to see if there is movement (of the foot for example)
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wake up test
- if unsure of accuracy of MEP or SSEP tracings
- tell pt about possibility pre-op
- ask pt to wriggle toes
- maintain 2-3/ 4 twitches to avoid full movement of pt!
- ensure enough narcotic on board
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NMB use and EMG
Avoid NMB
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Rank order of response to stimuli
- verbal
- memory (implicit then explicit)
- movement (purposeful then involuntary)
- ventilation
- sudomotor (tearing then sweating)
- HD (BP then HR)
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BIS
EEG monitor configured to give us a number that corresponds with depth of anesthesia
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T or F, pts are more likely to recall something unpleasant or threatening?
T
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Awareness incidence- total
0.15
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Awareness incidence- with NMB
0.18
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Awareness incidence- without NMB
- 0.1
- so avoid NMB if surgeon does not require it
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BIS- GA
- 40-60
- large amplitude, low frequency wave
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BIS- moderate sedation
60-80
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BIS- awake
- > 80
- small amplitude, fast frequency wave
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T or F, BIS monitors analgesic level?
F, only measures level of hypnosis!!
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With what pts is a BIS monitor recommended?
- Pt's with h/o awareness
- Is NOT the standard of care
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