ITE Neuro Flashcards
Name that pathway!
Peripheral nerve ->
Ipsilateral dorsal root ganglia ->
Ipsilateral posterior and lateral SPINAL CORD ->
Decussation (crossover) of nerve fibers at cervicomedullary junction ->
Contralateral medial lemniscus (w/in BRAINSTEM) ->
Contralateral ventroposterolateral nucleus of THALAMUS->
Contralateral thalamocortical radiation ->
Contralateral sensorimotor cerebral cortex
Pathway for Sensory Evoked Potentials (SSEPs)
- ascending pathway
Name that pathway!
Lower limb cortex -> Internal capsule -> Brainstem (decussate at medulla) -> Corticospinal tract -> Peripheral n.
Pathway for Motor Evoked Potentials (SEPs)
Name that pathway!
Retina -> Optic n -> Optic chiasm -> Optic tract -> Superior Colliculus -> Visual cortex
Pathway for Visual Evoked Potentials (SEPs)
During multilevel spinal fusion, the ________ nerves are monitored so that the RIGHT side of the posterior spinal cord and LEFT brainstem and cortex can be assessed.
Right Median and Tibial nerves
*Neuronal cells along sensory pathway are at risk for surgical damage or ischemia
Ischemic changes in SSEPs are quantified by reduction in _____ of the signal strength and increase in its _______ (time to signal detection
amplitude
latency
________ is the most cost-effective, accurate, and reliable method of monitoring intracranial pressure.
Ventriculostomy catheter
- it also provides a way to drain CSF and samples for lab analysis
Noninvasive way to measure ICP
measuring optic nerve sheath diameter via ultrasound
- new, not standard
Autonomic hyperreflexia (or autonomic dysreflexia) is a syndrome that may occur in pts with spinal cord injuries above the level of \_\_\_. This is usually seen at \_\_\_\_\_ (time) after spinal cord injury.
T12
- particularly above T5!
2 weeks - 6 months
Why does Autonomic hyperreflexia (or autonomic dysreflexia) occur?
- ie: reflex bradycardia, severe HTN, arrythmias, MI, intense vasoconstriction (cool, dry, pale skin below SCI)
It occurs d/t cutaneous or visceral stimulation below the level of the SCI, and inhibitory impulses from higher CNS centers cannot reach and no longer help regulate.
- there is reflex cutaneous vasodilation above lvl of SCI (nasal congestion, sweating, warm, flushed skin in UE)
Prevention of Autonomic hyperreflexia (or autonomic dysreflexia) is best done with ____
spinal or epidural anesthesia w/ local anesthetic and/or deep GA
Treatment of Autonomic hyperreflexia (or autonomic dysreflexia)
Stop triggering event
Administer fast acting direct vasodilators (sodium nitroprusside, nitroglycerin, or nicardipine)
*BB can worsen reflexive bradycardia if given in setting of unopposed a-stimulation -> hypertensive crisis
What is the receptor theory of muscle relaxants? What is the responses/sensitivities thought to be d/t?
Upregulation of receptors is associated with :
HYPERsensitivity to agonists (succinylcholine) and
HYPOsensitivity to antagonists (rocuronium)
Thought to be d/t presence/absence of an isoform of AChR that develop after denervation or burn injuries
Mature postjunctional AChRs are composed of what subunits?
What do immature isoforms of AChR look like that only form after denervation or burn injuries?
5 subunits
- 2 a1
- B1
- delta
- epsilon
Isoform: (Immature upregulated receptors)
7 subunits
- 2a1B1dy
Why does succinylcholine admin in the presence of upregulated AChRs (ie. denervation or burn injuries) result in potentially lethal hyperkalemia?
The whole muscle membrane depolarizes ->
Massive efflux of potassium from cell
*Succinylcholine is a molecule closely resembling ACh
The parasympathetic component of the facial (VII), glossopharyngeal (IX), and vagus nerves (X) lie in the _______ (structure).
Medulla oblongata (of brainstem)
The parasympathetic component of the oculomotor nerve (III) lie in the _______ (structure).
midbrain (of brainstem)
Which cranial nerve has the most extensive distribution of the PNS?
Vagus nerve X
Full-flow CPB is maintained for ____ min after reaching goal temperature to ensure ____
20-30
adequate cerebral cooling prior to stopping circulation
Pts with ALS have high risk of having pulmonary complications d/t ______ involvement and respiratory muscle weakness.
- How does management change for succinylcholine vs roc?
bulbar muscle
Avoid sux
- ALS assoc. w/ LOSS of motor neurons, forming extrajunctional ACh receptors and can mount exaggerated response
- life threatening hyperK
Lower dose of Roc
- higher sensitivity, prolonged, exaggerated response
- upregulation of extrajunctional receptors on postsynaptic neurons
Normal ICP is ___ mmHg.
Elevated is ____ mmHg
5-15 mmHg
20 mmHg
MAC of nitrous oxide is ___
105%
How does nitrous oxide cause increase in ICP?
Increase in:
- cerebral metabolic rate
- cerebral blood flow
- can diffuse into air filled cavities
Intracranial space has 3 major components, and any changes to ICP can be made by altering them.
- Brain parenchyma
- Blood
- CSF
How do propofol, thiopental, and etomidate affect ICP?
All
- decrease ICP
- decrease Cerebral metabolic rate of O2 (CMRO2)
- decrease CBF
*opioids have little to no effect on CBF
How does ketamine affect ICP?
No effect on CMRO2
Marked cerebral vasodilation ->
Increase ICP
When hyperventilating to decrease ICP (hypocarbic vasoconstriction of cerebral vessels), what is your target PaCO2?
25-35 mmHg
*any lower, you can cause local ischemia
The spinal cord receives 75% of its blood supply from ______ artery, and 25% of its blood supply from the ____ artery. Which one provides the motor and which one the sensory tract?
anterior spinal artery
- motor tracts
2 posterior spinal arteries
- sensory tracts
The anterior spinal artery receives most of its blood flow from the anterior radicular arteries in the thoracic segment of the spinal cord. The largest radicular artery is the _____
artery of Adamkiewicz
Why is hyperventilation during endovascular aneurysm coiling avoided?
hypocarbic vasoconstriction of cerebral vessels -> coils can end up in vessels rather than target aneurysm (improper coil placement)
In pts with myasthenia gravis, how does management change for succinylcholine vs roc?
Increase dose of sux
- more resistant to sux d/t decrease in total # of functioning receptors (smaller number of AChRs available for depolarization) and impaired plasma cholinesterase function
Lower dose of Roc
- higher sensitivity, exaggerated response
In pts with lambert-eaton myasthenic syndrome, how does management change for succinylcholine vs roc?
Lower dose of sux
- higher sensitivity d/t destruction of presynaptic VGCC -> decrease in release of ACh from nerve terminals, less competition
- (note: No receptor upregulation)
Lower dose of Roc
- higher sensitivity, exaggerated response
- Lambs are sensitive animals
Myasthenia gravis is caused by antibodies against _____
Lambert Eaten is caused by antibodies against _____
postsynaptic ACh receptor (80%) or Muscle specific tyrosine kinase MuSK-Ab (20%)
P/Q-type voltage gated calcium channels
Acute and chronic phenytoin use affecting nondepolarizing NMBs
acute: potentiates blockade
chronic: increases resistance
Volatile agent effects on cerebral blood flow
Opposing effects:
- Decrease CMRO2
- Increase CBF (cerebral vasodilation)
Why does methemoglobin cause hypoxia?
- Methemoglobin (MetHb) is an altered state of Hb where the Ferrous (Fe2+) form of heme is oxidized to Ferric (Fe3+).
- MetHb does not bind O2 and therefore cannot transport it for use
What value is falsely elevated in methemoglobin and what value will rise when you administer oxygen?
SpO2 falsely elevated since it is calculated based on the assumption that all hb is normal
PaO2 will increase appropriately since it is unaffcted by MetHb
General anesthetic effects on the brain resemble _____, with an EEG that shows _____
Naturally occuring non-rapid eye movement (NREM) sleep
EEG
- Slow frequency
- Large amplitude
EEG in an awake individual
Fast frequency
Low amplitude
EEG in REM sleep
Fast frequency
Low amplitude
Most common causes of atlantoaxial instability
- Trauma
- Achondroplasia
- Down syndrome
- RA
Least accurate measure of core body temp?
Bladder
Most common cause for a subarachnoid hemorrhage pt to lose consciousness during the first day of hospitalization
rebleeding
most common cause of death from SAH:
- first bleed
Second most common
- rebleed
Most common cause for a subarachnoid hemorrhage pt to lose consciousness 5-10 days out from surgery
vasospasm
Why is an opioid only spinal inadequate for a pt with a spinal cord injury?
Does not prevent autonomic hyperreflexia
-
Best sedation for deep brain stimulation placement
dexmedetomidine (alpha 2 agonist)
What meds should be avoided during deep brain stimulation placement?
Gabaminergic meds
- interferes with microelectrode recording (MER) and mapping for electrode placement
Parkinson disease is caused by loss of _____ neurons in the ______
dopamine-secreting neurons
substantia nigra of basal ganglia
_____ is the first line tx in pt with organophosphate poisoning
Atropine
- antagonize action of ACh at the muscarinic synpases
(or pralidoxime)
The main effect of organophosphates is to ______
inhibit acetylcholinesterase (AChE) and butyrylcholinesterase in the cholinergic nervous system
*end result is stimulating muscarinic synapses
Signs and symptoms of organophosphate poisoning
SLUDGE Mi
Salivation Lacrimation Urination Defecation Gi motility Emesis Miosis
In an awake craniotomy, a sz is caused by _____, and administration of propofol or (warm/iced) saline is first line of action
cortical stimulation
iced
Difference btwn Duchenne and Becker muscular dystrophy?
Duchenne: no dystrophin
Becker: decreased quantity of dystrophin
Pts in the _______ position who undergo posterior fossa or cervical dural incisions are at the highest risk for developing a clinically significant pneumocephalus
seated
What is Cushing’s Triad?
HTN
Bradycardia
Decreased RR
*sign of increased ICP
_________ is the best diagnostic tool to diagnose cerebral vasospasm after a subarachnoid hemorrhage
cerebral angiography
Vasospasm after SAH can occur ___ days after, and peaks at ____ days. Spasms typically resolve by day ____
3
6-10
14
Treatment for vasospasm following SAH
Triple H
- Hypervolemia
- Hypertension
- Hemodilution
When diagnosing brain death, _____ reflexes are permissible, and _____ reflexes are not
spinally-mediated
- patellar reflex
Brainstem
- light
- occulocephalic
- vestibular
- corneal
- facial
- pharyngeal (gag)
- tracheal (cough)
Myasthenia gravis vs lambert eaton
- which one is alleviated with movement?
Lambert eaton (myasthenic syndrome)
Transmural pressure equation
MAP - ICP
TMP of an aneurysm determines risk of rupture
*decrease in CSF will increase transmural pressure and can lead to aneurysm rupture
What are ECG changes during SAH d/t?
High circulating catecholamines ->
subendocardial ischemia
GCS score
Motor (6)
Verbal (5)
Eyes (4)
Metabolic (acidosis/alkalosis) exacerbates hypokalemia by _____
alkalosis
Intracellular H+ gets transported out of cell and K+ into cell ->
creating intracellular shift of potassium
Metabolic (acidosis/alkalosis) exacerbates HYPERkalemia by _____
Acidosis
H+ gets transported into cell and K+ out of cell ->
creating extracellular shift of potassium
Mothers with myasthenia gravis who are giving birth, need to have their infants monitored for _____ (time) after birth d/t maternal antibodies to _______ freely crossing placenta
24-48 hours after birth
acetylcholine receptors in postsynaptic neuromuscular junction
- Transient Neonatal Myasthenia Gravis (TNMG)
Treatment for infants with Transient Neonatal Myasthenia Gravis (TNMG)
Acetylcholinesterase inhibitors
Nutritional and respiratory support
The basilar artery of the circle of willis splits into ____
2 posterior cerebral arteries
The anterior inferior cerebellar artery of the circle of willis branches off of the ______ artery
basilar
The internal carotid of the circle of willis branches into ______
Middle and anterior cerebral arteries
For ALS, MG, and Lambert Eaton, how do you titrate rocuronium?
Lower dose of Roc
- higher sensitivity, prolonged, exaggerated response
Why is neuraxial anesthesia relatively contraindicated in ALS?
Lack of protective n sheath around spinal cord and demyelination makes spinal cord more susceptible to potential neurotoxic effects of LA
- if you have to, epidural > intrathecal
For ALS, MG, and Lambert Eaton, how do you titrate succinylcholine?
ALS
Avoid sux
- life threatening hyperK
Lambert Eaton:
- Lower dose of sux
- slighly more sensitive to
MG:
Increase dose of sux
- more resistant to
Most common cause of SAH is ______.
Ruptured cerebral aneurysm
Modified Hunt-Hess scale of grading SAH
0-5, progressively getting worse
0 - unruptured aneurysm
5 - Coma, decerebrate posture
Calcitriol
- What does it do?
- Where does it act?
Active form of Vit D
- Increases GI uptake of Ca2+
- Decreases renal Ca2+ excretion
What hormones are Secreted in the posterior pituitary?
ADH
Oxytocin
Bromocriptine and cabergoline are _____, and act as a negative feedback NT for the production of ______ in the anterior pituitary
Dopamine agonists
Prolactin
Why are pts with acromegaly d/t GH secreting tumor considered difficult airways? (5)
- Smaller size of glottic opening
- Hypertrophy of aryepiglottic folds
- Calcinosis of larynx
- Recurrent laryngeal n injury
- Hypertrophy of tongue
Pts with panhypopituitarism d/t pituitary tumor are generally prescribed _____ preoperatively
- Glucocorticoids
- brain swelling
- suppressed adrenal axis from ACTH insufficiency - Vasopressin
- lack of ADH - Thyroxine
Hyperkalemic periodic paralysis is a _______caused by _____
hereditary skeletal muscle ion channelopathy that causes MYOTONIC paralysis
VG-sodium channel defects
*same as Type 2 Hypokalemic Periodic paralysis but is hyperexcitable
Hypokalemic periodic paralysis is a _______caused by _____
hereditary skeletal muscle ion channelopathy that causes FLACCID paralysis that affects proximal muscles, limbs, trunks, respiratory m weakness
Type 1: calcium channel defect
Type 2: Sodium channel
- less functional
Myotonia congenita is a _______ channelopathy that is characterized by ____
chloride channel skeletal muscle
“warm up effect”
- muscle stiffness worsens after rest, improves with use
What is most effective at decreasing incidence of myalgia
preop NSAIDs
Clinical manifestations of Myasthenia Gravis vs Lambert Eaton (myasthenic syndrome)
- Muscle weakness location
- Muscle strength with movement/exercise
- Reflexes absent/present
- Muscle pain common/uncommon
Myasthenia gravis
- Extraocular, bulbar, facial
- Muscle strength worsens with movement/exercise
- Reflexes normal
- Muscle pain uncommon
LE
- Proximal limb
- Muscle strength improves with movement/exercise
- Reflexes decreased/absent
- Muscle pain common
Myasthenia Gravis vs Lambert Eaton (myasthenic syndrome)
- Response to anticholinesterase
Myasthenia Gravis:
- Good response
Lambert Eaton (myasthenic syndrome) - Poor response
Are children at high risk of post-op delirium?
Yes, extremes of age
- 30% in peds pt
What types of surgeries are at high risk of post op delirium?
Cardiac
Thoracic
Orthopedic (hip)
Limb-girdle muscular dystrophy causes weakness of proximal muscles and _______ that can lead to short life span.
Cardiomyopathy and AV conduction defects
Why should volatile anesthetics and succinylcholine be avoided in Limb-girdle muscular dystrophy?
Risk of rhabdo
Hyperkalemia
Why is using succinylcholine a bad idea in pts with prolonged use of NMB agents?
acetylcholine receptor upregulation -> inc sensitivity to succ -> hyperK
What predicts a decrease likelihood that postop mechanical ventilation is required in Myasthenia gravis pts?
- Disease for < ___ months,
- pyridostigmine dose > __ mg/d
- a vital capacity of ___L
- 72 months*
- 6 years (greatest risk)
> 750 mg/day
< 2.9 L
In a normotensive pt with increased ICP and PCO2 of 25 mmHg, the quickest way to reduce ICP is ____
propofol
Hoarseness following anterior cervical spinal cord surgery is most commonly d/t ____
vocal cord palsy (VCP)
- d/t direct pressure of ETT on recurrent laryngeal n during surgical retraction
In pts with mitochondrial myopathies (impairment in oxidative phosphorylation), you need to assess preop baseline function in: (4)
- Hypotonia
- Neuro function
- Multi organ dysfunction
- Cardiomyopathy
In pts with mitochondrial myopathies (impairment in oxidative phosphorylation), you need to minimize what stressors: (6)
- Prolonged fasting
- Hypoglycemia
- Hypothermia
- Tourniquet use
- N/V
- Anxiety
What is the “wake up” test?
Discontinuing or decreasing anesthetics to facilitate pts being able to follow commands
- Assess gross motor function -> Ask pts to move UE, then LE
- “All or nothing”
- If pt is able to do this, unlikely to have spinal cord compromised
- Then you re-apply rapidly active sedative (prop)
What is more concerning, decerebrate (extension) or decorticate (flexion) response to pain?
Decerebrate (extension)
- most people will withdraw to pain
Motor GCS
1 - no response 2 - Decerebrate (extension) 3 - Decorticate (flexion) 4 - Withdrawl from pain 5 - Localizes painful stimulus 6 - obeys commands
Verbal GCS
- No response
- Incoherent sounds
- Incongruent WORDS
- Confused speech
- Normal convo
Why should mannitol be given slowly over 10-15 min to reduce ICP?
Can paradoxically cause a vasodilatory effect -> engorgement of brain -> inc ICP
Why is succinylcholine bad for pts with Multiple SCLEROSIS and a recent spinal cord transection?
Upregulation of nicotinic ACh receptors –> hyperkalemia
How does succinylcholine work?
2 molecules of ACh linked by a methyl group
- stimulates ACH receptors at NMJ ->
Opens ion channels and cause depolarization
Then degraded by plasma cholinesterase or pseudocholinesterase
(not degraded by acetylcholinesterase)
How do all volatile anesthestics affect:
- CMRO2
- CBF
- ICP
- CMRO2: decrease (with seep)
- CBF: increase (d/t vasodilation in dose dependent manner)
- ICP: increase
The brain uses ___% of the total body’s oxygen consumption
20%
How does Propofol, etomidate, Benzo and thiopental affect:
- CMRO2
- CBF
- ICP
- CMRO2: decrease
- CBF: decrease
- ICP: decrease
Neostigmine reverses paralytic how?
Anticholinesterase that reverses nondepolarizing neuromuscular blockers
- prevents destruction of ACh -> potentiate ACh at receptors
*glycopyrrolate is anticholinergic agent
Why is deliberate hypotension performed at the time of embolization of AVMs?
Decrease flow of blood through the artery that feeds the AVM and prevent systemic embolization of the endovascular glue that is used
How long to pts with AVMs anticoagulated for periop?
at least 24h post op to prevent thrombus development
Parasympathetic stimulation of heart causes (depolarization/hyperpolarization) of the heart
Hyperpolarization
- efflux of potassium out of cell -> slow conduction -> decrease SA and AV node conduction
How can ketamine induce seizures? (4)
- Increase CMRO2
- Increase CBF
- Lower sz threshold
- Stim CNS
Serotonin syndrome presentation (6)
- HTN
- Hyperthermia
- Tachycardia
- Tremors
- Overactive reflexes
- Muscle rigidity
What spinal pathway tract carries fine touch and proprioception?
Dorsal column (posterior column) travels through
- Gracile faciculus -> nucleus
- Cuneate faciculus -> nucleus
What spinal pathway tract carries limb motor ?
Lateral corticospinal tract
What spinal pathway tract carries pain and temp?
Lateral spinothalamic tract
What spinal pathway tract carries crude touch?
Anterior spinothalamic tract
What spinal pathway tract carries axial motor?
Ventral corticospinal tract
What test differentiates CSF from normal saline (ie. during an epidural)
POC glucose test strip
- glucose is in CSF and not NS
SSEP are a poor monitor for detecting vascular compromise of which arterial blood supply?
Anterior spinal artery
- supplies anterior MOTOR portion of the spinal column
Fluid resuscitation in TBI pts
normal saline or hypertonic saline
- Increasing MAP while decreasing ICP
- hyperosmolar solns
What type of solutions should be avoided in neurosurgery?
Glucose containing solns (ie: D5)
- worsens cerebral edema
Cerebral vasospasm is a large cause of post-subarachnoid hemorrhage
- how do you treat it?
Triple H therapy
- Hypertension
- Hemodilution
- Hypervolemia
*increases perfusion past the spasm
Jugular venous oximetry (SjvO2) is a measure of _____, which is done by placing a catheter in the jugular vein at _____ level
global oxygenation and perfusion
C1-C2
Summary of Nervous system changes with aging: (5)
- Decreased gray/white matter
- Decreased NTs (ACh, dopamine)
- Decreased epidural space
- Decreased CSF volume
- Increased permeability of dura mater
