6901 Neuro Part II Flashcards
Low doses of volatile agents do what to CBF?
it’s either unchanged or increased
Low doses of volatile agents do what to CBF?
it’s either unchanged or increased
What happens to CBF in higher doses of volatile agent?
increases bc of the vasodilator effect
Autoregulation is impaired with what MAC?
> 1
Least and worst problematic inhalational agent?
sevo; halothane
Vasodilator influence of volatile agents is opposed by?
decreased CMRO2
Coupling includes what 2 values?
CBV and CMRO2
Coupling occurs at what MAC value?
What do volatile agents do to the coupling effect?
alter the coupling effect by redistributing the blood flow
Uncoupling is when?
CBF increases and CMR does not
What is circulatory steal?
increase in blood flow to normal areas but in ischemic areas vessels are maximally dilated and blood is redistributed away from ischemic area
Only what type of brain tissue can constrict?
normal
What happens to CBF in higher doses of volatile agent?
increases bc of the vasodilator effect
Autoregulation is impaired with what MAC?
> 1
Least and worst problematic inhalational agent?
sevo; halothane
Vasodilator influence of volatile agents is opposed by?
decreased CMRO2
Coupling includes what 2 values?
CBV and CMRO2
Coupling occurs at what MAC value?
less than 1
What do volatile agents do to the coupling effect?
alter the coupling effect by redistributing the blood flow
Uncoupling is when?
CBF increases and CMR does not
What is circulatory steal?
increase in blood flow to normal areas but in ischemic areas vessels are maximally dilated and blood is redistributed away from ischemic area
Only what type of brain tissue can constrict?
normal
What do volatile agents do to the coupling effect?
luxury perfusion which is when increased CBF causes decreased CMRO2
What type of MACs cause luxury perfusion/uncoupling?
higher
What is Robin Hood phenomenon?
vasoconstriction in normal vessels in the brain (decrease flow to normal area and increase flow to ischemic area)
Barbs cause what?
vasoconstriction
Effects of CBF last how long with all volatile agents?
2-5 hours
Which volatile agent causes the least vasodilation?
Iso
Which volatile agent causes biggest reduction in CMRO2?
Iso
Does N20 interfere with MEPs?
yes
What is the consensus about use of N20 in intracranial surgery?
controversial
N20 has been shown to increase what 3 things?
ICP, CBF, CMRO2
What’s significant about use of N20 with hypocapnia and IV anesthetics?
no change in CBF
Does Iso or Sevo increase the CBV more?
Iso
What does propofol do to CBF and CMRO2?
dose dependent decrease
Can you use propofol for MEP monitoring?
yes
What relaxes the brain better than volatile anesthetics?
propofol
What does etomidate do to CBF, CMRO2, and ICP?
decrease
The only agent that dilates cerebral vasculature and increases CBF by 60-80%?
ketamine
What type of effect do opioids have on CBF, CMRO2, and ICP?
minimal
What do benzos do to CBF, CMRO2?
decrease them to a lesser extent than barbs
What type of drug decreases CMRO2 the most?
barbs
What type of drugs decrease CBF the most?
propofol
Drug that is useful for awake craniotomy and carotid endarectomy?
dexmetomidine
Why is dexmetomidine a good drug for smokers?
their airways are really reactive and this allows for a smoother emergence
What does precedex do to CBF and CMRO2?
decreases CBF w/out decrease in CMRO2
Downfall to precedex?
may limit adequate cerebral oxygenation
Should you avoid suxxs when rapid paralysis is desired?
no
What is suxxs effect on CBF, CMRO2, ICP? What can you do to blunt that response?
increases prob d/t the fasciculations; give nonfasciculating dose
NMDAs effect on CBF, CMRO2, ICP?
little
Do you need to avoid NMDAs for cranial nerve monitoring?
yes
What about NMDAs may cause increased CBF?
histamine release that leads to dilation
What may NMDAs interact with?
seizure meds like phenytoin
If pt is on a lot of meds with hepatic enzyme induction what does that mean for suxxs and NMDAs?
rapidly metabolized and don’t last long; may need larger dose
These drugs are preferred for control of HTN after intracranial procedures?
Esmolol, Labetolol
What effect do Esmolol and Labetolol have on CBF and CMRO2?
none
Caution with use of these antiHTN drugs that impair autoregulation and dilate cerebral vessels and cause increased CBF and ICP?
nipride, nitro, hydralazine
Drug used to prevent vasospasm after subarachnoid bleed?
nimodipine
Adenosine is used for aneurysm clip surgeries why?
a lot easier to place clip if heart brady or stopped
Drug used during Na thiopental admin to offset hypotension?
phenylephrine
Most widely used drugs for decreasing CMR, with objective of causing coupled reduction in CBF and CBV?
barbs
What’s the end point for maximal brain protection?
burst suppression
Another drug that may cause coupled reduction in CBF and CBV?
propofol
How do glucocorticoids work for brain surgery?
penetrate the BBB and decrease edema associated with lesions
Most commonly used glucocorticoid regimen during intracranial surgery?
dexamethasone 4mg q6h
How long does it take to see effects from glucocorticoids in decreasing ICP?
several hours; so a lot are started 48 hours before surgery
A drug that is given prophylactically to decrease cortical irritation?
dilantin
These type of diuretics produce general diuresis and decrease the rate of CSF production and decrease cerebral edema?
loop diuretics
These type of diuretics decrease the water content of the brain?
osmotic
Do osmotic diuretics decrease ICF or ECF water?
both
Why do you give mannitol slowly?
may produce rapid vasodilation (hyperosmolarity), increased CBF, a transient rise in ICP, and increase in CBV
How quickly should you give mannitol and what should you monitor during it?
15 min; ICP
Dose of mannitol?
0.25-1g/kg
What do you have to do to prevent edema in prolonged surgeries if you have given mannitol during intracranial surgery?
check serum Na levels on regular basis
3 times fent, lido, prop should be given during intracranial surgery to blunt SNS response?
intubation, suctioning, skull pin application
Great risk of ICP spikes and brain herniation if midline shift >?
5cm
S/s increased ICP?
N/V, HTN, bradycardia, personality change, altered LOC, papilloedema, seizures, neuro deficits, resp pattern
How high should HOB be elevated to help with venous drainage?
15-30
How soon should intracranial surgery be delayed after balloon angioplasty, BMS, and DES?
> 2 weeks angioplasty, 4-6 BMS, 12 mos DES
Why do you use benzos and opioids with caution as premedication in brain surgery?
respiratory depression and increased ICP
In patients with midline shift and abnormal ventricular size what should you do with premedication?
omit
What 3 things should you avoid in neurosurgical patients?
hypotension, HTN, prolonged apnea
How should you treat hypotension in neurosurgical pts?
gentle volume and alpha adrenergic agonist
Which surgery do you need to be particularly mindful in preventing HTN with DL?
aneurysmal subarachnoid hemorrhage bc it can prevent recurrent hemorrhage from the aneurysm
Why should you prevent apnea in neurosurgical pt?
it causes increase in PaCO2 and corresponding cerebral vasodilation and decreases CPP
How can you blunt the effects of induction in neurosurgical pt?
fentanyl and lido 1.5 mg/kg
What does a flexed head impede?
jugular venous drainage and so it increases ICP
Why should you make sure all circuit connections are tight in neurosurgical pt?
bed is rotated 90-180 degrees
Cervical collar placement makes for a difficult what and therefore?
intubation; very sensitive to hypotension and HTN
2 contraindictions for suxxs use?
weakness or paralysis
2 conditions in which suxxs can only be used for the 48 hours following the injury? And why is that?
acute stroke or spinal cord injury; up regulation of the K receptors leading to hyperkalemia
Most IV agents (3) are indirect cerebral vasoconstrictors and decrease CBF, CMR leading to preserved autoregulation and CO2 activity?
propofol, thiopental, etomidate
Does dexmetomidine interfere with electrophysiological mapping?
no
What MAC of volatile agent should be used with SSEP monitoring and brain relaxation?
The 3 primary considerations in neurosurgery?
type of neuromonitoring planned, optimal brain relaxation, balance between adequate analgesia and ability to assess neuro function at the end of the surgical procedure
3 things to do to maintain brain relaxation?
o2/air infusion
4 ways to decrease ICP for optimal brain relaxation?
mannitol, hypertonic saline, TIVA, hypocapnia
One way to offset cerebral vasodilation from inhalation agents?
hypocapnia
MEP monitoring gets optimal signal with what type of anesthesia?
TIVA
A benefit of propofol infusion is that it provides better relaxation by further decreasing?
CBV
How does muscle relaxation facilitate venous drainage?
relaxes chest wall which decreases intrathoracic pressure and facilitates venous drainage
Some considerations with hyperventilation in neurosurgery?
cerebral vasoconstriction maintains decreased CBF and CBV, has a potential for causing or exacerbating cerebral ischemia, avoid in all pts with TBI, maintain PaCO2 between 30 and 35
What’s the exception for avoiding hyperventilation in all TBI pts?
if there is an acute increase in ICP hyperventilation can be done
A PaCO2 less than what should be discussed with the surgeon?
30
The goal for CVP in intracranial surgery?
euvolemia/ normal CVP
Fluid management in intracranial surgeries: pt should be kept (3)?
isovolemic, isotonic, and isooncotic
Fluid rate for intracranial surgery?
0.5-1 mL/kg/h
Should pre and intraop fluid and blood loss be replaced in intracranial pt?
yes
Is BBB subject to water movement?
yes
How does hypertonic saline reduce ICP?
osmotic effect and ability to remain outside of effective BBB
2 side effects of hypertonic saline?
electrolyte abnormalities, cardiac failure
What type of fluids should you avoid in intracranial pts?
dextrose containing
Why is it important to maintain normoglycemia in pts undergoing brain surgery?
high glucose levels may exacerbate neuro injury during ischemia
Target blood sugar in brain surgery?
140-180
When should you check glucose levels if pt having brain surgery?
definitely preop and check them frequently (q30 min) after
Intraop hyperglycemia is common in those undergoing?
emergent/urgent craniotomy following TBI
Increased variability in blood glucose can lead to?
increased osmotic shifts
How does hypoglycemia effect the brain?
it lowers brain tissue glucose concentration and the precipitation of brain energy crisis
Once the dura has been closed where do you maintain the BP?
at baseline
Signs of needing to delay extubation d/t upper airway edema?
facial edema and absence of cuff leak
3 considerations for prior to closure of dura?
- BP parameters should be set 2. PaCO2 should be allowed to return to normal; BP raised 120% above baseline 3. ability of brain to withstand such challenges can be directly assessed by the surgeon