Neurosurgery Flashcards
3 components of the non-expandable cranial vault
- brain tissue (80%)
- blood (12%)
- CSF (8%)
Cushing’s reflex
Increased ICP= Increased BP and Decreased HR
How are CBF and CMRO2 coupled?
In a direct manner. If one decreases, so does the other.
At what point in a craniotomy is there intense stimulation?
At the beginning and end of the procedure.
Minimal stimulation in the middle
What is the primary substrate of metabolism
glucose
what effect does hypoglycemia have on the brain
worsens hypoxic injury
How is the metabolic rate of the brain measured
oxygen consumption (CMRO2)
How much does the adult human brain weigh
1300-1400 gms
Amount of cerebral blood flow per minute
650-700ml
What % of total cardiac output does cerebral blood flow make up?
about 14%
The brain can increase flow as much as __ % of cardiac output
15-20%
Average CBF
50mL/100gm/min
but varies regionally from 30-300mL/100gm/min
What CBF is associated with slowing of EEG
<25mL/100gm/min
What CBF is associated with isoelectric EEG
~15-20mL/100gm/min
What CBF results in irreversible injury?
<10mL/100gm/min
Which 2 parts of the brain are more sensitive to hypoxic brain injury than others
- hippocampus
- cerebellum
CPP is = to ?
MAP-ICP or CVP (which ever is higher)
Why is CPP essentially = to MAP?
bc ICP/CVP is small
unless they have increased ICP…
CPP associated with EEG changes
CPP < 50 torr
CPP that results in irreversible damage
CPP < 25 torr
At what CPP is autoregulation diminished
below 50 torr
CBF is autoregulated at MAP between ___ torr
50-150
When does luxury perfusion occur? DO we want this during brain surgery
CBF> CMRO2
nope
What is CBF proportional to?
PaCO2
What happens to CBF when minute ventilation is doubled
decreases by half
When do volatile anesthetic drugs cause a CNS/metabolism uncoupling?
MAC above 1.5
What results from volatile anesthetic CNS uncoupling
reduced CMRO2 but also cerebral vasodilation so increased CBF and ICP
What type of anesthetic drugs preserve CNS coupling
IV anesthetics
Reduce CMRO2 but do not cerebrally vasodilate
which volatiles decrease cerebral vascular resistance
all of them
What effect do volatiles have on CBV, CBF, and ICP
increases
volatile effect on CMRO2
decreased
volatile effect on cortical activity
abolishes it
How does hyperventilation affect the increases in ICP
attenuates it (reduces the effect)
Should you use nitrous on a crani
no maam
expands closed gas spaces, increases CBF, ICP and can increase CMRO2
4 absolute contraindications to nitrous use
- intracranial air present
- EP signal is inadequate
- increased ICP
- tight brain
What class of drugs decreases CBF, ICP, and CMRO2, inhibits NT receptors, and slows EEG
barbiturates
effect of propofol on CBF
dose dependent decrease
What propofol dose results in an isoelectric EEG
500mcg/kg/min
What IV agent is associated with decrease CBF, ICP and CMRO2 but causes seizures in patients with a seizure history
etomidate
metabolite of what drug is associated with seizures
demerol
Opioids affect on CBF and CMRO2
dose dependent decrease
What limits the usefulness of benzodiazepines in cranial surgery
respiratory depression
What contraindicates the use of benzos in a crani
increased ICP
Ketamine effect on ICP and CBF
increases both.
ICP increased >80%
depolarizing NMB effects on ICP, CBF, CMRO2?
Increases all
When are depolarizing NMB contraindicated in neurosurgery
- denervated muscle
- CVA
- motor neuron lesions
nondepolarizing NMB effect on ICP, CBF, CMRO2
minimal effects
Which type of drug therapy can cause increased dosage requirement of nondepolarizers?
anticonvulsant meds like dilantin
Which type of fluids should be avoided in neurosurgery
dextrose fluids
What are the 2 preferred fluids for volume resuscitation in NSGY
- normal saline
- colloid
Can LR be used in neurosurgery?
yes but volume must be limited. NS is a better choice
Do not exceed __ L of hetastarch in order to avoid coagulopathy
1- 1.5L
Hct goal for NSGY pts
30-35
What may help reduce vasospasm for aneurysm clipping?
mild volume expansion
In general keep neurosurgery patients… ( the 3 I’s)
- isotonic
- isovolemic
- isooncotic
common monitors involved in neurosurgery (lots of them srry)
-EKG
-artline
-ETCO2, pulse ox, ABG
-peripheral nerve stimulator
-CVP
-temp
-UOP
EEG or SSEP
cerebral oxygen monitoring
What is more important…that a certain drug combo is used, or ensuring a smooth induction??
smooth induction :)
To facilitate a smooth induction what 3 things are we trying to avoid?
increased ICP
HTN
hypotension
What 2 things are used during induction to maximize venous drainage?
- avoid excessive neck flexion
- HOB >15 degrees
During preoxygenation for a NSGY case do we want to hyperventilate or hypoventilate the patient?
hyperventilate :)
What is used during induction to blunt SNS outflow
opioids
What is used during induction of NSGY pt to prevent bucking/coughing
muscle relaxant
What must be evaluated before extubation
intact neurological function
What do we want to avoid when waking up a neuro patient
bucking, straining, or coughing on ETT
When should the CRNA re-establish spontaneous breathing in a NSGY case and why?
prior to skin closure and pin removal
because once the pins are removed there is little stimulation and return of respirations may be delayed if you wait until after pin removal
What is the benefit of rapid awakening
promotes neuro assessment
What are the 4 major types of Intracranial mass lesions
- Congenital
- Neoplastic ( benign or malignant)
- Inflammatory/infectious (cyst or abscess)
- Vascular (hematoma or AVM)
name of a mass lesion that is located above the tentorium
supratentorial
infratentorial mass lesion is located where
below the tentorium
cerebellum
4 symptoms seen with Supratentorial mass
- Seizures
- Hemiplegia
- Headache
- Aphagia
(Supratentorial Hurts Head Alot)
What 2 things are associated with Infratentorial mass and what are the symptoms for each
Cerebellar dysfunction: ataxia and nystagmus
Brain stem compression: AMS or altered respirations
Infratentorial is what part of the brain
cerebellum
supratentorial is what part of the brain?
cerebrum
What do the symptoms of intracranial mass depend on
growth rate
Are slow-growing masses symptomatic or asymptomatic
asymptomatic
acute neurologic deficits are associated with what growth rate of intracranial mass
fast growing
Deficits from mass lesions are specific to what
where the mass is located
Do intracranial masses affect ICP and if so how?
yes, they increase ICP :)
What are the common neurologic symptoms seen with intracranial masses (3)
- Reduced cognitive function
- HA
- focal neurologic deficits
the majority of intracranial mass surgeries are supra or infratentorial?
supratentorial
are there different anesthetic implications depending on the type of mass?
no, all managed the same
What may be seen on CT with an intracranial mass
edema and midline shift
What 3 drugs are patients with intracranial masses often on that can result in electrolyte and glucose imbalance
- steroids
- anticonvulsants
- diuretics
What preop drugs should be avoided in NSGY pts and why?
benzos and opioids to ensure not to effect ability to obtain neuro exam
What degree should HOB be for neuro patients
15-30 degrees to control ICP
Symptoms of increased ICP
- Nausea/Vomiting
- AMS
- Focal neuro deficits
- HA
- Papilledema
(Neurologists Aim to Fix Head Patients)
What are the 7 potentially neuroprotective properties of anesthesia
- decrease CMRO2
- inhibits protein kinase C
- decreases the production of free fatty acids
- scavenging reactive oxygen species
- inhibiting WBC function
- inhibiting excitatory NT receptors
What allows the brain to tolerate disruption of metabolic substrate delivery when under GA
suppression of electrocortical activity
Increases of what 3 things are known to contribute to poor outcomes after cerebral ischemic events
- increased blood glucose
- increased temp
- increased CPP
What is burst suppression and what can cause it?
EEG slows to random burst of electrical activity
Caused by volatile agents and acts as a neuroprotective mechanism
goal ETCO2 with increased ICP
30-35mmHG
What diuretics are recommended for increased ICP
- mannitol 0.25-1g/kg
- lasix
When ICP is elevated what is the goal for fluid status?
want them normovolemic
-dont overhydrate
Positioning interventions for increased ICP
- raise HOB
- avoid excessive neck flexion/neck vein compression
If ICP is increased and hematoma is present what should be considered
decompressive crani
What drugs can be administered with increased ICP in order to cause cerebral vasoconstriction
- propofol
- thiopental
for increased ICP pt do we want to keep their temp higher or lower?
mild hypothermia should be considered
For posterior fossa( infratentorial) surgery what is most concerning about the location
close proximity to vital brain centers including circulatory and respiration centers, RAS, ANS, and cranial nerves
Which type of mass can obstruct CSF at the 4th ventricle and lead to obstructive hydrocephalus
Infratentorial
What do surgeons use to monitor for respiratory center damage during posterior fossa surgery
spontaneous ventilation
What position is preferred by the surgeons for posterior fossa surgery
sitting position
What surgery and position creates the highest risk for VAE
sitting crani
What increases the risk for VAE
open venous system subatomospheric (pulls air in vascular space) with surgery site above the heart
Large air bubble can impede pulmonary blood flow which leads to what effect on the heart?
increased RV pressure which causes decreased CO
What agent enhances VAE
nitrous
What can indicate VAE during surgery?
- decreased ETCO2
- decreased O2 sat
- sudden hypotension
- circulatory arrest
- increased ET nitrogen
What is the most sensitive non-invasive monitor for detecting VAE
Precordial doppler
When using precordial doppler and VAE is detected what do you hear
mill-wheel roaring sound
What is the most sensitive invasive monitor for detecting VAE. What is the smallest volume of air it can detect
TEE
detect 0.25ml aire
What tool has the least sensitivity for detecting VAE
esophageal stethoscope
will hear v faint mill-wheel with VAE
Symptoms of small < 0.5ml/kg of air entrainment (5)
Decreased ETCO2 Increased EtN2 Desaturation AMS Wheezing
Symptoms of 0.5-2ml/kg RV air entrainment
breathlessness, wheezing hypotension pulm HTN R heart strain ST changes, peaked p JVD AMS cerebral ischemia pulm vasoconstriction bronchoconstriction
symptoms of large > 2ml/kg of air entrainment (3)
chest pain
R heart failure
CV collapse
Surgeries considered low risk for VAE (7)
peripheral nerve anterior neck burr hole vaginal hepatic ophthalmic
surgeries/procedures with medium risk for VAE (7)
spinal fusion cervical laminectomy prostatectomy gastric endoscopy contrast radiology rapid blood transfusion coronary surgery
surgeries/procedures considered high risk for VAE (7)
sitting crani posterior foss/neck laprascopic Total hip C section Central line placement criniosynostosis
Advantages of precordial doppler
most sensitive noninvasive monitor
earliest detector
some disadvantages of precordial doppler
nonquantitative
false negative
difficult to place with obese or chest wall deformity
useless during cautery
what drug may mimic air when using precordial doppler
mannitol
Does ETN2 detect air before or after ETCO2
before
The earliest detector of air
precordial doppler
most sensitive detector of air
TEE
If you suspect VAE what should you do first
alert surgeon so they can flood the field with saline and wax bone edges
Therapy for VAE after alerting the surgeon
- discontinue N2O, 100% FIO2
- Valsalva or compression of jugular veins
- aspirate air from the central line
- CV support
- left lateral decubitus position with 15-degree head down tolt
What is paradoxical air embolism and what defects is it seen with
air enters systemic circulation
Seen with PFO or atrial/ventricular septal defect
What % of the population has a PFO
30-35%
What is a cerebral aneurysm
dilated intracrania arteries
complications of aneurysms (3)
Subarachnoid hemorrhage (SAH)
re-bleeding
vasospasm
What is the leading cause of subarachnoid non-traumatic hemorrhage
sacular aneurysm rupture
What is the peak rupture age for aneurysms?
55-60years
what gender are aneurysms more likely to occur
female
What are the most common cerebral aneurysms
internal carotid bifurcation
anterior cerebral artery
Subarachnoid bleed usually presents with what 3 symptoms
HA
transient LOC
N/V
How does HTN affect SA bleed
worsens it
Why is decreasing BP with a ruptured aneurysm, not a good option
bc autoregulation is impaired
What EKG changes are seen with ruptured aneurysm/ SA bleed
T and ST changes but non-ischemic with no adverse outcome
Is it likely for previously ruptured aneurysms to re-bleed?
yes, 50% will re-bleed with an 80% mortality rate
What is the major cause of mortality and morbidity with a ruptured aneurysm
cerebral vasospasm 4 days post rupture
When is surgical intervention required for an aneurysm
> 7mm requires clipping
Where should you place your transducer in order to monitor the circle of Willis CPP
external auditory meatus and tragus
How will the pressure at the circle of Willis compare to the pressure at the level of the heart? why?
lower pressure due to the vertical column and hydrostatic pressure difference
What is the formula for calculating the change in pressure to compensate for the distance that the base of the skull is above the heart
1mmHg for each 1.25 cm above the heart OR 7.5mmHG for every 10cm that the base of the skull is above the heart
Treatment of vasospasm
maintain cerebral perfusion CV support inotropes nicardipine or nimodipine (~but one of the H's for treatment is HTN so sos~) intravascular volume expansion relative hemodilution (Hct 32) correct hyponatremia transluminal angioplasty
blood collects b/t dura and arachnoid layers of the brain
subdural hematoma
subdural hematoma: venous or arterial bleed?
venous
which patients are at a greater risk for subdural hematoma
anti-coagulated pts
With subdural hematoma what symptoms occur and in what order to they occur
HA–> drowsiness–> cognitive decline–>obtunded
what surgical options are available for subdural hematoma
crani
burr holes
T/F with subdural hematoma hypocapnia is desired
false, normocapnia is preferred
For treatment of vasospasm, we want to hemodilute to a goal Hct of ?
< 32%
what is the “triple H” therapy for vasospasm
hemodilution
hypervolemia
HTN
What type of hemorrhage is seen with AVM
intracerebral
When do AVMs typically present and with what?
10-30 y/o with bleeding
2 symptoms often present with AVM
HA
seizures
Do AVMs result in more or less bleeding compared to an aneurysm
extensively more
What two interventions help facilitate surgical resection of AVM
mannitol
hyperventilation
what % of neoplasms are pituitary in origin
10%
What % of pituitary neoplasms are non-secretory
20-50%
Hypersecretory tumors lead to what 2 complications
hyperglycemia
acromegaly
What anesthesia complication do we worry about with hypersecretory tumors
- difficult intubation d/t enlarged facial features
- laryngeal hypertrophy
- enlarged tongue
What surgical approaches are common for pituitary mass
transsphenoidal or intracranial
What are the advantages to the transsphenoidal approach compared to intracranial
decreased blood loss
decreased morbidity and mortality
What comorbidities could a pt with a pituitary mass present with
Cushings HTN DM osteoporosis obesity friability of skin
What complication is seen post-op with pituitary surgery
DI
For the transsphenoidal approach, what must we consider when making our anesthetic plan
- shared airway
- surgical entry site is the nare, so ETT should be secured to the chin not the upper lip
- lubricate eyes with petroleum jelly to prevent fluids from entering eye
What side of the mouth should ETT be placed/taped for transsphenoidal approach
left side of the mouth and secured to the chin
Why should we avoid hyperventilation in pituitary surgery
causes pituitary to retract into the sella which hinders resection
raising ETCO2 forces the pituitary into view
what vessels lie in close proximity to the pituitary
carotid arteries, be prepared for blood loss
Stereostatic procedures are performed with what type of anesthesia
MAC or light sedation
yikes
What is used for stereostatic procedures that prevents DL
halo
if you have to intubate a pt in a halo what is your best option
fiberoptic bronchoscopy
for stereostatic procedures why must we be super careful when giving sedation
we absolutely do not want to eliminate respirations or compromise the patients ability to protect their airway
Malformation where medulla protrudes through the foramen magnum
Arnold Chiari malformation
fun fact my sister has this but its v small
How does Chiari affect CSF flow
obstructs flow and can cause hydrocephalus
is chiari more common in males or females
females
what is the treatment for chiari
decompressive pressure relief
anesthesia implications for chiari are similar to what other surgery
posterior fossa
What is an important consideration when doing a head trauma case (v broad)
they probably have multiple other injuries that you dont know about
all head traumas are assumed to have what other injury
c spine
all traumas are considered
full stomachs
can we use nitrous on a head trauma patient
nope
what do you treat head trauma HYPERtension with
increased agent, hyperventilation
be careful to avoid too much hyperventilation as it will result in decreased CBF
what do you treat a head trauma with hypotension with
alpha adrenergic agonist
CPP goal for head trauma
70-110mmHg
What do you treat enhanced vagal tone with for a head trauma
atropine
PEEP in head traumas should be avoided until when?
after dura is opened bc of increased ICP
T/F Head trauma patients are left intubated and paralyzed until increased ICP is resolved
true
