Monitoring and Neurosurgery Flashcards
What are the two monitoring modalities?
nervous system blood flow and function
What are the three way to monitor blood flow?
cerebral oximetry, transcranial doppler, jugular bulb venous O2 saturation
What are the five ways to monitor nervous system function?
EEG, SSEP, BAEP, VEP, MEP
What is NIRS?
monitors CBF in relation to CMRO2
NIRS monitoring is based off of what Law?
Beer Lambert
What does NIRS monitor estimate?
brain tissue saturation
Which monitoring modality most closely resembles the pulse oximeter?
NIRS
If your patient is going to be monitored with NIRS what should you do before they go to sleep?
get a baseline reading before induction
What can decrease the accuracy of a NIRS monitor?
changes in BP, PaCO2, Hgb, regional BV, peripheral oxygenation of the scalp
The risk of cerebral ischemia is reduced if your NIRS monitor says within which range of baseline?
75% of baseline or greater
What is a normal value for NIRS?
60-80%
What is a limitation of NIRS?
only measures regional blood flow, not global, electrocautery interferes with reading
What is spatial resolution?
depth of tissue measured for the actual cerebral oxygenation is directly proportional to the distance between the light emitting diodes and the sensors
What monitor uses ultrasound waves to measure blood flow velocity of the brain?
Transcranial doppler
Which monitor assesses the integrity of the circle of willis?
transcranial doppler
Where is transcranial doppler placed?
temporal bone
transcranial doppler most likely monitors which circle of willis vessel?
middle cerebral artery
Does transcranial doppler measure blood flow or velocity?
blood flow velocity
Transcranial doppler provides information specifically about what measurements?
flow direction, peak systolic and end-diastolic flow velocity, flow acceleration time, intensity of pulsatile flow, and detection of microemboli
What does SjVO2 measure?
global cerebral O2 extraction
SjvO2 measures blood from which segments of the brain?
blood draining from both cerebral hemispheres
What vessel drains cortical blood, and subcortical blood?
dominant internal jugular vein drains cortical (usually right), non dominant drains subcortical (usually left)
The jugular bulb receives how much blood from the contralateral and ipsilateral sides?
70% ipsilateral hemisphere - RIJV 30% contralateral - LIJV
Is inter cranial mixing of blood complete or incomplete?
incomplete, therefore we only measure from one side and not both.
Where is a blood sample drawn from to measure SjvO2?
1 cm below and 1 cm anterior to the mastoid process
Where is SjvO2 monitoring useful?
cerebral ischemia with increased ICP
What value of SjvO2 is considered normal?
55-75%
What does a SjvO2 reading below 55% suggest?
inadequate O2 delivery to the cerebral tissues or increased consumption.
What does a SjvO2 reading above 75% suggest?
hyperemia or stroke
What does EEG measure?
difference of electrical potentials between groups of neurons
Does EEG measure cortical or subcortical structures or both?
cortical - outer 3mm
What are the three basic components of the EEG?
frequency, amplitude, and morphology
What is frequency of EEG?
rate and duration of impoulses
What is amplitude of EEG?
peak to peak measurements
What is morphology of EEG?
shape of the waveform due to amplitude and frequency of wave appearance.
What is the frequency of gamma waves?
32-100 Hz
What do gamma waves represent?
heightened perception, learning, problem solving tasks, cognitive processing
What is the frequency of beta waves?
15-30 Hz
What do beta waves represent?
awake, alert consciousness
What is the frequency of alpha waves?
10-15 Hz
What do alpha waves represent?
physically and mentally relaxed
What is the frequency of theta waves?
5-10 Hz
What do theta waves represent?
dreams, meditation, light sleep
What is the frequency of delta waves?
0.5-5 Hz
What do delta waves represent?
deep sleep
What is frequency of EEG waves?
speed of impulses
What is amplitude of EEG?
height of waveform
What is the progression of EEG waveforms as a result of ischemia?
Increased Beta -> amplitude increases -> theta -> delta waves
What does Delta waves on EEG likely represent?
increased ischemia
When delivered in equal doses, do IV or Inhalation anesthetics cause more EEG depression?
inhalation anesthetics
Inhalation agents have the most effect on which EEG waves?
Beta waves
How do gases change amplitude and frequency?
increase frequency decrease amplitude
Which IV anesthetics increase Beta wave frequency and decrease amplitude?
Propofol, Etomidate, and ketamine
At 1 MAC which waves are seen?
delta, and theta
As the patient enters stage 3 of anesthesia which waves are demonstrated on EEG?
low frequency, high amplitude
After giving Ketamine what types of EEG waves are expected?
high oscillation waves, no theta or delta
If you induce with high doses of induction agents what is commonly seen on EEG?
burst suppression
What is burst suppression?
pattern of high frequency activity, and periods of electrical suppression with variable duration
At what MAC levels will burst suppression be seen on EEG?
1.2-1.5
At what MAC does Iso, Sevo and Des cause burst suppression?
Iso 1.5 Sevo, Des 1.2
Which volatile does not cause burst suppression?
N2O
What volatile requires the highest MAC to cause burst suppression?
Iso
What does the BIS value signify?
anesthetic depth
To prevent recall you would titrate your anesthetic to a BIS value of what?
<60
If you are a good CRNA you would keep your BIS value above what level to prevent increased mortality?
40
If your BIS falls below 40, make a change within what time frame?
5 minutes
What does Ketamine do to BIS values?
falsely elevates them
What BIS value will be consistent with burst suppression on EEG?
20
What is an evoked potential?
electrical potential in response to a stimulus and are used to warn of current or impending neurological dysfunction and ischemia
What are the four types of evoked potentials?
motor, brainstem auditory, somatosensory, visual
What are the sensory evoked potentials?
BAEP, SSEP, VEP
Motor evoked potentials are derived from which area of the brain?
Precentral gyrus
Sensory evoked potentials are derived from which area of the brain?
Postcentral gyrus
What things affect evoked potentials?
anesthetics, hypothermia, hypotension, anemia, positioning
What is the amplitude of a Evoked Potential?
intensity of the evoked potential (height)
What is latency of evoked potentials?
period of time until evoked response is measured (time)
What changes in amplitude and latency are consistent with ischemia?
50% decrease in amplitude and 10% increase in latency
How do SSEP’s detect localized injury to specific areas of the neural axis?
assessing cortically generated waves
SSEPs are a non specific indicator of what?
cerebral O2 delivery
SSEP specifically monitors what part of the brain and spinal cord?
Faciculus Cuneatus and Gracillis tracts of the dorsal lemniscal system
If ischemia occurs what happens to SSEP impulses?
they are reduced
SSEPs monitor the integrity of which cortex?
somatosensory
What sensations does the dorsal lemniscal system transmit?
touch (fine, discrete), vibration, and proprioception
The Fasciculus gracilis is more ____ and transmits sensation from ___ and ___ regions?
medial, lumbar, sacral
The Fasciculus Cuneatus is more ____ and transmits sensation from ___ and ___ regions?
lateral, thoracic, cervical
Trace the dorsal lemniscal system pathway from first order to third order neurons.
First Order fibers enter from the dorsal horn into the fasciculus gracilis or cuneatus, ascending to the medulla, then synapse with their second order neurons in the nucleus gracilis or nucleolus cuneatus. Then traveling to the thalamus to synapse with a third order neuron.
Which nerves are most frequently stimulated with SSEP’s?
posterior tibial and median nerves
Where are stimulating and detecting SSEP electrodes placed?
stimulating placed peripherally detecting placed centrally
Where is an alternative SSEP detecting lead placed for the lower extremity?
common perineal nerve
Where is an alternative SSEP detecting lead placed for the upper extremity?
ulnar nerve
If we were to stimulate the left posterior tibial nerve. Where would the central electrode be placed on the brain?
postcentral gyrus, right side, midline
Where would you place a peripheral electrode on the lower extremity to ensure stimulation is adequate for SSEP?
iliac crest
Where would you place a peripheral electrode on the upper extremity to ensure stimulation is adequate for SSEP?
Erbs point
SSEP latency increases how much for every 2 degrees Celsius decrease in temperature?
3ms
Hyperthermia suppresses SSEP amplitude by how much?
15%
In general how do anesthetics affect latency and amplitude?
increase latency and decrease amplitude of SSEP
How does etomidate and ketamine affect SSEP amplitude?
increase amplitude 200-600%
How can we optimize SSEP readings?
not making changes to gas or IV drugs
What nerve does BAEP monitor?
vestibulocochlear (CN8)
What procedures are BAEP’s monitored?
inner ear and auditory cortex
Which evoked potential monitor is least sensitive to anesthetics?
BAEP
How does hypothermia affect BAEPs?
increases latency
While monitoring BAEP’s what happens to amplitude as temperature increases?
amplitude decreases
What does electromyography monitor?
the facial nerve also 3, 4, 10, 11, 12
What is the standard of care monitor for acoustic tumor surgery?
electromyography
Does electromyography monitor ischemia?
no. only mechanical and thermal damage
What is electromyography very sensitive to?
muscle relaxation. Avoid
What monitor is used for the visual pathway for everything from the retina to the occipital cortex?
VEP
Where are VEP electrodes placed?
visual cortex
What do MEPs monitor?
motor cortex and descending tracts (corticospinal tracts)
Where are detecting and stimulating electrodes placed in MEP’s?
detecting electrodes peripherally stimulating electrons centrally
What suppresses MEP’s?
inhalation agents and NMB
What is the goal MAC when using MEP’s?
0.5 MAC
What is the most appropriate way to give NMB’s during MEPs?
infusion
What is the order of sensitivity to anesthetic gases of evoked potentials?
VEP>MEP>SSEP>BAEP Visual very, Motor moderately, Sensory somewhat, Brain barely
What is the first compartment to decrease in response o increased ICP?
CSF
What begins to occur as volume compensation mechanisms reach exhaustion?
local and focal ischemia
ICP has a direct relationship with what?
herniation risk, mechanical injury, & ischemia
ICP has a indirect relationship with what?
CPP
Sustained elevations in ICP lead to what?
catastrophic herniation of the brain
What are the four locations herniation can occur?
- the cingulate gyrus under the falx cerebri
- uncinate gyrus through the tentorium cerebelli
- cerebellar tonsils through the foramen magnum
- any area beneath a defect in the skull
Name the Herniations
- Subfalcine 2. Transtentorial (uncal) 3. Tonsilar 4. Transcalvarial
Pressure on the brainstem, rostral to caudal. altered consciousness, ocular and sight reflex issues, respiratory and cardiac dysfunction are symptoms of which type of herniation?
transtentorial
What are symptoms of uncal herniation?
pupillary dilation, ptosis, deviation of ipsilateral eye
What causes a tonsilar herniation?
increased infratentorial pressure -> compression on the medulla
What does a tonsilar herniation lead to?
cardio-respiratory instability
What is the gold standard for ICP monitoring?
intraventricular catheter
What is a major advantage of the ventriculostomy?
allows CSF drainage
Where is a ventriculostomy zeroed?
jugular foramen (tragus)
Draining CSF in a patient with brain tumor can lead to what?
tonsilar herniation
what is the most common complication of ICP monitoring?
infection
What is the most effective and rapid way of lowering ICP?
ventriculostomy, intraventricular catheter or lumbar subarachnoid
What do the ICP waveforms signify?
P1: percussion, highest, arterial compliance P2: tidal wave, cerebral compliance P3 dicrotic wave, aortic valve closure, the dicrotic notch
What does a P2 wave is greater than P1 wave signify?
intercranial hypertension
What maintains ICP?
inter cranial elastance
What is elastance the inverse of?
compliance
What is a plateau ICP wave called?
Lundberg A wave
How long does a Lundberg A wave last and what is the range of ICP?
20 minutes ICP of 20-100
What does Lundberg A waves tell you about brain elastace and compliance?
increased elastance or decreased compliance
Cushings Triad is common with Lundberg A waves? What is cushings triad?
HTN, tachycardia, irregular respirations
How long to Lundberg B Waves last and what is the typical ICP?
.5-2 minutes ICP 20-50
What does Lundberg B waves tell you about elastance and compliance?
increased elastance decrease compliance
Intracranial hypertension occurs with a sustained increase in ICP above what?
20
What are signs of increased intracranial pressure?
HEADACHE, nausea, vomiting, papilledema, blurred vision, neurological deficits, ventilatory deficits, decreasing consciousness, seizures, and coma
What happens to CBF when ICP exceeds 30?
CBF decreases -> brain edema -> increased ICP ->ischemia
What happens if increased ICP is not corrected?
herniation
What does expanding tissue mass, fluid mass, CSF absorption interference, excessive CBF, or systemic disturbances promoting brain edema lead to?
inter cranial HTN
How do brain tumors increase ICP?
size, edema formation, obstruction of CSF flow
What causes aqueductal stenosis?
obstructive hydrocephalous
How are the third and fourth ventricle affected by aqueductal stenosis?
enlarged 3rd ventricle, normal 4th ventricle
How is aqueductal stenosis treated?
ventricular shunt
Lack of cerebral lesions, and increased ICP with no known cause is called what?
benign intercranial HTN
Benign intracranial HTN is most common in which population?
obese women with autoimmune irregularities
What are potential symptoms of benign intracranial HTN?
Headache and bilateral visual disturbances
What is the treatment for benign intracranial HTN?
removal of CSF and administration of acetazolamide and corticosteroids
What can acetazolamide cause?
acidemia d/t hydrogen ion secretion by renal tubules
what is the anesthetic management of benign intracranial HTN?
avoid hypoxia and hypercarbia.
What is the safest type of anesthetic for someone with benign intracranial HTN?
general
What type of anesthesia should be avoided in someone with benign intracranial HTN?
Epidural
Which of the 4 intracranial sub compartments can anesthetists control?
CSF, fluid and blood. We can’t alter cellular compartment
It is not recommended to remove CSF in patients with increased risk of which types of herniation?
transtentorial (uncal) or tonsillar herniation
Which intracranial subcompartment can anesthesia rapidly alter?
blood
Does the venous or arterial system more likely increase ICP?
venous due to obstruction of drainage or increased intrathoracic pressure
How do volatile anesthetics affect ICP, CBV and CBF?
increase ICP, CBV, CBF by decreasing cerebrovascular dilation
What affect does gases have on CPP?
decreases CPP by decreasing MAP
What affect does gases have on auto regulation and CMRO2?
CMRO2 decreased, impaired autoregulation
CMRO2-CBF coupling becomes impaired at what MAC level?
0.6-1 MAC
Which gases cause the greatest increase in CBF and ICP?
Des > Sevo > Iso
Which gas increases absorption of CSF?
Iso
Are volatile agents beneficial in focal or global ischemia?
global. Focal causes steal
With a MAC above 1.5 which gas causes the greatest increase in CBF?
Iso
Gases cause activation of ATP-dependent potassium channels, up-regulation of nitric oxide synthase, reduction of excitotoxic stressors and CMR, augmentation of peri-ischemic CBF, and up-regulation of anti-apoptosis factors leading to what?
neuroprotection during ischemic insults
Does N2O affect auto regulation?
not on its own, but it does in combination with other gases
How does N20 affect CBF and CMRO2?
increase both
What happens to CBF at 0.5 MAC?
doubles
How does N2O affect ICP?
increase due to cerebral vasodilation
megaloblastic anemia, leukopenia, impaired fetal development, and a depressed immune system can be caused by what?
accumulation of metabolic breakdown products
Which gas should be avoided in patients with pneumocephalus, craniofacial trauma, recent craniotomy?
N2O
Which anesthetic is great for awake craniotomy?
Dexmedetomidine
What induction agent causes myoclonia, thrombophlebitis, nausea/vomiting, and suppression of the adrenal corticoid response to stress?
Ketamine
Which induction agents decrease CMRO2, CBF, and ICP?
all but ketamine
Which induction agent decreases production and enhances absorption of CSF?
etomidate
which induction agent activates seizure foci in patients with a history of epilepsy?
etomidate
which induction agent maintains CPP better than propofol due to lower decrease in MAP?
etomidate
Which induction agent is the most widely used for neurosurgery?
propofol
How do opioids affect cerebral vasculature, CMRO2, ICP, and CPP?
mild cerebral vasoconstrictors, mild effects on CMRO ICP CPP
Which opioid activates seizure foci in patients with epilepsy, but produces the greatest decreases in MAP and CPP?
Alfentanil
Which opioid should be avoided because it can enduce seizures?
Meperidine
Do Benzos decrease or incresae CBF, CMRO2, ICP, and CPP?
decrease
Which Benzo in large doses may activate seizures?
flumazenil
Is ketamine OK in multisystem trauma?
yes
Why is ketamine undesirable in neuroanesthesia?
Dissociative anesthesia and rocky emergence
How does Ketamine affect CBF, ICP, and CSF?
Increases CBF, ICP, and resistance to CSF reabsorption
If Ketamine is used in neuroanesthesia should it be used independently or in combination?
combination with a GABA agonist
How do NMBs affect CBF or CMRO2?
Nondepolarizers have little to no effect on CBF or CMRO2
How does Succinylcholine affect ICP, CBF, and CMRO2?
transient elevations in ICP, CBF, and CMRO2
How much does Succ increase ICP?
10-15 for 5-8 minutes
Muscle spindle activity for succinylcholine is caused by what?
jugular venous stasis
Why do histamine releasing NMB’s increase ICP and reduce CPP?
vasodilation
What medication could cause herniation if ICP already high?
nitrates
How do vasodilators affect cerebral vasculature and CBF?
induce cerebral vasodilation and increase CBF
CBV increases and can increase ICP in patients with decreased intracranial … compliance or elastance?
compliance
What two vasodilators are considered unsafe in someone with abdnormal cerebral elastance?
NTP and NTG
What are some benefits of hypnocapnia in neurosurgery?
reduces ICP by promoting cerebral vasoconstriction thereby increasing cerebral vascular resistance, reducing CBF and CBV
What are the two considerations for hyperventilation?
hypocapnia may cause ischemia, beneficial effects are not sustained
What are 1st and 2nd line PaCO2 goals?
30-35 1st line, 25-30 2nd line
What happens to the pH of CSF and brain ECF with hyperventilation?
they increase
How long does it take carbonic anhydrase to return pH to normal?
6-12 hours
What is the goal of CPP during CNS insults and neurosurgery?
normal to high normal
What happens to areas of the brain with compromised autoregulatory responses during HoTN?
pressure dependent
Which medications reduce edema and the increased BBB permeability that is seen with tumors?
steroids
If you want the benefits of steroids intraoperatively when should they be initiated?
24 hours. up to 72 hours for ICP reduction
Which steroid type can cross the BBB and increase edema?
glucocorticoids
Steroids are contraindicated for which patients due to negative effects?
TBI
Steroids alter which lab value?
blood glucose
What medications are useful to reduce brain intracellular contents?
hyperosmolar and diuretics
what medication can decrease water content in the brain?
mannitol
What medication works by creating an osmotic gradient and can cross a nonintact BBB and actually make edema worse?
Mannitol
Mannitol can cause problems in which patient population?
heart failure
What electrolyte derangements does mannitol cause?
plasma hyperosmolarity, hypokalemic hypochloremia metabolic alkalosis
What is the most commonly used intraoperative agent due to its rapid and effective reduction in brain volume?
mannitol
How much fluid does mannitol remove from the brain, time to decrease ICP, max effect, duration, UO in 1 hour?
~ 100 mL fluid from brain, decreases ICP in 30 min, max effect 2 hours, duration 6 hours, UO 1-2 L within 1 hour
Which diuretics decrease the rate of CSF formation?
loop diuretics
Which medication has an osmotic effect (similar to mannitol) but remains outside of the BBB
3% NS
How does 3% affect circulating plasma volume, ABP and CPP?
increases
Side effects of which drug cause natriuresis, hemodilution, immunomodulation, improved pulmonary gas exchange, cardiac failure, bleeding diathesis (bruise/bleed easily), vesicant
3%
Giving large volumes of 3% rapidly can cause what?
central pontine myelinolysis
serum Na+ should not be raised more than ___ in 24 hour period?
9mEq
What is the goal serum osmolarity when giving 3%?
< 320 mmol
TBI, SAH, cortical incisions, brain surface irritation can cause what?
seizures
What medications are used to induce coma in patients with increased ICP that is refractory to other treatment options?
barbiturates
Which medications decrease CMRO2 scavenging free radicals, hyperthermia (d/t ischemia) and prevents convulsions?
barbiturates
What is first and second line treatment HoTN caused by barbiturates?
1st: VOLUME EXPANSION 2nd: vasopressors
What signifies propofol infusion syndrome?
high anion gap metabolic acidosis
What is BG goal levels during neurosurgery?
140-180
Which patient should not have tight glucose control?
TBI and SAH
What causes injured brains to become hypoglycemic and suffer metabolic distress?
localized hyperglycolysis
What levels should BG be kept in patients with TBI or SAH?
treat if >250 and keep below 200
Which patients is intraoperative permissive hypothermia best utilized?
high risk for intraoperative ischemia
What are the risks of hypothermia?
coagulopathies and dysrhythmias?
What is the fluid management goal during neurosurgery?
maintain normovolemia/MAP during surgery
What are the most frequency used fluids in neurosurgery?
LR and NS
Which common fluid is slightly hyperosmolar (308 mOsm/L) and has the disadvantage that large volumes can cause hypercholremic metabolic acidosis?
NS
Which common fluid is slightly hypo-osmolar (274 mOsm/L) and in large quantities could produce cerebral edema by lowering serum osmolarity?
LR
What does reduced serum osmolarity lead to?
edema formation in normal/abdnormal brains
What is normal plasma osmolarity?
280-295
What is the goal UO during neurosurgery?
0.5-1 mL/kg/h
Hct should be maintained above ___ in neurosurgery?
28%
Reduced colloid oncotic pressure w/out change in osmolarity leads to what?
cerebral edema
In traumas that require large fluid administration, which fluids should be used?
Crystalloid/colloid combination
Which fluid should be used cautiously in neurosurgery due to dilutional reduction in coagulation factors, and direct inhibition of platelets and factor VIII?
Hetastarch
Which fluid interferes with platelet function?
Dextran
Which fluid should be avoided when the BBB is not intact?
albumin
What is the other name for the semi lateral position?
Janetta
If the patient is in supine or any position what is very important to avoid?
neck flexion
What does neck flexion do to cerebral blood volume and ICP?
increases
An axillary roll is used in the lateral position to prevent injury to what?
brachial plexus
What is another name for prone position?
concorde position
POVL, pressure necrosis, IVC compression, airway/tongue injury area ll risk factors for which position?
prone
What is the most frequent cause of POVL (post-operative vision loss)?
ION - ischemic optic neuropathy
Cortical ischemia, central retinal vessel occlusion (2/2 orbital compression) can also cause what?
POVL
Wilson frame, low ABP/Hct, males, obesity, lengthy surgery and Large IVF resusctitation are risk factors for what?
POVL
compression of the IVC directs blood to the ___ leads to increased risk of bleeding.
epidural space
Cervical/posterior fossa surgery requires neck flexion , how can you avoid injury in the mouth?
avoided excess equipment in the mouth, soft bite block
While in the sitting position where should the A-line transducer be placed?
external auditory canal
An A-line transducer placed at the ear, measures the BP where?
circle of willis
What is the formula to calculate the pressure difference in the BP cuff due to height?
1cm difference in height = 0.78 mmHg change in BP
Prepositioning hydration, compression stockings, and slow incremental table adjustments are ways to prevent what?
hypotension
What is the goal CPP in normal healthy patients?
60
In sicker patients should CPP be kept higher or lower?
higher
What is necessary for a patient in the sitting position?
A-line
What can occur as a result of edema formation in the pharyngeal structures, soft palate, and tongue?
Upper airway obstruction
This can occur secondary to stretching or compression of the cervical spinal cord while in the sitting position?
Unexplained quadriplegia
What position is contraindicated in those with intracardiac shunts (PFO, VSD) and relatively contraindicated in significant degenerative disease of the cervical spine and/or cerebral vascular disease?
sitting
What evoked potential monitor is potentially used for patients undergoing procedures in the sitting position?
SSEP
What is a common complication of posterior fossa surgeries in the head up position?
pneumocephalus
When does pneumocephalus typically occur?
after cranial closure
What is a potential cause of delayed or non-awakening after posterior fossa or supratentorial surgery?
pneumocephalus
VAE is principally a concern with which procedures?
posterior fossa and upper cervical spine procedures Super high risk if also in sitting position
What results from a negative pressure gradient between the operative site and the right side of the heart?
VAE
Does spontaneous or mechanical ventilation increase the risk of air entrainment?
spontaneous
Should pins be removed when the patient is in the sitting or supine position?
supine
What are the most common sites of critical VAE?
sigmoid and saggital sinus
What are the 4 pathways a VAE can travel?
R heart to lungs
R->L heart through a shunt
collect at SVC and RA junction
transverse the p. capillaries and enters circulation
Increased PAP & CVP, decreased CO, hypotension, dysrhythmias, up to cardiac arrest are S/S of what?
VAE
What develops with entry of air into the systemic circulation through an existing anatomic connection between the right and left heart?
paradoxical air embolus
Is the venous or arterial circulation the preferred route for a VAE?
venous
What should you avoid in a patient with a known VAE and R->L shunt?
PEEP
What position is contraindicated with a known VAE?
sitting
In VAE Endothelial mediators produce a reflex pulmonary vasodilation or constriction
constriction
Pulmonary vasoconstriction from VAE has what affects on the lungs?
Pulmonary HTN, hypoxemia, CO2 retention, dead space ventilation, ↓ETCO2
Air that enters the pulmonary artery in VAE can trigger reflex broncho______?
bronchoconstriction
Entry of air into the alveoli from VAE may be detected by presence of what?
end tidal nitrogen
This amount of entrained air cause decreased ETCO2, increased ETN2, oxygen desaturation, altered mental status, wheezing?
<0.5 mL/kg
This amount of entrained air cause difficulty breathing, wheezing, hypotension, ST changes, peaked P waves, JVD, myocardial and cerebral ischemia, bronchoconstriction, pulmonary vasoconstriction?
0.5-2mL/kg
This amount of entrained air causes chest pain, RHF, CV collapse, pulmonary edema?
>2mL/kg
What is the most sensitive monitor for VAE?
TEE
What is the most sensitive noninvasive monitor, and earlier detector for VAE?
precordial doppler
What are late signs of VAE?
hypotension, tachycardia, dysrhythmias, cyanosis
precordial doppler can a detect a VAE this size?
0.002mL/kg/min
Where is a precordial doppler placed?
right side of the heart (right sternal border between 3rd/6th ICS
a 10mL bolus of saline through a CVC helps confirm proper placement of what?
precordial doppler
What is a late sign of air entrainment with precordial or esophageal stethoscope?
mill wheel murmur
Is a PAC or EtCO2 more sensitive for VAE?
PAC
What is an early indication for potential VAE in a intubated patient?
gasp reflex
What is the treatment of VAE?
Stop, wax bone edges 100% FiO2, stop N2O Jugular vein compression Trendelenburg
What is another name for the left lateral position?
Durrant position
What are no longer treatments for VAE?
PEEP and valsalva
What is the most common induction agent for neurosurgery?
propofol
Which induction agent does not increase ICP?
propofol
NDNMB or DNMB for neurosurgery?
NDMB
Does risk of VAE increase by using N2O?
No
What is maintained due to risk of elevated ICP, increased surgical bleeding, and direct brain or head injury from sudden patient movement?
Paralysis
Monitoring a TOF in a paralyzed extremity leads to an increased or decreased TOF response?
Increased response in the paralyzed extremity.
What does coughing, straining, and arterial hypertension cause during emergence?
bleeding and edema formation
How can you manage HTN during the final stages of craniotomy?
lidocaine 1.5mg/kg, labetalol, esmolol, and dexmedetomidine
Should emergence occur during dressings application or suture placement?
dressing
What are the most common types of supratentorial tumors?
gliomas and meningiomas
Seizures, hemiplegia, headaches, & aphasia are s/s of which type of tentorial mass?
supratentorial
Cerebellar dysfunction (ataxia, nystagmus, dysarthria) and brainstem compression (cranial nerve palsies, altered LOC, abnormal respiration) are s/s of which type of tentorial mass?
intratentorial mass
What. indicates the presence of intracranial HTN?
brain edema
What medication class should not be given in patients with large mass lesions, midline shift, and abnormal ventricular size?
Benzos
What do benzos and opioids cause?
respiratory depression and hypercapnia
To control ICP the head of the bed should be kept at what degree in preop holding and during transport to the OR?
15-30 degrees
Some tumors may require excision around the hypothalamus and thus may result in postoperative what?
DI, within 12-24 hours
What approach to craniotomy may leave a patient with disturbed consciousness in the immediate postop period resulting in lethargy, disinhibition, or delayed emergence?
Subfrontal
What is the term used to describe lethargy, disinhibition, or delayed emergence?
Frontal Lobey
What type of craniotomy is reserved for patients in which a seizure foci may be suppressed by general anesthesia or surgical manipulation is adjacent to an area of eloquent cortical function?
Awake craniotomy
What is the single most important element of a successful awake craniotomy is what?
highly motivated, well informed patient
Who is allowed to talk to the patient with an awake craniotomy?
Surgeon and CRNA
What are common induction agents for awake craniotomy?
Fent, Prop, Dex
What medications do we give to induce seizure foci?
etomidate, methohexitol 0.03mg/kg, hyperventilation
What are the most common complications of awake craniotomy?
pain, seizures, nausea, confusion
What are abnormal, localized dilations of intracranial arteries?
cerebral aneurysms
What type of aneurysm is the most common cause of SAH?
berry or saccular
Where do cerebral aneurysms typically occur?
middle cerebral artery of Circle of Willis
Which diagnostic is best for localizing the site of a bleeding aneurysm?
CT scan
What typically presents as an abrupt, intense headache, in most patients with transient loss of consciousness in up to half?
SAH
What is meningismus (pseudo meningitis)?
Triad of nucal rigidity, photophobia, headache
What often accompanies acute SAH secondary to autonomic hyperactivity which can increase transmural pressure in the aneurysm?
HTN
How do you calculate transmural pressure?
MAP- ICP
What is the stress applied to an aneurysm sac called?
transmural pressure
What is the BP goal before aneurysm clipping?
120-150
What EKG changes are common after SAH?
T wave, ST, U wave, Qt prolongation, dysrhythmias
What is a life threatening complication of a previous ruptured aneurysm with a current SAH?
rebleeding
What is minimized by early surgical clipping, antifibrinolytics, and bp control during SAH/cerebral aneurysm?
Rebleeding
What is reactive narrowing/contraction of cerebral arteries after SAH?
vasospasm
What does cerebral vasospasm increase the risk of?
stroke and death
What is used as a treatment for vasospasm and is ideally done in those who have had aneurysm clipped?
angioplasty
Which medication is used to treat cerebral vasospasm?
Nimodipine
What is initiated by the release of oxyhemoglobin and related to free radicals, lipid peroxidation, and endothelin-1?
cerebral vasospasm
What is the most consistently effective treatment for cerebral vasospasm?
HHH therapy
Hypervolemia, HTN, hemodilution
What is the goal CVP in treating cerebral vasospasm?
10
What are the BP goals pre and post aneurysm clipping?
post 160-200 pre 120-150
What are the most commonly used vasopressors for HHH therapy in cerebral vasospasm?
Dopamine and phenylephrine
What is the goal Hct for HHH therapy for cerebral vasospasm?
27-30%
What medication is used to combat large urine output from HHH therapy?
Vasopressin
If urine output exceeds 200mL/hr during HHH therapy what is the medication you give and dose?
5 units IM vasopressin
In order to keep the HR 80-120 during HHH therapy what medication should you give and dose?
1mg Atropine Q4
How long is HHH therapy utilized?
3-7 days
What is the best indicator of survival for a SAH?
gross neurological condition preop
When is open surgery for SAH preferred?
Day 1-3
Patients with what grade of SAH often have procedures delayed to resolve vasospasm and improve preoperative neurologic status?
Grade 3 or worse
What are pulmonary complications of SAH?
pneumonia, atelectasis, and pulmonary edema
When should preoperative sedation for SAH be given?
in the OR
Which evoked potential is used for an anterior circulation SAH?
SSEP (median and posterior tibial nerve)
Which evoked potential is used for an posterior circulation SAH?
SSEP and BAEP
Correlation between alterations in what two things, with transient electrophysiologic changes corresponding to good outcomes and permanent changes to postoperative deficits
electrical signals and CBF
EEG monitoring is used to titrate anesthetics to what to decrease cerebral oxygen requirements during aneurysm clipping?
burst suppression
How can we avoid hypertensive responses to laryngoscopy in SAH?
propofol, opioid (5-10 mcg/kg fentanyl or 1-2 mcg/kg sufentanil, and lidocaine
What can Succs produce in comatose head injuried patients and SAH?
hyperkalemia
After a SAH, how long should hyperventilation be avoided?
24 hours
What position will the patient be in for a aneurysm in the anterior part of the circle of Willis?
supine
What position will the patient be in for an aneurysm arising from the posterior aspect of the basilar artery?
lateral
What position will the patient be in for an aneurysm in the vertebral artery or from lower basilar artery ?
sitting or prone
Does intraoperative hypothermia improve the neurologic outcome for patients with good grade SAH?
no
BP during cerebral aneurysm surgery should be kept within what percentage of baseline?
40%
What medications are most commonly used to induce controlled HoTN during cerebral aneurysm surgery?
NTP or gases
How should residual opioid side effects be reversed after cerebral aneurysm surgery?
small doses with Narcan
What is postoperative care after aneurysm repair aimed at?
avoid vasospasm
What is the MAP goal after aneurysm repair?
80-120
Changes in LOC after aneurysm repair are usually signs of what?
vasospasm
If a aneurysm ruptures during surgery what is your MAP goal?
40-50
How long can carotid arteries be occluded to prevent bleeding in a ruptured cerebral aneurysm?
3 minutes
Do Arteriovenous malformations autoregulate blood flow?
No
What is characterized by sudden engorgement and swelling of brain with protrusion through cranium?
perfusion pressure breakthrough
What is a AVM?
arteries flow directly into veins, no capillaries
AVM leads to what symptoms caused by steal?
bleeding, seizures, or ischemia
Preventing secondary insults to brain is an anesthetic goal of what?
head trauma
What physiologic derangements accompany head trauma?
hypercapnia, hypotension, and elevated ICP
What value of ICP leads to irreversible brain edema?
>60
All patients must be assumed to have what until proven otherwise by radiography?
cervical spine instability
Which NMB is best avoided in closed head injury?
succ
Name the brain hematoma.
.
Those with hypoventilation, absence of gag reflex, or GCS less than what require intubation?
8
What route of intubation is avoided in basilar skull fractures?
nasal
What breathing abnormality is characterized by crescendo-descrendo breathing from pattern followed by apnea, persists in sleep?
Cheyne-stokes
What breathing abnormality is characterized by irregular respiratory rate, rhythm and amplitude?
ataxia
What breathing abnormality is characterized by prolonged inspiration with a 2-3s pause then expiration?
apneusis
What breathing abnormality is characterized by irregular clusters of breaths followed by apnea episodes of variable duration?
cluster breathing
What breathing abnormality is characterized by loss of autonomic respiration during sleep?
central neurogenic hypoventilation, Ondines curse
What breathing abnormality is characterized by sustained hyperventilation >40?
central neurogenic hyperventilation
Maintaining ICP less than 20, preventing or reversing herniation, minimizing retractor pressure, and facilitating surgical access are important goals of what surgical treatment?
head trauma
What are essential monitors for head trauma?
ICP and a-line
What is goal CPP when performing fluid resuscitation for head trauma?
CPP >60
How long should hyperventilation be avoided post TBI?
24 hours
Which type of fluid is avoided in any patient undergoing neurosurgery?
Fluids with Dextrose
Which fluid decreases serum osmolarity can aggravate cerebral swelling?
anything with dextrose
Are steroids used in TBI?
no
Which type of subdural hematoma occurs slowly over time, usually not detected right away?
chronic SDH
chronic NSAID use, heavy alcohol use, anticoagulants, and blood disorders and risk factors for what?
chronic SDH
Patients with chronic SDH often have what lab value elevated?
INR
What is the preferred agent to reverse Warfarin?
prothrombin concentrate. vitamin K and FFP also reverse it
SDH & TBI increase the risk of what due to the release of tissue thrmoboplastin & activation of the complement system?
DIC and ARDS
What does Idarucizumab (praxbind) reverse?
dabigatran
What does platelet therapy reverse?
ASA and clopidogrel
The infratentorial space is contained in which cranial fossa?
posterior
Posterior fossa surgery includes things located around what?
cerebellum & brainstem
Neuropathology within this fossa can result in impaired airway control, respiratory dysfunction, cardiovascular dysfunction, autonomic dysfunction, and impaired consciousness?
Posterior
What is the preferred position for posterior fossa surgeries?
Sitting
Increased ICP is ___ common in infratentorial lesions?
less
Obstructive hydrocephalus is ___ common in infratentorial lesions?
more
Quadriplegia, macroglossia, pneumocephalus, VAE, and PAE are all potential risks of what position?
sitting
CSF outflow is typically obstructed where?
Aqueduct of sylvius (cerebral aqueduct) or 4th ventricle
What is the treatment of choice for intraoperative VAE during posterior fossa surgery?
mechanical ventilation
What nerves are common damaged during posterior cranial fossa surgery?
9, 10, 12
Damage to what cranial nerves can result in loss of airway patency and swelling of the brainstem could cause impairment of CN function or respiratory drive?
9, 10, 12
A small amount of intercranial neoplasms are found where?
pituitary gland
Pituitary gland neoplasms often compress which cranial nerve?
Optic - CN 2
What are the most common nonendocrine symptoms of a pituitary neoplasm?
frontotemporal headache and bitemporal hemianopsia (half vision)
If a patient has acromegaly do you size up or down the ETT?
size down
What hormone causes acromegaly, CAD, HTN, cardiomyopathy, and hyperglycemia?
growth hormone
What disease is associated with HTN, DM, osteoporosis, fragile skin/connective tissue and obesity?
Cushing’s disease
What is the preferred approach for pituitary surgery?
transphenoidal
Risk of panhypopituitarism & permanent diabetes insipidus is reduced with this pituitary surgery approach?
transphenoidal
What is avoided in pituitary surgery because decreased ICP may result in retraction of the pituitary gland into the sella turcica (access becomes more difficult)?
hyperventilation
What arteries lie close to the suprasellar area and can be inadvertently injured in pituitary surgery?
carotids
What is Diabetes Incipidus treated with?
**desmopressin (DDAVP)** or vasopressin.
During pituitary surgery what is the max of cocaine and epi?
Don’t exceed 200 mg cocaine, or 10 ml of 1:100,000 epi in 10 min in 70kg adult
What does cocaine block that leads to HTN and dysrhythmias?
catecholamines
Name the respiratory pattern characterized by the waveform.
A. Cheynes Stokes
B. Central Neurogenic Hyerventialtion
C. Apneusis
D. Cluster Breathing
E. Ataxia
Label the EEG waves.
