Neuro Flashcards
Normal CMRO2-and what is that?
Normal-3-3.5 mL
It is the rate of O2 consumption by the brain
Formula for CBF- Normal CBf? Impairment? Isoelectric? Irreversible brain damage?
CPP/CVR (cerebral vascular resistance) Normal-50mL/100g/min Impairment-20-25 Isoelectric-15-20 Irreversible-10
CBF is _____ proportional time Pa____.
When is CO2 responsiveness lost?
CBF is directly proportional to PACO2 between PACO2 of 20-80.
KIM that hyperventilation causes vasoconstriction, but that hypocarbia can lower BP.
CO2 responsiveness lost 24-48 hrs due to increase in CSF HCO3
How does O2 affect cerebral blood flow?
O2 at PaO2 less than 59, CVF markedly increases. PaO2 greater than 300, it slightly decreases
CBF is coupled to what?
How does temp affect CBF? When does CBF become isoelectric with regard to temp?
Hct less than 30 or less than 50 and CBF?
Coupled to CMRO2
CBF decreased 5-7% with hypothermia, isoelectricity iccurs at 20 degrees Cel
Less than 30-increases CBF. Less than 50-decreases CBF
Formula for CPP
Normal values
MAP-ICP (or CVP-whichever is greater) Normal-100 Slowing-50 mmHg Isoelectric-40-25 Irreversible brain damage-sustained <25
Compensation for increases in volume of brain:
Movement of CSF into spinal compartment, increase in CSF absorption, decrease in CSF production, decrease in Venus cerebral blood volume
What crossed the BBB?
O2, CO2, H2O, lipid soluble drugs
Severe HTN, rumors, CVA, hypercapnea, seizures
What do inhalational agents do to CMRO2? Volatiles are uncouplers-explain-
What do all agents do to ICP?
All decrease CMRO2. Isoflurane-the most can actually produce isoelectric EEG.
Volatiles decrease CMRO2 and increase CBF, they can also import auto regulation
In general, all agents increase ICP. N20 mood, but still does this
What do barbiturates do to CMRO2, CBF, ICP, CSF?
Reverse steal and barbiturates?
Barbiturates decrease CMRO2 and CBF, decrease ICP, increases resorption of CSF.
Robin Hood-by constricting normal areas, blood can be diverted to areas that have maximal vasodilation and are unresponsive to other stimuli (reverse steal)
Narcotics and CMRO2, CBF, ICP, CSF
Decreases ICP, CMRO2, CBF. Increases CSF resorption
Benzos and CMRO2, CBF, ICP, CSF
Decrease in everything- including CSF resorption
Ketamine and CMRO2, CBF, ICP, CSF
Unchanged CMRO2
Only agent that INCREASES CBF
ICP-increases
Impedes resorption if CSF
Etomidate and CMRO2, CBF, and ICP and CsF
CMRO2, CBF, ICP CSF resorption-decreased. KIM Etomidate should be avoider in pts with seizure disorders and myoclonus is seen
Propofol CMRO2, CBF, ICP, CSF
CMRO2-decreases,
CBF decreases,
ICP decreases
Lidocaine- CBF, CMRO2, ICP
CMRO2-decreases
CBF decreased usually without hypotension
ICP decreased
Do muscle relaxants affect CMRO2, CBF or ICP?
What about sux?
No-not directly, but the ones that release histamine (at Tacuri I’m, mivacarium) a can increase ICP by causing vasodilation, or decrease it by causing vasodilation.
Sux can cause a minor increase in ICP-can be pretreated with defasicykating dose of roc
Why maintain CbF?
Brain is one of the most metabolically active organs and is very sensitive to hypoperfusion and hypotension. Irreversible damage can occur within minutes or loss of CBF
What exactly is auto regulation?
It’s the maintenance of CBF over a given range it CPPs (usually a MAP between 50-150)
Both are important, but CBf is usually most important because CBF is maintained over a wide range of CPP
Advantage of etomidate
More hemodynakicbinstability die to its critical effect and less of a brain stem effect.
Is sux contraindicated for neurosurgery? Why or why not?
No, but the main concern with using Sux in a Neurosurgery case is the potential to increase ICP. ICP increases with six due to activation of gamma motor afterward with fasiculatuons causing increased metabolic activity of the sensory cortex and concomitant CBF increases are small.
Lidocaine and neurosurgery-
1-1.5 mg/kg 3 minutes before intubation can help blunt the sympathetic response to laryngoscopes and intubation
Types of waves and their amplitudes
How does ischemia appear on EEG?
Beta 13-30 Hx alert, open eyes state
Alpha-8-12 alert, closed eye state
Theta-4-8 drowsy or anesthetize state
Delta 0-4, deep sleep or deep anesthetize date
Ischemia appears as slowing, then complete loss of amplitude
Anesthetic agents-which type of response of activation happens and at which doses? What about Isofkurane and desfkurane and secofkurane? What about barbiturates, etomidate and Propofol? What is unique about their suppression?
Usually produce biphasic response of activation at sub anesthetic doses, followed by dose-dependent depression.
Isoflurane is the only volatile agent that produces burst suppression at clinical doses. Des does burst suppression at 1.2 and 1.5 MAC. Nitrous oxide depends on the anesthetic with which it is used. Barbiturates etomidate and propofol typical biphasic pattern and only agents capable of producing burst suppression and electrical silence at high doses
Opiates and amplitude changes
At high doses, amplitude slowing is observed.
Benzo and eeg
Initial increased amplitude and decreased frequency but no electrical silence.
Ketamine and EEG
High amplitude theta activity at low doses, followed by high amplitude Sigma and low amplitude beta activity to high doses.
Which factors cause slowing on an EEG?
Hypoxia, hypothermia, extreme hypo or hypercapnea, hypocalcemia, hepatic encephalopathy and renal failure.
Indications and limitations of the EEG
Indication-absolute-none
Relative-EEG can be used to detect cerebral ischemia during carotid endarterectomy and CPB. Can also be used to assess attainment of electrical silence or burst suppression.
Limits: artifacts, only cortical tissues are monitored so subcritical injury could happen, only certain cortical areas monitored, regional injury may be missed, lack of conclusive proof of efficiency
What is an evoked potential?
A recording of the neuromuscular responses to neural stimulation.
Somatosensory-it’s measuring which nerves?
Anesthetics (gas) do what to amplitude and latency?
All IV anesthetics ____ latencyband ____ amplitude except-
Peripheral nerves
Gas increases latency and decreases amplitude ILDA
All IV anesthetics increase latency and decrease amplitude except prop which has no effect on amplitude. Etomidate and ketamine which increase amplitude. Fentanyl has minimal effects.
Which factors affect SSEP monitoring?
Temp, ischemia, hypotension, anemia, and hypercapnea. TIHAH
BAEP and anesthetics
Very resistant to anesthetics, but not sensitive to hypoxia or intracranial HTN
VEPs
Most sensitive to anesthetics. Visual pathway including retina, optic chiasm, optic radiations, and occipital cortex
MEPs-are they more or less sensitive to anesthetics?
Less sensitive than visual, but still very affected by anesthetics. It involves stimulation of the motor cortex above site of surgery.
How does ischemia appear in EPS?
Increase in post stimulus latency or decrease in amplitude
N2O and EPs?
Reduces amplitude but doesn’t affect latency
What exactly is an EEG monitoring?
Spontaneous electrical activity in the cortex for signs of cerebral ischemia.
For which procedures would you consider using an EEG? Does every carotid need an EEG?
Those in which cerebral ischemia is likely, and that detection would lead to treatment, and that treatment would improve outcome.
Every carotid does not need an EEG-someone needs to be able to interpret it and there needs to be a plan for if ischemia were detected-I.e., shunt placement and hypertension
Somatosensory measures:
Measures function of the sensory tract, from peripheral nerve to cortex, including dorsal spine.