Neurosurgery Flashcards
Brain metabolism (% of O2 consumption)
20%
What is CMRO2?
Cerebral Metabolic Rate of O2 consumption
What is the CMRO2 of the average brain?
3-3.8mL/100g/min or 50mL/min
Where is the the CMRO2 the highest and why
Grey matter because the myelin sheath is present
Why is the brain so sensitive to hypoxia?
No O2 reserves
What is CBF?
Cerebral blood flow
What is the average CBF?
15-20% of CO
Circle of Willis Anatomy
What is CPP?
Cerebral Perfusion Pressure
CPP formula?
CPP=MAP-ICP or CVP
Whichever is greater
Normal CPP pressure?
80-100mmHG
What CPP value shows slowing on an EEG?
< 50mmHG
Autoregulation for the brain?
60-160mmHg
Relationship with MAP / PaO2 / PaCO2
Average PaC02 for the brain?
20-80mmHG
Why doesn’t metabolic acidosis affect CBF?
Ions do not cross the BBB but CO2 does
A reduction in temp does what two things in the brain?
Reduces CBF and CMRO2
A decrease in 10°C is a what reduction in CMRO2?
50%
An increase in 10°C is a what rise in CMRO2?
Double the CMRO2
Why is blood viscous?
The hematocrit
An increase in blood viscocity does what?
Reduces blood flow
What do tight junctions regulate?
Size
Charge
Lipid solubility
Protein binding
H2O moves freely throught tight junctions
What disrupts tight junctions selectivity?
SHITTSS
Severe HTN
Hypercapnia/Hypoxia
Infection
Tumors
Trauma
Stroke
Sustained seizures
What is CSF
Cerebrospinal Fluid
How much CSF is made per day?
500mL
Total volume of CSF?
150mL
Why do we make more CSF than the total volume?
It is constantly being reabsorbed in the arachnid layer
Where is CSF made?
Choroid Plexus
ependymal cells in ventricles
The skull is a fixed volume, what are some mechanism to help with increased pressure?
4 things
Displacment of CSF into spinal column
Increase in CSF absorption
Decrease in CSF production
Decrease in cerebral blood volume
What is considered a significant midline shift?
> 0.5cm
What is luxury perfusion?
A decrease in CMRO2 and increase in CBF
What is circulatory steal phenonmenon?
When there is vasodilation and ischemic areas, blood is shunted or “stolen” away from the narrowed vessels to the dilated ones
How can we protect the brain from furthter deline during periods of less O2 delivery?
6 things HAAAAN
- Hypothermia
- Anesthetics
- Adequate CPP
- Avoid hypotension
- Avoid blood sugars of 180mg/dl and above
- Nimodipine (prevents spasms)
Neuromonitoring Types: Blood Flow
CIT-JIT
- Cerebral Oximetry
- IV Tracer Flow
- Transcranial doppler ultrasound
- Jugular bulb venous O2 saturation
- Invasive tissue blood flow
- Tissue partial pressure of O2
Bold most common and the only one Adam has seen
Neuromonitoring Types: Nerve Function
- EEG (Electroencephalogram)
- EP (Evoked Potentials)
Different kind of EP’s?
- Sensory (SEPs)
- Motor (MEPs)
- Electromyograph (EMG)
Different kind of SEPs?
- Somatosensory Evoked Potentials (SSEPs)
- Brainstem Auditory Evoked Potentials (BAEPs)
- Visual Evoked Potentials (VEPs)
Different kind of MEPs?
- Transcranial Motor Evoked Potentials
- Spinal Motor Evoked Potentials
Most common cranial vessel to be involved in an acute stroke?
Middle cerebral artery (MCA)
neuromonitoring done by the transcranial doppler
What is the EEG
Electroencephalogram: summation of excitatory and inhibitory postsynaptic potentials of the cerebral cortex
Brain Waves: Gamma
IPE
Insight
Peak focus
Expanded consciousness
Brain Waves: Beta
ACC
Alertness
Concentration
Cognition
Brain Waves: Alpha
CRV
Creativity
Relaxation
Visualization
Brain Waves: Theta
MIM
Meditation
Intution
Memory
Brain Waves: Delta
DH
Detached awareness
Healing Sleep
Why do we care about brain waves in surgery?
- Helps identify inadequate BF
- Guides us reducing cerebral metabolism
- Predictor of neurological outcome
- BIS monitor
When it comes to brain waves and ischemia, what are we looking for?
Slowing frequency with preserved amplitude
Height is the same, wave form lengthens
What is BIS and what are the two types?
Bispectral Analysis
1. 2 Channel
2. 4 Channel
4 Channel can monitor left and right brain differences
BIS Monitor numbers scale
- 100 = Completely awake
- 60-80 = MAC / Sedation
- 40-60 = GA
- 0 = Isoelectric
Evoked potentials look for what in a stimulus?
Amplitude: Tall and potent
Latency: Short and fast
Can we paralyze if using MEPs?
No, sensory types only
Basic rule about anesthetc drugs and evoked potentials
Increased latency and decreased amplitude
5 Generalities of anesthetic drugs on evoked potentials
- IV agents have significantly less effect that equal potent doses of inhalation agents
- Combination of drug effects are additive
- Subcortical SEPs are very resistant to the effects of anesthetic agents
- MEPs are very sensitive to inhaled agents
- Des has stronger inhibitor effects than Sevo at high doses
Types of spine surgeries
RSSF-DVT
- Radiculopathy: compression on nerve root
- Spondylosis: wear on bone or cartlidge
- Scoliosis: congenital defect
- Fusions
- Decompression
- Vascular malformations
- Tumor resection
Spine surgery pre-op
Always evaluate neurological defecits
Neuromonitoring?
Airway issues? (C-Spine collar?)
multi-modal analgesia
Spinal surgery positioning
Usually prone arms out like superman
Difficult line access after positioned
POVL (Perioperative Vision Loss)
Hypotension due to abdominal compression
Facial edema
What is POVL
Perioperative Vision Loss
What is OIH
Opioid Induced Hyperalgesia
Hyper increase of pain sensation by short acting opiods
Opiods cause an increase in pain
Adams Neuromonitoring regiment for spine cases
PO Hydrocodone preop
Propofol infusion
low dose narcotic infusion
ketamine infusion
0.5 gas MAC
Neurogenic shock
Low blood pressure, bradycardia, and hypothermia due to disruption of the sympathetic nervous system with preserved parasympathetic activity.
Trauma to T6 and above
Neurogenic Shock Pathway
Spinal cord injury above T6
Decreased sympathetic output = vasodilation = decreased preload = decreased stroke volume -=decreased CO
Unopposed parasympathetic output = bradycardia = decreased CO
both add up to profound hypotension
treat with volume, then Levophed
AH and AD (same thing):
Autonomic Hyperreflexia / Dysreflexia
Usually injury to T6 or above
Sympathetic stimulaiton below injury causes increased BP
Above injury baroreceptors decrease HR
Causes high aferload: LV failure, Pulmonary edema, and arryhtmias
reduce affernent stimulus, treat with narcs, vaso dilators or propofol
Brain masses or lesions: Supratentorial
Presentations
Supratentorial = Cerebrum or all the lobes
Increase seizure activity
hemiplegia (weakness or loss of fuction on one side)
Aphasia (inability to understand language or articulate thoughts to language)
Brain masses or lesions: Infratentorial
Presentations
Infratentorial = Cerebellum and brainstem
Cerebellar:
Ataxia (lack of voluntary coordination of muscle movements)
Nystagmus (involuntary eye movements)
Dysarthria (muscle dysfunction in the lips, tongue and other speech muscles making it hard to pronounce words)
Brainstem:
Basic human funtion abnormalities (respiratory, conciousness, cranial nerve sensations)
Brain mass or lesion pre-op
ICP?
Neurological assesments
What meds? (steroids, diuretics, anticonvulsants)
Check sodium levels and glucose levels
Avoid pre-op medication, can cause issues post-op for assesments
Brain mass or lesion intra-op
ASA Monitors
Foley (diuretic for relaxed brain)
±Neuromonitoring
A-Line
±Central line
EVD (external ventricular drain)
What is an EVD and what does it monitor?
External Ventricular Drain
Monitors CSF pressure and allows acces to test and drain CSF
Draining CSF reduces pressure
Induction for brain masses
Extra propofol
phenylephrine
esmolol
Avoid succs if not a difficult airway (succs can potentially increase ICP)
Crani positioning
Variable but usually in mayfields (aka pinning)
When a patient is in mayfields (aka pinned) what do we need to make sure they do not do and how?
Do not let them cough, they can die
Propofol and esmolol at the ready
Crani maintenance
Paralyze if you can
limit fluids
avoid hyperglycemia
normocarbia
normotensive
Hypertension in a crani does what?
Increased brain mass and EBL
Hypotension in a crani does what?
greater chance of ischemia
Hypercarbia in a crani does what?
Increase CBF
Hypocarbia in a crani does what?
Decrease CBF
How does an increase/decrease of CBF affect ICP?
Increse/decrease ICP respectivly
Hyperventilation will only transceintly decrease CBF and ICP beauce of the bicarb buffering system. How long does this take?
6-8 hours
Relaxing the brain can cause what that makes the surgeon annoyed?
Changes in the imgaing when using naviagation
Crani emergence
Avoid coughing
rapid wakeup (no precedex, they are slow to emerge) for neuro assesment
Pain should not be too bad, dont over narc
Off to ICU after
Brainstem masses disrupt what
breathing
conciousness
BP/HR
Sleep
Cheyne-Stokes Respiration?
Biot Respiration
10 steps to an awake Crani mass
- ASA Monitors, facemask c̅ O2
- Sedation
- Scalp Block by doc (propofol before he starts helps)
- Pins placed
- Positioned then woken up
- Asked about comfort
- Sedation again, surgery starts
- Woken up for neural mapping (put back to sleep when done)
- Mass removed
- Sedated until emergence
Crani mass tidbits
Avoid benzos, slow wakeup
short acting agents
educate patients
lots of local used
Dura manipulations most painful
communication with doc
Unruptured aneurysms can be treated what two ways
- Coiling
- Clipping
Unruptured Aneurysm Pre-op
- Neuro assesment
- Type and Cross
- 4 units PRBC and 4 FFP in room and ready
- Avoid benzos if any altered mental status (othweise beneficial)
Unruptured Aneurysm Intra-Op
- Large bore IV
- A-Line
- Central Line
Unruptured Aneurysm Induction
Gentle
MAP strict control 60-60 mmHg
ETCO2: 35 mmHg
Propofol
Esmolol
Phenylephrine
Cardene
Labetalol
Unruptured Aneurysm Maintenance
Neuromonitoring
possible lumbar drain
if clipping cool patient to 34-35 °C
Temporary Clipping
Burst supression just prior to it
Then increase MAP to 90-100 mmHg to test it
After clip removed bring MAP back to 60-80 mmHg
Final Clipping
ICG dye to make sure its working
MAP goals of 70-90 mmHg
ICG Dye concentration and dosing
25mg in 10mL of normal saline
(2.5mg/1mL)
Dosing is 5mL with rapid saline flush(20mL)
Unrupture Aneurysm Emergence
No coughing
Pressors and dilators in line to control BP
Neuro assesment before xfer to ICU
Intra-op Aneurysm Rupture
Doc lets room know it busted
Immediate MAP of 40-50
If surgical intervention fails then:
Propofol for decreased CBF
Adenoside (6,12,18 mg)
Xfusion of PRBC
Ruptured Aneurysm brought in
Lare bore IV
PRBC stat
Art Line
Brain relaxation (Decadron, Mannitol, Lasix, Hyperventilate)
Keppra
What is Keppra
Anticonvolusant
What is AVM
Ateriovenous Malformation
AVM basic info
Differnet types of abnormalities, may increase or decrease bleeding risk depending on flow rate
Treat similar to unruptured aneurysm
Higher flow rare = higher bleeding risk / surgical risk
