Brain Flashcards
What is the most common cause of perioperative vision loss?
Ischemic optic neuropathy
What is the most common perioperative eye complication?
corneal abrasion
When does vision loss from ION occur?
Usually within 24-48 hours of surgery
Is ION painful?
No, it is not associated with pain
What are the procedural risk factors for developing ION?
Prone position
Wilson frame
Long anesthesia
Blood loss
Insufficient colloids with resuscitation
Hypotension
Which procedures carry the highest risk for ION?
Spinal surgery
CPB
Radical neck dissection
What is CRAO?
Central Retinal Artery Occlusion
What’s the difference between ION and CRAO?
ION is a problem with the nerve ischemia, usually due to venous congestion
CRAO is a problem with blood vessel occlusion
What are the risk factors for CRAO?
Horse shoe headrest
Using nitrous after retinal bubble placement
Embolism from CPB
Most brain tumors arise from _______ cells
glial
What is the role of astrocytes?
the most abundant type of glial cell
They regulate the metabolic environment and repair neurons after injury
What is the role of ependymal cells?
CSF production
What is the role of oligodendrocytes?
Form the myelin sheath in the CNS
What is the role of Schwann cells?
Form the myelin sheath in the PNS
What is the role of microglia?
Act as macrophages and phagocytize neuronal debris
What is Broca’s area?
Frontal lobe
motor control of speech
What is Wernicke’s area?
Temporal lobe
Understanding of speech
What structures are located in the diencephalon?
What cranial nerve is most likely to be compressed by a pituitary tumor?
Optic
What is the primary site of CSF production?
Choroid plexus
What is the primary site of CSF reabsorption?
Arachnoid villi
The BBB is composed of ______ junctions
tight junctions
What is approximate normal CSF volume?
About 150 ml
How quickly is CSF produced?
About 30ml/hr
Where in the brain is the BBB NOT present?
Chemoreceptor Trigger Zone
Hypothalamus
Pineal Gland
Posterior Pituitary
Choroid Plexus
What is the calculation for cerebral blood flow?
What percent of the cardiac output goes to the brain?
15%
What is a normal CMRO2?
3.0-3.8 ml/O2/100g Tissue
What percentage of brain oxygen is used for electrical activity?
60%
The other 40% maintains cellular integrity
How does temperature impact CMRO2?
Decreases 7% for every 1 degree C drop
CMRO2 is decreased by:
- hypothermia
- halogenated anesth.
- propofol
- etomidate
- barbiturates
CMRO2 is increased by:
- hyperthermia
- ketamine
- nitrous
- seizures
What is the calculation for cerebral perfusion pressure?
Cerebral perfusion is generally autoregulated. What things abolish cerebral autoregulation?
- Tumors
- Trauma
- Volatile anesthetics
The brain is able to autoregulated when the CPP is between _______ and ______
50 to 150 mmHg
CPP autoregulation is generally maintained when the MAP is between ______ and _______
60 - 160
Which patients are at greatest risk of developing cerebral ischemia intraop?
Patients with chronic hypertension
For every 1mmHg increase in PaCO2, CBF will:
increase by 1-2 ml/100g tissue
For every 1mmHg decrease in PaCO2, CBF will:
decrease by 1-2 ml/100g tissue
Maximal cerebral vasodilation occurs at a PaCO2 of:
80-100 mmHg
Maximal cerebral vasoconstriction occurs at a PaCO2 of:
~ 25 mmHg
The relationship between CBF and PaCO2 is:
linear
Will a patient with metabolic acidosis display changes in CBF?
NO!
Cerebral response is based on H+ ions in the CSF, but only CO2 can cross the BBB. Once across, it dissociates back into H+ ions
What is the Robinhood effect?
Using hyperventilation to increase cerebral vasoconstriction in healthy tissue to cause increased perfusion to ischemic tissue (which is permanently vasodilated). Nice in theory, but not supported by evidence
How does PaO2 impact CBF?
How does the CVP impact ICP?
What conditions impair venous drainage from the brain?
What is a normal ICP?
5-15 mmHg
Intracranial HTN occurs when ICP exceeds:
20 mmHg
Cushing’s triad includes:
Hypertension
Bradycardia
Irregular Respirations
The most common site of herniation is:
at the temporal uncus
Why does herniation result in fixed and dilated pupils?
herniation applies pressure to CN III (Occulomotor)
What is pseudotumor cerebri?
a condition where ICP is reduced for no apparent reason
Which fluids should be avoided in patients with increased ICP?
Anything with Glucose
In ischemic settings, any extra glucose in the brain is converted to lactic acid, making things worse
Anterior circulation in the brain is supplied by:
Posterior circulation of the brain is supplied by:
Venous blood from the cerebral cortex and cerebellum drains via:
The superior sagittal sinus and the dural sinuses
Venous blood from the basal brain structures drains via:
the inferior sagittal sinus, the vein of Galen, and the straight sinuses
Both of the brain’s venous pathways converge at _______ and exit the brain via ________
the confluence of the sinuses
the jugular veins
tPA must be given within _______ hours of an inschemic stroke
4.5 hours
In patients with ischemic stroke, what is the goal BP?
Their BP will likely be high in order to maintain CPP
Just keep it below 185/110
What is the leading cause of morbidity and mortality after a SAH?
Vasospasm
What is the best prevention of vasospasm in patients with SAH?
The three H’s:
Hemodilution
Hypervolemia
Hypertension
What is the most common cause of SAH?
Aneurysm rupture, usually in the circle of willis
Why does Nimodipine reduce morbidity from vasospasm?
It does NOT relieve the spasm,
BUT it does increase collateral flow
When a venous aneurysm ruptures, bleeding usually occurs in:
the subdural space
When an arterial aneurysm ruptures, bleeding usually occurs in:
the subarachnoid space
What is the treatment for SAH?
Endovascular coiling or clipping
What are the anesthesia goals when performing an aneurysm clipping or coiling?
Maintain SBP between 120 and 150
Patients with SAH are at risk for _________ syndrome
Cerebral salt wasting
What is Cerebral Salt wasting syndrome?
The brain releases natriuretic peptides, leading to sodium wasting by the kidney.
Causes hyponatremia and hypovolemia
Unlike SIADH, it does not cause hypervolemia
What are the two most common signs of cerebral vasospasm?
New neurological deficit
Altered LOC
When is cerebral vasospasm most likely to occur?
Within 4-9 days of the SAH
What are anesthetic considerations in the patient with TBI?
CPP> 70
Hypertonic saline
No steroids
No nitrous
No albumin
No glucose
Status Epilepticus is defined as:
Seizure > 30 min
OR
2 grand mal seizures without regaining consciousness in between
What are signs of a seizure under general anesthesia?
Tachycardia
Hypertension
Increased etCO2
Which IV anesthetic should be avoided in patients with seizures?
Ketamine
Which three IV anesthetics increase EEG activity and are used to locate seizure foci?
Etomidate
Methohexital
Alfentanil
How does carbamazepine impact hepatic enzymes?
Induces
How does valproic acid impact hepatic enzymes?
Inhibits
How does phenytoin impact hepatic enzymes?
Induces
How does gabapentin impact hepatic enzymes?
It doesn’t. It’s excreted unchanged by the kidneys
How does hepatic enzyme induction impact NMBA action?
It causes resistance, because NMBAs are being metabolized at a higher rate
What is the MOA of Valproic Acid, Carbamazepine, and Phenytoin?
Block voltage gated sodium channels, leading to membrane stabilization
Which anticonvulsant can cause purple glove syndrome?
Phenytoin, if it extravasates
Patients being treated for Alzheimer’s may have increased sensitivity to which NMBA?
They are usually taking cholinesterase inhibitors, which slows the metabolism of succinylcholine, mivacurium, and ester LAs