Neurosurgery Flashcards
unmyelinated neurons appear _____ and conduct _____ signals at a _____ speed; myelinated neurons appear _____ and conduct _____ signals at a _____ speed;
grey, action potential, slower
white, saltatory conduction, faster
saltatory conduction
action potential that moves in jumps on myelinated neurons at the nodes of Ranvier
astrocytes
- provide support to neurons
- blood brain barrier
ependymal
-CSF production
microglia
-phagocytosis within the CNS
oligodendrocytes
-provide the myelin sheath in the CNS
Schwann cells
-provide the myelin sheath outside the CNS
inhibitory neurotransmitter
GABA - opens Cl channels which hyperpolarizes the cell
excitatory neurotransmitter
glutamate - opens Na channels which hypopolarizes the cell
gyri
-outer 3 mm of cerebral cortex that is convoluted to increase surface area
brainstem (3 components)
- midbrain (RAS - consciousness, arousal, alertness)
- pons
- medulla (respiratory and cardiovascular control)
meninges spaces and layers (out to in)
- epidural
- dura (tough)
- subdural space
- arachnoid (web-like, BBB, avascular)
- subarachnoid (CSF)
- pia (soft)
mnemonics for cranial nerve - sensory versus motor
some say money matters, but my brother says big brains matter more
CNS vasculature
- anterior = carotid artery
- posterior = vertebral artery
*meet at Circle of Willis
cerebral blood flow rate and percentage of CO
- 50mL/100g/min of brain tissue
- 15-20% of CO
cerebral perfusion pressure (CPP)
CPP = MAP - ICP (or CVP)
neurology = ATP stores are depleted and cellular injury can occur within _____
3-8 minutes
CBF relationship with CMRO2
CBF is directly influenced by cerebral metabolic rate of oxygen (CMRO2) which parallels
glucose consumption
- 20% of body’s O2 consumption
- 3-3.8mL/100g/min
CBF relationship with CPP
CBF remains constant with CPP between 50-150 mmHg
CBF - PaCO2 and PaO2 effects
PaCO2 - increased produces vasoconstriction, decreased produces vasodilation, controls between 20-80 mmHg, 3% for each 1 mmHg **most important regulator
PaO2 - little effect until below 50 mmHg
CBF relationship with ICP
CBF decreases when ICP >30 mmHg
CBF relationship with temperature
CBF decreases 5-7%
with 1 degree Celsius decrease of temperature
Cerebral Spinal Fluid
- produced in choroid plexus in ventricles at 30 mL/hr; reabsorbed in arachnoid villi
- total volume = 150 mL
- CSF pressure 5-15 mmHg
intracranial components
- brain matter=80%
- blood=12%
- CSF=8%
normal ICP
5-15 mmHg
Cushing Reflex
- HTN, bradycardia, respiratory irregularities
- occurs in response to acute increased ICP
types of brain herniation
- uncal
- central: transtentorial
- cingulate
- transcalvarial: moves out hole in skull
- upward: cerebellar
- tonsillar: cerebellar down
how does edema appear on a CT of the brain
hypodensity
what is the gold standard for ICP monitoring
intraventricular catheter
**also allows for drainage
neurology: volatile anesthetics autoregulation
-autoregulation (coupling) is impaired in concentrations exceeding 1 MAC (uncoupling=CMR the same, CBF increased)
Robin Hood Phenomenon
only normal tissue can vasoconstrict, ischemic brain tissue cannot constrict
neurology: volatile anesthetics CMR
-decreased with all, nitrous may increase
neurology: volatile anesthetics CBF
-increased with all
neurology: volatile anesthetics CBV
-increased with iso
neurology: volatile anesthetics ICP
-increased with all
neurology: Propofol
-dose dependent decrease in CBF and CMROs
neurology: etomidate
-decrease in CMRO2, CBF, ICP
neurology: ketamine
- dilates cerebral vasculature
- increases CBF, ICP, CBV
neurology: opioids
-minimal effect
neurology: benzodiazepines
- decrease CBF and CMR to a lesser extent than barbiturates
- interfere with electrocorticography
neurology: precedex
-decrease in CBF WITHOUT decrease in CMRO2 = can produce ischemia
neurology: succinylcholine
- increase ICP, CBF, CMRO2
- usually not avoided if rapid paralysis is needed
- avoid after 48 hours from stroke or spinal cord injury due to up-regulation of acetylcholine receptor causes hyperkalemia
neurology: muscle relaxants
- no effect on ICP, CBF, CMRO2
- histamine (atracurium) produces vasodilation which increases ICP
- interaction with other anti-seizure medications: increased dose with decreased duration of action due hepatic enzyme induction
neurology: labetalol and esmolol
-no effect
**preferred for the control of HTN
neurology: nipride, nitroglycerin, hydralazine
- dilates cerebral vessels
- increases CBV, ICP
neurology: steroids
- reduce edema
- most common decadron
neurology: diuretics
- loop: general diuresis, decrease CSF production, decrease cerebral edema
- osmotic: decrease intra and extra cellular water: Mannitol – slow administration (fast produces vasodilation, rise in CBF, ICP, CBV), 0.25-1.0 g/kg over 10-15 min
neurology: diuretics
- loop: general diuresis, decrease CSF production, decrease cerebral edema
- osmotic: decrease intra and extra cellular water: Mannitol – slow administration (fast produces vasodilation, rise in CBF, ICP, CBV), 0.25-1.0 g/kg over 10-15 min
neurology: fluid goal
- euvolemia
- avoid dextrose-containing fluids
neurology: target blood sugar
140-180
venous air embolism versus paradoxic air embolism
- venous=stays within right ride of heart
- paradoxic=enters arterial circulation through patent foramen ovale
venous air embolism signs
- increase in expired nitrogen, EtCO2
- decrease in SaO2
most sensitive monitor to detect venous air embolism
transesophageal echocardiography
pituitary neoplasms
- rarely metastatic
- neurologic, hormonal, visual changes
- common for loss of ADH: treat with DDAVP 0.5-1 ug
classification for cerebral aneurysms
Hunt & Hess: 0-5
0=unruptured aneurysm
5=deep coma, decerebrate rigidity
subarachnoid hemorrhage risks
- cardiac dysfunction
- neurogenic or cardiogenic pulmonary edema
- hydrocephalus
- rebleeding: 50% chance
- vasospasm
aneurysm clipping
- removes the risk of recurrent hemorrhage
- should not be postponed
neurology: vasospasm
- occurs 4-9 days after in 1:4
- leading cause of m/m
- treatment: hypertension, hypervolemia, hemodilution,
- nimodipine or nicardipine decrease incidence
aneurysms: endovascular treatment
- coil in aneurysm clots blood
- avoid hyperventilation which causes vasoconstriction makes access difficult
- heparin/protamine
carotid artery stenting concerns
-bradycardia or asystole with angioplasty - do not pretreat with atropine
