Cerebral hemodynamic, CBF, and ICP Flashcards
3 main components of the intracranial vault:
Cerebral spinal fluid 10-15%
Brain 80-85%
Blood 5-10%
CSF is produced by the _____ _____ in the ventricles.
Choroid plexus
CSF flow in the brain: Pneumonic
Lateral ventricles
Monroe (foramen)
3rd ventricle
Sylvia’s (aqueduct)
4th ventricle
Luschka
Magendie
“Love My 3 Silly 4 Lorn Magpies”
Properties of CSF: % of intracranial volume,
____cc produced per 24hrs
CSF volume = _____
10% of intracranial volume
500cc produced per 24hrs
CSF volume is ~ 150ml at any given time
Purpose of CSF:
“maintains an environment in which the brain can function by regulating pH and electrolytes, carrying away waste products, and delivering nutrients.”
Increases CSF volume:
Choroid Plexus Papilloma
Hyperthermia
Decreased serum osmolality
Increased CSF osmolality
Decrease CSF volume:
Hypothermia
Increased hydrostatic pressure
Diamox
Increased serum osmolality
Decreased CSF osmolality
Blood supply of Brain:___-___% of intracranial volume (__-___mL)
5-10%
60-80ml
Circle of Willis:
_______ arteries provide the _____ cerebral circulation
Bifurcates into the external and internal carotid arteries
The ______ branch enters the base of the skull
Arterial supply of the eye via the ______ _____.
Ultimately bifurcates into the _____ and ______ cerebral arteries.
Carotid
anterior
internal
ophthalmic artery
anterior and middle
The posterior circulation results from the ____ ______.
vertebral arteries
Largest artery in the brain?
-Middle cerebral artery
Venous blood drains into the _____ _____which lie between the layers of the _______ and drain into the ______ _____ _____.
venous sinuses
dura mater
internal jugular vein
Venous System: Sinuses are _______ and blood can flow…..
Pressure within them is _____ (_______ ______).
_______ influenced. (little influence of autonomic)
valveless
back and forth
negative (air embolism)
Chemically
BBB: junctions are _____.
Allows passage of _______ _____ substances but restricts the movement of _____ or _____ _____ _____ substances
tight
lipid soluble
ionized or large molecular weight
BBB: Water enters how?
By bulk flow
BBB disrupted by:
Severe HTN, Tumors, Trauma, Stroke, Infection
High PaCO2, Hypoxia, and sustained Seizures.
BBB: allows for passage/transport of-
small molecules (H2O, O2, CO2)
lipophilic molecules (EtOH, heroin)
passive transport of glucose
active transport of amino acids
BBB: prevents passage of:
large molecules (dopamine)
charged (ionized) molecules
Many factors affect CBF because of their effect on metabolism:
Stimulation, arousal, nociception, and mild hyperthermia _____cerebral metabolism and flow.
Sedative-hypnotic agents, and hypothermia _____ both metabolism and flow.
elevate
decrease
DANGEROUS CBF FLOWS:
Less than 30ml/100gm/min = ______
Less than 20ml/100gm/min =____ ____ ____
Less than 15ml/100gm/min = ______ ______
ISCHEMIA
ABNORMAL EEG (INFARCT)
IRREVERSIBLE DAMAGE
In general, increased _______ leads to increased CBF.
CMRO2
CPP=……….
MAP-ICP or CVP (which ever is greater)
Normal CPP range:
Cerebral Perfusion Pressure (CPP) determines ___.
70-100 mmHg
CBF
Normal ICP= __-___ mmHg
significance of a raised ICP is two fold:
-it will _____ cerebral perfusion
-it will cause ____ and ____ of cerebral content
10-15
-decrease
-distortion and displacement
CBF at __-__ (MAP) mmHg remains constant
60-150
Loss of Autoregulation occurs with:
Acidosis
Hypoxia
Trauma
Volatile anesthetics (less so with Forane)
3 types of compensation for ICP:
- CSF Regulation
- Cerebral Blood Flow-Auto Regulation
- Metabolic-Auto Regulation
CSF regulation for ICP:
Compensation: ↓ CSF production or ↑ CSF absorption
Monro-Kelly Doctrine:
ICP is stable as long as volume added is balanced by volume displaced
Metabolic-Auto Regulation:
Compensation-
The balance of acid/base & oxygenation –
Vasoconstriction or vasodilation of cerebral vessels to ↓ or ↑ blood supply to brain in effort to rid the brain of waste products as needed
Metabolic-Auto Regulation:
Decompensation-
Hypoxia (↓ oxygen) and Acidosis (↑ carbon dioxide) triggers vasodilation
Blood supply increases trying to “wash away“ the waste product of carbon dioxide BUT a compromised brain can’t handle the ↑ blood supply causing increased ICP and build up of lactic acid
What is a potent cerebral vasodilator?
PaCO2
If you double PaCO2, you double CBF
CBF changes by ~__%for each __mmHg change in Paco2
4%
1mmHg
Also- CBF changes 1-2 ml/100g/min per mmHg change in PaCO2
Decreased pH →→→→ ________ CBF
(__________) (_________)
Increased pH →→→→ _________ CBF
(_________) (_____________)
Decreased pH →→→→ Increased CBF
(acidosis) (vasodilation)
Increased pH →→→→ Decreased CBF
(alkalosis) (vasoconstriction)
The brain uses ____-____% of the O2 consumption of the body
15-20%
An increase in CMRO2, such as with convulsions, increases………
CBF up to 50%
_________ will decrease CMRO2
Anesthesia
The primary substrate for the brain is ______.
glucose
**Approximately ___-___% of glucose is obtained via an oxidative pathway
Without ___ no glucose is utilized
85-90%
O2
There is a ________ in CBF with a decrease in body temperature.
decrease
________ decreases both CBF and CMRO2
Hypothermia
_______ increases both CBF and CMRO2.
Hyperthermia
There is a___% decrease in CMRO2 with an __ºC temperature decrease. CVR _____ with cooling which will decrease your CBF.
50%
8
increases
Other Control of CBF:
Age -
Trendelenberg -
Anemia -
Increased blood viscosity -
PEEP -
Age - decrease in brain mass and a decrease in CBF
Trendelenberg - increases CBF
Anemia - increases CBF
Increased blood viscosity - decreases CBF
PEEP - decreases CBF (Fine line between keeping alveoli open and CBF)
IV Agents: Generally all ↓ CBF and CMRO2 except _______.
Ketamine
Ketamine ↑ CBF & CMRO2.
Prior administration of thiopental or benzodiazepines can blunt ketamine-induced increases in CBF. Blocks CSF absorption
Minimal to no change in CBF, CMRO2, & ICP:
Narcotics
…………do not appear to have clinically significant direct effects on CBF or CMRO2, provided MAP is not altered after administration.
Nondepolarizing neuromuscular relaxants
Which paralytic can elevate ICP?
Succinylcholine
__________ at 1 MAC depresses CSF production up to 40%
Sevoflurane
Inverse Steal or Robin Hood Phenomenon:
A vasoconstriction caused by hypocapnia will cause a reduced blood flow to the normal responsive regions of the brain resulting into redistribution of blood to ischemic regions. This is called, “Robin Hood Phenomenon” or the “inverse- steal”.
The inverse steal redistributes more CBF to ischemic areas
TRAUMA PATIENTS!
