6. Neuro Response- Exam 2 Flashcards
how many cardiac surgical procedures are carried out worldwide
1.4 million
overt stokes occur in what % of patients
1-5%
Neurologic dysfunction may be present in what % of pts.
25-80%
Annual cost for treating these pts. exceeds how much per year
$2 billion/ yr
Neurologic Deficits Include what 6 things
Psychomotor speed Attention Concentration New Learning Ability Short term memory Pediatrics: Seizures, Movement disorders, developmental delays
Transient Ischemic Attack (TIA)=
Localized event
Rapid onset and recovery (minutes to hours)
Severity depends on collateral flow
Reversible Ischemic Neurologic Deficit (RIND)=
Similar to TIA but lasts longer (24-72hrs)
Lacunar Brain Infarct (stroke)=
Specific focal deficit from cerebral artery occlusion.
Much more severe, often doesn’t resolve
Hemiparesis/aphasia/sensory
Global Ischemia=
Results from long periods of hypoperfusion or massive embolic load
Poor recovery. >50% are brain dead and never wake
do symptoms of different classifications of strokes often overlap and share causative mechanism
yep
Many cardiac pts have ______ risk factors for stroke and cognitive impairment. Without added risk of ____ and ____
pre-existing
cardiac surgery and bypass
____ patients experience ___ serious neurologic morbidity than age, and health matched controls undergoing non-cardiac surgery
Cardiac
more
name 6 Risk Factors
- Advanced Age (65+)
- Atherosclerosis (increases w/ age)
- History of previous neurologic incident (previous TIA)
- Intracardiac operation (valves-hearts open to air)
- Hypertension and Diabetes (most all patients)
- Carotid Stenosis (impairs BF to the head)
Age of <45 years old = what % incidence of stroke
~ 0.2% incidence of stroke
Age of <60 years old = what % incidence of stroke
1% incidence of stroke
Age of 60-70 years old = what % incidence of stroke
3.0% incidence of stroke
Age of >75 years old = what % incidence of stroke
8.0% incidence of stroke
__% of pts with stroke show multiple infarcts, with an average of _ zones
75%
6
Hartman et al, (1996)
•__% stoke in pts with normal aorta
•__% stroke rate with large intraluminal plaques
5%
45%
Embolic events are related to what 3 things
Aortic Plaques [not in our control]
Platelet-fibrin and leukocyte aggregates [in our control]
Bubbles from CPB circuit [in our control]
in the one study- why did embolic events at 100 minutes jump up so high
happened during short filling of the heart- they were probably not venting
in the second study- at what time during CPB did the % of embolic load jump up considerably
cross clamp release
release of partial occlusion clamps
what % of cardiac patients have a history of TIA/Stroke
13%
cardiac patients with a history of TIA/Stroke are how many times at greater risk of new deficit or exacerbation of previous deficit
3x
what are some examples of Intracardiac operation? what do they increase the risk of?
Valves, ASD/VSD, Myxomas, etc.
Increased risk of air emboli
Intracardiac operations have a risk (____%) is ___ higher than CABG alone
5-13%
2X
what % of cardiac surgical patients have HTN
55%
what % of cardiac surgical patients have diabetes
25%
the risk factors of HTN and DM may be due to changes in cerebral autoregulation- such as what 3 things
Narrows arteries penetrating the brain
Decrease in collateral blood flow
Decrease ischemic tolerance
__% of cardiac surgery patients have greater than __% carotid stenosis.
15%
50%
Brenner et al.
•__% stroke rate in asymptomatic patients with carotid disease
•__% stroke rate in patients with no carotid disease
- 2%
1. 3%
Faggioli et al.
•__% stroke rate with >75% Carotid Stenosis
•__ of __ pts with >75% Carotid Stenosis before carotid endarterectomy had strokes
14%
0 of 19
Mechanism is unclear [Carotid Stenosis], whether embolic or ↓Q, but >50% of strokes occur when?
in immediate postoperative period
how many studies prove higher CPB / MAP is beneficial
None
name 9 other risk factors for neurologic injury
PVD Alcohol abuse IABP- balloon or preexisting condition?? MI Prolonged hypotension Arrhythmias CHF Gender Decreased Cardiac Output
Cerebral Metabolic Requirement of Oxygen (CMRO2)=
CMRO2 ~40-50mL of O2/min
Cerebral Metabolic Requirement of Oxygen (CMRO2) indexed=
Indexed at 3.0-3.5 mL of O2/100g/min
Cerebral Blood Flow (CBF)=
CBF~ 750mL/min
Cerebral Blood Flow (CBF) indexed=
Indexed at 50-60mL/100g/min (about 15% CO)
Average brain weighs about?
1400g
CBF:CMRO2 is typically?
10-15
CBF is influenced by what 4 things
CMRO2, PaCO2, Hct, MAP
–All may increase or decrease cerebral blood flow
Without bypass: Cerebral delivery of oxygen (CDO2) normally does what
exceeds the oxygen demand
Without bypass: When delivery decreases, CMRO2 does what
is maintained by increasing oxygen extraction
–Further decrease in delivery will result in ischemia
Autoregulation tries to maintain a constant CBF over what range of pressures
wide range of pressures
Due to changes in CMRO2 between an awake patient and an anesthetized patient at hypothermic temperatures, different CBF’s are maintained over?
variable MAP’s
Awake patients-Maintain autoregulation from?
50-150mmHg
Anesthetized patients at moderate hypothermia may have preserved autoregulation down to CPP of?
28mmHg
Anesthetized patients at Deeper Hypothermia may have preserved autoregulation down to CPP of?
down to 20mmHg
While intrinsic autoregulation strives to maintain a CBF:CMRO2 coupling, there are other factors that play major roles- such as what 4 things
- Temperature
- Carbon Dioxide
- Oxygen Tension
- Mean Arterial Pressure
what is the Primary determinant of CBF
temperature
flow-metabolism “coupling”: Brain regulates flow in response to it’s ___ demand
O2
flow-metabolism “coupling”: is maintained in _____ state
autoregulatory
flow-metabolism “coupling”: When there is an increase or decrease in CMRO2, ____ is adjusted accordingly
CBF
At profound levels of hypothermia (<22°C), what happens to flow-metabolism coupling
“coupling” disappears
CBF can become in excess of CMRO2
Alpha Stat: pCO2 is a large player in determining CBF. what is the relationship btwn pCO2 and CBF
↑CBF as ↑pCO2 and vice versa
–Effects are regardless of Temperature, MAP, Hct, pO2
pH-stat acid-base management= Maintain temperature CORRECTED pH= 7.40 and pCO2 = 40mmHg
By continually adding what?
CO2
–causes dilation so you increase flow and lose coupling
Alpha-stat acid-base management= Maintain an UNcorrected value of pH = 7.40 and pCO2 = 40mmHg
Keeping the total __ constant
CO2
what type of acid/base management is good for pediatric cases
ph management
- they do not have acquired diseases yet so they can use the increased flow without the extra chance of emboli
why is ph management not that good for adults
Adult patients lose cerebral autoregulation where CBF becomes dependent on CPP
–causes dilation so you increase flow which increases chance for emboli
Normal cerebral tissue pO2 =
35-40mmHg
a pO2 < 30mmHg indicates what
Immediate reduction in cerebral vascular resistance
Yielding an increase in CBF
Hyperoxia causes what
an increase cerebral vascular resistance.
Rogers et al,
–showed a __% reduction in CBF when PaO2 was increased from ___ to ___ mmHg (all other parameters constant)
15%
125 to 300mmHg
With alpha-stat:
- -CBF is relatively constant over varying ___
- -At mild hypothermia or normothermia, the safety margin for CDO2 vs. CMRO2 starts to narrow at MAP’s ____
MAP
< 50mmHg
With pH-stat
- -CBF is dependent on __
- -High pressures can yield _____
- -Low pressures can yield ______
MAP
excessive flow
hypoperfusion
is CPB responsible for cognitive injury
Nope
Attenuation of Neurological Injury via Surgical Management can be done what 6 ways
- Attention to Aorta
- Minimize aortic manipulations
- Flood chest cavity with CO2
- Use care during de/cannulation
- Utilize TEE to ensure de-airing prior to XC removal
- Pre-op carotid studies in older patients and those with a history of TIA/ Stroke/ Carotid Dz
describe attention to the aorta for attenuation of neurological injury
Use the epiaortic ultrasound (versus “feel”) for cannulation, cross clamp, and proximal anastamosis sites
–Devices to deflect / trap emboli
Attenuation of Neurological Injury via Anesthesia Management can be done what 3 ways
- Pharmacologic agents that reduce CMRO2
- Ensure air removed from IV’s and arterial lines
- Apply manual compression on carotid arteries with XC removal
name 2 Pharmacologic agents that reduce CMRO2
Thiopental
Propofol
Attenuation of Neurological Injury via Perfusion Management can be done what 6 ways
- Use of arterial line & cardiotomy filter
- Ensure proper de-airing of circuit (CO2 flush)
- Maintain adequate anticoagulation
- Monitor warming/cooling gradients
- Communicate with surgeon and understand surgical sequence of events
- Alpha-stat acid-base management
why is a slow rewarm is better
Better cognitive performance 6 weeks post op
37.5C is the max- Avoid Hyperthermia
additional attenuation of Neurological Injury include:
Check arterial line post CPB prior to?
transfusion of volume
-ask if all clamps are off at the field and is the cannula is clear
additional attenuation of Neurological Injury include:
Avoid hyperglycemia because..
(potential for ↑CMRO2)
May aggravate neurologic ischemic injury
additional attenuation of Neurological Injury include:
Discuss venous drainage problems- If SVC is congested then ___ is diminished
CPP
Near Infrared Spectroscopy=
Noninvasive transcutaneous assessment of regional brain oxygenation
Near Infrared Spectroscopy is sensitive too what?
temperature, pCO2, Hct, CPB flow
Near Infrared Spectroscopy hgb sat does NOT indicate what?
tissue utilization
Transcranial Doppler=
Measures blood velocity in middle cerebral artery
–Correlation to blood flow
Transcranial Doppler is sensitive too what?
Temperature, MAP, pump flow, pCO2, Hct
Transcranial Doppler reliable velocity requires what?
a constant vessel diameter
- Not always true on bypass
- Better trending device
Transcranial Doppler for peds=
much more useful – easier to obtain temporal window
Transcranial Doppler for adults=
better at emboli detection than indicator of CBF
with Antegrade Cerebral Perfusion, you put the patient in what position
Trendelenburg position
describe the flow for Antegrade Cerebral Perfusion
Flow up the axillary artery to the innominate artery, to the head via the right common carotid artery. Thru the Circle of Willis and down the jugular veins to the SVC/ Atrium.
–Can also do via direct cannulation of the head vessels
with Antegrade Cerebral Perfusion, what line do you have to leave open to drain the heart
venous line
Antegrade Cerebral Perfusion flow=
10ml/kg/min
describe the flow for Retrograde Cerebral Perfusion
Flow up the SVC through the Circle of Willis and down the carotid arteries
what was the 1st method used to treat massive air embolus
Retrograde Cerebral Perfusion
Retrograde Cerebral Perfusion may be useful for what surgeries
deair for aortic surgeries
Retrograde Cerebral Perfusion flow
<500ml/min
Retrograde Cerebral Perfusion SVC pressure=
<25mmHg