Neurologic Complications

Question 0

Percent of patients that have neurological dysfunction

Answer 0

25-80%

Question 1

Percent of patients that have a stroke

Answer 1

1-5%

Question 2

6 examples of neurological deficits

Answer 2

Psychomotor speed
Attention
Concentration
New learning ability
Short term memory
Peds: seizures, movement disorders, development delays

Question 3

Characteristics of a transient ischemic attack (TIA)

Answer 3

Localized event
Rapid onset and recovery (min-hrs)
Severity depends on collateral flow

Question 4

Difference between TIA and reversible ischemic neurological deficit

Answer 4

RIND lasts longer (24-72hrs)

Question 5

Lacunar brain infarct (stroke)

Answer 5

Specific focal deficit from cerebral artery occlusion
Much more severe, doesn’t resolve
Hemiparesis, aphasia, sensory

Question 6

Global ischemia

Answer 6

Results from long periods of hypoperfusion or massive embolic load
More than 50% are brain dead and never wake

Question 7

Risk factors for neurological dysfunction

Answer 7

Advanced age
Atherosclerosis
History of previous neurological incident
Intracardiac operation
Hypertension and diabetes 
Carotid stenosis

Question 8

Age ranges and their incidence of stroke

Answer 8

75: 8%

Question 9

Percent of patients with stroke that show multiple infarcts

Answer 9

75%
Average of 6 zones
Indicative of embolic origins

Question 10

3 causes of atherosclerosis/thromboembolic debris

Answer 10

Aortic plaques
Platelet-fibrin and leukocyte aggregates
Bubbles from CPB circuit

Question 11

Surgical event causing the largest surge in embolic events

Answer 11

XC removal/Filling of beating heart

Question 12

Percent of patients that have history of neurological events, and risk associated

Answer 12

13%

3x greater risk of new deficit or exacerbation of previous deficit

Question 13

Riss associated with Intracardiac operation

Answer 13

Valves, ASD/VSD, myxomas
Increased risk of air emboli
Risk (5-13%) is 2X higher than CABG alone

Question 14

Risks associated with HTN and diabetes

Answer 14

HTN: 55% of patients
Diabetes: 25% patients
May be due to changes in cerebral autoregulation (narrows arteries penetrating brain, decreased collateral BF, decreased ischemic tolerance)

Question 15

Stroke rates with differing severity of carotid stenosis

Answer 15

15% of pts have >50% carotid stenosis

9.2% stroke rate in asymptomatic pts with carotid disease
1.3% in pts with no cardiac disease
14% with >75% stenosis

Question 16

Greater than 50% of strokes occur during what period?

Answer 16

Immediately Postop

no evidence that higher MAP on CPB is beneficial

Question 17

List of “other” risk factors for neurological dysfunction

Answer 17

PVD
Alcohol abuse
IABP
Prolonged hypotension
Arrhythmias
CHF
Gender
Decreased CO

Question 18

Cerebral metabolic requirement of oxygen (CMRO2)

Answer 18

40-50mlO2/min

Index: 3-3.5 mlO2/100g/min

Question 19

Cerebral blood flow

Answer 19

750ml/min
Index: 50-50ml/100g/min
15% of CO

Question 20

Average brain weight

Answer 20

1400g

Question 21

Average CBF:CMRO2

Answer 21

10-15:1

So get more cerebral blood flow than metabolically required

Question 22

4 factors influencing CBF

Answer 22

CMRO2
PaCO2
HCT
MAP

Question 23

Auto regulation range in awake patients

Answer 23

50-150mmHg

Question 24

Auto regulation range for anesthetized patients at moderate hypothermia

Answer 24

Preserved auto regulation down to 28mmHg | Deeper hypothermia: down to 20mmHG

Question 25

Primary determinant of CBF

Answer 25

Temperature

Question 26

CMRO2-Temp (flow-metabolism) coupling

Answer 26

Brain regulates flow in response to its O2 demand Maintained in auto regulatory state CBF is adjusted according to CMRO2 Loses coupling <22C (CBF exceeds CMRO2)

Question 27

CO2 effects on CBF

Answer 27

Increased pCO2 = increased CBF | Effects are regardless of temp, MAP, HCT, pO2

Question 28

Blood stat management good for pediatric patients

Answer 28

pH stat | Adults toners lose auto regulation, causing luxury flow

Question 29

Effects of oxygen tension on CBF

Answer 29

Normal cerebral tissue pO2: 35-40mmHg If pO2 <30: immediate reduction in cerebral vascular resistance, yields an increase in CBF Hyperoxia: increased cerebral vascular resistance 15% reduction in CBF when PaO2 increased from 125 to 300mmHg

Question 30

MAP affect on CBF for alpha stat and pH stat

Answer 30

Alpha stat: CBF constant over varying MAP, safety margin narrows <50mmHg PH stat: CBF dependent on MAP, high pressure yields excessive flow, low pressure yields hypoperfusion

Question 31

Neurologic events on CPB vs off pump cases

Answer 31

3 months Postop: 21% off, 29% on 1 year Postop: 31% off, 34% on *CPB has no significant effect*

Question 32

7 Surgical techniques to attenuate neurological injury

Answer 32

1. Attention to aorta: Use epiaortic ultrasound for cannulation, XC, and proximal anastamosis sites vs. just feeling 2. Use devices to deflect/trap emboli 3. Do preop carotid studies in older pt, pt with hx of TIA, stroke, carotid disease 4. Minimize aortic manipulations 5. Flood chest cavity with CO2 6. Carefully decannulate 7. Use TEE to ensure deairing prior to XC removal

Question 33

3 Anesthesia methods to attenuate neurological injury

Answer 33

Pharmacological agents that reduce CMRO2: Thiopental and Propofol Ensure air removed from IVs and arterial lines Apply manual compression on carotid arteries during XC removal

Question 34

6 Perfusion methods to attenuate neurologic injury

Answer 34

``` Use ALF and cardiotomy filters Ensure proper deairing of circuit Maintain adequate anticoagulation Monitor warming/cooling gradients Communicate with surgeon and understand sequence of events Alpha stat management ```

Question 35

Intra operative methods to attenuate neurological injury

Answer 35

Check arterial line post CPB prior to transfusion of volume Avoid hyperglycemia (increases CMRO2, aggravates neurologic ischemic injury) Discuss venous drainage problems Decrease CO2 during embolic periods Avoid excessive pO2

Question 36

Characteristics of NIRS

Answer 36

Noninvasive transcutaneous assessment of regional brain oxygenation Sensitive to temp, pCO2, HCT, and CPB flow Hgb sat does not indicate tissue utilization

Question 37

Characteristics of transcranial Doppler

Answer 37

Measures blood velocity in middle cerebral artery Sensitive to temp, MAP, pump flow, pCO2, HCT Reliable velocity requires constant vessel diameter (so better as a trending device) Peds: more useful, easier to obtain temporal window Adults: better at emboli detection than indicating CBF

Question 38

Flow path for antegrade cerebral perfusion

Answer 38

Patient is in Trendelburg position Flow up Axillary artery-->innominate artery-->head via right common carotid artery-->circle of Willis-->down jugular veins-->SVC Must leave venous lime open to drain heart! Can also use direct cannulation of head vessels

Question 39

Flow for antegrade cerebral perfusion

Answer 39

10mL/kg/min

Question 40

Flow for retrograde cerebral perfusion

Answer 40

Up SVC-->circle of Willis-->down carotid arteries | Useful for deairing

Question 41

Flow and SVC pressure for retrograde cerebral perfusion

Answer 41

Flow: <25mmHg