test 5 part 3

Question 1

Neurologic Injury

Answer 1

• Over 1.4 million cardiac surgical procedures are carried out worldwide
• Neurologic deficits continue to be a major source of morbidity and mortality
• Overt stroke occurs in 1-5% of all patients
• Neurologic dysfunction may be present in 25-80% of patients
• Annual cost for treating these patients exceeds $2 billion/ year

Question 2

Neurologic Deficits Include

Answer 2

• Decreased psychomotor speed
• Lack of attention
• Lack of concentration
• New learning ability loss
• Short term memory loss
• Pediatrics: seizures, movement disorders, developmental delays

Question 3

Classification: Neurologic Deficit: Transient Ischemic Attack (TIA)

Answer 3

• Localized event
• Rapid onset and recovery (minutes)
• Usually produces no permanent damage

Question 4

Classification: Neurologic Deficit: Reversible Ischemic Neurologic Deficit (RIND)

Answer 4

• Similar to TIA but lasts longer (24-72hrs)

* Usually complete recovery

Question 5

What are the causes of TIA?

Answer 5

• Atherosclerosis
• A-fib
• LV thrombi
• Cardiogenic emboli
• Carotid plaque
• Aortic arch plaque

Question 6

Classification: Neurologic Deficit: Lacunar Brain Infarct (stroke)

Answer 6

• Specific focal deficit from cerebral artery occlusion
• Deep in brain
• Much more severe, often does not resolve

Question 7

Classification: Neurologic Deficit: Global Ischemia

Answer 7

• Due to long periods of hypoperfusion or massive embolic load
• Poor recovery: >50% of patients are brain dead and never wake

Question 8

Preoperative Risk Factors

Answer 8

• Many cardiac pts have pre-existing risk factors for stroke and cognitive impairment
  * Without added risk of cardiac surgery and bypass
• Cardiac surgical patients experience more serious neurologic morbidity than age- and health-matched controls undergoing non-cardiac surgery

Question 9

Examples of Preoperative Risk Factors

Answer 9

• Advanced age
• History of prior neurologic events
• Aortic atherosclerosis
• Carotid stenosis
• Atrial arrhythmias
• Hypertension
• Diabetes
• Genetic

Question 10

Preoperative Risk Factors: Age

Answer 10

• Age
  * < 60 years old: 1% incidence of stroke
  * >70 years old: 4 - 8.0% incidence of stroke
• Continued trend of older patients coming to surgery
• Cardiac surgical patients over age 80 will grow faster than any other group

Question 11

Preoperative Risk Factors: Atherosclerosis

Answer 11

• Embolic events related to aortic plaques
• Often associated with specific surgical events
- Age and atherosclerosis are the two main patient risk factors that largely determine post-surgical neurologic outcome

Question 12

Preoperative Risk Factors: HTN and DM

Answer 12

• HTN: 55% of cardiac surgical patients
• DM: 25% of cardiac surgical patients
• HTN and DM both cause:
  * Change in cerebral autoregulation
  * Narrow arteries penetrating the brain
  * Decrease collateral blood flow
  * Decrease ischemic tolerance

Question 13

Preoperative Risk Factors: History of previous neurologic incident

Answer 13

• 13% of cardiac patients have a history of TIA/stroke

* 3X greater risk of new deficit or exacerbation of previous deficit

Question 14

Preoperative Risk Factors: Carotid stenosis

Answer 14

• 15% of cardiac surgery patients have greater than 50% carotid stenosis

Question 15

Surgical Stress

Answer 15

• Brain ischemia during surgery may result from
  * Hypoperfusion
  * Inadequate tissue perfusion
  * Embolization
  * Obstruction of vessels
  * Inflammation
  * Endothelial damage compromising oxygen delivery

Question 16

Embolization

Answer 16

• On pump embolization
  * Primary cause of serious brain injury during cardiac surgery
• Embolic events related to:
  * Aortic plaques
  * Platelet-fibrin and leukocytes aggregates
  * GME from CPB circuit
• Embolic events associated with specific surgical events

Question 17

Hypoperfusion

Answer 17

• Regional hypoperfusion may occur as a result of:
  * Vascular disease
  * Inability to compensate for regional ischemia
  * Due to microembolization
• MAP may play a role in regional hypoperfusion

Question 18

Inflammation

Answer 18

• Many pathophysiologic mechanisms that may impact the vascular lining
• Endothelium regulates:
  * Vasomotor tone
  * Thrombosis
  * Fluid transport
  * Inflammatory response
• Alterations in these endothelial functions may play a role in post-CBP neurologic dysfunction
• CPB is associated with ischemia and reperfusion injury to heart and lungs
  * Potent triggers for activation of leukocytes and leukocyte-platelet binding
• Vascular integrity may be impaired by:
  * Capillary plugging
  * Free radicals
  * Proteolytic enzymes
• Exposure of blood to bypass circuit results in activation of platelets, monocytes, and neutrophils
• Inflammatory process has been associated with increased incidence of postoperative delirium
  * 26 – 50% of patient may develop post-op delirium

Question 19

Cerebral Metabolic Requirement for Oxygen (CMRO2)

Answer 19

• 3.3 ml/100g of brain tissue/min

Question 20

Cerebral Blood Flow (CBF)

Answer 20

• 55 – 60 ml/100g/min

Question 21

Utilization of total resting oxygen: (%)

Answer 21

20%

Question 22

Average brain weighs

Answer 22

about 1400g

Question 23

CBF is influenced by

Answer 23

• Cerebral Metabolic Requirement for Oxygen, PaCO2, Hct, MAP

* All may increase or decrease cerebral blood flow

Question 24

Cerebral Physiology Without bypass

Answer 24

• Cerebral oxygen delivery (CDO2) normally exceeds the oxygen demand
• When delivery decreases, CMRO2
is maintained by increasing oxygen extraction
• Further decrease in delivery will result in ischemia

Question 25

Brain regulates its flow in response to

Answer 25

• its oxygen demand • Increases or decreases in CMRO2 are associated with proportional changes in CBF (FLOW-METABOLISM COUPLING)

Question 26

Determinants of CPB

Answer 26

* Temperature * Mean arterial pressure (MAP) * Carbon Dioxide (PaCO2) * Hematocrit (Hct)

Question 27

Determinants of CPB - Temperature

Answer 27

* Primary determinant of cerebral blood flow (CBF) * 10oC temperature reduction decreases metabolic rate more than 50% * Hypothermic temperatures cause a change in blood flow characteristics * Changes responsiveness of the cerebral vasculature * Below 22oC – 23oC have flow-metabolism uncoupling * Changes in CBF does not track changes CMRO2

Question 28

Determinants of CPB - Mean Arterial Pressure (MAP)

Answer 28

* CBF autoregulation occurs at MAPs from 50 – 150 mmHg * Awake patients * Anesthetized patients at moderate hypothermia * May have preserved autoregulation down to 28mmHg * Deeper hypothermia – down to 20mmHg * Recommended to keep MAP at least 50 – 55 mmHg to allow some margin of safety * Most patient presumed to have cerebral vascular disease

Question 29

Determinants of CPB - Carbon Dioxide

Answer 29

• Major player in determining CBF • Changes in PaCO2 alter CBF independent of CMRO2 • Autoregulation is preserved with α-stat management • MAPs of 55 – 95 mmHg • CBF becomes largely pressure passive when PaCO2 is elevated

Question 30

Determinants of CPB - Hematocrit

Answer 30

• Hemodilution reduces blood viscosity and vascular resistance which increases CBF • CBF supports cerebral oxygen delivery (CDO2) as Hct is reduced • Progressive hemodilution compromises CDO2 and O2 consumption • CBF can no longer compensate for the reduced oxygen content • Oxygen extraction capacity has been exhausted

Question 31

Interventions to Reduce Neurologic Morbidity in Cardiac Surgery

Answer 31

* Attention to Aorta * Use epiaortic ultrasound for cannulation, cross clamp, and proximal anastomosis sites * Devices to deflect / trap emboli * Pre-op carotid studies in older patients and those with a history of TIA, stroke, or carotid disease * Minimize aortic manipulations * Single clamp technique vs. double clamp (cross-clamp plus partial clamp) * Flood chest cavity with CO2 * Use care during decannulation * Utilize TEE to ensure proper de-airing of heart * Pharmacologic agents that reduce CMRO2 * Ensure air removed from IV’s and arterial lines * Apply manual compression on carotid arteries with cross clamp removal * Use of arterial line and cardiotomy filters * Ensure proper de-airing of circuit (CO2 flush) * Maintain adequate anticoagulation * Monitor warming/cooling gradients * Slow rewarm is better * Avoid hyperthermia * Communicate with surgeon and understand surgical sequence of events * Alpha-stat acid-base management (preserve autoregulation)

Question 32

Near-Infrared Spectroscopy (NIRS)

Answer 32

* Noninvasive assessment of regional brain oxygenation * Sensitive to temperature, PaCO2, Hct, CPB flow * Monitoring of cerebral oxygen saturation can decrease the incidence of postoperative neurocognitive dysfunction

Question 33

Transcranial Doppler

Answer 33

* Measures blood velocity in middle cerebral artery * Correlation to CBF * Sensitive to temperature, MAP, pump flow, PaCO2, Hct * Reliable flow velocity requires a constant vessel diameter * Not always true on bypass * Better trending device * Better at emboli detection than indicator of CBF

Question 34

Take Home Message

Answer 34

* Despite the best surgical technique, patient selection, use of modern and appropriate perfusion equipment * Some patients will develop acute stroke in the post-op period * A structured stroke team is crucial for successful patient management