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Perf tech III > test 5 part 3 > Flashcards

test 5 part 3 Flashcards

1
Q

Neurologic Injury

A
  • 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
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2
Q

Neurologic Deficits Include

A
  • Decreased psychomotor speed
  • Lack of attention
  • Lack of concentration
  • New learning ability loss
  • Short term memory loss
  • Pediatrics: seizures, movement disorders, developmental delays
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3
Q

Classification: Neurologic Deficit: Transient Ischemic Attack (TIA)

A
  • Localized event
  • Rapid onset and recovery (minutes)
  • Usually produces no permanent damage
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4
Q

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

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

* Usually complete recovery

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5
Q

What are the causes of TIA?

A
  • Atherosclerosis
  • A-fib
  • LV thrombi
  • Cardiogenic emboli
  • Carotid plaque
  • Aortic arch plaque
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6
Q

Classification: Neurologic Deficit: Lacunar Brain Infarct (stroke)

A
  • Specific focal deficit from cerebral artery occlusion
  • Deep in brain
  • Much more severe, often does not resolve
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7
Q

Classification: Neurologic Deficit: Global Ischemia

A
  • Due to long periods of hypoperfusion or massive embolic load
  • Poor recovery: >50% of patients are brain dead and never wake
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8
Q

Preoperative Risk Factors

A
  • 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
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9
Q

Examples of Preoperative Risk Factors

A
  • Advanced age
  • History of prior neurologic events
  • Aortic atherosclerosis
  • Carotid stenosis
  • Atrial arrhythmias
  • Hypertension
  • Diabetes
  • Genetic
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10
Q

Preoperative Risk Factors: Age

A
  • 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
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11
Q

Preoperative Risk Factors: Atherosclerosis

A

• 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

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12
Q

Preoperative Risk Factors: HTN and DM

A
  • 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
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13
Q

Preoperative Risk Factors: History of previous neurologic incident

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

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

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14
Q

Preoperative Risk Factors: Carotid stenosis

A

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

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15
Q

Surgical Stress

A
  • Brain ischemia during surgery may result from
    * Hypoperfusion
    * Inadequate tissue perfusion
    * Embolization
    * Obstruction of vessels
    * Inflammation
    * Endothelial damage compromising oxygen delivery
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16
Q

Embolization

A
  • 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
17
Q

Hypoperfusion

A
  • 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
18
Q

Inflammation

A
  • 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
19
Q

Cerebral Metabolic Requirement for Oxygen (CMRO2)

A

• 3.3 ml/100g of brain tissue/min

20
Q

Cerebral Blood Flow (CBF)

A

• 55 – 60 ml/100g/min

21
Q

Utilization of total resting oxygen: (%)

A

20%

22
Q

Average brain weighs

A

about 1400g

23
Q

CBF is influenced by

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

* All may increase or decrease cerebral blood flow

24
Q

Cerebral Physiology Without bypass

A

• 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

25
Q

Brain regulates its flow in response to

A

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

26
Q

Determinants of CPB

A
  • Temperature
  • Mean arterial pressure (MAP)
  • Carbon Dioxide (PaCO2)
  • Hematocrit (Hct)
27
Q

Determinants of CPB - Temperature

A
  • 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
28
Q

Determinants of CPB - Mean Arterial Pressure (MAP)

A
  • 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
29
Q

Determinants of CPB - Carbon Dioxide

A

• 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

30
Q

Determinants of CPB - Hematocrit

A

• 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

31
Q

Interventions to Reduce Neurologic Morbidity in Cardiac Surgery

A
  • 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)
32
Q

Near-Infrared Spectroscopy (NIRS)

A
  • 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
33
Q

Transcranial Doppler

A
  • 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
34
Q

Take Home Message

A
  • 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

Perf tech III (55 decks)

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