Module 7
Anesthesia for Vascular and Endovascular Surgery
Pathophysiology of Atherosclerosis
- Atherosclerosis is defined as the generalized inflammatory disorder of the arterial tree with associated endothelial dysfunction.
- Endothelial damage caused by hemodynamic _______(1).
- Inflammation from _______(2).
- _______(3).
- Hypercoagulability resulting in _______(4).
- Destruction of the fibrous cap over a lipid deposit leading to plaque rupture and _______(5).
- Vasoactive influences can result in spasms and acute _______(6).
- _______(7) play a pivotal role in atherothrombosis after plaque rupture.
- ______(a) derived macrophages act as scavenging and antigen presenting cells and also produce several types of chemical mediators (_______(8), chemokines).
- Adhesion molecules expressed by inflamed endothelium recruit leukocytes, including monocytes, which then penetrate into the intima, predisposing the vessel wall to lipid accretion and _______(9).
Study the Development of Atherosclerosis
Concept Map
Answers:
- shear stress
- chronic infections
- Inflammatory response
- thrombosis
- ulceration
- thrombosis
- Platelets
a. Monocyte - cytokines
- vasculitis
The Role of LDL
- Primary injurious agents include lipoproteins containing _______(1), the most important of which is LDL.
- These filter into arterial intima through the _______(2).
- Entrapped lipoproteins become modified into _______(3).
- In the subendothelial space enriched with atherogenic lipoproteins, most macrophages transform into foam cells
- Foam cells aggregate to form the _______(4).
- The atheromatous centers become necrotic, consisting of lipids, cholesterol crystals and cell debris.
Risk Factors
- The National Veterans Affairs Surgical Risk Study found the highest predictors of morbidity and mortality after vascular surgery include:
- Low serum _______(5)
- High ASA physical classification
- Additional Risk Factors:
- Abdominal obesity
- Dyslipidemia: Elevated LDL, Low HDL, Elevated _______(6) and small LDL particles
- _______(7)
- Insulin resistance
- Proinflammatory state
- Prothrombotic state
- _______(8)
- Family history of premature coronary heart disease
- _______(9)
Please Study the Odds Ratio Image
Answers:
1. apolipoprotein B
2. endothelium
3. proinflammatory substances
4. atheromatous core
5. albumin
6. triglycerides
7. Hypertension
8. Smoking
9. Aging
Occurrence
- More than 25 million persons in the US have at least one clinical manifestation of _______(1).
- Coronary artery atherosclerosis has been a major focus of investigation;
- However, atherosclerosis must be recognized as a systemic disease with important sequelae in many regional circulations (_______(2), aorta and extremities).
- How can we optimize the patient prior to _______(3)?
Comorbidity
- [A Venn diagram showing the percentage overlap of coronary artery disease, cerebral artery disease, and peripheral artery disease (PAD) is present but not described due to the limitations of the text-only format]
Answers:
1. atherosclerosis
2. brain
3. surgery
Surgery or Cancellation?
(Please study the concept map)
- CAD: _______(1)
- ACS: _______(2)
- GDMT: _______(3) (HF trx)
- MACE: _______(4)
- MET: _______(5)
- NB: _______(6)
- CPG: _______(7) (ie: stent vs angioplasty)
Answers:
1. coronary artery disease
2. acute coronary syndrome
3. guideline directed medical therapy
4. major adverse cardiac event
5. metabolic equivalent
6. no benefit
7. clinical practice guideline
Principle Clinical Syndromes
- Abdominal aortic aneurysms (_______(1))
- Aortic _______(2)
- Peripheral _______(3)
- Penetrating aortic _______(4)
- Intramural _______(5)
- Patients with peripheral arterial disease (PAD) can develop disabling symptoms of claudication or critical limb ischemia.
- What is the test to differentiate reynaud vs claudication?
- Prevalence of claudication is 2% among older adults, but 10 times as many elderly patients have asymptomatic lower extremity _______(6).
Answers:
1. AAA
2. dissection
3. atheroembolism
4. ulcer
5. hematomas
6. atherosclerosis
Principle Clinical Syndromes
- Abdominal aortic aneurysms (AAA)
- Aortic _______(1)
- Peripheral _______(2)
- Penetrating aortic ulcer
- Intramural hematomas
- Patients with peripheral arterial disease (PAD) can develop disabling symptoms of claudication or critical limb ischemia.
- What is the test to differentiate reynaud vs _______(3)?
- Prevalence of claudication is 2% among older adults, but 10 times as many elderly patients have asymptomatic lower extremity _______(4).
Diagnostic Exams
- PAD affecting the lower extremities can be detected by the ankle-brachial index, the ratio of the highest systolic ankle pressure to the highest systolic arm blood pressure.
- The ankle-brachial index is the single best initial screening test to perform in a patient suspected of having PAD.
- The index is obtained with a blood pressure cuff and a hand held continuous wave doppler.
- It is calculated by dividing the systolic blood pressure at the ankle by the systolic blood pressure in the arm.
- A ratio < 0.9 is considered abnormal and a ratio of < 0.4 is often associated with limb threatening ischemia.
- Catheter based angiography is the standard method for diagnosing PAD, against which all other imaging modalities are compared for _______(5).
- Recent advances in noninvasive angiography (MRI & computed tomographic angiography) enable excellent noninvasive definition of the vascular anatomy.
- Carotid intima-media _______(6) is increasingly used as a surrogate marker for atherosclerosis.
- AAA occur in up to 5% of men older than 65 years most of which are small and require only infrequent follow-up.
Medical Therapy
- Continuation of chronic medical therapy may reduce perioperative morbidity and mortality in vascular surgery:
- Antihypertensives – beta blockers
- Statin drugs – reduce progression of plaque formation and reduce cardiovascular events in high risk patients; improve graft patency, limb salvage and decreased amputation rate
- _______(7)
- Hypoglycemics and/or insulin
- Other therapies:
- Meticulous foot care in diabetics to prevent infections
- Lifestyle changes – weight loss, exercise, _______(8)
- Chronic therapy with aspirin or other anti-inflammatory drugs may slow the progression of atherosclerosis and prevent myocardial vascular events.
- Patients should continue taking aspirin until the day of surgery for carotid _______(9).
- The decision should be individualized for patients scheduled for lower extremity vascular surgery.
- Several studies report that patients undergoing peripheral vascular surgery may benefit from statin therapy up to 48 hours before surgery showed no increase in major bleeding.
- What labs should be used to assess euglycics? AF-Xa Assay
- Urgent situations when patients develop acute ischemia, systemic anticoagulation may be initiated
- Discuss with the team whether heparin should be continued for patient with a high likelihood of clot.
Answers:
1. dissection
2. atheroembolism
3. claudication
4. atherosclerosis
5. accuracy
6. thickness
7. Aspirin
8. smoking
9. endarterectomy
CAD + PVD
- The absence of severe coronary stenosis can be predicted with a positive predictive value of 96% for patients without diabetes, prior angina, previous MI or _______(1).
- Short term post op cardiac morbidity and mortality rates after vascular surgery are higher than after other types of non-cardiac _______(2).
- Complications after carotid endarterectomy (CEA) are less frequent than other vascular surgeries but still produce > 50% of the mortality encountered after vascular _______(3).
- Table 40-1 in Barash: In 1000 consecutive patients presenting for elective vascular surgery, a coronary angiography identified an overall prevalence of CAD of approximately 50% in this population. Severe correctable CAD was noted in 25% of the entire _______(4).
Please study Table 40-1
Answers:
1. CHF
2. surgery
3. surgery
4. series
- The absence of severe CAD could be accurately predicted, with a predictive value of 96%, by the absence of clinical risk factors such as diabetes, prior angina, previous MI, and a history of congestive heart _______(1).
- Percutaneous coronary interventions (PCI) directed at reducing perioperative cardiac events do not appear to reduce perioperative MI (PMI).
- PCI performed in the distant past may be protective after vascular _______(2).
- Current guidelines recommend waiting at least 60 days following MI before elective noncardiac surgery in the absence of _______(3).
- Specific recommendations are made following PCI, and the ACC/AHA released a focused update on duration of dual antiplatelet therapy (DAPT) for patients with CAD in 2016; suggest delaying elective noncardiac surgery 30 days following _______(4) stent (BMS) placement and ideally 6 months following drug eluting stent (DES) placement.
- Two types of coronary stents: bare metal stents & drug eluting stents
- Drug eluting stents have reduced incidence of _______(5); they are also covered by endothelial cells.
- However, the exposed stent material remains thrombogenic after the vascular trauma stent s needs to be on antiplatelet therapy.
Treatment algorithm for the timing of elective noncardiac surgery in patients with coronary stents.. BMS indicates bare metal stent; DAPT, dual antiplatelet therapy; DES, drug-eluting stent; and PCI, percutaneous coronary intervention.
Answers:
1. failure
2. surgery
3. intervention
4. bare metal
5. restenosis
Types of Perioperative Myocardial Infarction (PMI)
- ______(a)-
- resembles that of acute nonsurgical MI probably due to acute coronary occlusion resulting from plaque rupture and _______(1).
- ______(b) -
- associated with sustained elevation of heart rate, absence of chest pain, and prolonged episodes of ST segment depression before overt MI
- associated with increased oxygen demand in the setting of fixed coronary stenosis; and, the O2 supply diminished by anemia or _______(2).
Perioperative Cardiovascular Risk
- Revised guidelines and classifications of clinical predictors of increased perioperative cardiovascular risk (MI, CHF and death)
- Guidelines place aortic and peripheral vascular surgery in the “______(c)” surgery category with an estimated cardiac risk (MI or cardiac related death) exceeding _______(3).
- Guidelines apply a stepwise approach to the evaluation of the patient incorporating clinical risk factors, exercise capacity and urgency of _______(4).
Risk Assessment
- Major predictors:
- active cardiac conditions to include acute MI (<7days)
- recent MI (7-30 days)
- unstable angina
- decompensated CHF
- severe valvular disease and significant arrhythmias
- cancellation of surgery is _______(5).
Answers:
a. Early
1. thrombosis
b. Delayed
2. hypotension
c. high risk
3. 5%
4. surgery
5. highly recommended
Preoperative Coronary Revascularization:
- Should coronary revascularization be needed before vascular surgery, then surgical revascularization is a suitable option compared with percutaneous coronary interventions (PCI)
- The safe time interval between coronary revascularization and vascular surgery is:
- _______(1) for CABG
- _______(2) for bare metal stent (BMS)
- _______(3) for drug eluting stent (DES) (2-6 months)
- _______(4) for coronary angioplasty
Please study
Answers:
1. 4 to 6 weeks
2. 6 weeks
3. 1 year
4. 2 weeks
Ischemia-Reperfusion Injury (IRI)
- Active process/biphasic process (ischemia and reperfusion)
- Both processes contribute to _______(1)
- The placement of a clamp directly injures perivascular endothelium and intima, including endothelial cells
- Injury and activation of endothelial cells triggers both immune/coagulation activation responses
- Ischemia/reperfusion injury (IRI) is a term used to describe functional and structural changes that become apparent during the restoration of the blood flow after a period of _______(2).
- In addition to the reversal of ischemia, the repair of blood flow can result in potentially very harmful effects such as necrosis of irreversibly damaged cells, marked cell swelling and nonuniform flow restoration to all portions of the _______(3).
- This chaotic restoration of the tissue flow, the _______(4) phenomenon, is the result of a vicious cycle of vascular, endothelial and mitochondrial dysfunction, with reduced local perfusion, intense dysfunctional changes, edema, and many more implications.
- The occurrence of metabolic disorders during ischemia or tissue hypoxia are currently well established, but clinical and experimental evidence shows that the significant events leading to cell and tissue dysfunctions are mostly related to the subsequent _______(5).
Please study the diagram of Ischemia and Reperfusion
Answers:
1. injury
2. ischemia
3. tissue
4. reflow
5. reperfusion
Prevention of Myocardial Injury
- Pharmacologic prophylaxis against acute vascular events, in patients undergoing vascular surgery:
- Perioperative _______(1)
- Beta2 _______(2)
- _______(3) therapy
- Calcium channel _______(4)
- _______(5)
- Non-pharmacologic Approaches
- Epidural anesthesia – reduce perioperative myocardial ischemia
- Red blood cell transfusion – ______(a) is an independent predictor of adverse short and long term outcomes
- Maintenance of ______(b) is cardio protective (shivering, tachycardia & hypertension should be avoided)
- Endovascular Aortic Repair (EVAR) – studies may reveal fewer cardiac _______(6)
Answers:
1. beta-blockade
2. agonists
3. Statin
4. blockers
5. Nitroglycerin
a. anemia
b. normothermia
6. events
Prevention of Kidney Injury
- _______(1) (AKI) is a common complication of vascular surgery and is associated with high morbidity & mortality
- Incidence 16-22% with aortic surgeries
- Mortality is 4-5 fold higher with kidney injury
- Pathophysiology is multifactorial and includes ischemia/reperfusion injury (IRI); the use of nephrotoxic drugs (ACE inhibitors, NSAIDs, aminoglycosides, diuretics); _______(2) to renal arteries; and, _______(3) secondary to injury or immobilization.
- _______(4) is the most powerful predictor of postoperative renal dysfunction
- If patients receive chronic dialysis treatments, they should receive dialysis the day before or the same day as surgery
- Some patients will actually be ______(5) as a result (hypotension on induction)
- ______(6) > Men: increased incidence of perioperative AKI
Acute Kidney Injury
- Intraoperative factors – hemodynamic instability, need for inotropic support and transfusion of > 5 units PC or autologous blood
- Okay to use LR with kidney disease conversion of LR to lactate acid is old thinking
- The level of the ______(7) is correlated with AKI (suprarenal decreases renal blood flow by 80% versus infrarenal 45%) and reduced flow can persist for 30 minutes after release of the cross-clamp.
Answers:
1. Perioperative kidney injury
2. atheroembolization
3. rhabdomyolysis
4. Preoperative renal dysfunction
5. hypovolemic
6. Women
7. aortic clamping
Pharmacologic Approaches to Renal Protection
- Unfortunately, despite multiple studies and bench research, there is a dearth of clinical evidence to support pharmacologic interventions and strategies. Regardless, mannitol, loop diuretics and dopamine are still used.
- ______(a) – induced osmotic diuresis, decreases epithelial and endothelial cell swelling, acts as a hydroxyl free-radical scavenger and increases synthesis of prostaglandin resulting in renal _______(1)
- ______(b) – used to maintain urine output not shown to improve renal _______(2)
- Dopamine – 0.5- 2mcg/kg/min renal blood flow, Na+ excretion, and glomerular filtration rate (_______3)
Non-Pharmacologic Approaches
- Goal is to minimize renal _______(4)
- Cold renal artery perfusion to produce local _______(5)
- Remote ischemic preconditioning is thought to prevent _______(6) in multiple organ systems by inducing ischemic protection pathways
- Cold renal artery perfusion to produce local _______(5)
- Intermittent cross clamping of the internal _______(7) reduces the incidence of renal insufficiency by 23%
- However, repeated clamping of non-operative arteries in patients with severe atherosclerosis increases the risk of adverse _______(8)
- Endovascular aortic repair (EVAR) decreases kidney _______(9) because of elimination of aortic cross clamping
- However, ______(c)-induced _______(10) is a significant cause of kidney dysfunction
- Preoperative prevention strategies are aimed at minimizing contrast _______(11)
- MRI or ______(d)-based contrast studies have been proposed for patients at risk for contrast mediated _______(12)
- Ensuring adequate _______(13) is important
Answers:
a. Mannitol
b. Loop Diuretics
1. vasodilation
2. outcome
3. GFR
4. ischemia
5. hypothermia
6. IRI
7. iliacs
8. events
9. IRI
c. contrast
10. neuropathy
11. exposure
d. gadolinium
12. nephropathy
13. hydration
Preventing Pulmonary Complications
- Common in vascular surgeries with an incidence of 10-30% in AAA patients; patients with abdominal surgeries lasting > 3 hours; emergency surgeries; pre-op CHF; and, pre-op chronic lung disease
- The most effective preventive measure is postoperative lung expansion, either _______(1) or incentive _______(2)
- Anesthetic technique is an independent _______(3)
- Postoperative _______(4) analgesia reduces post op respiratory failure and duration of mechanical ventilation; there is some discussion of using lower _______(5)
Protect CNS/Spinal Cord
- Vascular surgery patients are at high risk for post-op central nervous system disease, including delirium, stroke, and _______(6) ischemia
- Age, preoperative cognition, depression, alcohol abuse, intraoperative blood transfusions are _______(7) factors
- CVA nearly twice as common in AAA _______(8)
- Open thoracoabdominal aortic aneurysm repair carries a higher risk of _______(9) than AAA repair.
- TEVAR is _______(10)
- Patients with symptomatic carotid stenosis benefit from _______(11) prior to major vascular surgery
- What about patients with _______(12) and discontinuation of antiplatelet therapy?
Answers:
- CPAP
- spirometry
- factor
- thoracic epidural
- VT
- spinal cord
- risk
- repairs
- stroke
- lower
- CEA
- Afib
Protecting the Spinal Cord
- Spinal cord ischemia occurs up to 11% in operations involving a distal aortic _______(1)
- Spinal cord is supplied by two posterior arteries, together they supply ______(a)% of spinal cord blood _______(2)
- The anterior spinal _______(3)
- supplies ______(b)% of spinal cord blood flow and is the primary supply to the _______(4) cord
- The anterior spinal artery is fed by a series of radicular arteries arising from the _______(5), and collateralization is _______(6)
- The blood supply to the thoracolumbar cord is derived from the _______(7).
- EXAM QUESTION: In 75% of cases, it joins the anterior spinal artery between _______(8) and _______, and in 10% of cases it joins between _______(9) and _______(10)
Answers:
1. repair
a. 25
2. flow
3. artery
b. 75
4. anterolateral
5. aorta
6. poor
7. radicular artery of Adamkiewicz
8. T8
9. T12
10. L1 and L2
Protecting the Spinal Cord
- Much of the flow in the anterior spinal artery depends on the artery of _______(1)
- Flow in the spinal arteries is often bidirectional and the blood supply to the spinal cord can be shunted to the rest of the body when perfusion pressures are _______(2)
- Standard measures to prevent spinal cord _______(3)
- a short cross clamp _______(4)
- maintenance of normal cardiac _______(5)
- high perfusion _______(6)
- Surgeons may place a “______(a)” (a heparinized tube that can decompress the heart and also provide distal _______(7)); however, even with a Gott shunt or partial bypass, there may be a period of visceral _______(8)
- Other surgeons may place a temporary ex vivo right axillofemoral bypass graft before positioning for _______(9).
- After the thoracic surgery, graft is removed, placement of shunt attenuates the hemodynamic response to aortic cross clamping, acidosis, hormonal and metabolic changes with aortic _______(10)
- Partial bypass is another option either from left atrium or ascending aorta to the iliac or femoral artery to provide distal _______(11)
- A heat exchanger is used to induce hypothermia adds to _______(12)
- Segmental sequential surgical repair duration of _______(13)
- Intercostal artery reattachment in hopes of preserving blood flow to the anterior spinal artery may be _______(14)
- Atrial-femoral artery shunt with partial bypass lends for better
- operative field _______(15)
- Reduces _______(16)
- Maintains stable distal aortic _______(17)
- Reduces (but not eliminates) head and neck _______(18)
A markedly decreased incidence of neurologic deficits were reported with distal aortic perfusion combined with drainage of CSF
CSF drainage improves the pressure gradient → allowing spinal cord blood flow as aortic occlusion lowers distal arterial pressures and increases the CVP
CSF drainage is employed in both endovascular/open techniques
Answers:
1. Adamkiewicz
2. low
3. ischemia
4. time
5. function
6. pressures
a. Gott shunt
7. perfusion
8. ischemia
9. thoracotomy
10. occlusion
11. perfusion
12. neuroprotection
13. ischemia
14. beneficial
15. exposure
16. afterload
17. perfusion
18. edema
Carotid Stenosis
- Carotid disease is usually a problem with embolization and less often occlusion or insufficiency
- Most common non-invasive test is _______(1).
- Estimated sensitivity and specificity of this test to detect a carotid artery stenosis greater than _______(2) are approximately 94% and 92%, respectively, when using digital subtraction angiography as the reference standard.
- Positive tests are usually followed by confirmatory angiography
- Estimated sensitivity and specificity of this test to detect a carotid artery stenosis greater than _______(2) are approximately 94% and 92%, respectively, when using digital subtraction angiography as the reference standard.
- Optimal treatment of asymptomatic carotid stenosis is controversial
- Recommendations for medical therapy include: smoking cessation, aspirin therapy, blood pressure control and statin therapy
- CEA over medical therapy for asymptomatic stenosis only when both the perioperative risk is low, and the patient is expected to live more than _______(3) years
- Symptomatic carotid stenosis – CEA with _______(4) therapy
- Carotid stenting versus open _______(5)
- Carotid Stenosis: high risk of _______(6) or CVA
- CEA reduces stroke risk when carotid stenosis > _______(7)
- _______(8) (temporary one eye blindness) = sign of impending stroke; 25% of pt with high-grade stenosis
- Awake pt is the best method to assess neurologic integrity
- During cross-clamping, maintain a normal to slightly elevated _______(9)
- After the cross-clamp removed, keep SBP under _______(10) mmHg (\ bleeding)
Answers:
1. carotid duplex ultrasound
2. 60%
3. 10
4. aspirin
5. CEA
6. TIA
7. 70%
8. Amaurosis fugax
9. BP
10. 145
Carotid Endarterectomy (CEA)
Indications:
- History of _______(1)
- Symptomatic patients with stenosis of more than _______(2) occlusion
- Patients who have suffered a stroke are NOT candidates for CEA in the acute phases of recovery.
- Consideration to chronic issues related to the stroke must be evaluated.
Pre-Op for CEA
- Continue ______(3) until the day of surgery
- Antiplatelet therapy – stop ______(4) days before surgery (generally)
- Not advisable to delay urgent surgery that might prevent a stroke for extensive cardiac evaluation even in patients with known CAD
Answers:
1. TIA
2. 70%
3. aspirin
4. 5
Carotid Endarterectomy (CEA)
- What is the leading cause of perioperative mortality after CEA?
- _______(1)
- Remember:
- Myocardial Infarction
- Normal cerebral blood flow:
- _______(2) ml/100 g/min (15% of cardiac output)
- Normal CMRO2:
- _______(3) ml/100 g/min (20% of O2 consumption)
- Cerebral blood flow at which ischemia is apparent on EEG (critical regional CBF)
- _______(4) ml/100g/min
- Regional Cerebral Blood Flow (rCBF)
- Utilizes PET scanning and MRI
- Can be calculated by measuring the washout of radioisotopes from the distribution of the middle cerebral artery.
- These studies allow the determination of the critical regional cerebral blood flow, the flow rate below which _______(5) of patients show EEG signs of ischemia.
- Brain receives ~_______(6)% of Cardiac Output (CO)
- CBF average is _______(7) ml/100 g/min
- Gray matter is _______(8) ml/100 g/min
- White matter is _______(9) ml/100 g/min
- Flow rates below _______(10) ml/100g/min are associated with impairment
- Flow rates between _______(11) ml/100g/min show a flattened EEG.
- Flow rates below _______(12) ml/100g/min are associated with irreversible brain damage.
- What intravenous solution should NOT be given to a patient undergoing CEA?
Isolyte
Lactated Ringer’s
______(13)
Normal Saline
Avoid ______(13)
Moderate hyperglycemia worsens ischemic brain injury.
Elevated blood glucose levels contribute to the development of severe lactic acidosis during brain ischemia in carotid occlusion resulting in unfavorable neurological outcomes.
Answers:
1. Myocardial Infarction
2. 40-60
3. 3-4
4. 18-20
5. 50%
6. 15
7. 50
8. 80
9. 20
10. 20 - 25
11. 15-20
12. 10
13. D5W
Carotid Endarterectomy
- Regional anesthesia
- Local infiltration or Superficial/deep cervical plexus block (_______(1))
- Risk of ipsilateral _______(2) nerve block → dyspnea due to paralysis of the hemidiaphragm
- General anesthesia
- Does not require pt cooperation
- _______(3) airway
- Ability to administer agents that reduce cerebral metabolic rate
- May require monitors of _______(4)
- Monitors of adequate cerebral perfusion
- _______(5): high incidence of false-negatives
- Cerebral Oximetry: cerebral perfusion at risk when rSO2 ≥ _______(6)% baseline
- Transcranial doppler: assessment of continuous blood flow velocity _______(7)
- SSEP: _______(8) pathways only
- Carotid stump pressures: pressures distal to the clamp
- Special pops: how much stump pressure is your goal? _______(9) mmHg
Answers:
1. C2-4
2. phrenic
3. Controlled
4. CBF
5. EEG
6. 25
7. MCA
8. sensory
9. 50
Intra-Op Goals for CEA
- Hyperglycemia (glucose >_______(1) mg/dL) has a documented association with worse outcome after CEA
- All anesthetic agents reduce cerebral metabolism O2 demand of the brain
- Volatile agents provide “preconditioning” by inducing _______(2)
- ______(a) offer a degree of brain protection during periods of regional ischemia
- Thiopental cerebral metabolic O2 requirements to _______(3)% of baseline = silent EEG
- Etomidate and Propofol brain electrical activity and cellular O2 requirements
- Etomidate – preserves _______(4) stability
- Propofol – allows for rapid awakening with quick neuro assessment
- Comes off pretty fast, we can keep them deep and still _______(5)
- Cerebral autoregulation is impaired by ______(b) but preserved under propofol-remifentanil anesthesia
- Hypothermia can depress neuronal activity
- Temporary occlusion (cross clamp) of the carotid artery acutely disrupts _______(6)
- Important to know adequacy of blood flow in _______(7) carotid
- Continued blood supply to the brain depends on collateral blood flow through the Circle of Willis if a shunt is used
- Patients with bilateral carotid disease > risk of _______(8)
- Keep arterial blood pressure higher during cross-clamp to augment cerebral blood flow
- Blood vessels in ischemic areas of the brain have lost autoregulation
- Stroke is generally due to embolic events not necessarily hypotension or hypertension
- Surgeons will utilize a shunt to provide blood flow during cross clamp
- IVF, vasoconstrictors (phenylephrine) to maintain BP _______(9)% above baseline
- Perioperative MI may occur in these patients
- Avoid hypercapnia/hypocapnia during _______(10)
Answers:
1. 200
2. nitric oxide synthase
a. Barbiturates
3. 50
4. cardiovascular
5. wake up rapidly
b. sevoflurane
6. BF (blood flow)
7. OTHER
8. CVA
9. 20
10. GA (general anesthesia)
Carotid Endarterectomy (CEA)
- What about PaCO2?
- Inconclusive; current literature reviews describe no benefit from manipulating mechanical ventilation to vasodilate or vasoconstrict cerebral vessels during CEA.
- Therefore, it is currently recommended that PaCO2 should be maintained at near _______(1) values.
- What corrective measures should the nurse anesthetist implement if intraoperative bradycardia & hypotension occurs?
- Surgical manipulation of the _______(2) cause symptomatic bradycardia & hypotension.
- Request the surgeon locally _______(3) the carotid bifurcation with 1% Lidocaine to control the symptoms.
- Treat hypotension with _______(4).
- Baroreceptor reflex bradycardia, hypotension; anticholinergic
- Head position → compression of carotid +/or vertebral arteries
- Maintain normocapnia or mild hypocapnia → prevent “steal” phenomenon by shunting blood away from hypoperfused tissue
- Glucose > _______(5) mg/dL DOS → may increase risk of stroke or death
- Post-op complications: hematoma (think _______(6) if unable to grab surgeon!), RLN injury, labile BP (exposed baroreceptor), stroke (embolic, not perfusion); reduced ventilatory response to hypoxia (carotid body denervation)
Techniques for Brain Monitoring
- Carotid Stump Pressures
- Used to predict collateral flow distal to the occluded carotid artery.
- Defined as “the pressure in the ______(a) stump of the occluded artery.”
- Pressure and flow do not necessarily correlate.
- Stump pressures of _______(7) mmHg or above may not adequately ensure adequate regional perfusion.
Answers:
1. normal
2. carotid sinus & baroreceptors
3. infiltrate
4. phenylephrine
5. 200
6. thickened airway
a. distal
7. 40-50
Shunts
- Practice variations among surgeons _______(1) vs. asleep
- Placement of shunt associated with embolic related stroke rate of ~ _______(2)%
- Technical problems with shunts include: air embolism, kinking of the shunt, shunt occlusion, injury or disruption of the distal internal carotid artery which may impair surgical access to the artery and increase cross clamp time
- Monitoring for embolic events: _______(3) patient or use of a transcranial doppler, SSEP, EEG, or cerebral oximetry
Techniques for Brain Monitoring
- Changes in ______(a), signals are sensitive parameters for ischemia, because electrophysiologic activity accounts for about _______(4)% of normal cerebral energy expenditure.
- However, these changes in electrical activity are not necessarily specific for ischemia that is severe enough to threaten cellular integrity.
- EEGs/SSEPs
- They are also affected by changes in physiologic parameters to include temperature, PaCO2, and the depth of anesthesia.
- EEG/SSEPs reflect specific parts of the brain.
- EEG – _______(5)
- SSEPs – specific sensory central nervous pathways (i.e., _______(6) )
Answers:
1. awake
2. 1
3. awake
a. EEG or Somatosensory Evoked Potentials (SSEPs)
4. 60
5. cerebral cortex
6. dorsal columns and lateral funiculus
