Mod X: Anesthesia for CAROTID ARTERY DISEASE Flashcards
Anesthesia for CAROTID ARTERY DISEASE
OBJECTIVES
- State the indications for carotid endarterectomy
- State several frequent co-existing diseases in patients with carotid artery disease
- Describe the anesthetic management of patients undergoing carotid endarterectomy
- Discus intraoperative maneuvers that are utilized to preserve cerebral blood flow
BACKGROUND CVA AND CAROTID ARTERY DISEASE
What’sthe 4th leading cause of death in the U.S. and the leading cause of long-term disability?
Stroke
Stroke is the 4th leading cause of death in the U.S.
Leading cause of long-term disability
Also a Major contributor to increased health care costs
(estimated at $65.8 billion in 2008)
With aging population, an increasing amount of patients will present to the OR with cerebral vascular disease
BACKGROUND CVA AND CAROTID ARTERY DISEASE
There is a strong correlation between strokes and
Carotid artery disease
BACKGROUND CVA AND CAROTID ARTERY DISEASE
CVA may occur from
Embolization of a thrombus or
Plaque debris that cause a reduction in flow
BACKGROUND CVA AND CAROTID ARTERY DISEASE
Regardless of the cause of injury the degree of cerebral injury depends on:
Plaque morphology
Characteristics of the embolus
Duration of hypoperfusion
Integrity of the circle of Willis
Degree cerebral collateral circulation present
CEREBRAL BLOOD FLOW (CBF)
Brain is 2% of body weight, but receives what % of CO?
12-15% of cardiac output
CEREBRAL BLOOD FLOW (CBF)
Total CBF averages
50 ml/100g/min
(750 ml/min)
CEREBRAL BLOOD FLOW (CBF)
Which CBF levels constitute adequate blood flow?
CBF levels >50 ml/100g/min
CEREBRAL BLOOD FLOW (CBF)
Which CBF levels are inadequate? are these a/w permanent injury?
20-50 ml/100g/min CBF is inadequate, but
No permanent injury occurs if blood flow restored
CEREBRAL BLOOD FLOW (CBF)
Which CBF levels may lead to permanent injury?
CBF <20 ml/100g/min => injury will occur
CBF AUTOREGULATION
The phenomenom whereby cerebral blood flow adapts appropriately to changes in mean arterial pressure (MAP) is known as:
Autoregulation
Cerebral blood vessels will constrict when MAP increases and dilate when MAP decreases
CBF AUTOREGULATION
What’s the purpose of Autoregulation?
Serves to maintain a constant CBF despite swings in MAP
CBF AUTOREGULATION
CBF is autoregulated in humans between which MAP values?
60-160 mmHg
CBF AUTOREGULATION
What is CBF regulated by for MAP values >60 or >160?
CBP will be passively regulated by MAP
AUTOREGULATION CURVE
With chronic hypertension the Autoregulation curve shifts to:
The Right
Autoregulation curve shifts to the right with chronic hypertension
This causes the lower and higher ends of the autoregulation range to be higher than in a normotensive pt
This could potentially protect the brain from transient high MAPs
But it occurs at the expense of raising lower limits, which causes an increase risk of ischemia at lower MAPs that would be otherwise tolerated well in a normotensive pt
This is why Hypertensive patients may develop cerebral ischemia at MAPs easily tolerated by normotensive patients
AUTOREGULATION CURVE
With chronic hypotension the Autoregulation curve shifts to:
The Left
CBF AND CHEMICAL CONTROL
What type of relationship exist between CBF and PaCO2 between arterial CO2 25-75 mmHg?
Linear relationship
Linear relationship between CBF and PaCO2 between arterial CO2 25-75 mmHg
CBF AND CHEMICAL CONTROL
How does CO2 causes cerebral vasodilation?
B/c CO2 diffuses freely into the CNS, causing increased concentration of H+ and dilation of the cerebral vessels
This is how Hypoventilation => cerebral vasodilation and inc CBF
CBF AND CHEMICAL CONTROL
Oxygen tension has an inverse relation with CBF?
Hyperventilation => cerebral vasoconstriction and dec CBF
However, Low arterial oxygen tension increases CBF
When PaO2 fall bellow 50mmHg, there is a rapid inc in CBF
CAROTID ARTERY ENDARTERECTOMY
Most common peripheral vascular surgical procedure
CAROTID ARTERY ENDARTERECTOMY
Estimated 130K procedures performed annually
CAROTID ARTERY ENDARTERECTOMY
Stenosis most commonly at
the bifurcation of the common carotid artery
CAROTID ARTERY ENDARTERECTOMY
Endarterectomy used to reduce symptoms and prevent stroke for over 50 years - why?
Low risk procedure with excellent long-term durability
Many trials have been completed in an effort to recommend the best treatment for pts w/ carotid artery dz, which over the years has actually cause an increase in the number of carotid endarterectomy performed
While carotid surgery has demonstrated postive effects, the terminative benefit must be determined for each pt in order to keep peri-operative strokes and death rates low
Perioperative stroke and death rates must stay low in order to maintain the beneficial effects of surgery over medical therapy
AHA GUIDELINES FOR CAROTID ENDARTERECTOMY
Based on AHA practice recommendations regarding carotid endarterectomies, which Factors are r/t increased risk of stroke?
Age, HTN, ischemic heart disease, diabetes, hyperlipidemia, diabetes, cigarette smoking, & high HCT.
HTN and smoking = two most powerful and treatable risk factors for stroke
AHA GUIDELINES FOR CAROTID ENDARTERECTOMY
Based on AHA practice Recommendations for symptomatic and asymptomatic patients regarding carotid endarterectomies, CAE recommended for symptomatic patients with Carotid Artery Dz of what % stenosis?
>70% stenois
Must also consider operative stroke and death rate along with life expectancy
AHA GUIDELINES FOR CAROTID ENDARTERECTOMY
Based on AHA practice Recommendations for symptomatic and asymptomatic patients regarding carotid endarterectomies, CAE recommended for asymptomatic patients with Carotid Artery Dz of what % stenosis?
>60 stenosis
Must also consider operative stroke and death rate along with life expectancy
PREOPERATIVE ANESTHETIC EVALUATION
Pre-op considerations for carotid artery dz include
Carotid artery dz does not occur in isolation
Evaluate for Systemic arterial dz
Perform a detailed system assessment
Evaluate and Optimize clinical status regarding coexisting diseases
Defining pre-existing neurological deficits
PREOPERATIVE ANESTHETIC EVALUATION
Pre-op Manegment Poorly controlled HTN
Gradual decrease of BP over several weeks prior to surgery
May help reset autoregulation prior to surgery
PREOPERATIVE ANESTHETIC EVALUATION
Pre-op Manegment Poorly controlled diabetes
Manage BG levels prior to surgery
Hyperglyvemia during surgery may enhance cerebral ischemia intra-op
PREOPERATIVE ANESTHETIC EVALUATION
CAD is common in pts w/ Carotid artery dz - How should these two be managed when both are present?
Difficult sometimes to determine which dz to treat first
Evaluation of severity of coronary artery disease and of carotid artery dz must be performed
PREOPERATIVE ANESTHETIC EVALUATION
For which pts is carotid revascularization recommended before CABG?
Pts w/ symptomatic carotid dz
Pts w/ bilateral severe asymptomatic carotid stenosis
PREOPERATIVE ANESTHETIC EVALUATION
Which pre-op medications must be continued?
Beta-blockers
Statins
Antiplatelets
PREOPERATIVE ANESTHETIC EVALUATION
Which pre-op medications must be held?
Diuretics
PREOPERATIVE ANESTHETIC EVALUATION
General anesthesia versus Regional anesthesia
A choice must be made
MONITORING DURING CAROTID ENDARTERECTOMY
Basic monitors
EKG, pulse ox, arterial blood pressure monitoring on contralateral side of surgery and leveled at the head to measure CPP
CPP = MAP - ICP, normal 60-70 mmHg
Anticipate BP fluctuations
Have vasoactive drugs available (constrictors and dilators)
MONITORING DURING CAROTID ENDARTERECTOMY
Cerebral perfusion monitors
EEG
Stump pressure
Somatosensory Monitoring
Transcranial Doppler
Cerebral oximetry
Jugular venous bulb monitoring
MONITORING DURING CAROTID ENDARTERECTOMY- Cerebral Perfusion Monitors
”gold standard” for monitoring the adequacy of cerebral perfusion
16-channel EEG
MONITORING DURING CAROTID ENDARTERECTOMY- Cerebral Perfusion Monitors
Limitations of the 16-channel EEG monitoring include:
High false positive rate
False negative rate (esp. w/ previous strokes)
Does not detect subcortical or small cortical infarct
May impact readings in patients with previous stroke hx
EEG monitoring can be affected by changes in temperature, blood pressure, and anesthesia dept
(In fact, when using GETA, a stable physiologic and anesthetic depth are mandatory to ensure adequacy of EEG monitoring)
May not be sensitive or specific enough to predict need for shunting
MONITORING DURING CAROTID ENDARTERECTOMY- Cerebral Perfusion Monitors
What’s the most effective means of assessing cerebral blood flow during carotid endarterectomy under “regional anesthesia” ?
Keeping the patient awake!!!
Under “regional anesthesia” it states that keeping the patient awake allows for continuous neurological monitoring of the awake patient, which is considered to be the most sensitive method for detecting inadequate cerebral perfusion and function.
MONITORING DURING CAROTID ENDARTERECTOMY- Cerebral Perfusion Monitors
What do recent evidence show regarding EEG vs other methods to monitor Cerebral Perfusion Monitors?
No consistent data showing that EEG are superior to other methods
MONITORING DURING CAROTID ENDARTERECTOMY
The ipsilateral retrograde perfusion pressure that results from collateral flow through circle of Willis from the contralateral carotid artery is also known as:
Stump Pressure
Carotid stump pressure estimates hemispheric blood flow by measuring pressure in the carotid stump distal to the clamp. Stump pressure is more often used to determine whether or not a shunt should be placed intraoperatively.
MONITORING DURING CAROTID ENDARTERECTOMY
What’s the utility of Stump Pressure montitoring?
Used to evaluate the adequacy of CPP during carotid clamping, and whether collateral circulation is adequate enough to maintain CBF
Used to determine whether a shunt will be needed to maintain cerebral perfusion
MONITORING DURING CAROTID ENDARTERECTOMY
Which the Stump Pressure values are considered adequate?
Stump pressure should be >45 mmHg,
otherwise shunt is needed
MONITORING DURING CAROTID ENDARTERECTOMY
What’s a possible negative consequence of false negative values on Stump Pressure reading?
Can result in false negative values, which lead to unnecessary shunt placement
Inexpensive and simple, so still used
MONITORING DURING CAROTID ENDARTERECTOMY
What is Somatosensory monitoring (SSEP) based on?
Response of the sensory cortex to electrical impulses form peripheral sensory nerve stimulation
Sensory cortex= risk of ischemia during carotid artery clamping
MONITORING DURING CAROTID ENDARTERECTOMY
unlike EEG, SSEP are able to detect which type of ischemia?
Subcortical sensory pathway ischemia
Able to detect subcortical sensory pathway ischemia unlike EEG
MONITORING DURING CAROTID ENDARTERECTOMY
Which characteristic changes of SSEP occur with reduced CBF and ischemia?
Decreased amplitude
Increased latency
MONITORING DURING CAROTID ENDARTERECTOMY
Which may affect SSEP monitoring?
Anesthetic depth
Temperature
Blood pressure
MONITORING DURING CAROTID ENDARTERECTOMY
T/F: SSEP monitoring may not be sensitive or specific enough to predict need for shunting
True
False positives and negatives do occur
MONITORING DURING CAROTID ENDARTERECTOMY
Which monitoring technique offers Continuous measurement of mean blood flow velocity and detection of microemboli (air or particulate matter) in the middle cerebral artery
Transcranial doppler (TCD)
Most peri-op neuro deficits are thought to be thrombolic in origin, TCD has been shown to detect embolization in more than 90% of pts
TCD can be difficult to impliment d/t high rates of technical failures, it has limited use in clinical settings
TCD Can also be used post-operatively to monitor for cerebral hyperperfusion
Technically difficult to implement d/t high rate of technical failures
MONITORING DURING CAROTID ENDARTERECTOMY
Jugular Venous Bulb Monitoring
Refer to Module I and chapter reading
MONITORING DURING CAROTID ENDARTERECTOMY
Cerebral Oximetry
Refer to Module I and chapter reading
CAROTID ENDARTERECTOMY: GENERAL VS. REGIONAL
Regardless of the technique chosen, the ultimate anesthetic goals are
Maintain adequate cerebral perfusion of the brain
Awake patient following surgery, so that a neuro exam can be immediately performed
CAROTID ENDARTERECTOMY: GENERAL VS. REGIONAL
Common historical anesthetic technique for CEA was:
Cervical plexus block
Historically, regional anesthesia, in the form of a cervical plexus block most commonly used
Patients can be examined intraoperatively, more cost effective, shorter length of stay
CAROTID ENDARTERECTOMY: GENERAL VS. REGIONAL
T/F: There is no statistical difference in perioperative death, MI, and stroke with regional anesthesia when compared to general anesthesia
True
GALA trial showed no statistical difference in perioperative death, MI, and stroke when compared to general anesthesia
The decision between regional vs general anesthesia for CEA varies by institution
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA
Advantages of using General Anesthesia for CEA include:
General reduces cerebral metabolic oxygen demands
Better regulation of PaO2, PaCO2, and MAP under GA
No specific technique is more superior than the other
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA
BP consideration when using General Anesthesia for CEA
Must anticipate swings in blood pressure and be prepared to treat accordingly
Have Short acting vasoactive and vasodilating drugs available
(Phenylepherine, NTG, Nicardipine)
Specially important w/ Patients with poorly controlled HTN
Have IV fluid for volume depletion
Ready for meticulous titration of anesthetic gases
Prompt treatment of hypotension is very important
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Induction
Limit benzodiazepine use - Why?
May prolong wake up time at the end
Consider opioids for anxiety
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Induction
Typical hypnotic agent is
Propofol
(Unless limited cardiac reserves, in which case use Etomidate)
Etomidate
(for patients with limited cardiac reserve)
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Induction
Which drugs can be used at induction (as adjuntc) to blunt hypertensive reaction to laryngoscopy?
Small dose Opioids or Beta-blockers
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA
Which inhalation agents have been shown to provides greatest protection against ischemia
Isoflurane
(provides greatest protection against ischemia)
Sevoflurane
(similar protection against ischemia as Isoflurane)
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA
Which inhalation agent is appropriate in accelerating wakeup and allowing for more immediate neurological assessment?
Desflurane
accelerates wakeup, allowing for more immediate neurological assessment
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA
Both N2O or Remifentanil appropriate - If N2O is used, it should be d/cd befored the carotid artery is openned. Why?
A small amount of air present in the artery could potentially expend and cause an arterial air embolism
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - MAINTENANCE
Consider low dose Opioids, especially if
surgeon using local anesthetic in field
Not much pain experienced in such case
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - MAINTENANCE
BP and HR management
MAP maintained at or slightly above baseline
Avoid tachycardia
(Beta-blockers if needed in small increments/consider shorter acting)
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Other Considerations
What dose of Heparin would the surgeon request prior to clamping of the carotid artery?
Heparin 100 units/kg
prior to clamping of the carotid artery
Reversal of Heparin with Protamine after procedure
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Other Considerations
Where should MAP be maintained during carotid clamping?
During carotid clamping, maintain MAP within 20%(+/-) of patient’s baseline
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Other Considerations
Watch for reflex bradycardia - why?
Surgical manipulation of the carotid sinus could cause reflex bradycardia
Have Atropine available for treatment
Surgeon main inflitrate the surgical site w/ lidcaine to prevent this from hapenning
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Other Considerations
Maintain normocapnia (normal EtCO2) or mild hypocapnia during the procedure - why?
Hypercapnia can cause Steal phenomenon
This shunts blood avay from the ischemic areas af the brain
Theoretically, hypocapnia will vasoconstrict and has been advocated for as a reversal for the Steal phenomenon, however its benefits have not been proven clinically
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Other Considerations
Keep glucose levels < 180 mg/dl for diabetic pts - Why?
Studies show that BG levels > 200 mg/dL on post op Day 1 corellate w/ increased risks for strokes, TIAs, MI, and Death
CAROTID ENDARTERECTOMY: GENERAL ANESTHESIA - Other Considerations
Watch opioid administration, especially if surgeon injects local anesthetic - Why?
Not much pain associated with procedure,
CAROTID ENDARTERECTOMY: REGIONAL ANESTHESIA
Historically done in the form of
Deep and superficial cervical plexus block
C2 - C4 nerve roots
This technique has been around for > 40 yrs and many providers still prefer it
CAROTID ENDARTERECTOMY: REGIONAL ANESTHESIA
Advantages of Deep and superficial cervical plexus block for CEA
Minimal sedation required
Awake patient allows for continual neurological assessment, which is especially important during trial occlusion of the carotid artery
–No adverse effect –> continued procedure with RA
–Adverse effect –> shunt inserted &/or GA with ETT
Less intraoperative hypotension
Faster postoperative recovery and provides postop analgesia
Lower cost
CAROTID ENDARTERECTOMY: REGIONAL ANESTHESIA
What must be done if adverse effect occur with Deep and superficial cervical plexus block for CEA?
Shunt inserted &/or GA with ETT
CAROTID ENDARTERECTOMY: REGIONAL ANESTHESIA
Disadvantages of using regional anesthesia for CEA include:
More intraoperative hypertension (a/w a higher release of catecholamines)
Awkward airway control if need to convert to GA
Sedation may obscure neurological monitoring (and cause hypercapnia and hypoxia)
Patient discomfort (if the procedure is long of if ischemia develops)
Sedation causing hypercapnia or hypoxia
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Post-operative Hypertension r/t
Surgical denervation of ipsilateral carotid baroreceptor
Especially in pts w/ poorly control HTN prior to surgery
Regional anesthesia is a/w less hypertension
May need Labetalol or Nicardipine or Sodium Nitroprusside post-operatively
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Carotid body denervation can also occur - What causes it? what could it lead to?
Caused by surgical manipulation
May lead to impaired ventilatory response to mild hypoxemia
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Postoperative hoarseness and ipsilateral tongue deviation may occur - How does this happen?
Retractors use during the procedure to visualize the surgical field
These retractors can put pressure on the recurrent laryngeal nerve or the hypoglossal nerve
Careful in patients with hx of contralateral CEA or neck surgery
Should subside shortly after surgery
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Monitor for postoperative wound hematoma - why?
Airway compromise is possible
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Postoperative Cerebral Hyperperfusion Syndrome may occur - What causes it?
Abrupt increase in amount of blood flow and loss of autoregulation to the reperfused brain
Typically doesn’t occur until several days after the procedure
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
S/S of Postoperative Cerebral Hyperperfusion Syndrome include:
Headache, seizures, focal neurologic signs, brain edema, intracerebral hemorrhage
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Which pts are at increased risk for Postoperative Cerebral Hyperperfusion Syndrome?
Patients with severe postoperative HTN
Patients with severe preoperative internal carotid artery stenosis
CAROTID ENDARTERECTOMY: POSTOPERATIVE CONCERNS
Other post-op concerns following CEA include:
Postoperative hypotension
Loss of carotid body function
CEAs not associated with large blood loss of fluid shifts
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
Endovascular treatment of carotid artery disease includes:
Percutaneous angioplasty & stenting
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
Where are Percutaneous angioplasty & stenting procedures typically performed? which anesthetic technique is typically used?
Specialized endovascular suites under
Local anesthesia with light sedation (to facilitate pt’s comfort and the need for frequent neuro monitoring)
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
Monitors used:
Routine monitors and arterial line
ENDOVASCULAR TREATMENT: CAROTID ARTERY STENTING
Procedural approach
Femoral approach is standard
Brachial and high radial arteries are alternative sites
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
Embolic protection devices are mandatory - why?
Provide protection in the form of a filter or an occlusive balloon
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
Antiplatelet therapy:
Dual Antiplatelet therapy is used along w/ self-expanding stent
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
How does endovascular tx compares to traditional CEA?
Unfortunately, endovascular tx has been shown to be inferior to the traditional CEA in outcome studies related to stroke and death rates
Especially in pt > 70 yo
ENDOVASCULAR TREATMEBNT: CAROTID ARTERY STENTING
In which outcome areas is endovascular tx superior to traditional CEA?
Reduced rates of myocardial infarction, cranial nerve palsy, and access site hematomas
