Carotid Endarterectomy (CEA) – Flashcards
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What is intracerebral steal?
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The diversion of blood flow away from already maximally dilated vessels in occluded carotid arteries and toward normal areas of the brain. Simply a decrease in regional CBF (rCBF) in ischemic areas with an increase in CBF in normal areas.
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What promotes intracerebral steel?
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Vasodilation secondary to hypercapnia
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What is associated with hypocapnia?
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Inverse steel (aka Robin Hood phenomenon), this is the diversion of blood to maximally dilated, hypo perfused areas.
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Given the Robin Hood phenomenon, is hypocapnia preferred?
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No, no benefit is reported with this technique and it may actually increase ischemia. The recommendation is normocarbia (CO2 35-45)
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What is the most challenging aspect of CEA patients?
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BP control. 10-50% of patients experience hTN and 10-60% experience HTN.
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What is the cause of hTN?
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Carotid sinus baroreceptor stimulation
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What is the cause of HTN?
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Surgical manipulation of the carotid sinus.
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How does CBF remain consistent given labile BP in these patients?
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Autoregulation, so try and keep you MAP 60-160 mmHg. Remember if these patient's are normally HTN, then their autoregulation is shifted to the right.
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Why is glucose control important for CEA patients?
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Hyperglycemia can worsen ischemic injury d/t lactic acidosis secondary to anaerobic glycolysis. Hyperglycemia is also associated with an increased incidence of post-op complications like infection. BG goal is usually 100-150
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What are the types of anesthesia possible for CEA?
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Regional with a cervical plexus block (C2-C4 block) or local infiltration, or GA are all viable options. Generally based on surgeon preference.
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What are the advantages of regional anesthesia for CEA?
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-Awake patients allow for reliable cerebral monitoring (LOC/neuro exam) -Lower requirements for shunting -Lower costs d/t less time in the ICU, less vasoactive gtts, decreased MI incidences and less intra-op equipment
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What are the disadvantages associated with using regional for CEAs?
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-GA has benefits of cerebral protective effects b/c volatiles decrease CMRO2 -Requires patient cooperation -Patient may develop seizures/loose LOC with carotid cross clamping -Can be difficult to convert to GA once surgery has begun -Depending on regional technique, may be at risk for phrenic nerve block or Horner's syndrome
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Why are you concerned if your patient develops Horner's syndrome secondary to regional anesthesia for a CEA?
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S/sx of Horner's syndrome (one-sided ptosis, anhidrosis, miosis, tongue deviation) can mimic s/sx of a stroke
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What are the sedation challenges with a regional CEA approach?
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Poor sedation can cause restlessness, poor cooperation, agitation, disinhibition, and respiratory depression (especially with versed and older patients)
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What is the risk of using propofol/opioids instead of benzos/opioids?
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Suggested that propofol/opioids make increase requirements for shunting (possibly due to more significant hTN)
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Is Precedex a good choice for sedation with regional CEAs, if so why?
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Dexmedetomidine is an alpha 2 agonist; it can decrease opioid requirements, only mildly depresses ventilation, and can allow for continuous neuro monitoring.
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What monitors are needed for a CEA with regional?
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-ASASM -Precordial Non-invasive & invasive BP monitoring
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Why is a trial clamping of the carotid performed during CEAs? How is this done for a regional technique?
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To evaluate the need for a shunt and assessed via a neuro exam so warn patient pre-op
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What does the neuro exam entail?
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Strength of hand grip, LOC, and patient alertness; this is a very specific and sensitive method for assessing cerebral perfusion.
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What are the advantages GA technique for CEAs?
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-Motionless field -Volatiles offer cerebral protection d/t decreased CMRO2 and decreased cardiac metabolism via anesthetic preconditioning -Increased control of airway, ventilation and sympathetic responses
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What are the disadvantages of a GA technique?
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-Requires alternate method for monitoring cerebral function and cannot reliable do so -Prolonged emergence
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What monitors are required for a CEA under GA?
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Same as regional technique, but may consider use of CVP, PA catheter, or TEE
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If you placed a PAC, where would you want to consider placement?
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The brachial artery on the contralateral side
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What other equipment is required for CEAs?
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-Large bore IV with tri-connector (Crows foot) -Heparin -Protamine -Infusions: Neo, Nitro, and SNP
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What induction drugs are appropriate?
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Propofol and etomidate are good. Ketamine can increase CMRO2, and avoid versed induction usually because case is only ~1.5 hr long
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Barbiturates and propofol both have what benefit?
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Offer cerebral protection due to the 40% decrease in cerebral metabolism and decrease in CMRO2.
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What opioids are good for induction of GA?
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Remi, fentanyl and sufenta are all good choices d/t rapid metabolism.
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What NMBD are appropriate for the induction of GA?
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All non-depolarizing are acceptable. May avoid Succs if paralysis from previous stroke d/t risk for hyperkalemia.
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What are some of the benefits of maintaining a light level of GA (i.e. MAC 0.5-1% with fentanyl/precedex adjunct)?
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-Easy recognition of ischemic changes on EEG -Facilitates BP management -Lower peri-op MI incidence
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What volatile agents are acceptable for CEAs?
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All are fine
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Can N2O be used for these patients? If so, when?
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Yes! Recommended at 50/50 until clamp time when FiO2 should be 100%
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Is hypo or hyperthermia associated with decreased CMRO2?
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Hypothermia; 1 degree Celsius decrease in core temp -> 7-8% decrease in CMRO2
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What is the gold standard of cerebral monitoring during GA?
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EEG; it assesses cortical electrical function, but deep brain structures are not monitored.
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What changes on an EEG are indicative of neurological dysfunction?
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Loss of B wave activity, loss of amplitude and emergence of slow-wave activity.
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What is the concern with GA and EEG monitoring?
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General anesthetic agents cause EEG changes that mimic cerebral ischemia; usually keep MAC < 1% and use adjunct agents.
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What is the benefit of SSEP monitoring?
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Is can assess and identify inadequate CBF or ischemia in deep brain structures during cross-clamping.
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What GA technique is best for SSEP monitoring?
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TIVA b/c volatile agents can mimic ischemia
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What is the benefit of a BIS (processed EEG) monitor?
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Easy for CRNA to interpret and is a global (not hemisphere) measurement
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What are carotid stump pressures (CSP)?
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The measurement of distal pressure in the internal carotid artery after the cross-clamp application; this assesses perfusion pressure in the operative carotid artery.
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What is a transcranial doppler (TCD)?
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Assesses the blood flow velocity in the middle cerebral artery and helps detect cerebral emboli. The pulsality index (PI) measures changes in blood flow velocity.
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Why does an increase in PI reflect?
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An increase in vascular resistance. < 80 is generally an acceptable PI number.
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What are the limitations of TCD monitoring?
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Technical difficulties can interfere with data interpretation. It is also not as useful if the patient requires a shunt, however it can detect a malfunctioning shunt.
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What does jugular venous O2 saturation (SjO2) assess?
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Global ischemia, but doesn't reflect regional or focal ischemia. It depends on SaO2, CMRO2, and CBF. Range is 50-75%
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What does cerebral oximetry assess?
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Cerebral regional oxygen saturation. This referred to as Near Infra-Red Spectroscopy (NIRS)
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How does NIRS compare to stump pressures?
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Generally a little more accurate.
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Describe intra-arterial xenon injection.
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This assesses arterial xenon concentrations and has been proposed as a new means for measuring regional CBF
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What is the most sensitive and specific measurement of adequate cerebral blood glow?
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Continuous assessment of global and focal neurological status in the awake patient.
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What is the carotid triangle?
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A space bounded by the superior belly of the omohyoid muscle, by the anterior border of the sternocleidomastoid muscle, and by the posterior belly of the digastric muscle, containing the bifurcation of the common carotid artery.
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How might a surgeon differentiate between the internal and external carotid arteries?
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The internal carotid does not have any branches, the external does.
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When the surgeon asks for the administration of heparin, you are about _______ away from cross-clamping.
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3 minutes
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What lab value should be obtained to assess the efficacy of heparin administration?
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ACT
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After cross-clamp application and before the artery is open, how will the surgeon assess contralateral flow?
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Stump pressures
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To check stump pressures, what supplies will you need to have available?
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A stopcock, 24" pressure tubing extension, a-line setup and cable.
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What usually results from unclamping and is due to cerebral protective processes?
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Hypotension
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How does cerebral autoregulation protect the brain from reperfusion injury?
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By reducing the cerebral production of renin, vasopressin and norepinephrine which result from hTN.
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Carotid plaques do what to the response from baroreceptors? What happens after plaque removal?
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They dampen the baroreceptor response. After plaque removal, stimulation of baroreceptors is increased potentially causing hTN and bradycardia.
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What may result secondary to carotid sinus nerve injury?
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HTN
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How does protamine work? What is the dose?
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Forms a neutralization complex with heparin forming a stable salt. Dosage is 1mg protamine for every 100units (1mg) Heparin.
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What are some consideration with the administration of protamine?
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Give slowly (over 10 minutes) and consider H1/H2 blockers prior to administration.
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What are your post-op goals for these patients?
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-Stable hemodynamics (HTN most common; 2-3 hrs post-op up to 24 hrs) -Able to follow commands
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What are potential complications from this procedure?
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HTN, acute CVA, MI, respiratory insufficiency, emergent neck exploration, tension pneumothorax, carotid body damage, cerebral hyper-perfusion syndrome (CHS)
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What is the anesthetic of choice for carotid angioplasty and stenting?
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Local anesthesia is given via the femoral insertion site in combined with sedation.
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What is your heparin dose and ACT goal?
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Heparin is 50-100units/kg with an ACT goal of >250
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What can occur with balloon inflation?
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hTN and bradycardia (baroreceptor response)
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What are the four steps of stent placement?
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1. Guidewire passed through plaque 2. Embolic protection filter is placed 3. Carotid balloon angioplasty 4. Carotid stent placed
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What is the main complication of CAS?
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Stroke caused by microembolization of athersclerotc plaque into cerebral circulation
