Anesthesia for Vascular Surgery – Flashcards
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What is arteriosclerosis?
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occurs when the arteries in the body become thick and stiff, impairing the body's ability to carry oxygen and nutrients from the heart to the rest of the body
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What is the Windhessel effect?
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-pulsatile ejection converts to a steady, even blood flow at the capillary level [arterial stiffening interrupts this]
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What is atherosclerosis?
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-a type of arteriosclerosis, occurs when fat, cholesterol, and other substances build up in the walls of arteries and form hard structures called plaques -over time, these plaques can block the arteries or even burst causing a thrombus to form
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What accelerates damage to the endothelium of the arterial walls?
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-smoking -hypertension -elevated cholesterol/triglycerides
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When does blood supply down stream [in the body] become insufficient?
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-severe, usually 70-80% stenosis
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How does atherosclerosis develop in the body?
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-small low density lipoproteins pass into the arterial endothelium wall [LDLs penetrate wall] -LDLs are prone to free radicals and oxidize; the endothelium responds by attracting WBCs [macrophages] which penetrate the wall and ingest the LDLs -the oxidized LDLs [now called foam cells] triggers an immune response, over time can produce atheroma, if HDL does not keep up with removal of fats -walls stretch and thicken [compensate for additional bulk] and develop plaque, causing less compliance with each heart beat
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Why does atherosclerosis affect arteries and not veins?
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because of the pressure difference, the inner lining [tunica intima] is affected most
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What are the risk factors for atherosclerosis? (11)
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-*smoking* -*hypertension* -*hyperlipidemia* -diabetes -obesity -myocardial infarction -stroke -family history -elevated C reactive protein -advanced age [>70] -male gender
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How is vascular disease managed?
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-reducing modifiable risk factors [smoking, obesity, etc] -taking antihypertensive medication -statins to reduce hyperlipidemia -tight control of blood glucose if diabetic -aspirin -exercise -wine [raises HDL]
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What is the problem you may come across intraop if a patient is taking an alpha blocker?
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hypotension; will be difficult to increase BP intraop, will need lots of Neosynephrine! -example: doxazosin [Cardura], prazosin [Minipress]
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What is the beta blocker protocol?
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patient should be on a beta blocker for at least a month prior to surgery -hold if HR <50 bpm, or SBP <100 mmHg
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What are some considerations with a patient who has diabetes?
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-assess for end organ damage from complications [renal dysfunction, autonomic neuropathy, etc] -uncontrolled DM has an increased risk of death -hold all diabetic meds day of surgery, institute insulin protocol if CBG >180 -tight control of glucose to decrease risk of infection
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What are patients with diabetic autonomic neuropathy prone to?
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-silent or nonsymptomatic MI -hemodynamic instability
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What are some considerations with a patient who has renal disease?
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-often related to diabetes or hypertension; patient is unable to remove wastes -find out when last dialysis was, most recent labs [potassium/avoid Sux, H&H d/t anemia, coags if regional anesthesia] -listen to breath sounds to determine fluid overload if dialysis was not recent -watch fluid replacement, hang 0.9% NS 500 ml bag, mini drip
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How is blood supply delivered to your brain?
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-2 carotid arteries [front of the neck] and 2 vertebral arteries [back of the neck]
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What are the indications for carotid endarterectomy surgery?
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-TIAs with evidence of stenosis [more than half of all strokes are preceded by TIAs] -70% stenosis of the vessel wall -unstable neurologic status that persists despite anticoagulation
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What is cerebral autoregulation and what is normal cerebral blood flow?
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-tendency of cerebral tissue to maintain normal blood flow despite variations in blood pressure -mean arterial pressure: 50-150 mmHg [greater than 150 the cerebral vessels are maximally vasoconstricted; less than 50 the cerebral vessels are maximally dilated]
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What occurs with cerebral autoregulation and hypertensive patients?
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-there is a shift to the right of the autoregulation curve, meaning that the lower limits are at a higher set point and require higher pressures
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With CEA patients, what is true about cerebral vasculature and what are anesthetic considerations?
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-with a stroke, cerebral vasculature loses its autoregulatory ability and cerebral blood flow becomes passive and depends on blood pressure -maintaining adequate blood pressure is critical because they have minimal or no autoregulatory reserve to counter anesthetic induced reductions in blood flow
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How is carotid artery stenosis diagnosed?
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-auscultation of bruit over carotid -doppler ultrasound -MRA [magnetic resonance angiography] -arteriography
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What are the methods for clinical monitoring of cerebral perfusion during CEA?
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-most sensitive and specific is repeated neuro exams [using regional so patient is awake] -during general: EEG, SSEP, transcranial doppler, internal carotid stump pressure, and jugular venous oxygen saturation
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What nerve is located along the pathway of the carotid?
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hypoglossal nerve [responsible for tongue being midline, "stick your tongue out"]
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What is the recommended preoperative management for carotid endarterectomy?
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-check BP of both upper extremities -two 18g PIVs [one for drips, one for boluses] -arterial line -beta blocker protocol, aspirin therapy, & antihypertensives: take up to day of surgery -check CBG -assess baseline neuro status, discuss "wake up test" with patient -assess their METs; cardiac tolerance [30-50% of patients undergoing CEA have CAD]
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Positioning considerations in patients undergoing CEA:
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-keep head neutral during laryngoscopy -move head and ETT away from surgical side -roll will be placed under shoulders -arms tucked during procedure
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What are the recommended techniques for induction and medicine to have ready for CEA?
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-limit propofol use during induction -limit nondepolarizer muscle relaxants w/ EEG -avoid Sux in hemiparetic patients -usually 100 mcg Fentanyl is sufficient for case [or could do Remi drip with 1/2 MAC Des for fast wake up] -have Phenylephrine/Nipride drips attached to distal port [usually not warmed]
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What are important maintenance considerations during carotid endartectomy surgery?
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-maintain baseline blood pressure after induction -maintain normocapnia -heparin will be administered based on surgeon's recommendation [give heparin, set 3 min timer] -get blood pressure greater than 160 mmHg while waiting for the 3 min timer
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Intraoperative management during clamping of the carotid:
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-shunt may be placed based on EEG readings -maintain SBP greater than 160 until clamps released -once clamp is off, keep blood pressures at the patient's low normal range, usually not below 110-120 -reverse heparin w/ protamine [give slowly!!!]
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Why must SBP be elevated during clamping?
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-allows collateral vessels to get to the Circle of Willis and maintain cerebral perfusion
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During emergence/waking up patient for CEA
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-bupivicaine is locally injected around incision site -expect rapid wake up if Des/Remi used -extubate and perform "wake up" test when appropriate [evaluate patient's hand grasps, tongue for midline position, and good lower extremity movement]
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What is seen with EEG during general anesthesia?
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-high frequency and low voltage activity is seen with "light" anesthesia -low frequency and high voltage occurs with "deep" anesthesia
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What are considerations with superficial & deep cervical plexus blocks as the anesthetic technique during carotid endarterectomy?
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-able to assess neurological function in real time -patient will be awake during surgery and asked to perform a variety of tests such as honk horn, count backwards from 5, etc. -despite physiologic advantages, no difference in outcome between general or regional techniques -patients will get hot under the drapes, bair hugger may need to be on "ambient" temperature
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What may happen during surgical traction on the carotid sinus?
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-may cause intense vagal stimulus, leading to severe bradycardia -inform surgeon immediately, who will inject local around carotid baroreceptors -may need to give anticholinergic, but beware that it may increase HR on patient who already has CAD
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What are two major intraop concerns regarding carotid endarterectomy?
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-bradycardia with traction of carotid baroreceptors -difficulty increasing BP in those on alpha blockers to keep > 160 mmHg while clamp is on
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What happens once the patch graft is sewn in?
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-carotid will be unclamped -reflex vasodilation and bradycardia may be seen; goal is to get BP back down to low normal [120 mmHg] to aid hemostasis at graft site -titrate down inhalation agents once local anesthetic is infiltrated
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What are the indications for a carotid stent [in place of carotid endarterectomy]?
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patients with neck issues: -radiation -recurrent laryngeal nerve dysfunction -tracheostomy -neck immobility
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What are some important anesthetic considerations for carotid stents?
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-will need to give Atropine before balloon inflation of carotid stent to prevent profound bradycardia [give Robinul if elderly] -patients will have general anesthesia, heparin, and "wake up tests" -phrenic nerve block observed w/ these patients
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What is the leading cause of perioperative & late mortality after a CEA?
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myocardial infarction [periop risk 0-4%]
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What are postoperative complications observed with carotid endarterectomy & stents?
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-neuro deficits; occur from hypoperfusion or microemboli [minor changes usually resolve, major changes require immediate re-exploration] -hemorrhage at surgical site [can lead to tracheal deviation, loss of airway] -myocardial infarction [late mortality after CEA] -carotid baroreceptor dysfunction -chemoreceptor dysfunction -tension pneumothorax -reperfusion injury [cerebral hypoperfusion syndrome]
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What does carotid baroreceptor dysfunction lead to [postoperatively]?
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causes postop hypertension & tachycardia [due to carotid sinus dysfunction caused by surgical trauma]
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Chemoreceptor dysfunction after carotid endarterectomy:
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-nonfunctional up to 10 months after a CEA -loss of circulatory response to hypoxia & an increase in resting PaCO2 [~6 mmHg more] -serious concern for those with previous contralateral carotid endarterectomy [do not want bil. dysfunction!] -give supplemental O2; admin. opioids cautiously
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How does a tension pneumothorax occur postop following carotid surgery?
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results from air dissecting through the wound and the mediastinum to the pleura
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What is a rare, but often fatal complication following carotid endarterectomy?
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*reperfusion injury [cerebral hypoperfusion syndrome]* -involves developing cerebral edema after obstructed flow through the carotid artery has been relieved [loss of autoregulation d/t long standing hypoperfusion, unable to respond w/ vasoconstriction once increased perfusion occurs] -s/s: severe headache, visual disturbances, altered LOC, seizures
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What is considered the contributing factor causing a reperfusion injury?
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poorly controlled BP after the carotid cross clamp -maintain good blood pressure control with antihypertensives after the carotid obstruction is eliminated [nipride, labetalol]
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What is the difference between an AV graft and an AV fistula?
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-fistula: connecting an artery directly to a vein [requires 8-12 weeks to mature/be used for dialysis] -graft: synthetic tube implanted under skin that connects an artery to a vein [can be used in 2-3 weeks] -grafts have more problems with clotting & infection, need replacement sooner
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What is the OR set up & pre-op prep for an AV fistula/graft placement?
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-prepare for sedation intraop [often propofol infusion] -0.9% NS 500 ml bag, mini drip -be ready for GA [just in case] -have heparin 1000 units/ml available -vital signs: HTN controlled? -labs: K, H&H, coags -last dialysis
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What are the anesthetic techniques for AV graft/fistula placement?
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may be MAC, general, or brachial plexus block -MAC/local works well for brescia-cimino AVF or simple brachio-cephalic AVF -axillary block most common for lower arm procedures [brescia or AF loop grafts] -interscalene or infraclavicular blocks best for high upper arm [superficializations] -AV loop grafts require tunneling and need "good" block or plan on general anesthesia
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What ethnicities are at greater risk for arterial occlusion [requiring fem-distal bypass grafts]?
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African American & Cherokee
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What are the anesthesia options for fem-distal bypass grafts?
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general anesthesia, subarachnoid spinal block, or continuous lumbar epidural -know how long the procedure will take -check coags if using regional
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When the clamp is released during fem-distal bypass, what are potential findings?
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-prepare for drop in blood pressure when clamp is released -hemodynamic changes are dependent on the length of time the clamp was placed
