Anesthesia for aortic aneurysms – Flashcards
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What are the risk factors for AAA/TAA's?
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-age [the older you get, the higher risk] -gender [males >females] -***smoking***
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What are the associated conditions in pts who develop AAA/TAA's?
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-HTN -Diabetes -CAD -Renal disease
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What complications is hypertension associated with?
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-stroke -heart failure -heart attack -kidney failure
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Pre-op considerations r/t HTN meds
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-take all routine antihypertensives on DOS or night before as scheduled -some suggest hold ACE inhibitors to avoid refractory hypotension following induction -beta blocker protocol [don't hold, if not given, work in beta blocker intraoperatively]
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What is the latest diabetic protocol?
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-CBG < 180, no initial intervention -hold diabetic meds day of surgery -may give 1/2 dose long acting insulin [do not give regular insulin] -reimbursement/SCIP standards, keep normoglycemia
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What is diabetic autonomic neuropathy and what is it associated with?
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-poor control of HR, if BP decreases, HR doesn't increase like normal -diabetics are prone to "silent ischemia" -autonomic neuropathy may result in intraop hemodynamic instability
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What are the risks associated with renal disease and aortoocclusive disease?
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-pts w/ aortoocclusive disease who develop postop renal failure have a 50% mortality -renal dysfunction overlaid w/ fluid shifts & decreased blood flow probable cause of postop failure
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What is the best predictor of postop renal failure?
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-preop renal dysfunction -creatinine of > 2 mg/dl is predictor of cardiac morbidity
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What pre-op considerations must be taken w/ pts who have existing renal disease?
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check preop labs: K, Hct/Hgb [most common alterations] -significant anemia could be an issue w/ large blood loss -coags if doing regional anesthesia
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What are considerations taken w/ dialysis patients?
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-determine when last dialysis occurred [want at least the day before surgery, if not, may want to cancel] -check for signs of fluid of overload -watch for fluid replacement [usually 0.9% NS, not LR/PL d/t lytes such as Ca & K] [fluid restricted; if on diabetic protocol, no K in IVF]
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At what point does the risk of rupture increase?
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-over 5 cm rapidly increases the risk of rupture -an aneurysm is a bulge or ballooning in the wall of artery and can become large before causing any symptoms
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How can an AAA be detected?
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-often asymptomatic -physical examination [can be palpated if large] -ultrasound -CT scan
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What are the possible treatments for AAA?
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1. watch 2. open abdominal repair 3. endovascular [much less invasive]
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What is an open abdominal repair?
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-diseased part of the aorta is replaced with a dacron or teflon graft and sewn in place by the surgeon -major abdominal incision, general anesthesia -average stay in hosp is 7-10 days
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What is an endovascular repair?
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-recent advances in catheter based technologies, endovascular grafting via small incision in the groin
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What occurs with an open aneurysm repair?
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-replace the diseased vessel w/ an artificial graft -blood vessels above and below the aneurysm are clamped in order to control any bleeding and the aneurysm itself is opened -graft is made of Dacron, similar to Terylene
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Anesthesia technique for open AAA repair
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-general anesthesia [if elective, may place thoracic epidural in pre-op around the T12 level] -GOOD I.V. ACCESS; 2 large bore PIVs, CVL [huge blood loss risk] -arterial line for continuous BP evaluation & ABGs -foley, NGT
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When are PA catheters considered?
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CHF low EF [<30%] significant CAD significant renal impairment cor pulmonale if suprarenal or supraceliac cross clamps will be applied
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What vasoactive agents are used for open AAA?
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-have Neosynephrine & Nipride on pump -know where to get Dobutamine/Nitroglycerin if indicated -Dopamine for renal protection may be used [not often] particularly if suprarenal clamping -the higher the clamp location, the more risk of problems & comorbidities
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What occurs when the clamping is higher than infrarenal?
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-the majority of AAAs are infrarenal; the higher the clamp the more potential risks -renal preservation [1-2% renal failure for infrarenal] -renal cortical blood flow and UOP may decrease even w/ infrarenal aortic cross clamp [r/t RAA system effects, microemboli, & circulatory derangements] -adequate hydration & maintenance of urine flow are important
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What are anesthesia considerations for suprarenal aortic cross clamping?
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-PA lines more common -potential for greater blood loss -renal perfusion at greater risk [longer cross-clamp times and emboli] -paraplegia is possible when cross clamping is at/above the diaphragm [T-10 level, artery of Adamkiewicz]
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At what level does cross clamping increase the risk of visceral ischemia & profound acidosis?
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-celiac and superior mesenteric arteries -NaHCO3 is routinely given prior to unclamping [maybe] -most likely will give Mannitol and Lasix before suprarenal clamp
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What pre-op preparation should be taken for open AAA repair?
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-check H&P, labs, cardiac, & pulmonary studies -order T&C for 4 to 6 units PRBCs -place thoracic epidural if appropriate [talk patient into it!]
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What are the benefits to placing a thoracic epidural?
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-epidural reduces anesthesia requirement*, facilitates immediate extubation, provides postop analgesia -establish "level" in preop to verify placement
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What are the possible epidural dosing options used for open AAA repair?
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-don't dose up front/beginning: causes hypotension -give short acting LA [e.g. lidocaine 1.5%] and decrease narcotics intraop -give fentanyl 50-100 mcg prior to incision -wait until cross clamp is off, then give bupivicaine 0.25%
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What are the measurements for each location of the heart when floating a Swan-Ganz?
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RA: 15-20 cm balloon up, RV: 30 cm (go fast d/t ectopy risk) PA: 40 cm PAWP: 50-55 cm
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What is the recommended technique used for induction sequence during an open AAA repair?
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-place lines in preop [radial art line, introducer/PA cath, epidural, PIVs x2] -get baseline invasive hemodynamics pre-induction -induction with drug of choice -usually maintenance with volatile agent -most avoid N2O to avoid any possible bowel distention -muscle relaxation needed throughout -NGT common, may or may not keep postop
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What is the recommended intraop fluid management for an open AAA repair?
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-volume is depleted by hemorrhage, third spacing into bowel and peritoneal cavity, insensible loss -crystalloid 10-15 ml/kg/hr -colloids usually reserved for pts w/ severe blood loss & pts who can't tolerate large volumes of crystalloid -watch Hgb throughout, and coags once EBL >2000 ml -cell saver to decrease bank blood usage [return Hct 55-65%, just red cells; no clotting factors; always filter]
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What occurs with bowel manipulation during open AAA repair?
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-may decrease SVR --> hypotension [release of prostaglandins & vasoactive peptides] -treat with volume, neosynephrine, decrease anesthetic depth
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How is heat conserved during open AAA repair?
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-use upper Bair if possible [will cause burns on lower ext if lower Bair is on during cross clamping] -fluid warmers -foil hat -warm room
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What are anticipated treatments before/during cross clamping?
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-ensure adequate volume status -heparinize before [usually 100 ml/kg] -give Mannitol and Lasix if ordered -BP is going to increase with clamping [be ready with Nipride, NTG; may lower BP ahead of clamping; check CO and other hemodynamics pre/post clamp]
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What are the physiologic consequences of aortic cross clamping:
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-HTN above cross clamp/hypotension below -increase afterload, MAP, SVR -CO may decrease or remain unchanged [d/t inability to compensate] -increased afterload may cause ischemic changes on EKG -spinal cord damage is associated w/ aortic occlusion [interruption of blood flow in absence of collateral flow]
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What artery is affected causing possible spinal cord damage associated with aortic occlusion?
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greater radicular artery, AKA artery of Adamkiewicz
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What is the cause of most blood loss during open AAA repair?
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-most blood loss occurs b/c of back bleeding from the *lumbar & inferior mesenteric arteries* after the vessels have been clamped and the aneurysm is open -large loss of extracellular fluid and blood is expected with AAA repair -some times free flow bleeding while graft is being sewn, ask for Tburg, manual compression to "catch up" w/ EBL by giving PRBCs/using cell saver & IVF
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Goal for hemodynamics while aorta is cross clamped:
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-maintain normal or high BP/filling pressures prior to clamp removal -hopefully the surgeon will notify you when removing the clamp [if not happy w/ BP or volume status: tell them to wait!] -muscle relaxants TOF~1 twitch
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What occurs w/ release of cross clamp?
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-drop in BP -release of metabolites from anaerobic metabolism [release of lactate: induces vasodilation, release of venous endothelin] *consider NaHCO3 if suprarenal or long clamp time
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What happens to BP when the aortic cross clamp is removed?
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-drop in BP [treat hypotension w/ neo bolus, more volume/position, calcium chloride] -the higher the clamp, the worse response to unclamping
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What is release of venous endothelin [ET-1] associated with?
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declamping shock syndrome -positive inotropic effect on heart and both vasoconstricting and vasodilating action on blood vessels
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What is the technique for releasing an aorto-bifem clamp?
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-surgeon typically opens 1 leg at a time, which can decrease extent of hypotension -2nd leg usually comes quick after -if hypotension persists despite aggressive volume and blood replacement, put bed in Tburg and ask them to replace aortic clamp -check CV status [rate, rhythm, ST/T waves, BP, CVP, PAP] -increase vent rate to blow off subsequent incr etCO2 -send ABG after 10-20 min to further eval
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What are some important considerations when reaching the end of an open AAA repair?
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-calculate in/out -finish giving back cell saver -reverse heparin w/ Protamine if ordered -reverse muscle relaxation once abd muscles are closed up -dose epidural, have pump in room -get pt back breathing if planning to extubate
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What are recommended epidural doses for open AAA repair?
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-bolus 5 to 10 ml of 0.25% bupivicaine or -5 to 10 ml epidural solution [typically 0.125% bupiv + 2 mcg/ml fent] -then start infusion 6 to 10 ml/hr
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Aorto-bifemoral bypass details:
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-similar set up & management as open AAA repair -typically more stable because pt is "used to" occlusion so clamping is not a big issue -surgery for aorto occlusive disease rather than aneurysm -bifurcated graft rather than straight tube
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What are the details regarding an endovascular AAA repair?
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-used for pts who require repairing aneurysms but are high risk [elderly, heart disease] -minimally invasive, possibly less risk -put a "new pipe" in the "old pipe", blood flow is directed through a prothesis, tiny fabric tube supported by a metal frame -takes pressure off the wall of aorta and decreases chances of rupture
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What anatomical considerations exclude a patient from the endovascular approach?
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-the length, shape, and angulation of the infrarenal neck of the aorta -common iliac artery involvement w/ the aneurysm of having excessive occlusive disease of the common iliac artery -occlusive disease or marked tortuosity of the iliofemoral access vessels -severe angulation measurements -small iliac vessels
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What other considerations should be made for exclusion of the endovascular approach?
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-if aneurysm is ~5 cm or above, consider surgery due to increased risk of rupture -surgery still should be considered if aneurysm is rapidly expanding [via regular scans] or starts to cause other complications
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What is an endoleak?
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-a problem that only develops in patients undergoing endovascular repair -occurs when the seal between the graft and the normal arterial wall or between two segments of graft is incomplete -if the seal is not complete, blood can leak through the seal and re-fill the aneurysm [potential rupture!]
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What are the risks if an endoleak occurs?
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-small arterial branches of the aneurysm continue to fill the aneurysm sac, causes pressurization of partly excluded sac [endotension] and can lead to *aneurysm rupture*
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What is anesthesia management for an endovascular repair?
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-GA, SAB/Epidural, or MAC [GA usually chosen] -2 large bore PIVs -arterial line for continuous BP monitoring -PA cath/introducer unlikely [unless super critically ill] -may want SBP ~110-120 when deploying graft or inflating balloon dilators -patient heparinized after groin is cut down -respirations will be "held" frequently for x-rays -low narcotic requirements, local anesthetic at incisions
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During an endovascular repair, the BP drops acutely, what has happened?
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-*indicates arterial rupture* -notify surgeon immediately! -endo repair can be salvaged in spite of rupture by using occlusive balloon until graft is [quickly] placed
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What causes an aortic dissection?
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occurs when the layers of the wall of the aorta separate or are torn, allowing blood to flow between those layers and causing them to separate further
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What is the difference between aortic aneurysm and aortic dissection?
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-aortic aneurysms are caused by hardening of the arteries -aortic dissections are caused by connective tissue disorder and/or high blood pressure
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What condition is most commonly associated with aortic dissection?
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Marfan Syndrome [connective tissue is weak, tend to have weak heart valves and blood vessels that break easily]
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Aortic dissection: Type A
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-more common and dangerous -involves a tear in the ascending portion of the aorta just where it exits the heart, or a tear extending from the ascending portion down to the descending portion of the aorta [which may extend into the abdomen]
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Aortic dissection: Type B
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-involves a tear in the descending aorta only, which may also extend into the abdomen
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Anesthetic preparation for an emergency AAA repair
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-if stable hemodynamics, will go to CT to determine if candidate for endovascular [instead of open surgical] -need large PIVs, central access, arterial line -surgeons will prep and wait while you place introducer and cut when you say go -*very careful with induction*, less is more -may intubate without induction agent if obtunded
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Intraoperative management for an emergency AAA repair
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-send blood STAT for T&C [usually 4-6 units] -rapid infuser -cell saver -warm room and fluids! -check ABG & coags, likely will give PRBCs, FFP, Plts
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What happens with massive transfusion treatment?
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-coagulopathy of massive transfusion once 1-1.5x the patient's blood volume is replaced -thrombocytopenia -diffuse oozing and failure to clot
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What is needed for patient receiving large amounts of blood products?
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-adults need 5-10 units of platelets for each BV -usually diminished levels of fibrinogen and factor V, VIII, IX --> found in FFP -10 to 15 ml/kg of FFP will increase factors to 30% of normal
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What are risks of having thoracic aortic surgery?
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-most often requires CPB -large blood losses, lots of coagulopathy -hypertension preop, hypotension postop -myocardial ischemia -renal ischemia [up to 30%] -spinal ischemia [2%, cut off blood to spinal cord] -death [rupture-death #1 risk] -pulmonary failure [50%, tracheal &/or bronchial compression/deviation, laryngeal nerve compression]
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What is the clinical presentation of a patient who has a thoracic aneurysm?
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-back, some times chest pain -incidental finding of mass on CXR or CT -symptoms related to aortic insufficiency -stridor/cough
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What are the different types of thoracic aneurysms?
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-ascending: between aortic valve and innominate -arch: between innominate and left subclavian -descending: distal to left subclavian
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Anesthetic management & considerations for ascending/arch aneurysm repairs:
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-long aortic cross clamp times -large blood loss -right arterial line [assesses location of perfusion] -anterograde cerebral perfusion [perfuse just the brain] -hypothermia: deep hypothermic circulatory arrest [no flow at all to the rest of the body]
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What are the different techniques to preserve blood flow to the brain during ascending/arch aneurysm repair?
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-similar to cardiac surgery using CPB [but cannot place cross clamp] -consider fem-fem bypass [risk rupture w/ sternotomy] -commonest approach is now axillary cannulation [protects blood flow to brain & right arm]
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Anesthetic management for descending aneurysm repair:
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-can be with or without bypass, "clamp & sew" -left thoracotomy incision -one lung anesthesia/ventilation -PA cath, A-line, MANY large bore PIVs, TEE, cell saver, SSEP/MEP [evoked potentials] -lumbar drain [decrease perfusion pressure in spinal cord]
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What are the issues with cross clamping during repair of a descending aortic aneurysm?
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-increased SVR, increased BP, myocardial ischemia, CHF -limit fluids pre-clamping -increase anesthetic depth, give big dose Sufentanil -NTG, Nitroprusside drips primed and ready
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What are the two major issues with using CPB median sternotomy?
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-cerebral protection -coagulopathy
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How is cerebral protection maintained during CPB?
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-hypothermia -thiopental/propofol infusion -maintain flat EEG -corticosteroids -free radical scavengers
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What are the issues with releasing the cross clamp during thoracic aneurysm repair?
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-SEVERE HYPOTENSION, decreased SVR -preload with fluids [crystalloid, colloid] before release, vasodilators OFF -ABGs acidosis [bicarb, increase min. vent.] -paraplegia risk r/t thoracolumbar artery injury -renal failure -hypothermia [temp~34-33.3, increased risk of arrhyth] -coagulopathy
