Case 34 - open AAA repair Flashcards
What is LaPlace Law, how does it relate to aortic aneurysm?
Laplace Law
-
Wall Stress = Pressure x Radius / 2 x Wall thickness
- increase radius will increase aortic wall stress and make more prone to rupture
- elective sx - aneurysm > 6cm or symptomatic or increase rate of growth
How do you evaluate myocardial reserves for patients undergoing aortic repair?
Assess 1) RF, 2) cardiac reserve via testing
Risk factors for myocardial ischemia
- previous MI
- angina
- CHF
- Male
- Smoking
- DM
- limited excercise tolerence
Assessment
- Low Risk –> proceed with sx without further eval
- negative stress w/i 2 yrs or CABG and asymptom –> proceed with sx without further eval
- Moderate Risk –> Stress test
- High Risk for MI –> consider cath
negative stress test wi
What is stress tresting?
There are two components to stress testing: 1) stressing the myocardium, 2) detecting ischemia or infarction
Stressing
- mechanical (exercise treadmill)
- pharmacologic
- dobutamine - increase myocardial O2 demand
- dipyridamole - purposely cause myocardial steal
With stress testing, how do you detect myocardial ischemia?
Detection
- EKG, Nuclear Studies, Echo
- EKG
- changes in ST segment (elevation, depression)
- Nuclear Studies
- a) reversible defect
- rest - nuclear tracer uptake, stress - nuclear tracer absent
- b) old infarction
- absent nuclear uptake with rest and stress
- a) reversible defect
- Echo
- a) reversible defect
- wall motion abnormalites with stress
- b) old infarction
- akinetic segment with rest and stress
- a) reversible defect
Why is stress testing important?
- 1) allows us to determine if myocardium is a risk (ischemia with stress) as opposed to myocardum that is infarcted (old vs new)
- 2) if myocardium at risk, should patient be further optimized (pharmacologic vs intervential)
If patient undergoes myocardial revascularization, how long should they be on antiplatelet therapy for prior to surgical procedures?
Myocardial Revascularization –> PCI or CABG –> pts placed on dual anti-plt therapy (ASA + clopidogrel)
PCI
- balloon angioplasty
- anti-PLT for 2-4 weeks
- BMS
- anti-PLT for 6 weeks
- DES
- anti-PLT for at least 12 months
CABG
- unknown duration of anti-PLT therapy
Why do patients after myocardial revasc need to be on anti-PLT?
- all PCI procedures are assoc with re-stenosis
- During surgery, inflammation and hypercoagulable response, as well as premature d/c of anti-PLT therapy can lead in-stent thrombosis.
**If pts require aortic surgery and have significant CAD requiring PCI, type of interventiion and type of stent placed (if any) must be weighted against urgency of surgery.
What meds should administered preop to aortic sx pts?
- should take all anti-HTN and anti-angial meds prior to sx
- anxiolysis is recommended to decrease preop HTN and tachy –> increase o2 demand and stress on aortic wall –> myocardial ischemia and risk of rupture
What are main goals during aortic sx? What are the main goals during ruptured AAA sx?
- HD stability
- Anesthesia –> amnesia, analgesia, immobility
- Strict control of BP to limit risk of rupture or extent of dissection
- beta blockers, vasodilators
Ruptured (hypovolemic shock secondary to hemorrhage)
- maintain volume status
- secure airway
- immediate surgical control
Should patients continue beta blockers or start beta blockers when presenting for aortic surgery?
Beta blockers
- decrease contractility, decrease HR via B1 receptor antagonism in heart–> decrease O2 demand
To start to not start Beta blockade
- patients on beta blockers should continue beta blockers during sx
- acute d/c of long-term BB leads to increase myocardial events
- patients at high risk for ischemia should be started on Beta blockers
- titrate to HR and BP
- POISE Trial (periop ischemic evaluation) –> BB had lower incidence of myocardial events, but greater incidence of hypotension and assoc risk of stroke and mortality.
- Therefore TITRATE BB TO EFFECT
What are the goals for induction of anesthesia in aortic sx patients?
emergent sx
- RSI –> full stomach
Overall
- Goal - avoid hemodynamic aberrations during induction and tracheal intubation
- HTN = risk of rupture, Hypotension = decrease organ perfusion
- doesn’t matter what you use as long as you follow this induction goal
- vasoactive meds (nitroprusside, NTG, Esmolol) - fast on and off
How are patients undergoing aortic anuerysm surgery monitored?
- Standard ASA monitors
- EKG - Leads II and V5
- detects most MI and arrhythmias
- Foley Catheter
- monitor UOP, provide early indication of renal malprefusion
- Core temp (bladder, esophageal, PA)
- normothermia to prevent MI, coagulopathy, wound infection
- Arterial line
- beat to beat monitor of arterial pressure, frequent blood sampling
- CVP
- central route for drug admin, rapid infusion of fluids, measure filling pressures of heart
- right IJ or left SC preferable. Left IJ assoc with increas incidence of innominate vein perf
- PA vs TEE
What are causes of decreased blood pressure during aortic sx?
Major Causes:
- shifts in intravascular volume
- effects of anesthetic agents
- surgical manipulation
Intravasc Volume
- hemorrhage from intercostal artery back-bleeding
- aortic disruptions
- anastomotic suture leaks
- evaporative/ third space losses
Maintain Intravasc volume
- large bore IV
- CVC
- for rapid transfusion system
Blood salvaging techniques (cell saver)
- Pros
- scavanges and washes erythrocytes
- may decrease overall allogenic blood prod
- Cons
- takes time to wash blood cell (need to fill reservoir before process)
- lose plasma volume, protein, coag factor, PLT
Are CVP measurement accurate in measuring left heart pressure?
- CVP is indirect measure of left heart filling pressure by measuring right sided pressure
- correlates with left side if pt has good LV function
What are the benefits of pulmonary artery catherization?
Indications
- decrease LV function
- pulm HTN
- severe valv disease
- advanced systemic organ dysfucntion
Benefits
- determine afterload
- CO by thermodilution
- o2 delivery via MVO2 sample
