Case 1 - CAD Flashcards
What factors increase O2 demand?
- management of CAD pts involve maintaining a favorable balance between myocardial oxygen and demand
O2 demand (all increase O2 consumption)
- tachycardia
- high afterload (inc LV wall stress)
- high preload
- increased contractility
what factors increase O2 supply?
- management of CAD pts involve maintaining a favorable balance between myocardial oxygen and demand
O2 Supply
-
Do2 = CO x CaO2
- CaO2 = (1.34 x SaO2 x Hgb) + (PaO2 x .003)
- Hgb conc
- SaO2
- bradycardia (LV fills during diastole)
- low afterload
- low preload
- decreased contracility
How do you maintain coronary artery perfusion pressure?
- Left coronary filled during diastole
- Right coronary filled during diastole and systole
-
CPP
- CPP = aortic diastolic pressure - LVEDP
What are your goals to reduce O2 demand in CAD patients? (determinants are HR, contractility, afterload, preload)
1) Heart Rate
- Goal - Slow
- decrease HR prolongs diastole time = allows for coronary perfusion
- decrease O2 demand
- avoid severe bradycardia
- can decrease CO
- dec aortic diastolic pressure and increase LVEDP -> decrease CPP
- use BB
2) contractility
- goal: normal to decreased
- ability of heart to generate force at a given preload –> utlizes O2
- Tx: BB and volatile anesthestics
3) Preload
- Goal: Normal to low
- preload increases LVEDP -> decrease CPP
- o2 increased due to volume work (more o2 used to eject blood -> inc CO 2/2 frank starling mech)
- tx: NTG, diuretics
4) afterload
- goal: Normal to high
- increase CPP via inc aortic diastolic pressure
- avoid excessive high levels –> increase LV wall tension (inc O2 demand) despite inc CPP
- tx: phenylephrine
Patient has myocardial ischemia during surgery, what are your treatment options?
Goals: optimize CPP and control HR
CPP = aortic diastolic pressure - LVEDP
1) NTG
- venodilator -> dec preload and wall tension
- epicardial coronary artery vasodilator -> improve coronary flow
- mild arterial vasodilator -> dec afterload -> dec pressure work of myocardium
- pittfall = reflex tachy 2/2 hypo
2) BB
- slow hr -> improve diastolic coronary filling & dec o2 demand
- decrease myocardial contractility
- afterload reducer
3) phenylephrine
- increase aortic diastolic pressure -> improve CPP
- reflex bradycardia
patient comes for elective surgery with drug eluting stents placed 5 months ago. Should this case be delayed?
DES - wait at least 12 months before elective surgery
Patient with CAD comes for surgery. Is perioperative beta blockade indicated for him?
Per ACC/AHA periop BB recomendations:
1) continue BB in pts already receving them
2) pts with CAD, evidnce of cardiac ischemia, or are at high cardiac risk, initiate BB preop and intraop –> titrate HR and BP
3) do not give BB to pts who have contraindications to them
- acute CHF, low CO, cardiogenic shock, 2nd or 3rd degree AVB, asthma
4) pts undergoing noncardiac surgery and not taking BB should NOT be started on BB prior to surgery.
Which leads are important to detect ischemia in a majority of patient? How many millimeters depression or elevation is required to dx ischemia/infarction on EKG?
EKG
-
leads II and V5 detect > 90% ischemic episodes
- Lead II -> RCA
- V5 –> LCA
1 mm = 0.1 mV
EKG signs of ischemia
- > 0.1 mV of horizontal or downsloping ST-segment depression
- > 0.2 mV of ST-segment elevation
is TEE better than eKG to detect ischemia, what TEE view would you look at to detect ischemia?
TEE is more sensitive than EKG
- also more reliable to detect ischemia in pts with pre-existing LVH or LBBB (secondary repolarization)
- Transgrastic short-axis view of LV
