Cardiac Surgery Concepts Flashcards
CABG
coronary artery bypass
procedure where normal blood flow is restored to an area of the heart that has an obstructed coronary artery
3 steps for CABG
1- blood vessels are harvested
2- grafts are sewn proximal and distal to blockage
3- blood flows through graft and bypasses the blockage
what are the 3 vessels that can be harvested for CABG?
radial artery (not common) saphenous vein left internal mammary artery (LIMA)
where is proximal anastomosis
on the aorta
where is distal anastomosis
on the coronary artery distal to obstruction
In what case would you have 1 proximal anastomosis and 3 distal anastomosis’?
triple bypass using the LIMA
Which anastomosis’ usually get sewn on first?
the distals
What is the most commonly used graft?
left internal mammary artery LIMA
what is the LIMA usually anastomosed to?
LAD
Are arterial or venous grafts preferred for CABG?
arterial because they have to carry arterial blood
10 year rate of reocculsion for saphenous (%)
60% rate of reocculsion
10 year patency rate for LIMA (%)
90%
which is more patent the LIMA or radial artery?
LIMA
what is the most likely reason for the high patency of the LIMA?
it is a “live graft” meaning that the proximal origin is left intact
which is less invasive PCI or CABG?
PCI- percutaneous coronary intervention
balloon angioplasty or stenting (alternative to CABG)
better 5 year survival and patency? CABG or PCI?
CABG
lower risk of stroke at 5 years? CABG or PCI?
PCI
drug eluting stents
newer stents that slowly release a drug in order to slow the narrowing process
cardiopulmonary bypass machine
“heart lung machine”
functions as heart and lungs bc drains deox blood and oxygenates and removes CO2 then pumps back into body
purpose of CPB machine
some cardiac surgeries require the heart to stop or drain blood from heart
the CPB machine allows the pt to stay alive
does the heart have to be arrested for cardiac surgery?
it is not mandatory but it is common and sometimes the surgeon will do it anyway
does the heart have to be arrested when the patient goes on cardiopulmonary bypass?
no, it is possible for the heart to remain beating while on bypass
how is the heart arrested?
surgeons inject cardioplegia into heart
what is in cardioplegia?
potassium
other additives:
glucose, magnesium, calcium, bicarb, buffers, and free radical scavengers (mannitol)
it can be mixed and injected with blood
when do you need to drain the blood from the heart?
any surgery where you have to open up the heart
6 parts of the CPB machine circuit
1- deox blood is drawn from heart through venous cannula
2- venous blood is stored in venous reservoir
3- blood sent through oxygenator/heat exchanger and arterial filter
4/5- blood reinfused into the body via “main pump” that pumps blood into aorta through “arterial cannula”
6- aortic cross clamp is usually placed on ascending aorta
what are the places that the venous cannula is placed?
right atrium (most common)
SVC
IVC
femoral vein
what does the venous reservoir do?
stores a surplus of blood and helps remove any air that inadvertently entered the bypass circuit
what happens during step 3 of the CPB machine (4)
fat globules and air particles are filtered out
temp is controlled
blood oxygenated
CO2 removed
what are the two reasons that an aorta crossclamp is placed?
1-prevent blood from backing up into the heart
2- keep heart arrested by keeping cardioplegia solution in heart
what are the 8 bypass machine components?
venous cannula(s) venous reservoir main pump oxygenator heat exchanger arterial filter arterial cannula ultrafilter cell salvage suction
when can you not use a venous cannula in the RA?
when you have right sided heart operation
what is the most common venous cannulas to use for open right sided heart surgeries?
SVC and IVC cannulas
what cannula can you place without having to open the chest?
femoral cannula (venous and arterial)
when is the femoral and arterial cannulation for CPB particularly useful?
when bypass must be initiated emergently
what are the two primary purposes of the venous reservoir?
1-remove air that enters the venous drainage line
2- stores a surplus of blood in the bypass circuit
does the traditional venous reservoir remove all air in the venous blood?
no
what does the reservoir act as a buffer for?
imbalances between venous return and arterial flow, when the heart and lungs are exsanguinated the reservoir may need to hold as much as 1-3 L
main pump
pumps blood to the body via arterial cannula and it has the option of pulsatile flow or non pulsatile flow
non pulsatile flow
more common since 2016
centrifuge pump
pulsatile flow
new technique (less common since 2016) roller or diagonal pumps
advantage of pulsatile flow
perfusion is better because it is more physiologic and stimulates the endothelium
disadvantage of pulsatile flow
achieving pulsatile flow from CPB machine is difficult
you could damage the blood elements
heat exchanger
cools and heats blood
allows perfusionist to control the temp of pt
what can form when blood is heated?
air bubbles bc gas solubility decreases as temp increases
what type of temp control is implemented during CPB
modest hypothermia ~34 degrees C for organ protection
advantages to modest hypothermia (2)
decreases oxygen requirements
decreases anesthetic requirements (hypothermia acts as anesthetic)
decreasing body temp by 1 degree decreases cerebral oxygen consumption by how much
5%
decreasing body temp by 10 degree decreases cerebral oxygen consumption by how much
50%
disadvantages of hypothermia (2)
more likely coagulopathy (more bleeding)
increased blood viscosity (decrease perfusion)
3 things oxygenator does
oxygenates blood
removes co2
site for volatile agent entry into bypass machine (perfusionist controls volatile agent)
2 types of oxygenators
bubble oxygenator
membrane oxygenator
bubble oxygenator
simple and low cost
more trauma to blood
RARELY USED
membrane oxygenator
increased complex and cost
less blood trauma
USED MORE COMMON
what is the main problem with oxygenator
damages blood
inflammatory respinse/organ dysfunction
decrease white blood cells and platelets and increased PAP
arterial filter
removes fat globules and air bubbles from circuit
what causes the spontaneous formation of microbubbles in the extracorpreal circuit?
excessive negative pressure in particular in the venous part of circuit
ultrafilter
hemoconcentrator that is sometimes added
removes excess water and electrolytes when low Hct
what are the two types of suction used during CPB?
standard suction
blood salvage suction
what are the three types of blood salvage suction
cardiotomy suction
cell saver suction
left ventricular vent
blood salvage suction definition
blood that will eventually return to pt, decreases chance of pt needing donor transfusion
cardiotomy suction
aspirated blood from chambers and surgical field
prevents distension and air embolism
returned to extracorporeal circuit via cardiotomy reservoir
where does the blood go after it is in the cardiotomy reservoir?
venous reservoir
Is cardiotomy used before or after the patient is heparinized?
after
can cardiotomy suction be used when the patient is off the bypass machine?
No
cardiotomy suction advantage
it is whole blood
includes: clotting factors, platelets and PRBC
cardiotomy suction disadvantage (2)
1- blood is damaged by the bypass machine
2-contributes to hemolysis and particulate emboli during CPB
what type of suction is associated with a more pronounced systemic inflammatory response?
cardiotomy
How does the cardiotomy suction cause hemolysis, GME, fat globule formation, activation of coagulation and fibrinolysis, cellular aggregation and platelet injury or loss?
amount of room air that is aspirated with blood causes turbulence and high sheer stress that causes damage
cell saver suction definition (2)
1- blood suctioned from field, washed and centrifuged
2- RBCs moved to infusion bag and transfused back into patient
what is the Hct of cell saver blood?
50-70%
cell saver advantages 2
1- particles (fat, air, tissue) are filtered out
2- blood is less damaged bc it does not go through bypass machine
cell saver disadvantages 2
1 it is not whole blood (mostly PRBC)
2 takes longer before it can be reinfused
can you use cardiotomy and cell saver?
yes this is a good option to use both, choose one depending on the type of fluid
left ventricle vent placement
inserted into the left ventricle through the pulmonary vein
what blood does the LV vent remove?
venous blood not picked up by venous reservoir (bronchial and thebesian veins)
purpose of LV vent
prevent left ventricular distension
what is the most likely time to get an air embolism with LV vent? prevention?
insertion or removal of the vent, or excessive suction
prevention by letting heart fill before insertion and flooding the field with fluid during removal
what does excessive suction lead to?
air introduction drawn from purse string sutures in left atrium or aorta
what is the most common way of arresting the heart?
antegrade cardioplegia (CP)
antegrade cardioplegia definition
arresting the heart by injecting cardioplegia into the coronary arteries through the coronary ostia (os)
coronary ostia (os)
the openings from the aorta to the coronary arteries
what is the most common way to do antegrade cardioplegia?
CP is injected into the aortic root via cardioplegia cannula
cross clamp is needed to keep CP from washing out into the body
what is the less common way to do antegrade CP?
direct cannulation of the coronary os and CP is injected through those
how do we perfuse the heart during CPB?
the CP line can also infuse blood into the coronary arteries so the heart is perfused
what are the the two reasons that you would need to perfuse the heart via the CP line?
ascending aortic clamp is placed
heart needs to be arrested
retrograde CP definition
CP being injected retrograde through the coronary sinus
what is the main risk with retrograde CP?
coronary sinus is more likely to rupture during CP injection because its a vein, surgeon will measure pressure during injection
steps to monitoring pressure with retrograde cardioplegia (3)
1- surgeon throws sterile non compliant tubing over drape (attached to CP line)
2- anesthetist hooks tubing to either CVP or PAP stopcock on triple transducer
3- during phase when heart is arrested the stopcock will be off to the pt and open to the retrograde line
Stopcock on transducer is turning to the side; what are you measuring?
CVP or PAP
stopcock on transducer is turned up; what are you measuring?
retrograde cardioplegia (if attached)
what are the two indications for retrograde CP?
1- helps arrest areas of heart distal to high grade obstruction
2- helps arrest heart when antegrade CP would wash out easily
what situations would antegrade CP wash out easily?
ascending aorta repair
open aortic valve repair
where does the aortic cross clamp need to be placed in reference to the arterial cannula
proximal to the arterial cannula on the ascending aorta
what would happen if you placed the aortic cross clamp while the heart was beating and full of blood?
heart attack or aortic rupture and death
sequence for arresting the heart and going on bypass (3)
drain blood from heart via venous cannula
place aortic cross clamp
then arrest heart with CP solution
When can you place an aortic cross clamp on a beating heart?
when the heart has been drained of blood
this will happen when going on and coming off pump
what two ways can the heart be arrested without using an aortic cross clamp?
retrograde CP
directly cannulating the coronary os for CP
advantages of aortic cross clamp 3
1 easier to arrest heart
2 prevents air from entering circulation
3 prevents reinfused blood from backing up into heart
disadvantage to aortic cross clamp 2
1physiologic perfusion to the heart is not possible
is perfused through CP cannula
2 increases risk of stroke from possible dislodging of emboli
partial aortic cross clamp
used when graft is sewn in and hole must be made
also associated with emboli and stroke
when are the two times that CPB is necessary
heart needs to be empty
heart is going to be arrested
what are the two advantages to bypass
easier for surgeon
more hemodynamic stability
what are the 7 disadvantages of CPB
1-priming fluid causes hemodilution (Hct decrease) 2- aortic clamp usually placed 3- difficulty coming off pump 4- pulm complications more likely 5- perfusion less effective 6- pt blood is damaged 7- large volume shifts may occur`
how much fluid is the bypass machine primed with?
2,000mL
what % of the pts circulating blood volume is the hemofilutional bolus equal to
30-50%
what are the contents of the priming fluid
heparin bicarb mannitol colloid possible steroids or antifibrinolytics
when would the machine be primed with blood?
pediatrics, to prevent over dilution of blood
what are the two pulmonary complications that could be seen with bypass
pulmonary edema more likely from activation of complement
reduces the effectiveness of natural surfactant
what are the two organs that have decreased perfusion on bypass and why does it matter
renal, hepatic
drugs arent cleared well
3 causes of blood damage on bypass
hemolysis
platelet conc is reduced and clotting factor function decrease
intense inflammatory response
what can the intense inflammatory response cause?
disturbances in vascular tone, permeability, fluid shifts and organ dysfunction
heart function compromised when coming off pump
what can a large volume shift cause?
transient cerebral edema
what is the part of the machine that determines whether it is an open or closed bypass system
the type of venous reservoir
is an open or closed bypass system more common?
open bypass system
open bypass system definition
venous drainage flows by gravity into venous reservoir thats open to atmosphere
air naturally vented but in direct contact with air (bad)
hardshell reservoir
closed bypass system definition
venous reservoir removed from system or is closed to atmosphere
collapsible bag
benefits to using the open bypass system
automatically eliminates air (less risk of air embolism)
volume delineation is clear
actively purging air from closed system is distracting
advantages of closed bypass system 3
limited contact with air (limits injurt to elements of blood)
decreased inflammatory response and fewer hematological disruptions
some have smaller priming volumes
disadvantages of closed bypass 3
less precise visual monitoring of venous return air is not automatically purged (requires additional systems) less filters (more microemboli exiting)
what parts does a mini CPB circuit have
pump
oxygenator
reduced tubing length (reduction of priming volume)
arterial filter (usually)
what parts does a mini CPB circuit NOT have
venous reservoir
cardiotomy suction
heat exchanger
what is the priming volume reduced to in a mini cardiopulmonary bypass circuit?
600mL
Is the mini CPB circuit open or closed?
closed (limits air contact)
advantages of mini CPB circuit 4
advantages of closed system
improves myocardial protection (less problems restoring SR and less afib)
associated with less blood transfusion
associated with earlier recovery times and reduced ICU and hosp time
why is mini CPB circuit associated with less blood transfusion
lower priming volume
less hemodilution
disadvantages of mini cardiopulmonary bypass
demanding for perfusionist (must pay more attention to air handling)
some studies say it isnt beneficial
off pump heart surgery
suction clamps applied
good bc no negative effects from bypass machine
bad bc clamps may cause significant hypotension and/or arrhythmias
partial CPB
only drains part of venous blood and goes through the bypass machine and some blood goes through the pulmonary circulation
if a surgeon attempts an off pump and the pt cant tolerate it what are the two options?
full bypass: heart arrested and heart perfusion non physiologic
partial bypass: heart beating and heart perfusion physiologic
3 implications of partial CPB
heart must stay beating
pt needs to be oxygenated/ventilated/ volatile agent delivered
aortic clamp doesnt need to be placed
left heart partial bypass 6
1-blood travels through right heart and pulm
2-some blood removed from left atrium and travels through machine and perfuses lower extremities
3-some blood stays in left atrium and goes out the aorta to perfuse the head
4- only left heart bypassed
5- blood already oxygenated
6- heart must stay beating and lungs must be ventilated
left heart bypass circuit parts
tubing
centrifugal pump
indication of left heart partial bypass
open descending thoracic aortic aneurysm repair
what perfuses the head during partial left heart bypass
the heart
what perfuses the lower body during partial left heart bypass
arterial cannula
left/right heart bypass advantages 5
1 heart stays beating (physiological perfusion remains)
2 lower circuit prime volume
3 lower chance of postop renal failure
4 blood pressure is controlled by perfusionist
5 no air blood contact
what does lower circuit prime volume lead to? 3
less hemodilution
less blood damage
less heparinization needed
what is the target ACT?
150-200 seconds
what are the % chance of renal failure for left heart bypass, simple cross clamp, and CPB?
left- 4%
simple- 9%
CPB- 11%
left/right heart bypass disadvantages
no blood or fluid can be added to the bypass system (without reservoir)
pt cant be warmed or cooled by machine
air embolization may be more likely
right heart bypass 4
1- venous cannula in SVC and IVC remove blood and sent to machine
2- reinfused blood though arterial cannula in pulm artery, cross clamp on pulm artery
3- blood goes to lungs thus we need to ventilate and oxygenate
4- heart stays beating and lungs are ventilated
why is there a lower stroke risk with right heart bypass
no aortic cross clamp is needed
3 indications for right heart partial bypass
tricuspid valve repair
pulmonic valve repair
right ventricle assist device (RVAD) placement
when on right heart partial bypass the surgeon can complete surgery without: (3)
arresting heart
clamping aorta
using oxygenator
where do they place the cross clamps for ascending or aortic arch aneurysms?
proximal and distal to aneurysm
what are the options to protect the brain when total body perfusion isnt feasible with arterial cannula due to clamp location (3)
can you use these together?
deep hypothermic circulatory arrest (DHCA)
retrograde cerebral perfusion
antegrade cerebral perfusion
** yes you can use more than one of these techniques
deep hypothermic circulatory arrest
perfusionist makes pt so cold that oxygen demands are so low they can survive a short amount of time without perfusion
indications for DHCA
ascending aorta repair
aortic arch repair
descending aorta repair
clipping certain complex brain aneurysms
how does the circ arrest process work?
1- pt put on bypass
2- heat exchanger decreases temp
3- heart is arrested and circulation is slowed to near stand still
4- decrease in oxygen consumption allows for the pt to have minimal blood flow
during circ arrest where is the arterial cannula placed?
femoral artery or axillary artery
what is the target temp before starting circ arrest?
15 to 17 degrees C
longer the operation they may need to be colder
what monitors are used to monitor the depth of hypothermia and ensure electrial silence during DHCA
BIS and EEG
when is the EEG usually isoelectric?
between 15-20 degrees C
how much longer is the patient cooled after they are isoelectric?
10 minutes to ensure homogenous cooling of brain
how long is circ arrest safe? chart
temp – mins
20- 30-40
16- 45-60
circ arrest should not be performed for longer than?
60 min
time limit for most have no neurologic complications
<30 min
time limit for increased incidence of brain injury
> 40 min
time limit for most suffer from irreversible brain damage
> 60min
who can tolerate longer periods of circ arrest?
neonates and children
complications of DHCA 3
complications of hypothermia
neurologic complications
potential neurologic complications from cooling or rewarming pt too rapidly
what can rapid cooling cause
<20 min to deep hypothermia
lower neurodevelopmental outcome scores
what can rapid rewarming cause 4
organ damge
deleterious to neurologic outcome
promotes gas bubble formation (solubility decrease and temp increase)
cerebral desaturation and uneven warming
what is the rewarming rate not to exceed?
1C core temp per 3 min of bypass time
when should rewarming stop?
nasopharyngeal temp reaches 35C
DHCA anesthetic management 2
1- must use nasal temp probe (reflection of brain temp)
2- additional brain protection
- periop steroids
-hyperoxygenation before
- 20 min of cooling for adequate cerebral protection
- pack head in ice
-intermittent cerebral perfusion in 15-20 min periods
what are the two temp probes to have for circ arrest?
nasal (brain)
bladder (core)
retrograde cerebral perfusion during circ arrest
extra perfusion line, perfuses head through SVC
normothermic antegrade cerebral perfusion
extra perfusion line is placed in right axillary artery to perfuse head
USED WITHOUT CIRC ARREST
antegrade cerebral perfusion
used with normothermia or circ arrest
disadvantage: may increase incidence of stroke
cerebral oximetry
near infrared spectroscopy (NIRS) measure oxygen saturation in cerebral vessels (rSO2)
what is the normal rSO2?
60-80%
why is rSO2 lower than normal SO2?
cerebral vascular bed is 75% venous and 25% arterial
what is cerebral oximetry an indicatory of?
cerebral perfusion
if there is a low rSO2 value and cerebral perfusion has decreased what should you do?
increase blood flow and oxygenation to the head
what are two applications for cerebral oximetry
heart surgery (alerts the moment perfusion is disrupted to better intervene the issue) sitting/beach chair surgery (easier to know if you are perfusing the brain rather than using the BP)
when should the anesthetist intervene?
rSO2 < 50%
>20% drop from baseline rSO2
difference >30% from the left and right hemispheres
what are the rSO2 values that correspond to poor neurologic outcomes
<45% absolute
>25% declines
4 factors that decrease rSO2 values
decrease in cerebral blood flow (hypotension/low CO, hyperventilation)
hypoxemia
anemia
mechanical disturbances
ways to increase cerebral SpO2 (6)
1- increase cerebral perfusion pressure (MAP-ICP) 2- increase cerebral blood flow 3- increase FiO2 4- increase cardiac output 5- increase hematocrit 6- decrease cerebral metabolism
ways to increase the cerebral perfusion pressure
increase MAP (if hypotensive) potentially decrease intracranial pressure ICP
how do you decrease intracranial pressure ICP?
mannitol- decreases CSF production, shrinks brain cell volume
place lumbar drain
how do you increase cerebral blood flow
increase PaCO2
nitroglycerin?
PT
prothrombin time
examines extrinsic pathway of coagulation cascade
12-15sec
PTT
partial thromboplastin time
examines intrinsic pathway of cascade
25-40 sec
INR
international normalized ratio
standardized PT result
0.9-1.1
standard unfractioned heparin
binds and enhances activity of antithrombin III 1000 fold
effects intrinsic pathway
what can heparin be reversed by
protamine
lovenox (enoxaparin)
LMWH dosed subcutaneously longer lasting 12-24 hr doesnt prolong PTT as much not reversed reliably with protamine
what is the half life of standard heparin?
1 hr when dosed intravenously
what is a good test for lovenox
anti- Xa assay
coumadin
warfarin
by mouth vitamin K antagonist
effects extrinisic pathway
effects PT and INR more
what can warfarin be reversed with?
FFP
vitamin K
plavix
clopidogrel
by mouth antiplatelet
not reliably reversed (usually with platelets)
half life 5-7 days
dual antiplatelet therapy
aspirin and plavix
indicated for recent coronary balloon angioplasty or stent
pt that is on dual antiplatelet therapy should wait how long for elective surgery if balloon angioplasty?
at least 14 days
pt that is on dual antiplatelet therapy should wait how long for elective surgery if metal stent placed
at least 6 weeks
pt that is on dual antiplatelet therapy should wait how long for elective surgery if drug eluting stent placed
at least a year
what if the pt is on dual antiplatelet therapy and has to have emergency surgery?
aspirin usually continued and surgeon/cardio make plan for pt needs
xarelto (rivaroxiban)
by mouth direct Xa inhibitor
reversed with prothrombibn complex concentrates (PCC)
when should xarelto be discontinued before surgery?
at least 24 hours before
eliquis (apixaban)
direct factor Xa inhibitor
reversed with PCC
when should eliquis be discontinued before elective surgery?
at least 48 hours before
heparin dose for standard CPB
300-400 units/kg dosed before aortic cannulation
ACT
activated clotting time; blood test used to measure coagulation during cardiac surgery when heparin is given
normal ACT
100-150 sec
goal ACT prior to going on pump
> 450 sec
heparin induced thrombocytopenia (HIT)
patients immune system has antibodies against heparin which:
thrombocytopenia (lack of platelets)
thrombosis (clotting)
usually occurs with standard heparin
what is used for anticoagulation in patients that have HIT?
direct thrombin inhibitors (argatroban)
more difficult to control post op bleeding
antithrombin III deficiency
low levels of ATIII and show resistance to heparin
can be acquired as a result of recent heparin administration
anesthetic management of ATIII deficiency
replaced AT III (concentrates available) administer FFP (if concentrates are not available)
protamine
salmon sperm
reverses heparin
brings ACT back to normal
when is protamine given during cardiac surgery?
when the pt is taken off bypass
dose of protamine
1mg per 100 units heparin
how is heparin given?
peripherally and slowly over 10 min
protamine mechanism of action
binds heparin and it is no longer bound to ATIII
what does protamine do when given without prior administration of heparin?
it is an anticoagulant
what could excess protamine cause?
increase bleeding especially in thrombocytopenia or low VIII
2 adverse effects of protamine
(with rapid/central admin)
hypotension
anaphylactoid reaction
when is a anaphylactoid reaction to protamine more likely?
prior exposure to protamine
allergic to fish
male pts with vasectomy
diabetics exposed through insulin
why does a male with vasectomy have reaction to protamine?
because they can develop antibodies to sperm
what reverses the effects of warfarin?
FFP and vitamin K
FFP and PCC work quickest but they dont reverse they just replace the clotting factors
vitamin K will help the patient make their own clotting factors
Prothrombin Complex Concentrates (PCC)
contains vitamin K dependent clotting factors
reverse the effects of coumadin, xarelto, eliquis
What can PCC replace in massive transfusion protocol?
FFP
how much higher of a concentration are the clotting factors in PCC compared to FFP
25 fold higher
1 vial of PCC= _?__ units FFP?
2
advantages of PCC
twice as fast as FFP
single dose every 24 hours (less volume required)
half the adverse effects of FFP
faster prep time (no thawing)
disadvantages of PCC
20x more expensive
shorter acting than FFP
(should be administered with vitamin K)
FFP vs PCC???
jury still out
some studies say half blood products used for PCC
some studies say higher mortality rate at 45 days for PCC
