11. 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) right internal mammary artery (RIMA)
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 from the subclavina 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
keep the pt alive while the surgeon:
1. stop the heart
2. drain the blood
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
however, it is most common to be arrested for bypass
how is the heart arrested?
surgeons inject cardioplegia into heart
how does cardioplegia stop the heart?
it alters transmembrane electrical potential in cardiac myocytes
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 when blood goes through the oxygenator, heat exhanger, and filter
(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-prevent CP washout
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
most common method for removing deoxygenated blood from the pt during bypass
venous cannula in RA
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
how much blood may the venous reservoir need to hold?
1-3L
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
problems (6) with oxygenator
damages blood
inflammatory respinse
organ dysfunction
decr WBC
decr platelets
incr 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
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 (3)
1- blood is damaged by the bypass machine
2- Hct is lower
3- contributes to hemolysis and particulate emboli
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 3
1- particles (fat, air, tissue) are filtered out
2- Hct is higher
3- blood is less damaged
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
cardiotomy is during bypass
cell saver is off-bypass
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
risk of LV suction
air embolism causing a stroke
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 repaire
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
where must the aortic cross clamp be placed
ascending aorta to allow for total body perfusion
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)
- Bypass and drain blood from heart via venous cannula
- place aortic cross clamp
- 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 and going to the braine
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
- open valve repair
- open aorta repair
heart is going to be arrested
heart is going to be arrested
what are the two advantages to bypass
easier for surgeon
more hemodynamically stable
more hemodynamic stability
what are the 8
disadvantages of CPB
1 - hemodilution (decr Hct) 2 - aortic cross clamp risk for embolism 3 - blood damage 4 - large volume shift 5 - postperfusion syndrome 6 - less effective tissue perfusion 7 - difficulty coming off pump 8 - pulmonary complications more likely
how much fluid is the bypass machine primed with?
2,000mL
what % of the pts circulating blood volume is the hemodilutional bolus equal to
30-50%
what are the contents of the priming fluid
heparin bicarb mannitol colloid possible steroids or antifibrinolytics (amicar)
priming volume of bypass for adults
2L
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 decr clotting factor function
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
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
off pump pros
no negative effects from bypass machine
off pump cons
clamps cause:
- significant hypotension
- arrythmias
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
benefits of partial CPB
- pulsatile flow
(physiologic perfusion) - decr risk of stroke (no cross clamp)
LH partial
half the blood is taken out
left heart partial bypass 6
1-blood travels through right heart and pulm
2-some blood removed from LA with venous cannula to bypass machine to perfuse lower extremities via arterial cannula
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
implications of LH partial bypass
only LH is bypassed
lungs must be ventilated w/VA
heart must stay beating
no oxygenator required
do you need oxygenator for LH partial bypass
no
LH partial bypass requires
ventilator on
volatile agent on
left heart bypass circuit parts
tubing
centrifugal pump
indication of left heart partial bypass
open descending thoracic aortic aneurysm repair
LH Partial Bypass implications
only left hear is bypasses
lungs must be ventilated w/VA
heart must stay beating
bypass machine does not need oxygenator
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 = less blood damage
what does lower circuit prime volume lead to? 3
less hemodilution
less blood damage
less heparinization needed
what is the target ACT for partial CPB?
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
cant add blood or fluids
cant warm/cool pt
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
(cross clamp placed on pulmonary artery)
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)
circ arrest w/antegrade and/or retrograde
antegrade w/normothermia
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
innominate artery
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 (nasopharyngeal temp)
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
20C- 30-40mins
16C- 45-60mins
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
- DIC (coagulopathy)
- incr bleeding
neurologic complications
potential neurologic complications from cooling or rewarming pt too rapidly
what can rapid cooling cause
lower neurodevelopmental outcome scores
lower neurodevelopmental outcome scores
rapid cooling
<20 min to deep hypothermia
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)
why use nasal temp probe during circ arrest
accurate reflection of brain temperature
additional brain protection during DHCA
steroids
hyperoxygenation
packing head with ice
intermit cerebral perfusion between 15-20 min periods
retrograde cerebral perfusion during cxirc arrest
cold blood perfused to head via extra cannula in SVC
normothermic antegrade cerebral perfusion
extra perfusion line is placed in right axillary artery to perfuse head
USED WITHOUT CIRC ARREST
where is the extra perfusion line placed in antegrade cerebral perfusion?
proximal to cross clamp
antegrade cerebral perfusion
used with normothermia or circ arrest
disadvantage: may increase incidence of stroke
normothermic antegrade cerebral perfusion: head
extra perfusion line
(R axillary)
normothermic antegrade cerebral perfusion: lower extremity
arterial cannula
antegrade cerebreal perfusion CON
incr incidence of stroke
circ arrest is ______ perfusion
partial perfusion
antegrade normothermia is ______ perfusion
complete perfusion
PT
prothrombin time
Extrinsic pathway
normal PT
12-15 seconds
PTT
partial thromboplastin time
intrinsic pathway
normal PTT
25-40 sec
INR
international normalized ratio
standardized PT result
INR normal range
0.9-1.1
INR value that an epidural or catheter placement/removal is unsafe
INR > 1.4
how do pts survive aortic cross clamping?
pt is placed on the bypass and heart emptied prior to placing the clamp
order of cross clamping
bypass
cross clamp
CP solution
unfractionated heparin mechanism
enhances antithrombin III 1000x
unfractionated heparin pathway
Intrinsic
PTT
heparin reversal
protamine
how should heparin be given during cardiac surgery
via central line
hepain dose for bypass
300-400 units/kg prior to aortic cannulation
ACT
clotting time test used to assess coag
done when heparin is given
normal ACT
100-150 s
goal ACT prior to going on pump
> 450 s
HIT mechanism
pt immune system develops antibodies against heparin
HIT symptoms
thrombocytopenia
thrombosis
HIT is most often caused by
standard heparin
(sometimes fractionated heparin)
alternat to heparin for cardiac surgery
Argatroban
(direct thrombin inhibitor)
argatroban reversal
none
significance of Antithrombin III deficiency
heparin will not work
causes of antithrombin III deficiency
genetic
acquired from previous heparin admin
management for antithrombin III deficiency
- give antithrombin III
- give FFP
LMW heparin delivery
subQ
unfractionated heparin delivery
IV
LMW heparin duration
12-24 hrs (longer)
standard heparin duration
1 hr half life
most common type of fractioned heparine
lovenox (enoxaparin)
LMW heparin PTT impact
does not prolong as much
LMW heparin alternative to PTT
anti-Xa assay
which is reversed more easily: LMW or standard heparin
standard heparin is more easily reversed with protamine
vitamin K antagonist
coumadin (warfarin)
coumadin pathway
Extrinsic
coumadin delivery
PO
coumadin coag tests impacted
PT
INR
which factor does coumadin impact most
factor VII
how long should coumadin be withheld before elective surgery
5 day
management of coumadin for emergent surgeries?
reverse coumadin:
FFP
vit K
antiplatelet drugs
aspirin
plavix (clopidogrel)
plavix drug categroy
P2Y12 inhibitor
can plavix be reveresed
no
(plts might help)
delay elective surgery for ____ days after taking plavix
5-7 days
discontinue aspirin ____ days before elective surgery
7 days
dual antiplatelet therapy is typically used in which pts
pts with recent coronary baloon angioplasty and/or
stent
dual antiplatelet therapy drugs
plavix + aspirin
balloon angioplasty wait time for elective surgery
14 days
(continual DAT)
bare metal stent wait time for elective surgery
1 month
(continue DAT)
drug eleuting stent wait time for elective surgery
6 months
(continue DAT)
when can you consider elective surgery at 3 months after drug eluting stent (DAT)
risk for delay > risk for ischemia
DAT and urgent surgery
typically continue aspirin
balance risk of plavix based on thrombotic/hemorrhagic risk
what should pts take after DAT is discontinued
lifelong aspirin therapy
when should pts discontinue aspiring
low embolic
high hemorrhagic risk
spine
neuro
eye
direct factor Xa inhibitors
xarelto (rivaroxiban)
eliquis (apixaban)
xarelto delivery
oral
xarelto reversal
andexxa
xarelto discontinue before surgery
24 hrs
eliquis reversak
andexxa
eliquis discontinue prior to surgery
48 hrs
thrombolytics
rTPA
streptokinase
urokinase
thrombolytics discontinue before surgery
10 days
direct thrombin injibitors
argatroban
what can be used for anticoag in pts that cannot receive heparin due to HIT
direct thrombin inibitors
(argatroban)
when is protamine dosed in cardiac surgery
after pt is off bypass
protamine dose
1mg per 100 units heparin
prtamine should be given
peripherally
slowly (over 10 mins)
protamine mechanism
binds heparin
heparin cannot bind antithrombin iii
protamine side effects
hypotension
anaphylaxis
pulmonary vasoconstriction
anaphylaxis reactions to protamine are more common in
rapid/central admin
prior protamine delivery
fish allergies
male pts w/vasectomy
diabetics
warfarin reversal
FFP
vit K
what is an alternate to FFP
PCC
PCC
vit K dependent clotting factors
PCC can reverse
warfarin (coumadin)
vit K dep clotting factors
II
VII
IX
X
PCC advantages
2x fast as FFP
1 dose every 24 hrs (less volume)
less adverse effects
faster prep time
PCC disadvantages
20x more expensive
shorter acting
requires vit K co-admin
