Topic: Myocardial Protection (11A?) Flashcards
Qb stands for what?
Coronary Blood Flow
Coronary Blood Flow is determined by what?
is determined by hemodynamic factors such as perfusion pressure (P) and coronary vascular resistance (R)
The delivery of oxygen (DO2) to the myocardium (oxygen supply) is determined by two factors:
- coronary blood flow (CBF)
* oxygen content of blood(CaO2).
O2 delivery equation
O2 Delivery = CBF × CaO2
where CBF = ml/min and CaO2= ml O2/ml blood
The two terms are often used interchangeably although they are not equivalent
Oxygen Consumption and Oxygen Demand
Demand =Need
Consumption= Actual amount of oxygen consumed per minute.
Oxygen consumption will: (2)
•regenerate ATP used by membrane
transport (Na+/K+-ATPase pump) and by
•Myocyte contraction and relaxation (myosin ATPase)
- MVO2 (ml O2/min per 100gram)
Cardiac State:Arrested heart
2
- MVO2 (ml O2/min per 100gram)
Cardiac State: Resting Beating Heart
8
- MVO2 (ml O2/min per 100gram)
Cardiac State:Heavy Exercise
70
Fick Principle
MVO2= CBF×(CaO2− CvO2)
CBF= coronary blood flow (ml/min), and (CaO2–CvO2) is the arterial-venous oxygen content difference (ml O2/ml blood)
The unique relationship between MVO2, coronary blood flow (CBF), and the extraction of oxygen from the blood (A-V O2 difference) is
The Fick Principle
2 points during cardiopulmonary bypass the heart is prone to fibrillate?
- Cooling
* Post cross clamp (post ischemic episodes)
What are the dangers during the cooling or post cross clamp periods during CPB?
- Distension/Overfilling
- Muscular/cellular damage
- Starlings Curve
When is cardiac oxygen consumption (MVO2) at its Lowest level
•When heart is arrested
When is cardiac oxygen consumption (MVO2) at its Highest level
•Shortly after weaning from bypass–Heart is repaying oxygen debt
(catch up period-the heart needs time)
An imbalance of oxygen delivery and demand leads to what?
ANAEROBIC metabolism and the production of lactic acid
Decreased intracellular pH decreases the stability of what membranes?
cellular and mitochondrial membranes
Decreased intracellular pH also impairs what influx and overload?
Na-> K ATPase leading to calcium influx and calcium overload
ATP generated from AEROBIC metabolism is used preferentially for
myocardial contraction
anaerobically produced ATP is used for
cell survival and repair
% of O2 Cardiac muscle extracts
> 70%
True Coronary Perfusion Pressure
CoPP=
DBP–LVEDP
Coronary blood flow is dependent on what gradient?
the transmural gradient
increased myocardial oxygen demand is met primarily by ?
an increase in coronary blood flow
A diastolic aortic pressure of 80 and a
LVEDP pressure of 14 would get what value?
CPP of 66 (normal 60-80mmHg)
During cardiac arrest, CPP is one of the most important variables in achieving what?
the return of spontaneous circulation
which is why CPR compressions are important > respiration
A pressure gradient of what may be necessary for survival ? (mmHg)
15 mmHg at a minimum
Pre-Ischemic Intervention
Minimize on-going ischemia (i.e. NTG)
•Prevent ventricular distension
•Wall tension increases MVO2 and increases LVEDP
•Vent !
Myocardial preconditioning can be achieved by (2)
- Ischemia
- Drugs
- Bradykinin, nitric oxide, phenylephrine (neosynephrine), endotoxin, adenosine, Sevoflurane, desflurane, isoflurane
Myocardial preconditioning can be achieved by what drugs?
Bradykinin nitric oxide phenylephrine (neosynephrine) endotoxin adenosine Sevoflurane desflurane isoflurane
What may be the “best” preconditioning tool and override ischemia and drugs?
Cardiopulmonary bypass
Why give cardiplegia?
- Cardiac quiescence
- Bloodless field
- Preservation of myocardial function
- Induces myocardial hypothermia
Four Main Objectives of Hypothermic Cardioplegia (4)
KNOW!
- Immediate/sustained electromechanical arrest
- Rapid/sustained homogenous myocardial cooling
- Maintenance of therapeutic additives in effective concentrations
- Periodic washout of metabolic inhibitors
advocated the use of high potassium solutions to induce cardiac quiescence. Caused permanent myocardial injury
Melrose 1955
Buckberg & Follette
introduced 4:1 blood cardioplegia
Without cardioplegic arrest, irreversible ischemic injury to the myocardium would occur within how many minutes?
20 minutes
When myocardial protection strategies are
used, irreversible ischemic injury can be prolonged for how long without irreversible damage?
4-5 hours
Cardiac Action Potential Phase 0 ?
0–Na+influx
Cardiac Action Potential Phase 1?
1-Transient K+efflux
Cardiac Action Potential Phase 2?
2–Ca++influx
Cardiac Action Potential Phase 3?
3–K+efflux
Cardiac Action Potential Phase 4?
4–Na/K ATPase
Mechanism of Depolarizing Potassium Arrest
Disrupt Phase 3–K+efflux
(Mechanism of Depolarizing Potassium Arrest)
sodium gates_____
sodium gates do not reset:
(Mechanism of Depolarizing Potassium Arrest)
fast-gates _____
fast-gates remain open;
(Mechanism of Depolarizing Potassium Arrest)
slow gates _____
slow gates remain closed
sodium gates ____: fast-gates ____;
slow gates _____
(Mechanism of Depolarizing Potassium Arrest)
sodium gates do not reset:
fast-gates remain open;
slow gates remain closed
(Mechanism of Depolarizing Potassium Arrest)
Because the extracellular potassium is so high
the cell cannot what?
cannot repolarize and the sodium remains inside the cell.
Mechanism of Sodium Arrest
Low sodium environment
Disrupts Na+ gates and influx
(Mechanism of Sodium Arrest)
•sodium gates ___
– sodium gates disrupted –
Because the extracellular sodium is low the cell cannot depolarize.
Mechanism of Sodium Arrest - which phase is disrupted ?
Phase 0
Gauge and size are related how?
inversely
Smaller Gauge= ___ diameter
greater
French size and diameter are related how?
directly;
Larger French= ___ diameter
larger
French= to determine diameter size (mm)
divide by 3
Gauge= to determine diameter size (mm)
1/gauge
Antegrade Delivery initial dose adults
Initial dose = ~10-15 mL/kg
Keep in mind that if blood cardioplegia is used, a 1000mL dose would only be 200mL of crystalloid at a ratio of 4:1
Antegrade Delivery in pediatrics initial dose
Up to 30mL/kg in pediatric patients.
Antegrade Flow generally?
ml/min and in ml/min/m2
Flow is generally 250-400mL/min
•150 ml/minute/m2
Antegrade Flow the goal is to maintain root pressure of what?
the goal is to maintain root pressure 50-100mmHg
Antegrade Delivery Benefits (5)
•Easy •Physiological flow pattern •Quick arrest •Appropriate distribution to the right and left heart. •Root is tolerant of higher pressures
Antegrade Delivery Disadvantages (3)
- Requires competent aortic valve
- Poor distal perfusion in diseased arteries
- Poor subendocardial perfusion (especially in LVH)
Retrograde Cardioplegia delivery flow? ml/min
Flow is ~ 150-200 mL/min
Retrograde Cardioplegia flow should be titrated to maintain coronary sinus pressure of what?
Flow should be titrated to maintain a coronary sinus pressure 40 mmHg
Retrograde Delivery Benefits (5)
- Ideal for aortic valve regurgitation
- Good distal perfusion of obstructed arteries
- Good subendocardial perfusion
- Retrograde flushing of emboli–augments de-airing
- Does not impede conduct of case-can run continuously (ie, warm)
Which cardioplegia delivery is ideal for aortic valve regurgitation?
Retrograde delivery
Retrograde Delivery Disadvantages (6)
- Catheter placement can be difficult
- Impaired right heart protection
- Right coronary veins drain into the right atrium
- Surgical skill required for placement of cannula
- Distracting to perfusionist
- Possible coronary sinus rupture
Which cardioplegia delivery method does not impede conduct of case-can run continuously (ie, warm)?
Retrograde Delivery
Cardioplegia delivery that gives Appropriate distribution to the right and left heart?
Antegrade Delivery
Which cardioplegia delivery method:
- Requires competent aortic valve
- Can interrupt and delay surgery
Antegrade Delivery
Which is the most complex of the Cardioplegia Delivery methods?
Integrated Delivery
CPG delivery method that you cannot use if patient has advanced CAD?
Antegrade
Direct Ostial Delivery
Hand-held cannula directly perfuse ostia
Not as common as other methods
Direct Ostial Delivery circuit pressure required?
Approximately 250 mmHg required (circuit pressure)
•high pressures due to small cannula orifice
Direct Ostial Delivery Normal Flow? mL/min
50-150 mL/min flow seen on delivery
•Variable with disease and technique
•Normal perfusion is 5-8% of cardiac output
Doing distal anastamosis first allows what type of cardioplegia to be given?
allows Vein Graft cardioplegia to be given
Delivery through vein graft infusion pressure of what?
•Infusion pressure of 50 mmHg
Delivery through vein graft flow rate range of what? mL/min
Flow rate of 50-100 mL/min
Delivery through vein graft allows the surgeon to check what?
allows the surgeon to check the anastomosis and adequacy of flow, and also allows flow to previously underperfused areas
Delivery Through Grafts Benefits (3)
- Allows antegrade protection of areas of coronary artery disease
- Obviates limitations from aortic insufficiency and coronary artery disease
- Allows delivery without need to pressurize aortic root or interrupt surgery
Delivery Through Grafts Disadvantages (3)
- Requires graft placement
- Complexity
- Distribution only to those areas perfused by graft
Cardioplegia method that obviates limitations from aortic insufficiency and coronary artery disease?
Cardioplegia delivery through vein graft
Integrated Cardioplegia Delivery Doses?
It is common to give a large arresting dose of
antegrade cardioplegia 1-1.5 L, followed by a
smaller dose of retrograde cardioplegia 0.5 L.
Pressure Drop and CArdioplegia Delivery main determinant
The main determinant: velocity and viscosity
Pressure drop _______ to shear forces
increases proportionally
High flow velocities and fluid viscosities result in what kind of pressure drop during cpg delivery ?
in a larger pressure drop
A lower pressure drop across a cpg cannula results from what?
a low velocity of CPG
