Topic 11A Flashcards
1
Q
Coronary blood flow (Qb) is determined by
A
hemodynamic factors such as perfusion pressure (P) and
coronary vascular resistance (R).
2
Q
The delivery of oxygen (DO2) to the myocardium
(oxygen supply) is determined by two factors:
A
coronary blood flow (CBF)
oxygen content of blood (CaO2)
3
Q
O2 delivery= [formula]
A
CBF * CaO2
where CBF = ml/min and CaO2= ml O2/ml blood
4
Q
To assess myocardial protection it is imperative to
assess
A
myocardial function and O2 consumption
5
Q
Oxygen demand is a concept closely related to
A
oxygen consumption
6
Q
Oxygen consumption and demand are often used interchangeably although they are not equivalent because:
Demand=
Consumption=
A
Demand = Need Consumption= Actual amount of oxygen consumed per minute
7
Q
Oxygen consumption will: regenerate
A
ATP used by membrane transport (Na+/K+- ATPase pump) and by Myocyte contraction and relaxation
(myosin ATPase)
8
Q
ml O2/min per 100g (from small chart)
Cardiac state: Arrested Heart
Cardiac state: Resting heart rate “beating working”
Cardiac state: heavy exercise
A
Arrested Heart= 2
Resting heart rate “beating working”= 8
heavy exercise= 70
9
Q
O2 consumption: ml/min per 100g
Temp: 37C
Beating non-working
A
5.5
10
Q
O2 consumption: ml/min per 100g
Temp: 32C
Beating non-working
A
5.0
11
Q
O2 consumption: ml/min per 100g
Temp: 28C
Beating non-working
A
4.0
12
Q
O2 consumption: ml/min per 100g
Temp: 22C
Beating non-working
A
3.0
13
Q
O2 consumption: ml/min per 100g
Temp: 37C
Fibrillating
A
6.5
14
Q
O2 consumption: ml/min per 100g
Temp: 32C
Fibrillating
A
3.9
15
Q
O2 consumption: ml/min per 100g
Temp: 28C
Fibrillating
A
3.5
16
Q
O2 consumption: ml/min per 100g
Temp: 22C
Fibrillating
A
2.0
17
Q
O2 consumption: ml/min per 100g
Temp: 37C
Arrested
A
1.0
18
Q
O2 consumption: ml/min per 100g
Temp: 32C
Arrested
A
0.9
19
Q
O2 consumption: ml/min per 100g
Temp: 28C
Arrested
A
0.4
20
Q
O2 consumption: ml/min per 100g
Temp: 22C
Arrested
A
0.3
21
Q
ml/min per 100g
organ: brain
A
3
22
Q
ml/min per 100g
organ: kidney
A
5
23
Q
ml/min per 100g
organ: skin
A
0.2
24
Q
ml/min per 100g
organ: resting muscle
A
1
25
ml/min per 100g
| organ: contracting muscle
50
26
There is a unique relationship between MVO2, coronary blood flow (CBF), and the extraction of oxygen from the blood (A-V O2 difference). This relationship is an application of the
Fick Principle
27
Fick Principle= [Formula]
MVO2= CBF * (CaO2 − CvO2)
- CBF= coronary blood flow (ml/min)
- (CaO2-CvO2) is the arterial-venous oxygen content difference (ml O2/ml blood).
28
If MVO2 Demands are NOT met the heart may be prone to
arrhythmias
29
Name 2 points during bypass the heart is prone to fibrillate?
1. Cooling
| 2. Post cross clamp (post ischemic episodes)
30
how much blood flow through the SVC will you get if the IVC is not yet cannulated when you start going on bypass
1/3
31
consequences of fibrillating
Distension/Overfilling
Muscular/cellular damage
Starlings Curve
32
Cardiac Oxygen Consumption (MVO2) varies ____ during cardiac surgery using bypass
widely
33
MVO2 lowest levels at
when heart is arrested
34
MVO2 highest levels at
Shortly after weaning from bypass- Heart is repaying oxygen debt (catch up period-the heart needs time)
35
ischemia is when
oxygen delivery ≠ oxygen demand
36
An imbalance of oxygen delivery and demand leads to
ANAEROBIC metabolism and the production of lactic acid
37
Decreased intracellular pH decreases the
stability of the cellular and mitochondrial membranes
38
Decreased intracellular pH impairs the
Na --> K ATPase leading to calcium influx and calcium overload
39
ATP generated from AEROBIC metabolism is used
preferentially for myocardial contraction
40
anaerobically produced ATP is used for
cell survival and repair
41
Cardiac muscle extracts much more oxygen than other
| organs... %
>70%
42
Because cardiac muscle extracts more oxygen than other organs, an increased myocardial oxygen demand is met primarily by an...
increase in coronary blood flow
43
Coronary blood flow is dependent on the
transmural gradient
44
True Coronary Perfusion Pressure
| CoPP= [Formula]
DBP-LVEDP
45
What parameter can we estimate LVEDP from?
Wedging the swan= PA wedge pressure
46
CPP normal value
60-80 mmHg
47
During cardiac arrest, CPP is one of the most ...
important variables in achieving the return of spontaneous circulation (which is why CPR compressions are important > respirations)
48
A pressure gradient of _____ at a minimum may be necessary for survival
15 mmHg
49
On the waveform, at the aortic pressure dicrotic notch, coronary pressure is at its
highest
50
Minimize on going ischemia with
nitroglycerin
51
Wall tension increases MVO2 and increases
LVEDP
52
Myocardial preconditioning=
Myocardium that has undergone one or more brief periods of ischemia may be better able to tolerate subsequent prolonged ischemia
-life style choices alter normal values- the body adapts and resets their own "normal" values"
53
Pre-ischemic intervention includes
Minimize ongoing ischemia (i.e. NTG)
Prevent ventricular distension
Vent !!!!!!!!!!!!!!
54
Myocardial preconditioning can be achieved by:
Ischemia
Drugs
•Bradykinin, nitric oxide, phenylephrine (neosynephrine), endotoxin, adenosine
•Sevoflurane, desflurane, isoflurane
55
Cardiopulmonary bypass itself may override these
| other methods and be the ___ preconditioning tool
"best"
56
Why give cardioplegia
Cardiac quiescence
Bloodless field
Preservation of myocardial function
Induces myocardial hypothermia
57
Four Main Objectives of Hypothermic Cardioplegia
| are: (Know these)
1. Immediate/sustained electromechanical arrest
2. Rapid/sustained homogenous myocardial cooling
3. Maintenance of therapeutic additives in effective
concentrations
4. Periodic washout of metabolic inhibitors
58
History of Myocardial Protection: Pre-1955
Systemic hypothermia
59
History of Myocardial Protection: 1955
Melrose
-advocated the use of high potassium solutions to induce cardiac quiescence. Caused permanent myocardial
injury.
60
History of Myocardial Protection: 1956
Lillehei
| -introduced retrograde cardioplegia.
61
History of Myocardial Protection: 1973
Gay & Ebert
| -reintroduced hyperkalemic arrest with lower potassium concentrations (<20 mmol), preventing permanent myocardial injury
62
History of Myocardial Protection: 1979
Buckberg & Follette
| -introduced blood 4:1 cardioplegia.
63
Without cardioplegic arrest, irreversible ischemic injury to the myocardium would occur within
20 minutes
64
When myocardial protection strategies are
| used, ischemic injury can be prolonged to more than
4-5 hours without irreversible damage.
65
Most cardioplegia strategies are based on arresting the heart with
high doses of potassium (But that is changing)
66
Depolarization= potential becomes more
positive
67
Repolarization= potential becomes more
negative
68
Ion potential step 0:
Na+ channels open and more Na+ enters the cell- makes it more positive
69
Ion potential step 1:
K+ channels open and K+ begin to leave the cell
70
Ion potential step 2:
Na+ becomes more refractory so no more Na+ enters the cell. Ca++ influxes= plateau
71
Ion potential step 3:
K+ continues to leave the cell, causes membrane potential to return to resting level- makes it more negative
72
Ion potential step 4:
K+ channels close and Na+ channels rest. Extra K+ outside will diffuse away
73
With a blood potassium of 8-10 mEq/L=
depolarization of the cell occurs and sodium rushes into the cell
74
When the extracellular potassium is so high the cell
| cannot repolarize and the sodium remains...
inside the cell.
| •sodium gates do not reset: fast-gates remain open; slow gates remain closed
75
As potassium washes out of the extracellular
| space...
the cells can begin to repolarize
76
Sodium arrest mechanism= Low sodium environment extracellular...
Disrupts Na+ gates and influx
•Because the extracellular sodium is low the cell
cannot depolarize.
•sodium gates disrupted
77
Components of Myocardial Protection:
| Route of delivery
```
Antegrade
Retrograde
Ostial
Via conduits
Integrated
```
78
Components of Myocardial Protection
| Composition of solution
Crystalloid
Blood
Microplegia
79
Components of Myocardial Protection
| Temperature
Warm
Tepid
Cold
80
Components of Myocardial Protection
| Delivery interval
Intermittent
| Continuous
81
Components of Myocardial Protection
| Additives
Electrolyte
Pharmacologic
Metabolic
82
Components of Myocardial Protection
| Monitoring
Temperature
| Myocardial pH
83
Components of Myocardial Protection
| Preparation for reperfusion
This may be underestimated...
84
Single lumen catheters are sized by
gauge
85
Multi-lumen catheters are measured by
french size
86
French size and diameter are related how
directly;
| Larger French=larger diameter
87
Gauge and size are related how
inversely;
| Smaller Gauge= greater diameter
88
French= to determine diameter size (mm) divide by
3
89
Gauge= to determine diameter size (mm)
1/gauge
90
Antegrade Delivery Initial dose adults
~10-15 mL/kg
91
Antegrade Delivery Initial dose peds
Up to 30mL/kg
92
Antegrade delivery: Keep in mind that if blood
| cardioplegia is used, a 1000 mL dose would only be ____ mL of crystalloid at a ratio of 4:1.
200
93
Antegrade delivery Subsequent doses=
less in volume and in potassium concentration than the arresting dose
94
Antegrade delivery: Line pressure depends on the pressure drop in mmHg- the goal is to maintain root pressure of
50-100 mmHg
95
Antegrade delivery: Flow is generally
| ml/min) and (ml/min/m2
250-400 mL/min
| 150 ml/minute/m2
96
Antegrade Delivery
| •Benefits
```
Easy
Physiological flow pattern
Quick arrest
Appropriate distribution to the right and left heart.
Root is tolerant of higher pressures
```
97
Antegrade Delivery
| • Disadvantages
Requires competent aortic valve
Poor distal perfusion in diseased arteries
Poor subendocardial perfusion (especially in LVH)
98
Retrograde cardioplegia is given into the
coronary sinus and must be vented out of the heart
99
Retrograde delivery: A balloon is inflated on the cannula that provides two functions
Prevents back flow
| Holds cannula in place
100
Retrograde Delivery: flow is
~ 150-200 mL/min
101
Retrograde Delivery: Flow should be titrated to maintain a coronary sinus pressure
40 mmHg
102
Retrograde Delivery: benefits
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)
103
Retrograde Delivery: disadvantages
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
104
Direct Ostial Delivery is Not as common as
antegrade or retrograde
105
Direct Ostial Delivery=
Hand
-
held cannula directly perfuse ostia
106
Direct Ostial Delivery: how much circuit pressure is required
250 mmHg
| high pressures due to small cannula orifice
107
Direct Ostial Delivery: flow seen on delivery=
50-150 mL/min
| Variable with disease and technique
108
Direct Ostial Delivery: Normal perfusion is ___% of cardiac output
5-8%
109
Vein graft cardioplegia: Doing ____ anastamosis first allows VG cardioplegia to be given
distal
110
Vein graft cardioplegia: Infusion pressure of
50 mmHg
111
Vein graft cardioplegia: Flow rate of
50-100 mL/min
112
Vein graft cargioplegia: allows the surgeon to check the
anastomosis and adequacy of flow, and also allows flow to previously underperfused areas.
• Surgeon may use hand-held syringe
113
Vein graft cargioplegia: Benefits
- 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
114
Vein graft cargioplegia: Disadvantages
Requires graft placement
Complexity
Distribution only to those areas perfused by graft
115
Integrated Combined Delivery: It is common to give a large arresting dose of antegrade cardioplegia ____ L, followed by a smaller dose of retrograde cardioplegia ____ L
1-1.5 L
| 0.5
116
Integrated Combined Delivery: Using this technique, you are more likely to perfuse
all areas of the heart
117
Integrated Combined Delivery: benefits
Benefits of all methods utilized
118
Integrated Combined Delivery: disadvantages
Complexity
| lots of cricket clamps for a surgeon
119
Flow Rate and Cardioplegia:Direct Measurement=
Measured directly at the site
120
Flow Rate and Cardioplegia:Calculated Measurement=
Pressure drop calculation
121
Flow Rate and Cardioplegia: Flowing blindly is
NOT a good thing
122
Pressure Drop increases proportionally to
to shear forces
123
frictional forces do what to resistance
```
increase resistance
(small cannula = increased R)
```
124
The main determinants for pressure drop are
velocity and viscosity
125
High flow velocities and fluid viscosities result in a
larger pressure drop
126
Low velocity will result in
lower pressure drop
