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1
Q

Counterpulsation physics

A
  • Balloon inflation causes volume displacement within the descending thoracic aorta, by creating 2 compartments.
  • Proximal compartment contains aortic root and coronary arteries, distal compartment is the systemic circulation.
  • inflation causes proximal volume displacement and improves distal perfusion via enhancement of intrinsic Windkessel effect
  • Deflation causes sudden volume displacement with lowering of pressure and reduction of LV impedance, lowering afterload component of cardiac work
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2
Q

IABP placement

A

Proximal end should be high enough to maximize augmentation and limit time delay but without impeding great vessels; 1-2 cm distal to the sublcavian above the level of the renal arteries to occlude no more than 90% of the aorta
-Tip should be between 2nd ICS and first lumbar vertebra

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3
Q

IAPB improvement in Cardiac output

A

(Quaal) Usually 0.5-1 LPM increase.

Hensley: maximum 15% decrease in myocardial energy balance

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4
Q

Effects of IABP on myocardial oxygen supply/demand

A

Demand is caused by contraction during systole, supply is caused by diastolic flow to the endocardium during diastole for the LV. AUC for LV pressure vs time graph indicates supply/demand.
-IABP reduces systolic pressure (assisted systole) and increases AUC for diastole (augmented diastolic pressure) improving supply-demand ratio

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5
Q

IABP inflation and coronary artery perfusion

A
  • Effective augmentation of coronary perfusion is dependent on the degree of vasodilation within the coronary bed.
  • MI causes vasodilation from local effects
  • in severe CAD there is no improvement in perfusion to stenosed vessels, but can stimulate collateral vessel perfusion and limit cardiac demand
  • IABC increases coronary blood flow velocity and likely is the effect of ischemic relief in hypotensive patients
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6
Q

IABP afterload reduction mechanism

A

Leplace’s law: stress (LV wall tension) is proportional to aortic pressure x radius. Balloon deflation decreases aortic end diastolic pressure, causing an opening of AoV during static work (work before AoV opening)

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7
Q

IABP afterload reduction and hypotension

A

Systolic unloading only occurs with normal/high blood pressure. In hypotension the aortic compliance increases. Increased Ao compliance causes expansion with balloon inflation and limits work reduction effects

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8
Q

IABP effects on baroreceptor response

A

Baroreceptors are in the aortic arch and carotid sinus bodies and respond to pressure increases by vagal stimulation, decreasing HR.

  • IABP inflation increases diastolic pressure, stretching baroreceptors and decreasing HR with vagal stimulation. This increases diastolic filling time and decreases work.
  • Vagal stimulation also decreases SVR causing improvement in blood flow
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9
Q

IABP and preload

A

Increasing EF with increased ejection efficiency, allowing the heart to empty. This decreases RA wall stretch and decreases preload and the increase in HR form atrial receptors

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10
Q

Decreased urine output following IABP placement

A
  • Assess for aortic dissection
  • Assess for juxtarenal balloon position
  • Assess for persistent low cardiac output, usually the most likely cause
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11
Q

Factors affecting IABP augmentation

A

-Position: closer to AoV the better. Lower balloons decrease volume displacement momentum
-Volume: Aug is maximized when SV=balloon volume.
SVR: High resistance causes decreased system compliance.
-Balloon diameter, shape
-Driving gas: volume and molecular weight
-Timing: inflation, deflation and duration of inflation

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12
Q

Optimum balloon occlusivity (Quaal)

A

Augmentation is greatest at 100% aortic diameter occlusion but this causes RBC destruction and balloon friction.
Estimated optimum occlusivity is 90-95%

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13
Q

Withdrawal of medications with IABP

A

Withdraw all medications prior to removing IABP, other than heparin.
Re-starting drugs is easier than restarting a balloon

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14
Q

IABP and CPR

A

Counterpulasion should be triggered from arterial line so that counter pulsation can be timed with chest compressions

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15
Q

IABP contraindications

A
  • Thoracic or abdominal aortic aneurysm: counter pulsation against diseased aortic wall risks dissection
  • AI: with risk/benefit analysis
  • PVD: inability to pass balloon through atherosclerotic vessels
  • Lack of definitive therapy for underlying condition
  • Sepsis (Hensley) due to bacterial infection of surface
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16
Q

IAPB Complications

A

Quaal: Limb ischemia is the most common.

  • Vascular complications: thromboembolism, compartment syndrome, aortic dissection, local injury like pseudo aneurysm, infection complications, balloon rupture
  • hematologic: hemolysis, thrombocytopenia
  • Hensley: vascular complications most common
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17
Q

Ankle brachial index for IABP assessment

A

ABI: brachial systolic/calf systolic. Normal is 0.8-1.2

Lower calf relative pressure is an indication of poor perfusion

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18
Q

IABP skin incision location

A

1.5 cm below the inguinal ligament

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19
Q

Quaal’s recommendation for heparin administration with IABP

A

5000 units on injection and infusion at 600-1000 u/hr to achieve PT (not APTT) of 50-60. Stop heparin infusion 2-4 hours prior to removal

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20
Q

Contraindications to sheathless IABP insertion

A

Fibrosis and extensive scarring or obesity which causes excessive distance between the skin surface and the femoral artery

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21
Q

IABP balloon volume limitation

A

Ideal balloon volume is equal to the blood volume in the aorta at any given time, with the correct diameter and length.
-Increasing volume only causes aortic distension and not increased blood displacement

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22
Q

Ideal IABP balloon volume

A

CI (in mL) x BSA/(HR x 2)

  • Quaal: Balloon should have at least 50% of the stroke volume
  • Hensley: Set balloon volume to 50-60% of ideal SV
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23
Q

Phlebostatic axis definition

A

External reference point for the level of the right atrium.

The junction of the 4th ICS and the right mid axillary line

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24
Q

Conventional IABP timing

A

Inflation: T wave midpoint as electrical signal of diastole
Deflation: R wave

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25
Ideal pressure wave for IABP timing, invasive pressure monitoring limitations
- Aortic root pressure is the only reliable means, and all other pressure sites are not considered central pressures. - Pulse wave velocity is faster than the velocity of blood flow itself and is determined by compliance of arteries. - Differing locations, pulse wave, impedance limit timing accuracy. Femoral artery should not be used for timing due to 120 msec delay
26
IABP pressure timing delay
Pulse wave takes 25 msec from AoV closure to reach 1-2 cm distal to subclavian, and the same amount of time for augmented pressure to reach AoV Therefore, inflation needs to be timed to occur 40-50 msec from midpoint of dicrotic notch to account for delay, when monitoring with IABP tip at optimal position On standard paper, 0.4 sec= 1 little box
27
Indications of proper IABP deflation
- Assisted systole is equal to or less than unassisted systole; systole is lowered because of the diastole - Assisted diastole is less than unassisted diastole; diastole is lowered because of volume displacement
28
Indications of improper IABP deflation
Early: assisted systole is higher than unassisted systole. The diastolic drop occurs Late: assisted diastole is higher than unassisted.
29
IABP Fill pressure definition
Balloon pressure baseline pressure, caused by the pressure of helium needed to prime the system itself pneumatically
30
IABP balloon pressure waveform correlation with augmented arterial pressure
- balloon wave should be same width as duration of diastole - balloon plateau pressure should reflect peak augmented arterial diastolic pressure, +/- 20-25 mmHg for adults and 10 for children
31
IABP waveforms and MAP
High MAP or SVR causes increased resistance to balloon flow and a HIGH pressure. Low MAP causes low resistance to balloon He flow and causes LOW pressure
32
Causes of abnormally low IABP balloon waveform plateau pressure
- Balloon is too small - Balloon doesn't have enough volume - Low SVR, low MAP, hypovolemia.
33
Cause of abnormally high IABP balloon waveform plateau pressure
- Patient is hypertensive, causing more resistance to flow and high pressures - if Aug is not increased, then balloon is likely kinked or not inflating correctly - Balloon too large for the aorta; decrease the filling volume to resolve the problem
34
IABP and manual blood pressure cuff use
Highest pressure generated is augmented diastolic pressure, which is now the first korotkoff sound.
35
Rationale for use of He in IABP inflation
Low density, resulting in decreased Reynolds number and slowing for same flow through a physically smaller driveline
36
Turning off an IABP
IABP should never be turned off unless the patient is anticoagulated fully Do not let balloon remain deflated for longer than 30 min If pump fails, inflate manually with 40 cc air by hand once every 5 min
37
IABP and requirements for anticoagulation
- Heparin not required for first hours following CPB until chest tube drainage is less than 100-150 mL/hr - No-heparin protocol has acceptable rates of thrombosis compared to risk of bleeding - If prolonged use needed, consider heparin to achieve APTT 1.5-2 normal
38
Determinants of venous drainage flow from siphon-based venous line
- Pressure (volume) within the patient's central veins - difference in height between patient and top of blood level in venous reservoir (pressure gradient is height in cm h20) - resistance of venous line, cannulas, connectors
39
Gravlee recommendations for 2 stage venous cannulas
BSA 1.8-2.5 is 32/40, greater than BSA 2.5 is 36/46. | 32/40 gives a max flow of 6LPM. 36/46 gives max flow 8 LPM
40
Air in Venous line and GME production
60% of bubbles transferred from venous reservoir to arterial line despite use of 40 micron filter are transmitted to patient. 98% of GME reduction occurs by removing all visible air from venous cannulas and lines before initiating CPB
41
Bicaval Cannulation and persistent LSVC
LSVC drains into the coronary sinus or RA. - If right heart is entered there is potential for air to enter retrograde through coronary sinus into LSVC and systemically - if bicaval cannulation is used, then using caval tapes (which should be opened during cardioplegia) prevents systemic drainage to venous line
42
Augmented venous drainage pressure monitoring recommendation
pressure transducer located 10 cm before the inlet to either the KAVD centrifugal pump or above the inlet to the hard shell reservoir
43
VAVD pressure limit
Gravlee: do not exceed -60 to -100 mmHg, with -40 increasing the amount of GME. Usual application is -20 mmHg
44
Table height and siphon pressure
40 cm from the table to the top of the blood level of the reservoir causes -32mmHg suction
45
Venous reservoir pressure relief valve recommendations
Low pressure valve of -100 mmHg | High pressure valve of +5 mmHg
46
Sources of potential air emboli with augmented venous drainage
- aspiration into venous line across the purse string sutures - IV ines or instrumentation with the use of VAVD - air lock resulting in transmission of air into reservoir/centrifugal pump - charged cardiotomy and retrograde air generation up the venous line - imbalance of flow from art and venous flow causing change in patient blood flow - all effects worsened with PFO which can lead to systemic embolization
47
Cannula performance index
Pressure drop vs outer diameter at any given flow
48
Arterial cannula pressure drop recommendation
Less than 100 mmHg; greater than this causes excessive hemolysis and protein denaturation
49
Gravlee assessment of aortic cannula position
Test infusion through arterial line is recommended regardless of the location of cannulation. Higher than expected pressures warns of dissection. Lack of negative flow or flow less than 500 mL/min during RAP suggests misplacement
50
Signs of cannulation of arch vessels or malposition of aortic cannula
- high systemic pressure line readign - unilateral facial blanching with clear prime initiation - assymetric cooling of neck during cooling - unilateral edema, hyperemia, petechai, conjunctival tearing or dilated pupils - decreased pulsation prior to CPB on the cannulated side - radial artery changes/dampening
51
Coanda effect
Jet stream adheres to the boundary wall and produces a lower pressure along the opposite wall. This causes carotid hypoperfusion Wiki: tendency for fluid to stick to the convex surface
52
Advisable maximum blood velocity in tubing
100 cm/sec to avoid hemolysis and trauma
53
Maximum critical blood Reynold's number
1000. Turbulence occurs above this number. | Max flow through 3/8" tubing to achieve this is only 3.7LPM
54
Recommended pressure tolerance of all tubing connections
500 mmHg for all connections distal to the pump
55
Roller pump occlusion (Gravlee)
Most commonly cited is 30 inches of fluid, drop is less than 1 inch/min, or 30 cm and 1 cm/min Mike: Pressure drop: 90 mmHg in 120 seconds, which is 2 mmHg in 3 seconds starting at 300 mmHg Each roller should be checked in 3 positions
56
Spallation generation
Particulate emboli form on inner surface of the tubing and at the fold of the edges of the tubing occurs
57
Arterial pump blood handling characteristics
Roller pumps are based on setting of occlusion by operator to minimize hemolysis Roller pump handling is based on operator technique to ensure that high RPM and low flow does not generate unnecessary shear
58
Gravlee pressure monitoring recommendation
Pre and post membrane oxygenator to allow for assessment of high pressure gradients
59
Gravlee occlusion discrepancy
In the even that the 2 roles in the pump head do not yield the same rate of fluid drop, the occlusion should be set to the roller that is most occlusive
60
Pre-Bypass filter size
0.2-5 micron pore size
61
CO2 Flush
Advantageous for de airing membrane oxygenators. | Most effective when the CO2 is directed through all blood-contacting components
62
Gravlee recommendation for use of roller pump suction
Occlusion of roller pumps used for field suction and venting should be slightly non occlusive to reduce RBC trauma, and requires constant adjustment to minimize tissue and blood damage
63
Recommendations for venous reservoir and deformer to
Direct blood injection into defoamer, no inlet turbulence, all blood passes through defoamer, avoid free fall into the reservoir, store the blood in reservoir as long as possible, use microporous filter
64
Screen filters
- woven polymer thread - defined pore size - filters by interception - smallest is the pre bypass filter, which is not woven polymer but is a membrane - small screen filters block particles and GME
65
Bubble point pressure
Pressure that overcomes inherent surface tension within filters resulting release of trapped bubbles
66
Use of leukocyte depleting filters
Only favourable evidence is for use in cardioplegia line just before unclamping, such as with hot shot. Some evidence suggests increased cardiac output, Vfib and cardiac enzymes
67
Purpose of venting the LV
- reduction of LV distension and wall stress - reduce myocardial rewarming - prevent cardiac ejection of air - facilitate surgical view
68
Causes of blood return to LV requiring venting
- Blood that gets around the venous cannula and passes through the lungs - bronchial and Thebesian drainage - persistant LSVC - PDA - ASD/VSD - Anomolous venous drainage - BT and Waterston Shunt - Coronary collateral flow
69
Standardized cardioplegia delivery temperatures
Cold=4 Tepid is 28-35 Warm is 35-37
70
Gravlee recommendation for cardioplegia pump occlusion
Must be fully occlusive to prevent retrograde Flow and possible air entrainment and thus coronary air embolization
71
Recommended antegrade aortic root pressure during cardioplegia delivery
60-100 mmHg in the root (Gravlee) | Line pressure= 160-200 (Mike)
72
Ideal cardiac arrest time during induction dose of cardioplegia
Arrest within 30 seconds with antegrade cardioplegia

CPC (8 decks)

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