Core Topic 1: Cardiopulmonary Bypass, Myocardial Protection, Thoracic Aortic Injury, Thoracic Trauma

Question 1

What are the general goals that CPB achieves?

Answer 1

maintain CO and organ perfusion, blood oxygenation, CO2 elimination, temperature control; bloodless field and ability to manipulate the heart

Question 2

How is CO2 production affected by temperature (in the setting of CPB)?
How does this affect vent mgmt?

Answer 2

CO2 production decreases as temperature decreases, so less ventilation is required through the oxygenator with a cooler patient.

Question 3

In the context of CPB, how does reducing body temp affect the body’s metabolism? What is the range of this temperature?

Answer 3

Reduces metabolism (ie oxygen consumption) to allow the body to tolerate lower CO or even total circulatory arrest.
16-28 C.

Question 4

What are the components of the CPB circuit?

Answer 4

venous drainage cannula, reservoir, blood pump, oxygenator, heat exchanger, arterial filter, and arterial return cannula

Question 5

What is Poiseuille’s Law as it relates to the CPB circuit?

Answer 5

Resistance is directly related to the length of a tube and indirectly related to the internal radius to the 4th power.

Question 6

What are the advantages of vac assisted venous drainage (VAVD)?
What are the risks?

Answer 6

permits use of dry venous drainage lines, smaller drainage cannulas, minimizes air lock

risks - can draw air into venous lines if misplaced

Question 7

In terms of drainage, what is a disadvantage of the single/dual stage cannulation of the RA?

Answer 7

poor drainage from the vena cava, e.g. if the heart is rotated to expose a coronary target, the superior cavoatrial jct can kink, leading to obstructed cerebral drainage

Question 8

What is the preferred femoral vein for CPB?

Answer 8

R femoral vein - straighter trajectory to the heart

Question 9

What would be some typical indications for femoral venous cannulation?

Answer 9

Minimally invasive cardiac surgery, redo sternotomy, descending aortic surgery

Question 10

If atriocaval kinking is anticipated (ie rotation of the heart for an extended period of time), what cannulation strategy should be employed?

Answer 10

Bicaval.
This may be beneficial for mitral surgeries and lung transplant (if on CPB/ECMO).

Question 11

What are the typical surgeries that utilize bicaval cannulation?

Answer 11

mitral valve, tricuspid valve, intracardiac surgery to remove blood from the field; surgeries that cause kinking to improve drainage (particularly from SVC)

Question 12

Which arterial cannulation location has the best coronary perfusion?

Answer 12

Ascending aorta

Question 13

In an ascending aorta cannulation strategy for CPB, what must be evaluated on imaging to minimize dissection and stroke risk?

Answer 13

calcified aorta

Question 14

What is the best option for emergency arterial cannulation?

Answer 14

femoral artery

Question 15

What are some of the hemodynamic limitations of femoral arterial cannulation in CPB?

Answer 15

when heart is beating, there is competitive flow in the descending aorta; increased LV afterload

Question 16

What is the ideal site for aortic cannulation?

Answer 16

opposite of the innominate artery in the inner curve of the aorta, which provides a thicker wall to hold sutures; avoid plaque by palpating

Question 17

What are some options for aortic cannulation in ascending aorta aneurysm/dissection, heavy atherosclerotic burden in ascending?

Answer 17

Innominate, axillary, subclavian arteries.
If no other options, and the patient needs the surgery, may need circ arrest.

Question 18

What are the advantages and disadvantages of soft-bag vs hard-shell venous reservoirs in CPB?

Answer 18

heard-shell - open to air, allowing release of air from venous line, used for VAVD; large air-blood surface, which can lead to activation of blood elements

soft-bag reservoirs - no air-blood interface; work best with centrifugal pumps; can’t use VAVD

Question 19

What are the three mechanisms used to protect the heart during cardiac surgery?

Answer 19

hypothermia, chemical arrest, decompression

Question 20

How does temperature management in CPB affect the myocardium and the systemic temperature differently?

Answer 20

myocardium and systemic temp are uncoupled - systemic hypothermia ranges from mild (>28), moderate (20-28), and deep (<20), myocardial temp goal is 10-14 C

Question 21

What pressure do you expect in the aortic root when deliver cardioplegia in an adult? Child?
When delivering cardioplegia, when should you expect arrest?

Answer 21

180-220 mmHg in adults and 110 in neonates

30-60 seconds

Question 22

What pressure do you expect to deliver through a retrograde cardioplegia strategy? Why is it so much lower than via the aorta?

Answer 22

30-50 mmHg. Any higher can injure the coronary sinus. Arrest in 2-4 minutes.

Question 23

What is a standard UFH dose for CPB?

What ACT are you looking for?

Answer 23

400 u/kg IV

480 ACT

Question 24

How do you treat heparin resistance?

Answer 24

FFP or AT III

Question 25

What is the generally accepted flow in adults during CPB?

Answer 25

2.2-2.4 L/min/m2

Question 26

Weaning from CPB requires what?

Answer 26

``` warm and remove cross-clamp (end of coronary ischemia) ventilation good contractility stable rhythm adequate de-airing balanced electrolytes -> start wean -> inc CO and dec CPB until venous line completely clamped -> turn off vent ```

Question 27

How do you calculate VO2 (ie Fick equation)?

Answer 27

VO2 = Q x 1.34 x Hgb x (SaO2 - SvO2) x 10

Question 28

What organ is particularly vulnerable to congestion in the setting of CPB?

Answer 28

liver - 75% of hepatic blood flow occurs by venous pressure through the portal vein

Question 29

What parameters are measured during CPB as surrogates to VO2 (ie outside of this than this require higher flow)?

Answer 29

SVO2 >75%, base deficit > -5, lactate <4

Question 30

What is a shortfall of measuring the Fick?

Answer 30

systemic measurement, so does not detect regional hypoperfusion (brain, coronary system, kidney, gut)

Question 31

What is the risk if DHCA (18-20 C) is extended longer than 40 mins?

Answer 31

brain injury risk increases; at 60 mins, the majority of patients will suffer brain injury; longer periods are tolerated in neonates and children

Question 32

What does elevated venous pressure during CPB do to effective perfusion pressure in an organ?

Answer 32

reduces it; ie if the MAP is 60 during CPB, and venous pressures start to rise, perfusion pressure decreases even though MAP may be maintained; the back pressure also increases transudation/congestion

Question 33

What venous drainage strategy for CPB has the best LV unloading efficiency?

Answer 33

BiCaval cannula (SVC/IVC)