Core Topic 1: Cardiopulmonary Bypass, Myocardial Protection, Thoracic Aortic Injury, Thoracic Trauma Flashcards
What are the general goals that CPB achieves?
maintain CO and organ perfusion, blood oxygenation, CO2 elimination, temperature control; bloodless field and ability to manipulate the heart
How is CO2 production affected by temperature (in the setting of CPB)?
CO2 production decreases as temperature decreases, so less ventilation is required through the oxygenator with a cooler patient.
In the context of CPB, how does reducing body temp affect the body’s metabolism? What is the range of this temperature?
Reduces metabolism (ie oxygen consumption) to allow the body to tolerate lower CO or even total circulatory arrest. 16-28 C.
What are the components of the CPB circuit?
venous drainage cannula, reservoir, blood pump, oxygenator, heat exchanger, arterial filter, and arterial return cannula
What is Poiseuille’s Law as it relates to the CPB circuit?
Resistance is directly related to the length of a tube and indirectly related to the internal radius to the 4th power.
What are the advantages of vac assisted venous drainage (VAVD)?
What are the risks?
permits use of dry venous drainage lines, smaller drainage cannulas, minimizes air lock
risks - can draw air into venous lines if misplaced
In terms of drainage, what is a disadvantage of the single/dual stage cannulation of the RA?
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
What is the preferred femoral vein for CPB?
R femoral vein - straighter trajectory to the heart
What would be some typical indications for femoral venous cannulation?
Minimally invasive cardiac surgery, redo sternotomy, descending aortic surgery
If atriocaval kinking is anticipated (ie rotation of the heart for an extended period of time), what cannulation strategy should be employed?
Bicaval
What are the typical surgeries that utilize bicaval cannulation?
mitral valve, tricuspid valve, intracardiac surgery to remove blood from the field; surgeries that cause kinking to improve drainage (particularly from SVC)
Which arterial cannulation location has the best coronary perfusion?
Ascending aorta
In an ascending aorta cannulation strategy for CPB, what must be evaluated on imaging to minimize dissection and stroke risk?
calcified aorta
What is the best option for emergency arterial cannulation?
femoral artery
What are some of the hemodynamic limitations of femoral arterial cannulation in CPB?
when heart is beating, there is competitive flow in the descending aorta; increased LV afterload
What is the ideal site for aortic cannulation?
opposite of the innominate artery in the inner curve of the aorta, which provides a thicker wall to hold sutures; avoid plaque by palpating
What are some options for aortic cannulation in ascending aorta aneurysm/dissection, heavy atherosclerotic burden in ascending?
Innominate, axillary, subclavian arteries.
If no other options, and the patient needs the surgery, may need circ arrest.
What are the advantages and disadvantages of soft-bag vs hard-shell venous reservoirs in CPB?
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
What are the three mechanisms used to protect the heart during cardiac surgery?
hypothermia, chemical arrest, decompression
How does temperature management in CPB affect the myocardium and the systemic temperature differently?
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
What pressure do you expect in the aortic root when deliver cardioplegia in an adult? Child?
When delivering cardioplegia, when should you expect arrest?
180-220 mmHg in adults and 110 in neonates
30-60 seconds
What pressure do you expect to deliver through a retrograde cardioplegia strategy? Why is it so much lower than via the aorta?
30-50 mmHg. Any higher can injure the coronary sinus. Arrest in 2-4 minutes.
What is a standard UFH dose for CPB?
What ACT are you looking for?
400 u/kg IV
480 ACT
How do you treat heparin resistance?
FFP or AT III
What is the generally accepted flow in adults during CPB?
2.2-2.4 L/min/m2
Weaning from CPB requires what?
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
How do you calculate VO2 (ie Fick equation)?
VO2 = Q x 1.34 x Hgb x (SaO2 - SvO2) x 10
What organ is particularly vulnerable to congestion in the setting of CPB?
liver - 75% of hepatic blood flow occurs by venous pressure through the portal vein
What parameters are measured during CPB as surrogates to VO2 (ie outside of this than this require higher flow)?
SVO2 >75%, base deficit > -5, lactate <4
What is a shortfall of measuring the Fick?
systemic measurement, so does not detect regional hypoperfusion (brain, coronary system, kidney, gut)
What is the risk if DHCA (18-20 C) is extended longer than 40 mins?
brain injury risk increases; at 60 mins, the majority of patients will suffer brain injury; longer periods are tolerated in neonates and children
What does elevated venous pressure during CPB do to effective perfusion pressure in an organ?
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
What venous drainage strategy for CPB has the best LV unloading efficiency?
BiCaval cannula (SVC/IVC)
