Cardiopulmonary Bypass Flashcards
When is CO2 extracted from blood?
At the same time that O2 is added back
Process of blood going through CPB stuff
Venous Reservoir
Oxygenator/Heat exchanger (CO2 is extracted from the blood while adding O2 back)
Main pump
Arterial filter (removes fat, thrombi, calcium, and tissue debris)
Patient
Roller vs centrifugal pump:
Roller: non pulsatile flow, constant regardless of pressure generated.
Centrifugal: pressure dependent, less traumatic to RBCS
Which perfusion pressure is recommended to maintain systemic organ function?
50-80 mmHg
Why do we use heparin to anticoagulant patients for CPB?
Consistent in its dose and achievement of adequate AC
Rapid onset time
Easy to monitor
Adequate therapeutic window.
We want it because we don’t want thrombosis to occur in CPB circuit.
How does ACT work? Normal pre-heparin ACT? What do surgeons want before starting? Normal heparin dose?
small aliquot of blood added to a medium which stimulates thrombosis. In a normal, pre-heparinized state, the ACT is 90-150 seconds. Following administration of heparin, 300-400 U/kg, ACT is repeated after 2 minutes. Most surgeons want ACT >400, others want >480
Why is CPB so harmful to the system?
It destroys RBCs, Activates and destructs platelets, stimulates inflammatory and complement system leading to further stimulation of coagulation system after reversal of heparin
How does heparin work?
It enhances the activity of anti-thrombin 3 leading to an enhanced destruction of thrombin and thereby making it difficult to form clots
What situations would make a person be exposed to heparin thereby increasing their chances of having HIIT?
previous MI or STEMI, This could cause decreased levels of heparin and/or decreased activity of antithrombin 3 leading to an inability to reach adequate ACT values
What can you give to patents who have less AT3, or aren’t responding to heparin?
you could give ATIII via 1-2 units of FFP
What makes CPB worse for a person’s system?
Length of time on CPB. So longer surgeries with more parts to it=more time on CPB, and more time for issues of destruction of RBCs, and platelets.
One thing that can affect patients undergoing cardiac surgery as far as getting back to normal after CPB is:
Temperature! if you’re having a problem with coagulation after CPB. Consider their temperature.
How does protamine work? What are 3 potential reactions that can happen with administration of protamine? How do you treat these?
It binds to heparin to form a stable salt
3 reactions: Anaphylactic (profound vasodilation and CV collapse), this can happen in its who have been exposed to protamine before (previous exposure, diabetics using insulin NPH) since protamine is used to prolong effects. Men who have had vasectomies or episodes of orchitis.
tx: support of CV system, admin of diphenhydramine or epinephrine to block histamines and stop degranulation of leukocytes
2. Fulminate pulmonary vasoconstriction-can happen in its with elevated pulmonary pressures. Tx: stop admin of protamine and support CV system. Methylene blue could help counteract increase in pulmonary pressures
3. Giving it too rapidly could cause decrease in intravascular calcium and stimulate release of histamine leading to drop in SVR and hypotension. Rec that no more than 50 mg of protamine be given in a 10 min period.
Tell me about the type 1 HIT:
what happens? why do they think this? what is heparin binding to? What does this binding facilitate?
Heparin induced thrombocytopenia Type 1:
Results in a decrease in the number and function of platelets following admin of heparin-thought to be due to an aggregation of platelets. Heparin binds to the surface of platelets as well as to Platelet factor 4. This binding facilitates platelets clumping together and these aggregates are removed from circulation by the RES
Type 2 HIT: Usually happens in which patient population? What decreases (like in HIT 1), and what else happens? Tell me more about that additional thing and what it leads to. Complications?
Seen in those who have been treated with heparin for a more prolonged time 5-10 years. Decrease in platelet levels due to aggregation and removal from circulation however, there is an additional antibody mediated effect. Antibodies are generated and bind to heparin platelet factor 4 complex-this leads to activation of inflammatory system as well as activation of complement cascade. Thrombotic complications are a thing with HIT 2
So, for type 2 HIT: can you get antibody levels afterwards? Does repeated exposure to heparin always reproduce the HIT type 2 reaction?
Antibody levels in patients who survive a HIT type 2 reaction become undetectable several weeks after cessation of heparin. Repeated exposure does not always reproduce this.